Comparison of the fate of the top six non-O157 shiga-toxin producing Escherichia coli (STEC) and E. coli O157:H7 during the manufacture of dry fermented sausages

Fate of Listeria monocytogenes and Shiga Toxin-Producing Escherichia coli on Slices of Beef Bresaola During Refrigerated Storage

The viability of multi-strain cocktails of geneticallymarked strains of Listeriamonocytogenes and Shigatoxin-producing Escherichiacoli (STEC) wereseparately monitored on slices of one brand of a commercially-producedbresaola (ca. pH 6.7 and aw 0.899) during extendedrefrigerated storage. Two slices (ca. 8 g each; ca. 10.2 cm wide, ca. 11 cmlong) of bresaola were layered horizontally within a nylon-polyethylene bag.The outer surface of each slice was inoculated (50 µL total; ca. 3.5 logCFU/package)with a rifampicin-resistant (100 mg/ml)cocktail of either L.monocytogenes (fivestrains) or STEC (eight strains). Bags were vacuum-sealed and then stored at 4°or 10°C for 180 or 90 days, respectively. In each of five trials, three bagswere analyzed for pathogen presence at each sampling interval via the USDA-ARSpackage rinse method. In general, levels of L. monocytogenes and STEC decreased by 3.0and 2.4log CFU/package, respectively, after 180 days when bresaola was stored at 4°C.When bresaola was stored at 10°C for 90 days, levels of L. monocytogenes and STEC decreased by 2.4 and 3.1log CFU/package, respectively. Thus, the (brand of) sliced bresaola evaluatedherein did not provide a favorable environment for either persistence oroutgrowth of surface-inoculated cells of L. monocytogenes or STEC.

Virulence factors, serogroups, and antibiotic resistance of Shiga-toxin producing Escherichia coli from raw beef, chicken meat, and vegetables in Southwest Iran

Background

Shiga-toxin-producing Escherichia coli (STEC) is an important food-borne pathogen causing human diseases with severe symptoms. Although the O157 serotype has been mostly isolated from human specimens, the increasing incidence rates of non-O157 serogroups have attracted special attention in recent years.

Aims

Evaluation of the epidemiology and identification of different characteristics of STEC isolates from raw beef, chicken meat, and vegetable samples in Shiraz, Southwest Iran.

Methods

Two hundred beef and chicken meat samples from different parts of carcasses and four hundred vegetable samples (carrots, lettuce, cucumber, and leafy greens) were randomly taken; STEC were isolated and confirmed using standard microbiological methods. Antimicrobial susceptibility testing (AST) was performed using the Kirby-Bauer disc diffusion method. Polymerase chain reaction (PCR) was used for the identification of O-serogroups, virulence, and antibiotic resistance genes.

Results

52% of beef, 8% of chicken, and 7.2% of vegetable samples were STEC-positive. Further, the highest frequency of virulence factors belonged to the co-existence of stx1 and stx2. O157 serogroup was only detected in beef (3.8%) and lettuce (16.6%) isolates, while the rates of the non-O157 serogroups were relatively high (up to 44.2%). The highest resistance rate in the STEC isolates of different samples belonged to nalidixic acid (62.5%), tetracycline (55.7%), and ampicillin (48%).

Conclusion

Paying more attention to non-O157 serogroups in future studies is recommended due to the relatively high prevalence of theses STEC serogroups in our study. Besides, the high level of resistance to some antibiotics observed in this study needs to be addressed.

Effect of cranberry pomace on the physicochemical properties and inactivation of Salmonella during the manufacture of dry fermented sausages

