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Papers by kidon sung

Cells

Staphylococcus epidermidis is a leading cause of biofilm-associated infections on implanted medic... more Staphylococcus epidermidis is a leading cause of biofilm-associated infections on implanted medical devices. During the treatment of an infection, bacterial cells inside biofilms may be exposed to sublethal concentrations of the antimicrobial agents. In the present study, the effect of subinhibitory concentrations of tigecycline (TC) on biofilms formed by S. epidermidis strain RP62A was investigated using a quantitative global proteomic technique. Sublethal concentrations of TC [1/8 (T1) and 1/4 minimum inhibitory concentration (MIC) (T2)] promoted biofilm production in strain RP62A, but 1/2 MIC TC (T3) significantly inhibited biofilm production. Overall, 413, 429, and 518 proteins were differentially expressed in biofilms grown with 1/8 (T1), 1/4 (T2), and 1/2 (T3) MIC of TC, respectively. As the TC concentration increased, the number of induced proteins in each Cluster of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway increased. The TC concentr...

Korean Journal of Chemical Engineering, 1998

A freshwater microalga, which has tolerance to high concentrations of CO,, was isolated. The KR-1... more A freshwater microalga, which has tolerance to high concentrations of CO,, was isolated. The KR-1 strain was identified to be as genus Chlorellu. Though Chlorellu KR-1 showed maximum growth at 10% COr, the strain showed a good growth rate up to 50% CO,. The results indicated the feasibility of the KR-1 strain for mass cultivation using condensed stack gases.

Antibiotics

Pseudomonas aeruginosa is the most common Gram-negative pathogen causing nosocomial multidrug res... more Pseudomonas aeruginosa is the most common Gram-negative pathogen causing nosocomial multidrug resistant infections. It is a good biofilm producer and has the potential for contaminating medical devices. Despite the widespread use of antibacterial-impregnated catheters, little is known about the impacts of antibacterial coating on the pathogenesis of P. aeruginosa. In this study, we investigated the adaptive resistance potential of P. aeruginosa strain PAO1 in response to continuous antibiotic exposure from clindamycin/rifampicin-impregnated catheters (CR-IC). During exposure for 144 h to clindamycin and rifampicin released from CR-IC, strain PAO1 formed biofilms featuring elongated and swollen cells. There were 545 and 372 differentially expressed proteins (DEPs) identified in the planktonic and biofilm cells, respectively, by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Both Cluster of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes ...

Data, 2022

Biofilms are complex surface-attached bacterial communities that serve as a protective survival s... more Biofilms are complex surface-attached bacterial communities that serve as a protective survival strategy to adapt to an environment. Bacterial contamination and biofilm formation on implantable medical devices pose a serious threat to human health, and these biofilms have become the most important source of nosocomial infections. Although antimicrobial-impregnated catheters have been employed to prevent bacterial infection, there have been concerns about the potential emergence of antibiotic resistance. To investigate the risk of developing resistance, we performed RNA-sequencing gene expression profiling of P. aeruginosa biofilms in response to chronic exposure to clindamycin and rifampicin eluted from antibiotic-coated catheters in a CDC biofilm bioreactor. There were 877 and 178 differentially expressed genes identified in planktonic and biofilm cells after growth for 144 h with control (without antibiotic-impregnation) and clindamycin/rifampicin-impregnated catheters, respective...

Microbiology Resource Announcements, 2022

We report here the draft genome sequences of 16 fluoroquinolone-resistant extraintestinal Escheri... more We report here the draft genome sequences of 16 fluoroquinolone-resistant extraintestinal Escherichia coli isolates from human patients. These isolates had high MICs (32 to 256 μg/mL) for ciprofloxacin and contained point mutations in the quinolone resistance-determining region (QRDR) of both gyrA and parC that confer resistance to fluoroquinolone.

Microbiology Resource Announcements, 2022

We present the draft genome sequences of nine hospital-associated methicillin-susceptible Staphyl... more We present the draft genome sequences of nine hospital-associated methicillin-susceptible Staphylococcus aureus (HA-MSSA) strains. All strains were from Minnesota (eight from blood and one from bone), harbored various virulence genes, and showed diverse multilocus sequence typing and spa types.

