Survival of Escherichia coli O157:H7 in bottled natural mineral water

A non-verotoxin-producing isolate of Escherichia coli O157:H7 was inoculated at final concentrations of 10(3) or 10(6) ml-1 into natural non-carbonated mineral water (MW), sterile natural mineral water (SMW) and sterile distilled deionized water (SDDW) and stored at 15 degrees C for 10 weeks. Samples were examined every 7 d for the presence of E. coli O157:H7 using a resuscitative/selective agar procedure. The MW samples were also plated onto a non-selective agar, R2A, to enumerate E. coli O157:H7 and the autochthonous flora. There was a significant difference in the survival of E. coli O157:H7 (10(3) ml-1 inoculum) between the MW and the SDDW at time periods 0, 7, 14 (P < 0.005) 21, 28, 35 (P < 0.001) and 42 d (P < 0.05) and between the MW and the SMW at time periods 7, (P < 0.05) 14, 21 (P < 0.005) 28 (P < 0.01) and 35 d (P < 0.05), with the pathogen surviving longest in the MW samples. In contrast, at 10(6) ml-1, no significant differences in the survival of E. coli O157:H7 were observed between the water types. The presence of E. coli O157:H7 (10(3) ml-1) in the MW samples did not have an antagonistic effect on the recovery of the autochthonous flora. Transmission electron microscopy analysis demonstrated that the E. coli O157:H7 cells lyse during storage, releasing their contents into the surrounding environment. These substances may have been utilized by the autochthonous flora and thereby explain why the numbers of flora recovered from the inoculated MW samples were higher than those recovered from the uninoculated samples.     

Survival of Escherichia coli O157:H7 on cattle hides

The objective of this study was to determine the time period that Escherichia coli O157:H7 survives on the hides of cattle. Extensive research has been conducted and is ongoing to identify and develop novel preharvest intervention strategies to reduce the presence of E. coli O157:H7 on live cattle and subsequent transfer to processed carcasses. If a reduction of E. coli O157:H7 levels in feces can be achieved through preharvest intervention, it is not known how long it would take for such reductions to be seen on the hide. In the study presented herein, three trials were conducted to follow E. coli O157:H7 hide prevalence over time. For each trial, 36 animals were housed in individual stanchions to minimize or prevent hide contamination events. Through prevalence determination and isolate genotyping with pulsed-field gel electrophoresis, survival of E. coli O157:H7 on the hides of live cattle was determined to be short lived, with an approximate duration of 9 days or less. The results of this study suggest that any preharvest interventions that are to be administered at the end of the finishing period will achieve maximum effect in reducing E. coli O157:H7 levels on cattle hides if given 9 days before the cattle are presented for processing. However, it should be noted that interventions reducing pathogen shedding would also contribute to decreasing hide contamination through lowering the contamination load of the processing plant lairage environment, regardless of the time of application.     

Association of Escherichia coli O157:H7 with houseflies on a cattle farm

The ecology of Escherichia coli O157:H7 is not well understood. The aims of this study were to determine the prevalence of and characterize E. coli O157:H7 associated with houseflies (HF). Musca domestica L. HF (n = 3,440) were collected from two sites on a cattle farm over a 4-month period and processed individually for E. coli O157:H7 isolation and quantification. The prevalence of E. coli O157:H7 was 2.9 and 1.4% in HF collected from feed bunks and a cattle feed storage shed, respectively. E. coli O157:H7 counts ranged from 3.0 x 10(1) to 1.5 x 10(5) CFU among the positive HF. PCR analysis of the E. coli O157:H7 isolates revealed that 90.4, 99.2, 99.2, and 100% of them (n = 125) possessed the stx1, stx2, eaeA, and fliC genes, respectively. Large populations of HF on cattle farms may play a role in the dissemination of E. coli O157:H7 among animals and to the surrounding environment.     

