YISHAN YANG - Academia.edu (original) (raw)

Papers by YISHAN YANG

Food Control, 2017

This study investigated the biofilm formation by three S. Enteritidis strains in a simulated liqu... more This study investigated the biofilm formation by three S. Enteritidis strains in a simulated liquid egg processing environment using 0.1% peptone water (PW) (control), 10% whole eggs (WE), 10% egg yolks (EY) and 10% egg whites (EW) as growth media, and evaluated the effectiveness of chlorine (200 ppm, 5 min) and hot water (71 °C, 30 s) treatments against S. Enteritidis biofilms. The results showed that S. Enteritidis formed significantly (P < 0.05) denser biofilms in PW and EW compared to those in WE and EY. However, biofilms formed in PW were less resistant to chlorine treatment than those formed in WE, EY, and EW, with average log reductions of 6.34, 2.28, 0.67 and 0.95 CFU/cm2, respectively. Microscopic observation showed that biofilm morphology was greatly affected by the growth medium, and the egg matrices might act as protective barriers, contributing to the greater chlorine resistance. All biofilms were very sensitive to hot water treatment, which reduced the cell populations by 4.30–7.08 log CFU/cm2. This study could advance our understanding towards the biofilm forming abilities of S. Enteritidis in liquid egg processing environments and the effectiveness of sanitation methods against S. Enteritidis biofilms, which may aid in the development of better sanitation strategies.

International journal of food microbiology, Jan 2, 2016

Fresh mung bean sprouts have been identified as a source of many Salmonella outbreaks worldwide. ... more Fresh mung bean sprouts have been identified as a source of many Salmonella outbreaks worldwide. The aim of this study was to develop a rapid and accurate detection methodology for low levels of healthy and sanitizer-injured Salmonella on mung bean sprouts using real-time PCR coupled with either immunomagnetic separation (PCR-IMS) or centrifugation (PCR-cen). Initially, three parameters of IMS; specificity/sensitivity, bacterial concentration and bead incubation time were optimized. Secondly, limit of detection (LOD) was determined for the optimized PCR-IMS and PCR-cen. These two methods were compared against PCR alone (PCR) and the standard culture method (ISO) for their ability to detect Salmonella using inoculated and uninoculated sprouts. Under optimum IMS conditions (10(5)CFU/ml for 30min), capture efficiency of Salmonella in sprout suspensions was lower than 40%, most probably due to the non-specific binding of the background microbiota. PCR-IMS and PCR-cen had a similar LOD a...

COSMOS, 2015

Food safety and food security are interrelated concepts with a profound impact on the quality of ... more Food safety and food security are interrelated concepts with a profound impact on the quality of human life. Food security describes the overall availability of food at different levels from global to individual household. While, food safety focuses on handling, preparation and storage of foods in order to prevent foodborne illnesses. This review focuses on innovative thermal and non-thermal technologies in the area of food processing as the means to ensure food security through improving food safety with emphasis on the reduction and control of microbiological risks. The antimicrobial efficiency and mechanism of new technologies to extend the shelf life of food product were also discussed.

LWT - Food Science and Technology, 2014

The effect of temperature (28, 37 and 42 C) and pH (6 and 7) on the biofilm formation capability ... more The effect of temperature (28, 37 and 42 C) and pH (6 and 7) on the biofilm formation capability of Salmonella Typhimurium on stainless steel and acrylic was investigated. The rate of biofilm formation increased with increasing temperature and pH, while the number of attached cells after 240 h decreased with increasing temperature and was not different between pH 6 and 7. The surface hydrophobicity of bacterial cells was not significantly (p > 0.05) different among tested conditions. Electron-donating/ accepting properties changed with pH and temperature, although these changes did not correlate with the ability to form biofilms under respective conditions. Attachment of S. Typhimurium showed a preference for stainless steel compared to acrylic surfaces under all conditions tested. The results suggest that salmonellae were less adherent to acrylic than to stainless steel surfaces; thus, acrylic-type surfaces should be considered for use in the food industry over stainless steel where applicable. The rate of biofilm formation increased at higher temperatures and pH levels within the tested ranges. Hurdle technology using lower temperatures reduced pH may help delay biofilm formation on food contact surfaces contaminated with S. Typhimurium.

Food Microbiology, 2015

The ability of nine commercial broths to enrich healthy and 90% sanitizer-injured Salmonella Typh... more The ability of nine commercial broths to enrich healthy and 90% sanitizer-injured Salmonella Typhimurium and Salmonella cocktail on mung bean sprouts was evaluated to select an optimum broth for detection. Results showed that S. Typhimurium multiplied faster and reached a higher population in buffered peptone water (BPW), Salmonella AD media (AD) and ONE broth-Salmonella (OB), compared with other broths. Healthy and 90% sanitizer-injured Salmonella at low concentrations increased by 4.0 log CFU/ml in these three broths. However, no Salmonella growth was observed in lactose broth (LB). Further investigation showed that during incubation, pH of LB dropped from 6.7 to 4.2, due to production of lactic (66 mM) and acetic acids (62 mM) by lactic acid bacteria that were identified as dominant microbiota in bean sprouts. Though no cell membrane damage was detected by propidium monoazide combined with real-time PCR, it was found that LB inhibited Salmonella growth, especially from low inoculum levels. This study suggests that in consideration of effectiveness and cost, BPW would be a suitable enrichment broth to use for isolating and detecting Salmonella on mung bean sprouts, while using LB might cause false negative results in Salmonella detection by either PCR or standard cultural method.