Journal of Hazardous Materials, 2018

Comprehensive in vitro and in vivo risk assessments of chitosan microparticles using human epithe... more Comprehensive in vitro and in vivo risk assessments of chitosan microparticles using human epithelial cells and Caenorhabditis elegans, Journal of Hazardous Materialshttp://dx.

International Journal of Food Microbiology, 2012

A study was undertaken to isolate and characterize tetracycline and nalidixic acid-resistant Kleb... more A study was undertaken to isolate and characterize tetracycline and nalidixic acid-resistant Klebsiella spp. in farm-raised, imported shrimp sold in the United States. Sixty-seven multiple antibiotic-resistant Klebsiella spp. strains were isolated from imported shrimp samples. Using morphological and biochemical methods, fifty-three strains were tentatively identified as Klebsiella pneumoniae and fourteen as K. oxytoca. Although all isolates were resistant to tetracycline, only 8 were resistant to nalidixic acid. These 8 isolates were further screened by PCR for quinolone resistance genes (qnrA, B, S, gyrA, B and parC). PCR protocols failed to amplify any qnr genes. The purified PCR amplicons of gyrA, gyrB and parC were sequenced and analyzed for point mutations that confer resistance to fluoroquinolone antibiotics. Analysis of the sequences of the gyrA amplicons from nalidixic acid-resistant Klebsiella spp. indicated two point mutations in gyrA at positions 83 (Ser → Phe) and 87 (Asp → Ala). Sequence analysis of the parC amplicons indicated an amino acid change at position 80 (Ser → Ile). No mutations were detected in gyrB. Template DNA from all isolates was screened for tetracycline resistance genes (tetA-E). Oligonucleotide primers specifically targeting a 305-bp region of tetB and a 477-bp region of tetD successfully amplified sequences from 91.0 and 44.0% of the isolates, respectively. None of the isolates contained tetA, tetC or tetE genes. Plasmids (2.0-16.0 kb) were found in 23 of the 67 isolates. XbaI-PFGE identified 32 distinct macro restriction patterns (mrps) among the 61 multiple drugresistant Klebsiella spp. that were typable. Our results indicate that imported shrimp is a reservoir for multidrug resistant Klebsiella spp. and potential health risks posed by such strains should not be underestimated.

International Journal of Antimicrobial Agents, 2008

A clinical strain of Enterococcus faecium ATCC 51559 exhibits heteroresistance, i.e. a high level... more A clinical strain of Enterococcus faecium ATCC 51559 exhibits heteroresistance, i.e. a high level of resistance to vancomycin (minimum inhibitory concentration (MIC) > 256 g/mL) by broth dilution but sensitivity to vancomycin by Etest (MIC = 1.8 g/mL). Three variants of this strain, EF1, EF2 and EF3, exhibit high levels of resistance to vancomycin both by broth dilution and Etest assays. The four strains were used to study heteroresistance by pulsed-field gel electrophoresis (PFGE), polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP) and sequence analysis of a partial region of the van operon. Minor differences between SalI and SmaI restriction profiles of the variants and the parental strain were observed by PFGE analysis. PCR analysis confirmed the presence of the vancomycin resistance marker vanA (0.73 kb) and a larger than expected amplicon (8.2 kb vs. 6.7 kb) of the van operon in all the strains. The 8.2 kb van operon was cloned for EcoRI RFLP and sequence analysis. All of the clones exhibited distinctly different RFLP profiles when grown in the presence of kanamycin or vancomycin + kanamycin. The presence of these antibiotics during overnight growth of EF1 on plates also resulted in altered SalI PFGE profiles. Sequence analysis of the van operon clones revealed a 1.5 kb IS1251-like insertion element between the vanS and vanH genes in all the strains. Several novel point mutations in the vanR, vanS, vanH, vanA, vanX and vanY genes were also discovered. Some of these mutations were present in the parental strain only and included base substitutions T → C, A → G, T → A and T → C at nucleotide positions 4202, 4597, 4763 and 6207 of Tn1546, resulting in amino acid replacements I76 → T and K208 → E of vanR, S19 → T of vanS and L64 → P of vanH genes, respectively. We believe that these are responsible for the observed heteroresistance. The present study clearly shows how independent novel mutations can give rise to polymorphism, heteroresistance and clonal diversity among vancomycin-resistant enterococci strains as a result of continuous exposure to antibiotics.