Fluctuations in the occurrence of Escherichia coli O157:H7 on a Norwegian farm*

AIM: To describe the distribution of Escherichia coli O157:H7 on a sporadically positive dairy farm and on possible contact farms over a one-year period. METHODS AND RESULTS: Environmental and faecal samples from all animals at the farm, and faecal samples from animals at contact farms were analysed for E. coli O157:H7 by immunomagnetic separation methods or VIDAS.Confirmed isolates were tested for cytotoxicity in the Vero cell assay and typed by PFGE. Escherichia coli O157:H7 (stx2 and eae) of the same PFGE type were isolated from cattle, sheep, hens and environmental samples at variable levels during summer and fall 2002, but were not detected in 2003. CONCLUSIONS: Escherichia coli O157:H7 had a widespread distribution on the farm investigated, but the original source of contamination could not be identified. The occurrence of this bacterium on the farm did not result in any detectable increase in gastrointestinal disease in the associated population. SIGNIFICANCE AND IMPACT OF THE STUDY: Despite a low endemic level of E. coli O157:H7 in the Norwegian cattle population, the growth and spread of this potentially important bacterium may occur.     

Prevalence of enterohemorrhagic Escherichia coli O157:H7 in a survey of dairy herds.

The prevalence of Escherichia coli O157:H7 in dairy herds is poorly understood, even though young dairy animals have been reported to be a host. From February to May 1993, 662 fecal samples from 50 control herds in 14 states, and from June to August 1993, 303 fecal samples from 14 case herds in 11 states were collected for isolation of E. coli O157:H7. Case herds were those in which E. coli O157:H7 was isolated from preweaned calves in a previous U.S. Department of Agriculture study, whereas control herds from which E. coli O157:H7 had not been isolated previously were randomly selected from the same states as case herds. Among the control herds, E. coli O157:H7 was isolated from 6 of 399 calves (1.5%) that were between 24 h old and the age of weaning and from 13 of 263 calves (4.9%) that were between the ages of weaning and 4 months. Eleven of 50 control herds (22%) were positive. Among the case herds, E. coli O157:H7 was isolated from 5 of 171 calves (2.9%) that were between 24 h old and the age of weaning and from 7 of 132 calves (5.3%) that were between the ages of weaning and 4 months. Seven of 14 case herds (50%) were positive. Sixteen of 31 isolates were obtained by direct plating, with populations ranging from 10(3) to 10(5) CFU/g. Fifteen of 31 isolates were isolated by enrichment only. Nineteen of the isolates produced both verocytotoxin 1 (VT-1) and VT-2, whereas 12 produced VT-2 only.     

Survival of Escherichia coli O157:H7 in wastewater from dairy lagoons

AIM: To determine the survival of Escherichia coli O157:H7 in dairy wastewater from on-site holding lagoons equipped with or without circulating aerators. METHODS AND RESULTS: Survival was monitored in dairy lagoon microcosms equipped with or without scale-size circulators. Both laboratory strains of E. coli O157:H7 and an isolate of E. coli H7 from wastewater had poor survival rates and none proliferated in water from waste lagoons with or without circulators. Furthermore, the decline of E. coli O157:H7 was not enhanced in those microcosms equipped with circulators. Strain variation in survival was observed in both circulated and settling waters. The decline rate of E. coli O157:H7 Odwalla strain increased proportionately with the inoculum load. Escherichia coli failed to establish itself in wastewater even after four sequential inoculations simulating continuous faecal input into the lagoon. The native aerobic bacteria survived longer with a decimal reduction time of 21.3 days vs either introduced or native E. coli, which declined rapidly with decimal reduction time of 0.5-9.4 days. CONCLUSIONS: Escherichia coli O157:H7 failed to establish and proliferate in dairy wastewater microcosms equipped with or without circulating aerators. SIGNIFICANCE AND IMPACT OF THE STUDY: This study furthers our knowledge of pathogen survival in wastewater, and suggests that proper management of wastewater before its use in irrigation is essential to reduce pathogen transfer to crops.     