Conventional culture detection methods are time consuming and labor-intensive. For this reason, a... more Conventional culture detection methods are time consuming and labor-intensive. For this reason, an alternative rapid method combining real-time PCR and immunomagnetic separation (IMS) was investigated in this study to detect both healthy and heat-injured Salmonella Typhimurium on raw duck wings. Firstly, the IMS method was optimized by determining the capture efficiency of Dynabeads ® on Salmonella cells on raw duck wings with different bead incubation (10, 30 and 60 min) and magnetic separation (3, 10 and 30 min) times. Secondly, three Taqman primer sets, Sal, invA and ttr, were evaluated to optimize the real-time PCR protocol by comparing five parameters: inclusivity, exclusivity, PCR efficiency, detection probability and limit of detection (LOD). Thirdly, the optimized real-time PCR, in combination with IMS (PCR-IMS) assay, was compared with a standard ISO and a real-time PCR (PCR) method by analyzing artificially inoculated raw duck wings with healthy and heatinjured Salmonella cells at 10 1 and 10 0 CFU/25 g. Finally, the optimized PCR-IMS assay was validated for Salmonella detection in naturally contaminated raw duck wing samples. Under optimal IMS conditions (30 min bead incubation and 3 min magnetic separation times), approximately 85 and 64% of S. Typhimurium cells were captured by Dynabeads® from pure culture and inoculated raw duck wings, respectively. Although Sal and ttr primers exhibited 100% inclusivity and exclusivity for 16 Salmonella spp. and 36 non-Salmonella strains, the Sal primer showed lower LOD (10 3 CFU/ml) and higher PCR efficiency (94.1%) than the invA and ttr primers. Moreover, for Sal and invA primers, 100% detection probability on raw duck wings suspension was observed at 10 3 and 10 4 CFU/ml with and without IMS, respectively. Thus, the Sal primer was chosen for further experiments. The optimized PCR-IMS method was significantly (P = 0.0011) better at detecting healthy Salmonella cells after 7-h enrichment than traditional PCR method. However there was no significant difference between the two methods with longer enrichment time (14 h). The diagnostic accuracy of PCR-IMS was shown to be 98.3% through the validation study. These results indicate that the optimized PCR-IMS method in this study could provide a sensitive, specific and rapid detection method for Salmonella on raw duck wings, enabling 10-h detection. However, a longer enrichment time could be needed for resuscitation and reliable detection of heat-injured cells.

International Journal of Food Microbiology, 2014

This study evaluated the acid and heat resistance of Salmonella Enteritidis in simulated gastric ... more This study evaluated the acid and heat resistance of Salmonella Enteritidis in simulated gastric fluid (pH 2.0) and during thermal treatment (54-60°C), respectively, after adaptation to lactic acid (LA) or trisodium phosphate (TSP) at various pHs (pH 5.3-9.0). The changes in membrane lipid composition and expression levels of RpoS and RpoH were examined to elucidate their roles in bacterial stress resistance. Transcriptional profile of several virulence-related genes was also analyzed. Results showed that LA-adapted cells at pH 5.3 and 6.3 had higher acid and heat resistance than control cells and cells adapted to TSP at pH 8.3 and 9.0. LA-adapted cells had the lowest ratio of unsaturated to saturated fatty acids, indicating that they might possess a less fluid membrane. It was observed that the expression levels of RpoH and RpoS were upregulated in TSP-adapted cells but not in LA-adapted cells. Thus, these results indicate that the increased acid and heat resistance of LA-adapted S. Enteritidis was possibly due to the decreased membrane fluidity instead of the upregulation of RpoS and RpoH. About 6.0, 2.1, and 2.46-fold upregulation of spvR, avrA, and hilA were observed in cells adapted to TSP at pH 9.0, except sefA that had its highest expression level in the control cells, indicating that the expression of these virulence genes highly depends on environmental conditions. This is the first study to show that the alteration in the cytoplasmic membrane rather than RpoS and RpoH plays a more crucial role in conferring greater acid and heat resistance on LAadapted S. Enteritidis, thus providing a better understanding on the bacterial stress response to acidic conditions.