FEMS Microbiology Letters, 2003

A fast, reliable, and inexpensive Triton X-100 boiling procedure for RNA isolation from both the ... more A fast, reliable, and inexpensive Triton X-100 boiling procedure for RNA isolation from both the Gram-positive and Gram-negative bacteria was developed. The yield of RNA was 0.2^2 mg per 10 ml bacterial culture. The method was tested on Gram-positive and Gramnegative bacteria of eight genera and nine species and yielded reproducible results. In parallel experiments, the Qiagen and hot phenol extraction methods both yielded RNA that contained contaminating 16S and 23S rRNA. The Triton X-100 boiling method reported here yielded RNA that was free from 16S and 23S rRNA, contained full-length transcripts and did not require additional purification. The presence of specific mRNA in one of the RNA samples obtained by this procedure was demonstrated by partial amplification of a 732 bp vancomycin resistance gene, vanA, by reverse transcription-polymerase chain reaction (RT-PCR). The presence of a full-length transcript (1031 bases) of the vanA gene was verified by Northern hybridization and probing with a digoxigenin (DIG)-labeled vanA PCR partial product. The method provides a rapid, reliable, and simple tool for the isolation of good quality RNA suitable for various molecular biology experiments.

Foodborne Pathogens and Disease, 2009

A study was undertaken to investigate the occurrence of tetracycline-resistant genes and to chara... more A study was undertaken to investigate the occurrence of tetracycline-resistant genes and to characterize the integrons present in Escherichia coli isolated from catfish. Sixty-three tetracycline-resistant E. coli strains were isolated from the intestinal contents of 407 farm-raised catfish. All strains were resistant to multiple antibiotics. A polymerase chain reaction (PCR) assay detected tetA in the DNA of 15 of 63 (25.0%) isolates by amplifying a PCR amplicon measuring 957 bp. Oligonucleotide primers targeting a 436-bp region of tetB successfully amplified a PCR amplicon from 47 of 63 (77.0%) isolates, indicating that tetB was predominant. Oligonucleotide primers specific for tetC amplified a 589-bp PCR amplicon from 3 of 63 (5%) isolates. Eleven (17.0%) of the isolates contained both tetA and tetB genes. Class I integrons amplified from the genomic DNA of 14 of 63 (22.0%) isolates measured 1.6 and 1.8 kb. Sequence analysis of the 1.6 kb integrons indicated the presence of three different gene cassettes: a dfrA12, conferring resistance to trimethoprim; an open reading frame, orfF, a hypothetical protein of unknown function; and aadA2, conferring resistance to aminoglycosides. Sequence analysis of the 1.8-kb integron indicated the presence of dfrA17 and aadA5. PCR assays for the detection of the six predominant virulence genes failed to amplify any genes from the genomic DNA. Pulsed-field gel electrophoresis using XbaI identified 16 distinct macro restriction patterns among the 63 isolates. The dendrogram analysis indicated that the DNA from 4 of 16 isolates had a similarity index of 90.0%. Our results indicate that the use of oxytetracycline and Romet 30 (sulfadimethoxine and ormetoprim) in farm-raised catfish may select for multiple antibiotic-resistant E. coli that could serve as a reservoir of tetracycline, trimethoprim, and aminoglycoside resistance genes.

Microbiology Resource Announcements

Infections caused by hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) st... more Infections caused by hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) strains have higher morbidity and mortality rates and require longer hospital stays than do those caused by hospital-associated methicillin-sensitive Staphylococcus aureus strains. To gain insight into their genomic makeup, antimicrobial resistance, biofilm formation, and virulence potentials, here we present the draft whole-genome sequences of 27 HA-MRSA strains isolated in Minnesota.