Survival of Escherichia coli O157:H7 in potato starch as affected by water activity, pH and temperature

A study was done to determine the survival characteristics of Escherichia coli O157:H7 in potato starch powder as affected by aw (0.24-0.26, 0.51-0.52 and 0.75-0.78), pH (4.1 and 6.7) and temperature (4, 20 and 37 degrees C) over a 33-week storage period. Survival was enhanced as the aw decreased. The rate of death was higher as the storage temperature increased. Survival did not appear to be affected by pH. Since the composition of foods greatly affects the viability of E. coli O157:H7 at reduced aw, development of models to predict patterns of inactivation in a given food should be carried out using data generated from that food or one with very similar composition, aw and pH.     

Persistence and metabolic activity of Escherichia coli O157:H7 in farm animal faeces

Ruminants, and to a lesser extent monogastric farm animals, are known to be natural reservoirs of Escherichia coli O157:H7, and contact with contaminated faeces has been linked to human infection. This study used a nontoxigenic, chromosomally marked, lux reporter strain to compare the persistence and activity (bioluminescence) of E. coli O157:H7 over 21 days in the faecal liquor of five farm animals: horse, sheep, cow, pig and piglet. Samples were inoculated with the lux E. coli O157:H7 (7.82 log CFU mL(-1)) and stored at 20 +/- 1 degrees C. The organism was recovered from all samples throughout the experimental period, although lower numbers were recovered from horse faecal liquor relative to all other types (P<0.001). The organisms' activity declined in all samples over time and no luminescence could be detected in any sample 21 days postinoculation. However, activity did increase greatly within pig and piglet faeces during initial stages of monitoring and overall luminescence was greater in piglet samples compared with all other samples (P<0.001). This is the first study to demonstrate how both the persistence and metabolic activity of E. coli O157:H7 notably varies within a range of ruminant and nonruminant animal faeces. Further research is needed to elucidate the factors that govern differential persistence and metabolic activity of E. coli O157:H7 within such matrices.     

Survival of Escherichia coli O157: H7 in drinking water associated with a waterborne disease outbreak of hemorrhagic colitis

Survival characteristics were similar for two strains of Escherichia coli O157: H7 and a typical indicator strain of E. coli in a portable ground water source. Die-off was more rapid at 20°C than at 5°C. There was no significant difference among the rates of survival for the strains examined.     

Survival and growth of Escherichia coli O157:H7 on salad vegetables.

The influence of modified-atmosphere packaging, storage temperature, and time on survival and growth of Escherichia coli O157:H7 inoculated onto shredded lettuce, sliced cucumber, and shredded carrot was determined. Growth of psychotrophic and mesophilic microorganisms and changes in pH and sensory qualities of vegetables, as judged by subjective evaluation, were also monitored. Packaging under an atmosphere containing 3% oxygen and 97% nitrogen had no apparent effect on populations of E. coli O157:H7, psychotrophs, or mesophiles. Populations of viable E. coli O157:H7 declined on vegetables stored at 5 degrees C and increased on vegetables stored at 12 and 21 degrees C for up to 14 days. The most rapid increases in populations of E. coli O157:H7 occurred on lettuce and cucumbers stored at 21 degrees C. These results suggest that an unknown factor(s) associated with carrots may inhibit the growth of E. coli O157:H7. The reduction in pH of vegetables was correlated with initial increases in populations of E. coli O157:H7 and naturally occurring microfloras. Eventual decreases in E. coli O157:H7 in some samples, e.g., those stored at 21 degrees C, are attributed to the toxic effect of accumulated acids. Changes in visual appearance of vegetables were not influenced substantially by growth of E. coli O157:H7. The ability of E. coli O157:H7 to growth on raw salad vegetables subjected to processing and storage conditions simulating those routinely used in commercial practice has been demonstrated.     

