Minimum and Maximum Temperatures for Growth and Verotoxin Production by Hemorrhagic Strains of Escherichia coli

bEffluents discharged from wastewater treatment plants are possible sources of pathogenic bacteria, including Escherichia coli, in the freshwater environment, and determining the possible selection of pathogens is important. This study evaluated the impact of activated sludge and physicochemical wastewater treatment processes on the prevalence of potentially virulent E. coli. A total of 719 E. coli isolates collected from four municipal plants in Québec before and after treatment were characterized by using a customized DNA microarray to determine the impact of treatment processes on the frequency of specific pathotypes and virulence genes. The percentages of potentially pathogenic E. coli isolates in the plant influents varied between 26 and 51%, and in the effluents, the percentages were 14 to 31%, for a reduction observed at all plants ranging between 14 and 45%. Pathotypes associated with extraintestinal pathogenic E. coli (ExPEC) were the most abundant at three of the four plants and represented 24% of all isolates, while intestinal pathogenic E. coli pathotypes (IPEC) represented 10% of the isolates. At the plant where ExPEC isolates were not the most abundant, a large number of isolates were classified as both ExPEC and IPEC; overall, 6% of the isolates were classified in both groups, with the majority being from the same plant. The reduction of the proportion of pathogenic E. coli could not be explained by the preferential loss of one virulence gene or one type of virulence factor; however, the quinolone resistance gene (qnrS) appears to enhance the loss of virulence genes, suggesting a mechanism involving the loss of pathogenicity islands.

Section: Discussionmentioning

confidence: 74%

Section: Discussionmentioning

confidence: 99%

Biological and Physicochemical Wastewater Treatment Processes Reduce the Prevalence of Virulent Escherichia coli

Frigon

Biswal

Mazza

et al. 2013

“…The type and concentration of nutrients are known to have a strong influence on the growth potential of E. coli O157:H7 at incubation temperatures ranging from 5.5 to 9.5°C (22). Also, the minimum growth temperature of many E. coli O157:H7 strains under optimal culturing conditions in broth is 8°C (28). This temperature limit may increase to approximately 10°C under low-nutrient conditions (22) and with competition by the natural flora in meat washings.…”

Section: Discussionmentioning

confidence: 99%

Survival or Growth of Escherichia coli O157:H7 in a Model System of Fresh Meat Decontamination Runoff Waste Fluids and Its Resistance to Subsequent Lactic Acid Stress

Samelis¹,

Sofos²,

Kendall

et al. 2005

A potential may exist for survival of and resistance development by Escherichia coli O157:H7 in environmental niches of meat plants applying carcass decontamination interventions. This study evaluated (i) survival or growth of acid-adapted and nonadapted E. coli O157:H7 strain ATCC 43895 in acetic acid (pH 3.6 ؎ 0.1) or in water (pH 7.2 ؎ 0.2) fresh beef decontamination runoff fluids (washings) stored at 4, 10, 15, or 25°C and (ii) resistance of cells recovered from the washings after 2 or 7 days of storage to a subsequent lactic acid (pH 3.5) stress. Corresponding cultures in sterile saline or in heat-sterilized water washings were used as controls. In acetic acid washings, acid-adapted cultures survived better than nonadapted cultures, with survival being greatest at 4°C and lowest at 25°C. The pathogen survived without growth in water washings at 4 and 10°C, while it grew by 0.8 to 2.7 log cycles at 15 and 25°C, and more in the absence of natural flora. E. coli O157:H7 cells habituated without growth in water washings at 4 or 10°C were the most sensitive to pH 3.5, while cells grown in water washings at 15 or 25°C were relatively the most resistant, irrespective of previous acid adaptation. Resistance to pH 3.5 of E. coli O157:H7 cells habituated in acetic acid washings for 7 days increased in the order 15°C > 10°C > 4°C, while at 25°C cells died off. These results indicate that growth inhibition by storage at low temperatures may be more important than competition by natural flora in inducing acid sensitization of E. coli O157:H7 in fresh meat environments. At ambient temperatures in meat plants, E. coli O157:H7 may grow to restore acid resistance, unless acid interventions are applied to inhibit growth and minimize survival of the pathogen. Acid-habituated E. coli O157:H7 at 10 to 15°C may maintain a higher acid resistance than when acid habituated at 4°C. These responses should be evaluated with fresh meat and may be useful for the optimization of decontamination programs and postdecontamination conditions of meat handling.Escherichia coli O157:H7 has become the primary target organism of food animal carcass decontamination interventions, which are of increasing commercial use in North America (3,13,21,39,41). In-plant applications have shown effectiveness of decontamination in reducing the percentage of carcass samples being E. coli O157:H7 positive from preevisceration to postprocessing (2, 19). However, there is a need to evaluate the potential for development of acid resistance in E. coli O157:H7 during application of acid decontamination interventions in meat (31). Studies have shown that the pathogen may survive decontamination of meat with lactic or acetic acid (7,16,17), suggesting that survivors can exist and may potentially adapt to the residual organic acid in situ in commercial meat processing environments (31).Berry and Cutter (6) demonstrated that previous acid adaptation of E. coli O157:H7 by culturing in media with 1% glucose (9) reduced the effectiveness of a 2% acetic acid solution to ina...