Methicillin-resistant Staphylococcus aureus (MRSA) has become a growing concern in companion and ... more Methicillin-resistant Staphylococcus aureus (MRSA) has become a growing concern in companion and food-producing animals. The presence of multidrug-resistance with a wide range of extracellular enterotoxin genes, virulence factors, and Panton-Valentine leukocidin (pvl) cytotoxin genes confer life-threatening traits on MRSA and makes them highly pathogenic and difficult to treat. Clonal complex 398 (CC398), a predominant clonal lineage of livestock-associated-MRSA in domestic animals and retail meat, is capable of infecting humans. In order to monitor and prevent MRSA contamination, it is critical to understand its source and transmission dynamics. In this review, we describe MRSA in food-producing animals (pig, cattle, chicken), horses, pet animals (dogs, cats), and food products (pork, beef, chicken, milk, and fish).

Exponential growth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in Campylob... more Exponential growth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in Campylobacter media has become a common problem for the detection of Campylobacter in chicken meats. We investigated the minimum inhibitory concentration of 40 ESBL-producing E. coli isolates from meats obtained from various countries against antibacterial agents in Bolton broth (cefoperazone, vancomycin, and trimethoprim). All ESBL-producing E. coli strains were resistant to cefoperazone and vancomycin, whereas 50% of them were resistant to trimethoprim and grew in Bolton broth. We found that 20 μg/mL of rifampicin inhibited the growth of trimethoprim-resistant E. coli strains. Hence, we added 20 μg/mL of rifampicin to Bolton broth to improve the isolation of Campylobacter from chicken carcass rinses. The isolation rate of Campylobacter was significantly higher in the modified broth (44 out of 58, 75.9%, P < 0.05) than in the normal broth (0 out of 58, 0%). Furthermore, the number of agar plates with non-Campylobacter spp. was much lower after enrichment in the modified broth (4 out of 58, 6.9%, P < 0.05) than in the normal broth (58 out of 58, 100%).

Cells

Staphylococcus epidermidis is a leading cause of biofilm-associated infections on implanted medic... more Staphylococcus epidermidis is a leading cause of biofilm-associated infections on implanted medical devices. During the treatment of an infection, bacterial cells inside biofilms may be exposed to sublethal concentrations of the antimicrobial agents. In the present study, the effect of subinhibitory concentrations of tigecycline (TC) on biofilms formed by S. epidermidis strain RP62A was investigated using a quantitative global proteomic technique. Sublethal concentrations of TC [1/8 (T1) and 1/4 minimum inhibitory concentration (MIC) (T2)] promoted biofilm production in strain RP62A, but 1/2 MIC TC (T3) significantly inhibited biofilm production. Overall, 413, 429, and 518 proteins were differentially expressed in biofilms grown with 1/8 (T1), 1/4 (T2), and 1/2 (T3) MIC of TC, respectively. As the TC concentration increased, the number of induced proteins in each Cluster of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway increased. The TC concentr...

Korean Journal of Chemical Engineering, 1998

A freshwater microalga, which has tolerance to high concentrations of CO,, was isolated. The KR-1... more A freshwater microalga, which has tolerance to high concentrations of CO,, was isolated. The KR-1 strain was identified to be as genus Chlorellu. Though Chlorellu KR-1 showed maximum growth at 10% COr, the strain showed a good growth rate up to 50% CO,. The results indicated the feasibility of the KR-1 strain for mass cultivation using condensed stack gases.

Antibiotics

Pseudomonas aeruginosa is the most common Gram-negative pathogen causing nosocomial multidrug res... more Pseudomonas aeruginosa is the most common Gram-negative pathogen causing nosocomial multidrug resistant infections. It is a good biofilm producer and has the potential for contaminating medical devices. Despite the widespread use of antibacterial-impregnated catheters, little is known about the impacts of antibacterial coating on the pathogenesis of P. aeruginosa. In this study, we investigated the adaptive resistance potential of P. aeruginosa strain PAO1 in response to continuous antibiotic exposure from clindamycin/rifampicin-impregnated catheters (CR-IC). During exposure for 144 h to clindamycin and rifampicin released from CR-IC, strain PAO1 formed biofilms featuring elongated and swollen cells. There were 545 and 372 differentially expressed proteins (DEPs) identified in the planktonic and biofilm cells, respectively, by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Both Cluster of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes ...