Journal of Food Safety, 2012

The aim of this study was to investigate survival of Salmonella Newport and Salmonella Saintpaul ... more The aim of this study was to investigate survival of Salmonella Newport and Salmonella Saintpaul in simulated gastric fluid (SGF) at pH 1.9 or at 56C after storage in mango or pineapple juice at 4 or 24C for 24 h. In SGF, only Salmonella Saintpaul adapted to mango juice at 4C significantly (P < 0.05) enhanced its acid resistance with D value of 3.88 min, whereas both serovars stored in mango juice at 24C had significantly lower D values with 0.88 and 0.72 min, respectively. The D56C values of both serovars adapted to juices significantly decreased compared with nonadapted cells, except for Salmonella Newport stored in pineapple juice at 24C. Overall, two Salmonella serovars tested in this study did not show the enhanced acid or heat resistance after storage in these two tropical fruit juices, indicating that introduction of Salmonella Newport and Salmonella Saintpaul to mango and pineapple juices is unlikely to enhance their survival during gastric transit or thermal processing. PRACTICAL APPLICATIONS Salmonella spp., one of the leading causative agents of gastroenteritis, are a major public health concern in the world. It has been reported that Salmonella spp. can survive in unpasteurized orange juice or apple cider and become more resistant to subsequent exposure to acid or heat conditions.However,there is limited information in the literature on the effect of survival of Salmonella spp. in tropical fruit juices on their acid and heat resistance. This research was conducted to investigate the survivability of Salmonella Newport and Salmonella Saintpaul in simulated gastric fluid at pH 1.9 or at 56C after adaptation in mango or pineapple juice.The results of this study would enrich our understanding on the stress response of Salmonella spp. in these juices, as well as provide guidance to developing intervention technology to eliminate Salmonella Newport and Salmonella Saintpaul in mango and pineapple juices.

Journal of Food Protection, 2013

This study was performed to optimize Salmonella Typhimurium recovery from raw duck wings with fiv... more This study was performed to optimize Salmonella Typhimurium recovery from raw duck wings with five nonselective broths (buffered peptone water, tryptic soy broth, lactose broth, universal preenrichment broth, nutrient broth) and four selective broths (selenite broth, BAX System MP media [MP], Salmonella AD media [AD], ONE broth-Salmonella [OB]). Healthy or heat-injured (50 and 85% injury) cells were inoculated at a level of 102, 101, or 100 CFU/25 g on raw duck wings. Growth was modeled using DMfit with four growth parameters: lag-phase duration, maximum growth rate, doubling time, and maximum population density. Most enrichments were able to recover Salmonella Typhimurium to greater than 6 log CFU/ml. AD, MP, and OB had significantly (P < 0.05) higher maximum growth rate (0.9 to 1.0/h) and lower doubling time (0.7 to 0.8 h). Buffered peptone water, AD, MP, and OB recovered healthy and 50%-injured cells at low inoculum levels to more than 6.0 log CFU/ml; OB achieved the greatest ...

International Journal of Food Microbiology, 2014

The influence of growth temperature (10, 25, 37, and 42 °C) on the survival of Salmonella Enterit... more The influence of growth temperature (10, 25, 37, and 42 °C) on the survival of Salmonella Enteritidis in simulated gastric fluid (SGF; pH=2.0) and during heat treatment (54, 56, 58, and 60 °C), on the membrane fatty acid composition, as well as on stress-/virulence-related gene expression was studied. Cells incubated at temperatures lower or higher than 37 °C did not increase their acid resistance, with the maximum D-value of 3.07 min in cells grown at 37 °C; while those incubated at higher temperature increased their heat resistance, with the maximum D60 °C-values of 1.4 min in cells grown at 42 °C. A decrease in the ratio of unsaturated to saturated fatty acids was observed as the growth temperature increased. Compared to the control cells grown at 37 °C, the expression of rpoS was 16.5- and 14.4-fold higher in cells cultivated at 10 and 25 °C, respectively; while the expression of rpoH was 2.9-fold higher in those cultivated at 42 °C. The increased expression of stress response gene rpoH and the decreased ratio of unsaturated to saturated fatty acids correlated with the greater heat resistance of bacteria grown at 42 °C; while the decreased expression of stress response gene rpoS at 42 °C might contribute to the decrease in acid resistance. Virulence related genes-spvR, hilA, avrA-were induced in cells cultivated at 42 °C, except sefA which was induced in the control cells. This study indicates that environmental temperature may affect the virulence potential of S. Enteritidis, thus temperature should be well controlled during food storage.

Comprehensive Reviews in Food Science and Food Safety, 2013

ABSTRACT

Food Microbiology, 2016

This study determined the effects of temperature (4 and 25 C), pH (5.3, 7.3, and 8.3), and nutrie... more This study determined the effects of temperature (4 and 25 C), pH (5.3, 7.3, and 8.3), and nutrient availability (TSB and 20 times diluted TSB (1/20 TSB)) on Salmonella Enteritidis biofilm formation and its resistance to chlorine treatment (pH 6.8, 50 ppm for 1 min). The results showed that biofilm density was significantly higher (P < 0.05) at 25 C or in 1/20 TSB, regardless of pH and bacterial strains. Moreover, 1/ 20 TSB significantly enhanced the chlorine resistance of biofilms formed at 25 C, especially for S. Enteritidis with rdar morphotype, with an average reduction of 1.52 log CFU/cm 2 compared to that of biofilm in TSB with 4.07 log reduction. All biofilms formed at 4 C were very sensitive to chlorine treatment. In most cases, acidic pH sensitized biofilms to chlorine treatment compared with neutral and alkaline pHs. The further analysis of cellulose production of biofilms indicated that it had a positive impact on biofilm resistance to chlorine treatment. This study suggests that environmental stress conditions encountered in food processing plant might alter S. Enteritidis biofilm resistance to sanitizer treatment possibly by acting on the cellulose production.