The effect of cranberry pomace (CP) incorporation on S. enterica serovars inactivation, starter culture population, and physicochemical properties of sausages during the manufacture of dry fermented sausages (DFS) was studied. Sausages containing a five-strain cocktail of S. enterica serovars at 7-log CFU/g, with different levels of CP (control, 0%; low, 0.55%; medium, 1.70%; high, 2.25% wt/wt), or liquid lactic acid (0.33% vol/wt, LA) were subjected to typical fermentation and drying conditions. A significant (P < 0.05) reduction in initial pH was observed in all CP treatments on day 0 as a result of CP native acidity. All treatments except low CP showed a significantly lower pH than the control throughout the study. Water activity (a_w) was not significantly affected by CP level during fermentation. However, sausages containing medium and high CP levels showed a significantly lower final product a_w than the control. DFS with CP exhibited a significantly (P < 0.05) faster and greater Salmonella inactivation during the first 5 days; reduction rate and level directly correlated to CP level. In the presence of medium and high levels of CP, Staphylococcus spp. growth was suppressed, while Lactobacillus spp. and Pediococcus spp. exhibited a stimulatory response. All treatments except low CP had no significant effect on product chemical composition, and Moisture Protein ratio (MPr). Low CP level yielded DFS with a slightly higher (P < 0.05) moisture content and MPr. Medium and high CP levels resulted in darker, duller and redder DFS with a softer texture. Findings suggest that low CP levels can be utilized by DFS manufacturers as a natural functional ingredient to further minimize the risk associated with Salmonella during DFS production without altering final product characteristics.

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Cranberry pomace inclusion in dry fermented sausages enhances Salmonella inactivation.

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Increase in cranberry pomace levels negatively affects quality of dry fermented sausages.

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Cranberry pomace inclusion does not affect growth of starter culture bacteria.

Evaluation of post-fermentation heating times and temperatures for controlling Shiga toxin-producing Escherichia coli cells in a non-dried, pepperoni-type sausage

Coarse ground meat was mixed with non-meat ingredients and starter culture (Pediococcus acidilactici) and then inoculated with an 8-strain cocktail of Shiga toxin-producing Escherichia coli (ca. 7.0 log CFU/g). Batter was fine ground, stuffed into fibrous casings, and fermented at 35.6°C and ca. 85% RH to a final target pH of ca. pH 4.6 or ca. pH 5.0. After fermentation, the pepperoni-like sausage were heated to target internal temperatures of 37.8°, 43.3°, 48.9°, and 54.4°C and held for 0.5 to 12.5 h. Regardless of the heating temperature, the endpoint pH in products fermented to a target pH of pH 4.6 and pH 5.0 was pH 4.56±0.13 (range of pH 4.20 to pH 4.86) and pH 4.96±0.12 (range of pH 4.70 to pH 5.21), respectively. Fermentation alone delivered ca. a 0.3- to 1.2-log CFU/g reduction in pathogen numbers. Fermentation to ca. pH 4.6 or ca. pH 5.0 followed by post-fermentation heating to 37.8° to 54.4°C and holding for 0.5 to 12.5 h generated total reductions of ca. 2.0 to 6.7 log CFU/g.

The Probiotic Escherichia coli Strain Nissle 1917 Combats Lambdoid Bacteriophages stx and λ

Shiga toxin (Stx) producing E. coli (STEC) such as Enterohemorrhagic E. coli (EHEC) are the major cause of foodborne illness in humans. In vitro studies showed the probiotic Escherichia coli strain Nissle 1917 (EcN) to efficiently inhibit the production of Stx. Life threatening EHEC strains as for example the serotype O104:H4, responsible for the great outbreak in 2011 in Germany, evolutionary developed from certain E. coli strains which got infected by stx2-encoding lambdoid phages turning the E. coli into lysogenic and subsequently Stx producing strains. Since antibiotics induce stx genes and Stx production, EHEC infected persons are not recommended to be treated with antibiotics. Therefore, EcN might be an alternative medication. However, because even commensal E. coli strains might be converted into Stx-producers after becoming host to a stx encoding prophage, we tested EcN for stx-phage genome integration. Our experiments revealed the resistance of EcN toward not only stx-phages but also against lambda-phages. This resistance was not based on the lack of or by mutated phage receptors. Rather it involved the expression of a phage repressor (pr) gene of a defective prophage in EcN which was able to partially protect E. coli K-12 strain MG1655 against stx and lambda phage infection. Furthermore, we observed EcN to inactivate phages and thereby to protect E. coli K-12 strains against infection by stx- as well as lambda-phages. Inactivation of lambda-phages was due to binding of lambda-phages to LamB of EcN whereas inactivation of stx-phages was caused by a thermostable protein of EcN. These properties together with its ability to inhibit Stx production make EcN a good candidate for the prevention of illness caused by EHEC and probably for the treatment of already infected people.