Data, 2022

Biofilms are complex surface-attached bacterial communities that serve as a protective survival s... more Biofilms are complex surface-attached bacterial communities that serve as a protective survival strategy to adapt to an environment. Bacterial contamination and biofilm formation on implantable medical devices pose a serious threat to human health, and these biofilms have become the most important source of nosocomial infections. Although antimicrobial-impregnated catheters have been employed to prevent bacterial infection, there have been concerns about the potential emergence of antibiotic resistance. To investigate the risk of developing resistance, we performed RNA-sequencing gene expression profiling of P. aeruginosa biofilms in response to chronic exposure to clindamycin and rifampicin eluted from antibiotic-coated catheters in a CDC biofilm bioreactor. There were 877 and 178 differentially expressed genes identified in planktonic and biofilm cells after growth for 144 h with control (without antibiotic-impregnation) and clindamycin/rifampicin-impregnated catheters, respective...

Microbiology Resource Announcements, 2022

We report here the draft genome sequences of 16 fluoroquinolone-resistant extraintestinal Escheri... more We report here the draft genome sequences of 16 fluoroquinolone-resistant extraintestinal Escherichia coli isolates from human patients. These isolates had high MICs (32 to 256 μg/mL) for ciprofloxacin and contained point mutations in the quinolone resistance-determining region (QRDR) of both gyrA and parC that confer resistance to fluoroquinolone.

Microbiology Resource Announcements, 2022

We present the draft genome sequences of nine hospital-associated methicillin-susceptible Staphyl... more We present the draft genome sequences of nine hospital-associated methicillin-susceptible Staphylococcus aureus (HA-MSSA) strains. All strains were from Minnesota (eight from blood and one from bone), harbored various virulence genes, and showed diverse multilocus sequence typing and spa types.

Journal of Hazardous Materials, 2018

Comprehensive in vitro and in vivo risk assessments of chitosan microparticles using human epithe... more Comprehensive in vitro and in vivo risk assessments of chitosan microparticles using human epithelial cells and Caenorhabditis elegans, Journal of Hazardous Materialshttp://dx.

International Journal of Food Microbiology, 2012

A study was undertaken to isolate and characterize tetracycline and nalidixic acid-resistant Kleb... more A study was undertaken to isolate and characterize tetracycline and nalidixic acid-resistant Klebsiella spp. in farm-raised, imported shrimp sold in the United States. Sixty-seven multiple antibiotic-resistant Klebsiella spp. strains were isolated from imported shrimp samples. Using morphological and biochemical methods, fifty-three strains were tentatively identified as Klebsiella pneumoniae and fourteen as K. oxytoca. Although all isolates were resistant to tetracycline, only 8 were resistant to nalidixic acid. These 8 isolates were further screened by PCR for quinolone resistance genes (qnrA, B, S, gyrA, B and parC). PCR protocols failed to amplify any qnr genes. The purified PCR amplicons of gyrA, gyrB and parC were sequenced and analyzed for point mutations that confer resistance to fluoroquinolone antibiotics. Analysis of the sequences of the gyrA amplicons from nalidixic acid-resistant Klebsiella spp. indicated two point mutations in gyrA at positions 83 (Ser → Phe) and 87 (Asp → Ala). Sequence analysis of the parC amplicons indicated an amino acid change at position 80 (Ser → Ile). No mutations were detected in gyrB. Template DNA from all isolates was screened for tetracycline resistance genes (tetA-E). Oligonucleotide primers specifically targeting a 305-bp region of tetB and a 477-bp region of tetD successfully amplified sequences from 91.0 and 44.0% of the isolates, respectively. None of the isolates contained tetA, tetC or tetE genes. Plasmids (2.0-16.0 kb) were found in 23 of the 67 isolates. XbaI-PFGE identified 32 distinct macro restriction patterns (mrps) among the 61 multiple drugresistant Klebsiella spp. that were typable. Our results indicate that imported shrimp is a reservoir for multidrug resistant Klebsiella spp. and potential health risks posed by such strains should not be underestimated.