Food Control, 2020

Abstract This study investigated the microbiological and physical qualities of shell eggs pasteur... more Abstract This study investigated the microbiological and physical qualities of shell eggs pasteurized with radio frequency treatment combined with hot water (RF/HW) during 5 weeks of storage at 7.2 or 10 °C. Shell eggs inoculated with low or high levels of Salmonella Typhimurium were subjected to RF/HW pasteurization. The results showed that regardless of storage temperature, shell eggs pasteurized by RF/HW treatment were Salmonella free during 5 weeks of storage if initial counts were 2.5 log CFU/mL. However, when the inoculation level was 6.5 log CFU/mL, 0.7 log CFU/mL of Salmonella survived the pasteurization process. This small population remained stable over 5 weeks when eggs were stored at 7.2 °C, but grew to 7.4 log CFU/mL when stored at 10 °C after 4 weeks. Physical qualities, including weight loss, yolk pH, albumen pH, Haugh unit, yolk index, and albumen turbidity were also assessed during storage. In general, pasteurized shell eggs had similar quality as untreated eggs during storage at 7.2 °C for 5 weeks. Therefore, this study demonstrated that shell eggs pasteurized by RF/HW process are microbiologically safe and resemble untreated eggs during 5 weeks of storage at 7.2 °C.

Microbiology Resource Announcements, 2020

Escherichia coli sequence type 131 (ST131) has recently emerged as a leading multidrug-resistant ... more Escherichia coli sequence type 131 (ST131) has recently emerged as a leading multidrug-resistant pathogen that causes urinary tract and bloodstream infections in humans. Here, we report the draft genomic sequences of three E. coli ST131 isolates, H45, H43ii, and H43iii, from urine samples of patients in Lagos, Nigeria.

Food Microbiology, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Journal of Food Engineering, 2018

Radio frequency (RF) power, treatment time and cooling water temperature affect inactivation of S... more Radio frequency (RF) power, treatment time and cooling water temperature affect inactivation of Salmonella Typhimurium in shell eggs and internal quality. Eggs were processed using 40.68 MHz RF at 30-45 W, 2.5-8 min and 30-38°C, followed by hot water (HW) treatment at 56.7°C for 15 min. Five conditions achieved > 5 log reduction of Salmonella without observable quality change. Analyses of the longest (8 min at 30 W and 30°C) and shortest (4.5 min at 35 W and 38°C) treatments indicated that combined RF/HW treatments significantly (P < 0.05) preserved quality better than HW pasteurization (56.7°C for 60 min). No significant (P ≥ 0.05) difference in egg quality was observed between the longest and shortest treatment, except that the shortest resulted in greater albumen turbidity. As the longest treatment required 78% more time and 47% more energy than the shortest, industry may wish to use the shortest RF treatment time.

Journal of microbiology (Seoul, Korea), 2018

Monascus spp. are commonly used for a wide variety of applications in the food and pharmaceutical... more Monascus spp. are commonly used for a wide variety of applications in the food and pharmaceutical industries. In previous studies, the knock-out of mrflbA (a putative regulator of the G protein α subunit) in M. ruber led to autolysis of the mycelia, decreased pigmentation and lowered mycotoxin production. Therefore, we aimed to obtain a comprehensive overview of the underlying mechanism of mrflbA deletion at the proteome level. A two-dimensional gel electrophoresis analysis of mycelial proteins indicated that the abundance of 178 proteins was altered in the ΔmrflbA strain, 33 of which were identified with high confidence. The identified proteins are involved in a range of activities, including carbohydrate and amino acid metabolism, hyphal development and the oxidative stress response, protein modification, and the regulation of cell signaling. Consistent with these findings, the activity of antioxidative enzymes and chitinase was elevated in the supernatant of the ΔmrflbA strain. F...

Fungal Biology, 2012

FlbA (fluffy low brlA expression), a regulator of the G protein signalling (RGS) pathway, has bee... more FlbA (fluffy low brlA expression), a regulator of the G protein signalling (RGS) pathway, has been implicated in the control of hyphal development, sporulation, mycotoxin/pigment production in many kinds of filamentous fungi and yeasts. In the current study, a FlbA-like protein gene mrflbA (Monascus ruber flbA) was isolated, sequenced, and disrupted in order to investigate the RGS function in M. ruber. The results revealed that the derived protein of the mrflbA gene consisted of 734 amino acids and had the conserved RGS domain at the C-terminus and two DEP (dishevelled, Egl-10, pleckstrin) domains at the N-terminus similar to the structure of RGS proteins in other filamentous fungi. Deletion of the mrflbA gene resulted in the formation of an abnormal colony phenotype with fluffy aerial hyphae that autolyzed as the colony grew on potato dextrose agar (PDA) at 28 C. Additionally, mrflbA deletion could repress conidial germination and pigment/citrinin production in M. ruber M-7. Real-time RT-PCR analysis demonstrated that the transcription level of the G protein a subunit (Ga) was remarkably increased in the mrflbA deletion strain. These results suggest that mrflbA is involved in the modulation of aerial hyphal development and secondary metabolism, as well as, negative regulation of Ga subunit expression in M. ruber M-7.

