Effect of Stress on Non-O157 Shiga Toxin–Producing Escherichia coli

Abstract

Non-O157 Shiga toxin-producing Escherichia coli (non-O157 STEC) strains have emerged as important foodborne pathogens worldwide. Non-O157 STEC serogroups O26, O45, O103, O111, O121, and O145 have been declared as adulterants in beef by the U. S. Department of Agriculture Food Safety and Inspection Service. While documentation is limited, treatments including heat and acid that have been shown to inactivate E. coli O157:H7 will likely also destroy non-O157 STEC; however, non-O157 STEC strains show variability in their responses to stress. It has been shown that non-O157 STEC may survive in fermented sausages and cheeses, and treatments such as high pressure may be necessary to eliminate non-O157 STEC from these products. The mechanisms used by non-O157 STEC to resist acid environments are similar to those used by O157:H7 strains and include the acid tolerance response, the oxidative system, and the glutamate and arginine decarboxylase systems. However, one study demonstrated that some non-O157 STEC strains utilize a chaperone-based acid stress response (HdeA and HdeB) to combat acidic conditions, which is lacking in E. coli O157:H7. Genomic studies suggest that while non-O157 STEC can cause diseases similar to those caused by E. coli O157:H7, O157 and non-O157 STECs have different evolutionary histories. Non-O157 STECs are a heterogeneous group of organisms, and there is currently a limited amount of information on their virulence, fitness, and stress responses, rendering it difficult to draw firm conclusions on their behavior when exposed to stress in the environment, in food, and during processing.

The Gut Bacterium Bacteroides thetaiotaomicron Influences the Virulence Potential of the Enterohemorrhagic Escherichia coli O103:H25

“…It has not yet been described if, or how, non-O157 EHEC strains may use strategies to conserve energy in the human gut. Non-O157 EHEC strains have a different evolutionary history compared to O157 and represent a heterogeneous group consisting of strains with varying virulence potential [14,50,51]. …”

The effect of oxidative stress on gene expression of Shiga toxin-producing Escherichia coli (STEC) O157:H7 and non-O157 serotypes

“…In recent years, non-O157 STEC serotypes, including O26:H11, O103:H2, O104:H4, O111:NM and O145:NM, have caused severe outbreaks worldwide (Bradley et al, 2012, Brown et al, 2012, Norman et al, 2012, Rounds et al, 2012, Smith and Fratamico, 2012, Smith et al, 2014. However, the influence of environmental stresses on non-O157 E. coli serotypes remains unclear.…”

Developments in sampling and test methods for pathogens in fresh meat

“…Antimicrobial agents are added to the agar medium used for isolation with the intention of allowing the growth of target VTEC while inhibiting the growth of other Enterobacteriacea , including verotoxin negative E. coli . Unfortunately, it appears unlikely that such a goal can be achieved, because there is no evidence that VTEC as a subpopulation are more resistant to any inhibitors or selective conditions than E. coli generally (Smith and Fratamico, 2012 ). This problem could be partially addressed by adopting a more permissive formulation of the medium, but isolation requires labour intensive and costly screening of large numbers of suspect colonies.…”