International Journal of Antimicrobial Agents, 2008

A clinical strain of Enterococcus faecium ATCC 51559 exhibits heteroresistance, i.e. a high level... more A clinical strain of Enterococcus faecium ATCC 51559 exhibits heteroresistance, i.e. a high level of resistance to vancomycin (minimum inhibitory concentration (MIC) > 256 g/mL) by broth dilution but sensitivity to vancomycin by Etest (MIC = 1.8 g/mL). Three variants of this strain, EF1, EF2 and EF3, exhibit high levels of resistance to vancomycin both by broth dilution and Etest assays. The four strains were used to study heteroresistance by pulsed-field gel electrophoresis (PFGE), polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP) and sequence analysis of a partial region of the van operon. Minor differences between SalI and SmaI restriction profiles of the variants and the parental strain were observed by PFGE analysis. PCR analysis confirmed the presence of the vancomycin resistance marker vanA (0.73 kb) and a larger than expected amplicon (8.2 kb vs. 6.7 kb) of the van operon in all the strains. The 8.2 kb van operon was cloned for EcoRI RFLP and sequence analysis. All of the clones exhibited distinctly different RFLP profiles when grown in the presence of kanamycin or vancomycin + kanamycin. The presence of these antibiotics during overnight growth of EF1 on plates also resulted in altered SalI PFGE profiles. Sequence analysis of the van operon clones revealed a 1.5 kb IS1251-like insertion element between the vanS and vanH genes in all the strains. Several novel point mutations in the vanR, vanS, vanH, vanA, vanX and vanY genes were also discovered. Some of these mutations were present in the parental strain only and included base substitutions T → C, A → G, T → A and T → C at nucleotide positions 4202, 4597, 4763 and 6207 of Tn1546, resulting in amino acid replacements I76 → T and K208 → E of vanR, S19 → T of vanS and L64 → P of vanH genes, respectively. We believe that these are responsible for the observed heteroresistance. The present study clearly shows how independent novel mutations can give rise to polymorphism, heteroresistance and clonal diversity among vancomycin-resistant enterococci strains as a result of continuous exposure to antibiotics.

FEMS Microbiology Letters, 2003

A fast, reliable, and inexpensive Triton X-100 boiling procedure for RNA isolation from both the ... more A fast, reliable, and inexpensive Triton X-100 boiling procedure for RNA isolation from both the Gram-positive and Gram-negative bacteria was developed. The yield of RNA was 0.2^2 mg per 10 ml bacterial culture. The method was tested on Gram-positive and Gramnegative bacteria of eight genera and nine species and yielded reproducible results. In parallel experiments, the Qiagen and hot phenol extraction methods both yielded RNA that contained contaminating 16S and 23S rRNA. The Triton X-100 boiling method reported here yielded RNA that was free from 16S and 23S rRNA, contained full-length transcripts and did not require additional purification. The presence of specific mRNA in one of the RNA samples obtained by this procedure was demonstrated by partial amplification of a 732 bp vancomycin resistance gene, vanA, by reverse transcription-polymerase chain reaction (RT-PCR). The presence of a full-length transcript (1031 bases) of the vanA gene was verified by Northern hybridization and probing with a digoxigenin (DIG)-labeled vanA PCR partial product. The method provides a rapid, reliable, and simple tool for the isolation of good quality RNA suitable for various molecular biology experiments.

