Acid Tolerance and Survival of Escherichia coli O157:H7 Inoculated in Fruit Pulps Stored under Refrigeration (original) (raw)
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International Journal of Food Sciences and Nutrition
The survival of Escherichia coli O157:H7 in acidic foods and its enhanced survival in refrigerated acid foods are well documented. This prompted the present study to evaluate the growth potential of E. coli O157:H7 in fresh tropical fruit juices. The pH of the various juices ranged between 3.57 (pineapple) and 6.2 (avocado). Samples were separately inoculated with a mixture of four E. coli O157:H7 strains at initial levels of approximately 10 3 cfu/ml, and stored at refrigeration (48C) and ambient (20 Á/258C) temperatures for 120 h. In pineapple juice, some decline in count was noted during ambient temperature storage but complete inhibition was not observed. At refrigeration temperature, the test strains survived without a noticeable decline in number. The pH remained unchanged throughout the experiment at both incubation temperatures. In papaya and avocado juices, counts of the test strains increased at varying rates at both storage temperatures. A decrease in pH was also noted in the stored juice. This study demonstrated that E. coli O157:H7 can survive well in acidic pineapple juice at both incubation temperatures and could also grow luxuriously in fruit juices with relatively higher pH values ( /5.7) when stored at ambient and refrigeration temperatures.
International journal of food sciences and nutrition, 2005
The survival of Escherichia coli O157:H7 in acidic foods and its enhanced survival in refrigerated acid foods are well documented. This prompted the present study to evaluate the growth potential of E. coli O157:H7 in fresh tropical fruit juices. The pH of the various juices ranged between 3.57 (pineapple) and 6.2 (avocado). Samples were separately inoculated with a mixture of four E. coli O157:H7 strains at initial levels of approximately 10(3) cfu/ml, and stored at refrigeration (4 degrees C) and ambient (20-25 degrees C) temperatures for 120 h. In pineapple juice, some decline in count was noted during ambient temperature storage but complete inhibition was not observed. At refrigeration temperature, the test strains survived without a noticeable decline in number. The pH remained unchanged throughout the experiment at both incubation temperatures. In papaya and avocado juices, counts of the test strains increased at varying rates at both storage temperatures. A decrease in pH wa...
The survival of Escherichia coli O157:H7 in acidic foods and its enhanced survival in refrigerated acid foods are well documented. This prompted the present study to evaluate the growth potential of E. coli O157:H7 in fresh tropical fruit juices. The pH of the various juices ranged between 3.57 (pineapple) and 6.2 (avocado). Samples were separately inoculated with a mixture of four E. coli O157:H7 strains at initial levels of approximately 10 3 cfu/ml, and stored at refrigeration (48C) and ambient (20 Á/258C) temperatures for 120 h. In pineapple juice, some decline in count was noted during ambient temperature storage but complete inhibition was not observed. At refrigeration temperature, the test strains survived without a noticeable decline in number. The pH remained unchanged throughout the experiment at both incubation temperatures. In papaya and avocado juices, counts of the test strains increased at varying rates at both storage temperatures. A decrease in pH was also noted in the stored juice. This study demonstrated that E. coli O157:H7 can survive well in acidic pineapple juice at both incubation temperatures and could also grow luxuriously in fruit juices with relatively higher pH values ( /5.7) when stored at ambient and refrigeration temperatures.
Journal of Food Protection, 2014
Numerous outbreaks involving fresh juices contaminated with Escherichia coli O157:H7 have occurred in the United States and around the world, raising concern for the safety of these products. Until now, only a few studies regarding the thermal tolerance of this pathogen in acidic juices over a wide range of pH values have been published. Therefore, the effect of varying the pH with different organic acids on the thermal inactivation of non–acid-adapted and acid-adapted E. coli O157:H7 (strain C7927) was determined. The decimal reduction times (D-values) and the change in temperature required for the thermal destruction curve to traverse 1 log cycle (z-values) were calculated for non–acid-adapted E. coli in an apple-carrot juice blend (80:20) adjusted to three pH values (3.3, 3.5, and 3.7) by the addition of lactic, malic, or acetic acid and at a pH of 4.5 adjusted with NaOH. Thermal parameters were also determined for acid-adapted cells in juices acidified with malic acid. The effec...
Survival and characterization of Escherichia coli strains in a typical Mexican acid-fermented food
International Journal of Food Microbiology, 2001
In this study, the acid resistance and the changes in outer membrane protein (Omps) profiles of Escherichia coli strains isolated from pozol, an acid-fermented maize beverage consumed in Southeastern Mexico, were determined. Results showed that adaptation to acid by these E. coli strains significantly enhances their survival in acid conditions. Changes in Omp profiles were found in non-adapted acid challenged cells compared with non-challenged cells that had not been adapted to acid. Challenged adapted cells showed no significant changes in these profiles when compared with the acid adapted non-challenged strains. N-terminal sequences of some of the Omps were determined. The intensity of the main porins OmpC and OmpA was lower in the acid challenged strains, than in the non-challenged ones. The OmpF porin was identified in non-challenged K12 strain, but did not appear in adapted or non-adapted pozol strains nor in E. coli O157:H7.
