Escherichia coli is a Gram-negative, facultatively anaerobic rod and a natural inhabitant of the gastrointestinal tract of warm-blooded animals. While most strains are commensal, several pathogenic groups cause foodborne illness. Shiga toxin-producing E. coli (STEC), also known as verotoxigenic E. coli (VTEC), is the most significant group in food safety. Serotype O157:H7 is the most clinically prominent STEC, though non-O157 serotypes (O26, O103, O111, O121, O45, O145) are increasingly recognized and regulated.
STEC produces Shiga toxins (Stx1 and Stx2) that inhibit protein synthesis in host cells, causing hemorrhagic colitis and hemolytic uremic syndrome (HUS), particularly in young children and the elderly. The infectious dose is extremely low, estimated at fewer than 100 cells. Major reservoirs include cattle and other ruminants. Transmission occurs through consumption of undercooked ground beef, raw leafy greens, unpasteurized dairy, and contaminated water. Secondary person-to-person transmission is also significant in outbreaks.
E. coli and coliforms are widely used as indicator organisms for fecal contamination and process hygiene. Coliforms (including Enterobacter, Klebsiella, and Citrobacter) indicate general sanitation, while fecal coliforms (E. coli, thermotolerant organisms) specifically indicate fecal contamination. Detection of E. coli O157:H7 employs selective and differential media such as sorbitol MacConkey (SMAC) agar, where O157:H7 appears colorless due to lack of sorbitol fermentation, confirmed by O157 latex agglutination. PCR and real-time PCR targeting stx1, stx2, and eae genes are used for confirmation and typing.
In the United States, STEC O157:H7 and six non-O157 serotypes are classed as adulterants in raw ground beef, and zero tolerance is applied in processed products. Control measures include proper cooking (71°C for ground beef), pasteurization of juice and dairy, Good Agricultural Practices for fresh produce, and stringent hygiene in slaughterhouses. Pre-harvest interventions such as vaccination of cattle and feed additives are also employed to reduce carriage. E. coli O157:H7 shares transmission routes with Salmonella and Campylobacter. Indicator organisms are used to assess fecal contamination and the potential presence of enteric pathogens. Understanding microbial spoilage helps differentiate between spoilage microbiota and pathogenic contaminants.