Foodborne Pathogens and Disease, 2009

A study was undertaken to investigate the occurrence of tetracycline-resistant genes and to chara... more A study was undertaken to investigate the occurrence of tetracycline-resistant genes and to characterize the integrons present in Escherichia coli isolated from catfish. Sixty-three tetracycline-resistant E. coli strains were isolated from the intestinal contents of 407 farm-raised catfish. All strains were resistant to multiple antibiotics. A polymerase chain reaction (PCR) assay detected tetA in the DNA of 15 of 63 (25.0%) isolates by amplifying a PCR amplicon measuring 957 bp. Oligonucleotide primers targeting a 436-bp region of tetB successfully amplified a PCR amplicon from 47 of 63 (77.0%) isolates, indicating that tetB was predominant. Oligonucleotide primers specific for tetC amplified a 589-bp PCR amplicon from 3 of 63 (5%) isolates. Eleven (17.0%) of the isolates contained both tetA and tetB genes. Class I integrons amplified from the genomic DNA of 14 of 63 (22.0%) isolates measured 1.6 and 1.8 kb. Sequence analysis of the 1.6 kb integrons indicated the presence of three different gene cassettes: a dfrA12, conferring resistance to trimethoprim; an open reading frame, orfF, a hypothetical protein of unknown function; and aadA2, conferring resistance to aminoglycosides. Sequence analysis of the 1.8-kb integron indicated the presence of dfrA17 and aadA5. PCR assays for the detection of the six predominant virulence genes failed to amplify any genes from the genomic DNA. Pulsed-field gel electrophoresis using XbaI identified 16 distinct macro restriction patterns among the 63 isolates. The dendrogram analysis indicated that the DNA from 4 of 16 isolates had a similarity index of 90.0%. Our results indicate that the use of oxytetracycline and Romet 30 (sulfadimethoxine and ormetoprim) in farm-raised catfish may select for multiple antibiotic-resistant E. coli that could serve as a reservoir of tetracycline, trimethoprim, and aminoglycoside resistance genes.

Microbiology Resource Announcements

Infections caused by hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) st... more Infections caused by hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) strains have higher morbidity and mortality rates and require longer hospital stays than do those caused by hospital-associated methicillin-sensitive Staphylococcus aureus strains. To gain insight into their genomic makeup, antimicrobial resistance, biofilm formation, and virulence potentials, here we present the draft whole-genome sequences of 27 HA-MRSA strains isolated in Minnesota.

Methicillin-resistant Staphylococcus aureus (MRSA) has become a growing concern in companion and ... more Methicillin-resistant Staphylococcus aureus (MRSA) has become a growing concern in companion and food-producing animals. The presence of multidrug-resistance with a wide range of extracellular enterotoxin genes, virulence factors, and Panton-Valentine leukocidin (pvl) cytotoxin genes confer life-threatening traits on MRSA and makes them highly pathogenic and difficult to treat. Clonal complex 398 (CC398), a predominant clonal lineage of livestock-associated-MRSA in domestic animals and retail meat, is capable of infecting humans. In order to monitor and prevent MRSA contamination, it is critical to understand its source and transmission dynamics. In this review, we describe MRSA in food-producing animals (pig, cattle, chicken), horses, pet animals (dogs, cats), and food products (pork, beef, chicken, milk, and fish).

Exponential growth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in Campylob... more Exponential growth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in Campylobacter media has become a common problem for the detection of Campylobacter in chicken meats. We investigated the minimum inhibitory concentration of 40 ESBL-producing E. coli isolates from meats obtained from various countries against antibacterial agents in Bolton broth (cefoperazone, vancomycin, and trimethoprim). All ESBL-producing E. coli strains were resistant to cefoperazone and vancomycin, whereas 50% of them were resistant to trimethoprim and grew in Bolton broth. We found that 20 μg/mL of rifampicin inhibited the growth of trimethoprim-resistant E. coli strains. Hence, we added 20 μg/mL of rifampicin to Bolton broth to improve the isolation of Campylobacter from chicken carcass rinses. The isolation rate of Campylobacter was significantly higher in the modified broth (44 out of 58, 75.9%, P < 0.05) than in the normal broth (0 out of 58, 0%). Furthermore, the number of agar plates with non-Campylobacter spp. was much lower after enrichment in the modified broth (4 out of 58, 6.9%, P < 0.05) than in the normal broth (58 out of 58, 100%).