Survival of Escherichia coli O157:H7 in Soils from Jiangsu Province,China

Escherichia coli O157:H7 (E. coli O157:H7) is recognized as a hazardous microorganism in the environment and for public health. The E. coli O157:H7 survival dynamics were investigated in 12 representative soils from Jiangsu Province, where the largest E. coli O157:H7 infection in China occurred. It was observed that E. coli O157:H7 declined rapidly in acidic soils (pH, 4.57 – 5.14) but slowly in neutral soils (pH, 6.51 – 7.39). The survival dynamics were well described by the Weibull model, with the calculated t_d value (survival time of the culturable E. coli O157:H7 needed to reach the detection limit of 100 CFU g⁻¹) from 4.57 days in an acidic soil (pH, 4.57) to 34.34 days in a neutral soil (pH, 6.77). Stepwise multiple regression analysis indicated that soil pH and soil organic carbon favored E. coli O157:H7 survival, while a high initial ratio of Gram-negative bacteria phospholipid fatty acids (PLFAs) to Gram-positive bacteria PLFAs, and high content of exchangeable potassium inhibited E. coli O157:H7 survival. Principal component analysis clearly showed that the survival profiles in soils with high pH were different from those with low pH.     

Survival of Escherichia coli O157:H7 in feces from corn- and barley-fed steers

The survival of Escherichia coli O157:H7 in feces from steers fed corn (CO) or barley (BA) was evaluated at -10, +4 and +22 degrees C. Fecal pats were inoculated with a four-strain mixture of nalidixic-acid resistant E. coli O157:H7 at two levels: 10(3) CFU g(-1) (low, L) and 105 CFU g(-1) (high, H). At -10 degrees C, duration of survival of E. coli O157:H7 was reduced (p < 0.05) in CO-L (35 days) compared to BA-L (49 days), likely due to the effects of fecal volatile fatty acids in combination with a fecal pH of <6.5. At 4 degrees C, E. coli O157:H7 was detected in BA-H, CO-H, CO-L and BA-L for 77, 77, 56 and 63 days, respectively, with no difference (p > 0.05) observed in the duration of survival or rate of decline of E. coli O157:H7 among treatments. Survival of E. coli O157:H7 was twice as likely (p < 0.05) at 22 degrees C than at 4 degrees C and -10 degrees C. While pH and dry matter content increased, and volatile fatty acid concentrations decreased over 84 days at all three temperatures, these changes were most pronounced at 22 degrees C. Survival of E. coli O157:H7 for extended periods of time in feces from both corn- and barley-fed animals was demonstrated, thus fecal material may serve as a vector for the transmission of the organism. The greater survival of E. coli O157:H7 at 22 degrees C suggests that temperature may play a role in the seasonality of transmission and prevalence of this bacterium in feedlot cattle. The reported greater prevalence of E. coli O157:H7 in cattle fed barley as compared to those fed corn does not appear to be related to elevated risk of transmission arising from differential survival of the bacterium in feces.     

Persistence of Escherichia coli O157:H7 and its mutants in soils

The persistence of Shiga toxin-producing E. coli O157:H7 in the environment poses a serious threat to public health. However, the role of Shiga toxins and other virulence factors in the survival of E. coli O157:H7 is poorly defined. The aim of this study was to determine if the virulence factors, stx ₁, stx ₂, stx _1–2, and eae in E. coli O157:H7 EDL933 play any significant role in the growth of this pathogen in rich media and in soils. Isogenic deletion mutants that were missing one of four virulence factors, stx ₁, stx ₂, stx _1–2, and eae in E. coli O157:H7 EDL933 were constructed, and their growth in rich media and survival in soils with distinct texture and chemistry were characterized. The survival data were successfully analyzed using Double Weibull model, and the modeling parameters of the mutant strains were not significantly different from those of the wild type. The calculated T_d (time needed to reach the detection limit, 100 CFU/g soil) for loamy sand, sandy loam, and silty clay was 32, 80, and 110 days, respectively. It was also found that T_d was positively correlated with soil structure (e.g. clay content), and soil chemistry (e.g. total nitrogen, total carbon, and water extractable organic carbon). The results of this study showed that the possession of Shiga toxins and intimin in E. coli O157:H7 might not play any important role in its survival in soils. The double deletion mutant of E. coli O157:H7 (stx ₁ ⁻ stx ₂ ⁻) may be a good substitute to use for the investigation of transport, fate, and survival of E. coli O157:H7 in the environment where the use of pathogenic strains are prohibited by law since the mutants showed the same characteristics in both culture media and environmental samples.     