Applied and Environmental Microbiology, 2004
Escherichia coli O157:H7 is a highly acid-resistant food-borne pathogen that survives in the bovine and human gastrointestinal tracts and in acidic foods such as apple cider. This property is thought to contribute to the low infectious dose of the organism. Three acid resistance (AR) systems are expressed in stationary-phase cells. AR system 1 is σ S dependent, while AR systems 2 and 3 are glutamate and arginine dependent, respectively. In this study, we sought to determine which AR systems are important for survival in acidic foods and which are required for survival in the bovine intestinal tract. Wild-type and mutant E. coli O157:H7 strains deficient in AR system 1, 2, or 3 were challenged with apple cider and inoculated into calves. Wild-type cells, adapted at pH 5.5 in the absence of glucose (AR system 1 induced), survived well in apple cider. Conversely, the mutant deficient in AR system 1, shown previously to survive poorly in calves, was susceptible to apple cider (pH 3.5), ...
Journal of Food Protection, 2016
The enhanced thermal tolerance and survival responses of Escherichia coli O157:H7 in acid and acidified foods is a major safety concern for the production of low-pH products, including beverages. Little is known about this phenomenon when using UV light treatments. This study was conducted to evaluate the effects of strain (E. coli O157:H7 strains C7927, ATCC 35150, ATCC 43895, and ATCC 43889 and E. coli ATCC 25922) and physiological state (control-unadapted, acid adapted, and acid shocked) on the UV tolerance of E. coli in apple juice treated under conditions stipulated in current U.S. Food and Drug Administration regulations. A greater than 5-log reduction of E. coli was obtained under all tested conditions. A significant effect of strain (P < 0.05) was observed, but the physiological state did not influence pathogen inactivation (P ≥ 0.05). The UV sensitivity of three spoilage microorganisms (Aspergillus niger, Penicillium commune, and Alicyclobacillus acidoterrestris) was als...
Journal of Food Protection, 2011
Outbreaks of disease due to vegetative bacterial pathogens associated with acid foods (such as apple cider) have raised concerns about acidified vegetables and related products that have a similar pH (3.2 to 4.0). Escherichia coli O157:H7 and related strains of enterohemorrhagic E. coli (EHEC) have been identified as the most acid resistant vegetative pathogens in these products. Previous research has shown that the lack of dissolved oxygen in many hermetically sealed acid or acidified food products can enhance survival of EHEC compared with their survival under aerobic conditions. We compared the antimicrobial effects of several food acids (acetic, malic, lactic, fumaric, benzoic, and sorbic acids and sulfite) on a cocktail of EHEC strains under conditions representative of non–heat-processed acidified vegetables in hermetically sealed jars, holding the pH (3.2) and ionic strength (0.342) constant under anaerobic conditions. The overall antimicrobial effectiveness of weak acids use...
Journal of food protection
The ability of Escherichia coli O157:H7 to survive in acidified vegetable products is of concern because of previously documented outbreaks associated with fruit juices. A study was conducted to determine the survival of E. coli O157:H7 in organic acids at pH values typical of acidified vegetable products (pH 3.2 and 3.7) under different dissolved oxygen conditions (< or = 0.05 and 5 mg/liter) and a range of ionic strengths (0.086 to 1.14). All solutions contained 20 mM gluconic acid, which was used as a noninhibitory low pH buffer to compare the individual acid effect to that of pH alone on the survival of E. coli O157:H7. E. coli O157:H7 cells challenged in buffered solution with ca. 5-mg/liter dissolved oxygen (present in tap water) over a range of ionic strengths at pH 3.2 exhibited a decrease in survival over 6 h at 30 degrees C as the ionic strength was increased. Cells challenged in 40 mM protonated L-lactic and acetic acid solutions with ionic strength of 0.684 achieved a...
Food Microbiology, 1999
The ability of pH-dependent, stationary phase acid resistance to cross-protect Escherichia coli O157:H7 against a subsequent lethal thermal stress was evaluated using microbiological media and three liquid foods. Three strains were grown for 18 h at 378C in acidogenic (TSB+G, ¢nal pH 4Á6±4Á7) and non-acidogenic (TSB-G, ¢nal pH 7Á0±7Á2) media to provide stationary phase cells with and without induction of pH-dependent acid resistance. The cells were then heated in BHI broth (pH 6Á0) at 588C, using a submerged coil apparatus. The TSB+G grown strains had greatly increased heat resistance, with the heating time needed to achieve a ¢ve-log inactivation, being increased two-to fourfold. The z-values of TSB+G and TSB-G grown cells were 4Á78C and 4Á38C, respectively. Increases in heat resistance withTSB+G-grown E. coli O157:H7 were also observed using milk and chicken broth, but not with apple juice. However, cross-protection was restored if the pH of the apple juice was increased from 3Á5 to 4Á5. The data indicate that pH-dependent acid resistance provides E. coli O157:H7 with cross-protection against heat treatments, and that this factor must be considered to estimate this pathogen's thermal tolerance accurately.