Food Control, 2017

This study investigated the biofilm formation by three S. Enteritidis strains in a simulated liqu... more This study investigated the biofilm formation by three S. Enteritidis strains in a simulated liquid egg processing environment using 0.1% peptone water (PW) (control), 10% whole eggs (WE), 10% egg yolks (EY) and 10% egg whites (EW) as growth media, and evaluated the effectiveness of chlorine (200 ppm, 5 min) and hot water (71 °C, 30 s) treatments against S. Enteritidis biofilms. The results showed that S. Enteritidis formed significantly (P < 0.05) denser biofilms in PW and EW compared to those in WE and EY. However, biofilms formed in PW were less resistant to chlorine treatment than those formed in WE, EY, and EW, with average log reductions of 6.34, 2.28, 0.67 and 0.95 CFU/cm2, respectively. Microscopic observation showed that biofilm morphology was greatly affected by the growth medium, and the egg matrices might act as protective barriers, contributing to the greater chlorine resistance. All biofilms were very sensitive to hot water treatment, which reduced the cell populations by 4.30–7.08 log CFU/cm2. This study could advance our understanding towards the biofilm forming abilities of S. Enteritidis in liquid egg processing environments and the effectiveness of sanitation methods against S. Enteritidis biofilms, which may aid in the development of better sanitation strategies.

International journal of food microbiology, Jan 2, 2016

Fresh mung bean sprouts have been identified as a source of many Salmonella outbreaks worldwide. ... more Fresh mung bean sprouts have been identified as a source of many Salmonella outbreaks worldwide. The aim of this study was to develop a rapid and accurate detection methodology for low levels of healthy and sanitizer-injured Salmonella on mung bean sprouts using real-time PCR coupled with either immunomagnetic separation (PCR-IMS) or centrifugation (PCR-cen). Initially, three parameters of IMS; specificity/sensitivity, bacterial concentration and bead incubation time were optimized. Secondly, limit of detection (LOD) was determined for the optimized PCR-IMS and PCR-cen. These two methods were compared against PCR alone (PCR) and the standard culture method (ISO) for their ability to detect Salmonella using inoculated and uninoculated sprouts. Under optimum IMS conditions (10(5)CFU/ml for 30min), capture efficiency of Salmonella in sprout suspensions was lower than 40%, most probably due to the non-specific binding of the background microbiota. PCR-IMS and PCR-cen had a similar LOD a...

COSMOS, 2015

Food safety and food security are interrelated concepts with a profound impact on the quality of ... more Food safety and food security are interrelated concepts with a profound impact on the quality of human life. Food security describes the overall availability of food at different levels from global to individual household. While, food safety focuses on handling, preparation and storage of foods in order to prevent foodborne illnesses. This review focuses on innovative thermal and non-thermal technologies in the area of food processing as the means to ensure food security through improving food safety with emphasis on the reduction and control of microbiological risks. The antimicrobial efficiency and mechanism of new technologies to extend the shelf life of food product were also discussed.

LWT - Food Science and Technology, 2014

The effect of temperature (28, 37 and 42 C) and pH (6 and 7) on the biofilm formation capability ... more The effect of temperature (28, 37 and 42 C) and pH (6 and 7) on the biofilm formation capability of Salmonella Typhimurium on stainless steel and acrylic was investigated. The rate of biofilm formation increased with increasing temperature and pH, while the number of attached cells after 240 h decreased with increasing temperature and was not different between pH 6 and 7. The surface hydrophobicity of bacterial cells was not significantly (p > 0.05) different among tested conditions. Electron-donating/ accepting properties changed with pH and temperature, although these changes did not correlate with the ability to form biofilms under respective conditions. Attachment of S. Typhimurium showed a preference for stainless steel compared to acrylic surfaces under all conditions tested. The results suggest that salmonellae were less adherent to acrylic than to stainless steel surfaces; thus, acrylic-type surfaces should be considered for use in the food industry over stainless steel where applicable. The rate of biofilm formation increased at higher temperatures and pH levels within the tested ranges. Hurdle technology using lower temperatures reduced pH may help delay biofilm formation on food contact surfaces contaminated with S. Typhimurium.

Food Microbiology, 2015

The ability of nine commercial broths to enrich healthy and 90% sanitizer-injured Salmonella Typh... more The ability of nine commercial broths to enrich healthy and 90% sanitizer-injured Salmonella Typhimurium and Salmonella cocktail on mung bean sprouts was evaluated to select an optimum broth for detection. Results showed that S. Typhimurium multiplied faster and reached a higher population in buffered peptone water (BPW), Salmonella AD media (AD) and ONE broth-Salmonella (OB), compared with other broths. Healthy and 90% sanitizer-injured Salmonella at low concentrations increased by 4.0 log CFU/ml in these three broths. However, no Salmonella growth was observed in lactose broth (LB). Further investigation showed that during incubation, pH of LB dropped from 6.7 to 4.2, due to production of lactic (66 mM) and acetic acids (62 mM) by lactic acid bacteria that were identified as dominant microbiota in bean sprouts. Though no cell membrane damage was detected by propidium monoazide combined with real-time PCR, it was found that LB inhibited Salmonella growth, especially from low inoculum levels. This study suggests that in consideration of effectiveness and cost, BPW would be a suitable enrichment broth to use for isolating and detecting Salmonella on mung bean sprouts, while using LB might cause false negative results in Salmonella detection by either PCR or standard cultural method.