Survival of Escherichia coli O157:H7 applied to cantaloupes and the effectiveness of chlorinated water and lactic acid as disinfectants

Initial survey of four packinghouses indicated that bacterial and fungal populations on the surface of cantaloupes were significantly reduced by sanitizing procedures particularly on faecal coliforms. In this study, several combinations of disinfectants were tested in an attempt to obtain a more effective antimicrobial activity on aerobic bacteria, fungi and total coliforms. The efficacy of aqueous chlorine (200 mg l^–1) and lactic acid (1.5%) on inactivation of inoculated Escherichia coli O157:H7 on cantaloupe surfaces was investigated using different temperatures (25 and 35 °C) and immersion times (1 and 10 min). Maximal log reductions were achieved with both sanitizing agents when the initial bacterial population of E. coli was 7.42 log c.f.u. cm^–2. A highly significant 7.2 log reduction (P < 0.01) was obtained with a solution of lactic acid with and without Tergitol (0.3%) surfactant when cantaloupes were immersed for 10 min regardless of the temperature of the solution. Although the sanitizers caused substantial mortality, some bacterial cells remained attached at relatively low numbers on the fruit surface. The development of sanitizers more efficacious than chlorine for total elimination of this pathogen from the surface of cantaloupes is needed.     

Dose-Response Envelope for Escherichia coli O157:H7

Escherichia coli O157:H7 is an emerging food and waterborne pathogen in the U.S. and internationally. The objective of this work was to develop a dose-response model for illness by this organism that bounds the uncertainty in the dose-response relationship. No human clinical trial data are available for E. coli O157:H7, but such data are available for two surrogate pathogens: enteropathogenic E. coli (EPEC) and Shigella dysenteriae. E. coli O157:H7 outbreak data provide an initial estimate of the most likely value of the dose-response relationship within the bounds of an envelope defined by beta-Poisson dose-response models fit to the EPEC and S. dysenteriae data. The most likely value of the median effective dose for E. coli O157:H7 is estimated to be approximately 190[emsp4 ]000 colony forming units (cfu). At a dose level of 100[emsp4 ]cfu, the median response predicted by the model is six percent.     

Role of rpoS in Escherichia coli O157:H7 Strain H32 Biofilm Development and Survival

The protein RpoS is responsible for mediating cell survival during the stationary phase by conferring cell resistance to various stressors and has been linked to biofilm formation. In this study, the role of the rpoS gene in Escherichia coli O157:H7 biofilm formation and survival in water was investigated. Confocal scanning laser microscopy of biofilms established on coverslips revealed a nutrient-dependent role of rpoS in biofilm formation, where the biofilm biomass volume of the rpoS mutant was 2.4- to 7.5-fold the size of its rpoS⁺ wild-type counterpart in minimal growth medium. The enhanced biofilm formation of the rpoS mutant did not, however, translate to increased survival in sterile double-distilled water (ddH₂O), filter-sterilized lake water, or unfiltered lake water. The rpoS mutant had an overall reduction of 3.10 and 5.30 log₁₀ in sterile ddH₂O and filter-sterilized lake water, respectively, while only minor reductions of 0.53 and 0.61 log₁₀ in viable counts were observed for the wild-type form in the two media over a 13-day period, respectively. However, the survival rates of the detached biofilm-derived rpoS⁺ and rpoS mutant cells were comparable. Under the competitive stress conditions of unfiltered lake water, the advantage conferred by the presence of rpoS was lost, and both the wild-type and knockout forms displayed similar declines in viable counts. These results suggest that rpoS does have an influence on both biofilm formation and survival of E. coli O157:H7 and that the advantage conferred by rpoS is contingent on the environmental conditions.     