“…The ability to specifically identify the presence of an organism within a fraction of the time required by standard approaches makes molecular tests ideal for use in food systems (2). A number of recent reports have applied molecular tools for specific detection of pathogenic E. coli in food systems (10,24,31,32). Most of these assays have used DNA as the target molecule; however, recent literature has shown that DNA is not a good indicator of viable pathogens due to its persistence following cell death (12,17,18).…”

mentioning

confidence: 99%

“…Past research investigating the effect of aeration on SLT toxin production has shown that increased aeration results in optimal toxin production (33). Others have examined the production of Shiga toxin as a function of enrichment temperature, allowing a specific range of temperatures to be determined for SLT production (24).…”

mentioning

confidence: 99%

Optimization of Reverse Transcriptase PCR To Detect Viable Shiga-Toxin-Producing Escherichia coli

McINGVALE

Elhanafi

Drake

2002

The ability of reverse transcriptase PCR (RT-PCR) to detect viable Shiga-toxin-producing Escherichia coli (STEC) was investigated. Four primer sets, each targeting a specific region in the slt-II operon, were evaluated for their stringency and specificity for slt-II mRNA. STEC were evaluated for toxin expression under various conditions, including cell growth phase, growth medium, incubation temperature, and aeration. Following primer optimization, STEC were inoculated into Trypticase soy broth and cooked ground beef enrichments. Cells were harvested and RNA or DNA was extracted at 4, 8, 12, and 24 h. RT-PCR or PCR was conducted, and the products were visualized by gel electrophoresis and by Southern blots. mRNA targets were detected in 12-h cooked ground meat enrichments with an initial inoculum of 1 CFU/g. These results indicate that RT-PCR of E. coli slt-II mRNA is useful for detection of viable STEC in ground beef.Escherichia coli O157:H7 was first isolated as a human pathogen in 1982 and has since become a well-known agent of food-borne illness. Cases of hemorrhagic colitis, hemolytic uremic syndrome, and death have been reported following the consumption of raw or undercooked ground beef (8). Although most commonly associated with foods of animal origin, enterohemorrhagic E. coli (EHEC) may also be isolated from contaminated drinking water and acidic foods such as mayonnaise, salad dressings, and buttermilk (6,16,29). The infectious dose for E. coli O157:H7 and other serotypes of EHEC varies greatly between populations. For susceptible individuals such as the elderly and infants, the infectious dose may be as low as 10 cells (8).Without an animal model, there is much controversy over which virulence factors of EHEC contribute to human pathogenicity (8). EHEC produce Shiga-like toxins (SLTs) that characterize this group of pathogenic E. coli. Other virulence markers include intimin, hemolysin, and the locus of enterocyte effacement (8). Food-borne illnesses have occurred with isolates that possess all or only a few of these markers (8, 9). Possession of slt genes is a consistent virulence marker (1), but without evidence of human illness, E. coli possessing slt are often referred to as Shiga toxin-producing E. coli (STEC). Despite the fact that EHEC strains containing slt-I and slt-II have been isolated from patients with hemorrhagic colitis, studies have shown that strains possessing only slt-II are more frequently associated with human disease complications (8, 25).Molecular methods for the detection of E. coli O157:H7 are becoming more widely accepted as an alternative to traditional growth-based tests. The ability to specifically identify the presence of an organism within a fraction of the time required by standard approaches makes molecular tests ideal for use in food systems (2). A number of recent reports have applied molecular tools for specific detection of pathogenic E. coli in food systems (10,24,31,32). Most of these assays have used DNA as the target molecule; however, recent literature has sh...