Conventional culture detection methods are time consuming and labor-intensive. For this reason, a... more Conventional culture detection methods are time consuming and labor-intensive. For this reason, an alternative rapid method combining real-time PCR and immunomagnetic separation (IMS) was investigated in this study to detect both healthy and heat-injured Salmonella Typhimurium on raw duck wings. Firstly, the IMS method was optimized by determining the capture efficiency of Dynabeads ® on Salmonella cells on raw duck wings with different bead incubation (10, 30 and 60 min) and magnetic separation (3, 10 and 30 min) times. Secondly, three Taqman primer sets, Sal, invA and ttr, were evaluated to optimize the real-time PCR protocol by comparing five parameters: inclusivity, exclusivity, PCR efficiency, detection probability and limit of detection (LOD). Thirdly, the optimized real-time PCR, in combination with IMS (PCR-IMS) assay, was compared with a standard ISO and a real-time PCR (PCR) method by analyzing artificially inoculated raw duck wings with healthy and heatinjured Salmonella cells at 10 1 and 10 0 CFU/25 g. Finally, the optimized PCR-IMS assay was validated for Salmonella detection in naturally contaminated raw duck wing samples. Under optimal IMS conditions (30 min bead incubation and 3 min magnetic separation times), approximately 85 and 64% of S. Typhimurium cells were captured by Dynabeads® from pure culture and inoculated raw duck wings, respectively. Although Sal and ttr primers exhibited 100% inclusivity and exclusivity for 16 Salmonella spp. and 36 non-Salmonella strains, the Sal primer showed lower LOD (10 3 CFU/ml) and higher PCR efficiency (94.1%) than the invA and ttr primers. Moreover, for Sal and invA primers, 100% detection probability on raw duck wings suspension was observed at 10 3 and 10 4 CFU/ml with and without IMS, respectively. Thus, the Sal primer was chosen for further experiments. The optimized PCR-IMS method was significantly (P = 0.0011) better at detecting healthy Salmonella cells after 7-h enrichment than traditional PCR method. However there was no significant difference between the two methods with longer enrichment time (14 h). The diagnostic accuracy of PCR-IMS was shown to be 98.3% through the validation study. These results indicate that the optimized PCR-IMS method in this study could provide a sensitive, specific and rapid detection method for Salmonella on raw duck wings, enabling 10-h detection. However, a longer enrichment time could be needed for resuscitation and reliable detection of heat-injured cells.

International Journal of Food Microbiology, 2014

This study evaluated the acid and heat resistance of Salmonella Enteritidis in simulated gastric ... more This study evaluated the acid and heat resistance of Salmonella Enteritidis in simulated gastric fluid (pH 2.0) and during thermal treatment (54-60°C), respectively, after adaptation to lactic acid (LA) or trisodium phosphate (TSP) at various pHs (pH 5.3-9.0). The changes in membrane lipid composition and expression levels of RpoS and RpoH were examined to elucidate their roles in bacterial stress resistance. Transcriptional profile of several virulence-related genes was also analyzed. Results showed that LA-adapted cells at pH 5.3 and 6.3 had higher acid and heat resistance than control cells and cells adapted to TSP at pH 8.3 and 9.0. LA-adapted cells had the lowest ratio of unsaturated to saturated fatty acids, indicating that they might possess a less fluid membrane. It was observed that the expression levels of RpoH and RpoS were upregulated in TSP-adapted cells but not in LA-adapted cells. Thus, these results indicate that the increased acid and heat resistance of LA-adapted S. Enteritidis was possibly due to the decreased membrane fluidity instead of the upregulation of RpoS and RpoH. About 6.0, 2.1, and 2.46-fold upregulation of spvR, avrA, and hilA were observed in cells adapted to TSP at pH 9.0, except sefA that had its highest expression level in the control cells, indicating that the expression of these virulence genes highly depends on environmental conditions. This is the first study to show that the alteration in the cytoplasmic membrane rather than RpoS and RpoH plays a more crucial role in conferring greater acid and heat resistance on LAadapted S. Enteritidis, thus providing a better understanding on the bacterial stress response to acidic conditions.