Survival in acidic and alcoholic medium of Shiga toxin-producing Escherichia coli O157:H7 and non-O157:H7 isolated in Argentina

Background

In spite of Argentina having one of the highest frequencies of haemolytic uraemic syndrome (HUS), the incidence of Escherichia coli O157:H7 is low in comparison to rates registered in the US. Isolation of several non-O157 shiga toxin-producing Escherichia coli (STEC) strains from cattle and foods suggests that E. coli O157:H7 is an uncommon serotype in Argentina. The present study was undertaken to compare the survival rates of selected non-O157 STEC strains under acidic and alcoholic stress conditions, using an E. coli O157:H7 strain as reference.

Results

Growth at 37°C of E. coli O26:H11, O88:H21, O91:H21, O111:H^-, O113:H21, O116:H21, O117:H7, O157:H7, O171:H2 and OX3:H21, was found to occur at pH higher than 4.0. When the strains were challenged to acid tolerance at pH as low as 2.5, viability extended beyond 8 h, but none of the bacteria, except E. coli O91:H21, could survive longer than 24 h, the autochthonous E. coli O91:H21 being the more resistant serotype. No survival was found after 24 h in Luria Bertani broth supplemented with 12% ethanol, but all these serotypes were shown to be very resistant to 6% ethanol. E. coli O91:H21 showed the highest resistance among serotypes tested.

Conclusions

This information is relevant in food industry, which strongly relies on the acid or alcoholic conditions to inactivate pathogens. This study revealed that stress resistance of some STEC serotypes isolated in Argentina is higher than that for E. coli O157:H7.     

Survival of Escherichia coli O157:H7 in the rhizosphere of maize grown in waste-amended soil

AIMS: To assess whether the persistence of Escherichia coli O157:H7 in soil amended with cattle slurry and ovine stomach content waste is affected by the presence of a maize rhizosphere. METHODS AND RESULTS: Cattle slurry and ovine stomach content waste were inoculated with E. coli O157:H7. Wastes were then applied to soil cores with and without established maize plants. The pathogen survived in soil for over 5 weeks, although at significantly greater numbers in soil receiving stomach content waste in comparison to cattle slurry. Persistence of the pathogen in soil was unaffected by the presence of a rhizosphere. CONCLUSIONS: Other factors may be more influential in regulating E. coli O157:H7 persistence in waste-amended soil than the presence or absence of a rhizosphere; however, waste type did have significant affect on the survival of E. coli O157:H7 in such soil. SIGNIFICANCE AND IMPACT OF THE STUDY: Escherichia coli O157:H7 can be present within animal-derived organic wastes that are routinely spread on land. Introduced measures with regards to such waste disposal may decrease exposure to the organism; however, the persistence of E. coli O157:H7 for considerable periods in waste-amended soil may still pose some risk for both human and animal infection. This study has shown that whilst survival of E. coli O157:H7 in waste-amended soil is not significantly affected by the presence or absence of a maize rhizosphere; it may vary significantly with waste type. This may have implications for land and waste management.     

Direct PCR detection of Escherichia coli O157:H7

AIMS: This paper reports a simple, rapid approach for the detection of Shiga toxin (Stx)-producing Escherichia coli (STEC). METHODS AND RESULTS: Direct PCR (DPCR) obviates the need for the recovery of cells from the sample or DNA extraction prior to PCR. Primers specific for Stx-encoding genes stx1 and stx2 were used in DPCR for the detection of E. coli O157:H7 added to environmental water samples and milk. CONCLUSIONS: PCR reactions containing one cell yielded a DPCR product. SIGNIFICANCE AND IMPACT OF THE STUDY: This should provide an improved method to assess contamination of environmental and other samples by STEC and other pathogens.