Journal of Food Safety, 2012

The aim of this study was to investigate survival of Salmonella Newport and Salmonella Saintpaul ... more The aim of this study was to investigate survival of Salmonella Newport and Salmonella Saintpaul in simulated gastric fluid (SGF) at pH 1.9 or at 56C after storage in mango or pineapple juice at 4 or 24C for 24 h. In SGF, only Salmonella Saintpaul adapted to mango juice at 4C significantly (P < 0.05) enhanced its acid resistance with D value of 3.88 min, whereas both serovars stored in mango juice at 24C had significantly lower D values with 0.88 and 0.72 min, respectively. The D56C values of both serovars adapted to juices significantly decreased compared with nonadapted cells, except for Salmonella Newport stored in pineapple juice at 24C. Overall, two Salmonella serovars tested in this study did not show the enhanced acid or heat resistance after storage in these two tropical fruit juices, indicating that introduction of Salmonella Newport and Salmonella Saintpaul to mango and pineapple juices is unlikely to enhance their survival during gastric transit or thermal processing. PRACTICAL APPLICATIONS Salmonella spp., one of the leading causative agents of gastroenteritis, are a major public health concern in the world. It has been reported that Salmonella spp. can survive in unpasteurized orange juice or apple cider and become more resistant to subsequent exposure to acid or heat conditions.However,there is limited information in the literature on the effect of survival of Salmonella spp. in tropical fruit juices on their acid and heat resistance. This research was conducted to investigate the survivability of Salmonella Newport and Salmonella Saintpaul in simulated gastric fluid at pH 1.9 or at 56C after adaptation in mango or pineapple juice.The results of this study would enrich our understanding on the stress response of Salmonella spp. in these juices, as well as provide guidance to developing intervention technology to eliminate Salmonella Newport and Salmonella Saintpaul in mango and pineapple juices.

Journal of Food Protection, 2013

This study was performed to optimize Salmonella Typhimurium recovery from raw duck wings with fiv... more This study was performed to optimize Salmonella Typhimurium recovery from raw duck wings with five nonselective broths (buffered peptone water, tryptic soy broth, lactose broth, universal preenrichment broth, nutrient broth) and four selective broths (selenite broth, BAX System MP media [MP], Salmonella AD media [AD], ONE broth-Salmonella [OB]). Healthy or heat-injured (50 and 85% injury) cells were inoculated at a level of 102, 101, or 100 CFU/25 g on raw duck wings. Growth was modeled using DMfit with four growth parameters: lag-phase duration, maximum growth rate, doubling time, and maximum population density. Most enrichments were able to recover Salmonella Typhimurium to greater than 6 log CFU/ml. AD, MP, and OB had significantly (P < 0.05) higher maximum growth rate (0.9 to 1.0/h) and lower doubling time (0.7 to 0.8 h). Buffered peptone water, AD, MP, and OB recovered healthy and 50%-injured cells at low inoculum levels to more than 6.0 log CFU/ml; OB achieved the greatest ...

International Journal of Food Microbiology, 2014

The influence of growth temperature (10, 25, 37, and 42 °C) on the survival of Salmonella Enterit... more The influence of growth temperature (10, 25, 37, and 42 °C) on the survival of Salmonella Enteritidis in simulated gastric fluid (SGF; pH=2.0) and during heat treatment (54, 56, 58, and 60 °C), on the membrane fatty acid composition, as well as on stress-/virulence-related gene expression was studied. Cells incubated at temperatures lower or higher than 37 °C did not increase their acid resistance, with the maximum D-value of 3.07 min in cells grown at 37 °C; while those incubated at higher temperature increased their heat resistance, with the maximum D60 °C-values of 1.4 min in cells grown at 42 °C. A decrease in the ratio of unsaturated to saturated fatty acids was observed as the growth temperature increased. Compared to the control cells grown at 37 °C, the expression of rpoS was 16.5- and 14.4-fold higher in cells cultivated at 10 and 25 °C, respectively; while the expression of rpoH was 2.9-fold higher in those cultivated at 42 °C. The increased expression of stress response gene rpoH and the decreased ratio of unsaturated to saturated fatty acids correlated with the greater heat resistance of bacteria grown at 42 °C; while the decreased expression of stress response gene rpoS at 42 °C might contribute to the decrease in acid resistance. Virulence related genes-spvR, hilA, avrA-were induced in cells cultivated at 42 °C, except sefA which was induced in the control cells. This study indicates that environmental temperature may affect the virulence potential of S. Enteritidis, thus temperature should be well controlled during food storage.

Comprehensive Reviews in Food Science and Food Safety, 2013

ABSTRACT

Food Microbiology, 2016

This study determined the effects of temperature (4 and 25 C), pH (5.3, 7.3, and 8.3), and nutrie... more This study determined the effects of temperature (4 and 25 C), pH (5.3, 7.3, and 8.3), and nutrient availability (TSB and 20 times diluted TSB (1/20 TSB)) on Salmonella Enteritidis biofilm formation and its resistance to chlorine treatment (pH 6.8, 50 ppm for 1 min). The results showed that biofilm density was significantly higher (P < 0.05) at 25 C or in 1/20 TSB, regardless of pH and bacterial strains. Moreover, 1/ 20 TSB significantly enhanced the chlorine resistance of biofilms formed at 25 C, especially for S. Enteritidis with rdar morphotype, with an average reduction of 1.52 log CFU/cm 2 compared to that of biofilm in TSB with 4.07 log reduction. All biofilms formed at 4 C were very sensitive to chlorine treatment. In most cases, acidic pH sensitized biofilms to chlorine treatment compared with neutral and alkaline pHs. The further analysis of cellulose production of biofilms indicated that it had a positive impact on biofilm resistance to chlorine treatment. This study suggests that environmental stress conditions encountered in food processing plant might alter S. Enteritidis biofilm resistance to sanitizer treatment possibly by acting on the cellulose production.

Food Control, 2020

Abstract This study investigated the microbiological and physical qualities of shell eggs pasteur... more Abstract This study investigated the microbiological and physical qualities of shell eggs pasteurized with radio frequency treatment combined with hot water (RF/HW) during 5 weeks of storage at 7.2 or 10 °C. Shell eggs inoculated with low or high levels of Salmonella Typhimurium were subjected to RF/HW pasteurization. The results showed that regardless of storage temperature, shell eggs pasteurized by RF/HW treatment were Salmonella free during 5 weeks of storage if initial counts were 2.5 log CFU/mL. However, when the inoculation level was 6.5 log CFU/mL, 0.7 log CFU/mL of Salmonella survived the pasteurization process. This small population remained stable over 5 weeks when eggs were stored at 7.2 °C, but grew to 7.4 log CFU/mL when stored at 10 °C after 4 weeks. Physical qualities, including weight loss, yolk pH, albumen pH, Haugh unit, yolk index, and albumen turbidity were also assessed during storage. In general, pasteurized shell eggs had similar quality as untreated eggs during storage at 7.2 °C for 5 weeks. Therefore, this study demonstrated that shell eggs pasteurized by RF/HW process are microbiologically safe and resemble untreated eggs during 5 weeks of storage at 7.2 °C.

Microbiology Resource Announcements, 2020

Escherichia coli sequence type 131 (ST131) has recently emerged as a leading multidrug-resistant ... more Escherichia coli sequence type 131 (ST131) has recently emerged as a leading multidrug-resistant pathogen that causes urinary tract and bloodstream infections in humans. Here, we report the draft genomic sequences of three E. coli ST131 isolates, H45, H43ii, and H43iii, from urine samples of patients in Lagos, Nigeria.

Food Microbiology, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Journal of Food Engineering, 2018

Radio frequency (RF) power, treatment time and cooling water temperature affect inactivation of S... more Radio frequency (RF) power, treatment time and cooling water temperature affect inactivation of Salmonella Typhimurium in shell eggs and internal quality. Eggs were processed using 40.68 MHz RF at 30-45 W, 2.5-8 min and 30-38°C, followed by hot water (HW) treatment at 56.7°C for 15 min. Five conditions achieved > 5 log reduction of Salmonella without observable quality change. Analyses of the longest (8 min at 30 W and 30°C) and shortest (4.5 min at 35 W and 38°C) treatments indicated that combined RF/HW treatments significantly (P < 0.05) preserved quality better than HW pasteurization (56.7°C for 60 min). No significant (P ≥ 0.05) difference in egg quality was observed between the longest and shortest treatment, except that the shortest resulted in greater albumen turbidity. As the longest treatment required 78% more time and 47% more energy than the shortest, industry may wish to use the shortest RF treatment time.

Journal of microbiology (Seoul, Korea), 2018

Monascus spp. are commonly used for a wide variety of applications in the food and pharmaceutical... more Monascus spp. are commonly used for a wide variety of applications in the food and pharmaceutical industries. In previous studies, the knock-out of mrflbA (a putative regulator of the G protein α subunit) in M. ruber led to autolysis of the mycelia, decreased pigmentation and lowered mycotoxin production. Therefore, we aimed to obtain a comprehensive overview of the underlying mechanism of mrflbA deletion at the proteome level. A two-dimensional gel electrophoresis analysis of mycelial proteins indicated that the abundance of 178 proteins was altered in the ΔmrflbA strain, 33 of which were identified with high confidence. The identified proteins are involved in a range of activities, including carbohydrate and amino acid metabolism, hyphal development and the oxidative stress response, protein modification, and the regulation of cell signaling. Consistent with these findings, the activity of antioxidative enzymes and chitinase was elevated in the supernatant of the ΔmrflbA strain. F...

Fungal Biology, 2012

FlbA (fluffy low brlA expression), a regulator of the G protein signalling (RGS) pathway, has bee... more FlbA (fluffy low brlA expression), a regulator of the G protein signalling (RGS) pathway, has been implicated in the control of hyphal development, sporulation, mycotoxin/pigment production in many kinds of filamentous fungi and yeasts. In the current study, a FlbA-like protein gene mrflbA (Monascus ruber flbA) was isolated, sequenced, and disrupted in order to investigate the RGS function in M. ruber. The results revealed that the derived protein of the mrflbA gene consisted of 734 amino acids and had the conserved RGS domain at the C-terminus and two DEP (dishevelled, Egl-10, pleckstrin) domains at the N-terminus similar to the structure of RGS proteins in other filamentous fungi. Deletion of the mrflbA gene resulted in the formation of an abnormal colony phenotype with fluffy aerial hyphae that autolyzed as the colony grew on potato dextrose agar (PDA) at 28 C. Additionally, mrflbA deletion could repress conidial germination and pigment/citrinin production in M. ruber M-7. Real-time RT-PCR analysis demonstrated that the transcription level of the G protein a subunit (Ga) was remarkably increased in the mrflbA deletion strain. These results suggest that mrflbA is involved in the modulation of aerial hyphal development and secondary metabolism, as well as, negative regulation of Ga subunit expression in M. ruber M-7.