Understanding Escherichia coli

[Kevine]

Escherichia coli, commonly known as E. coli, is a bacterium that resides in the intestines of humans and animals such as cows, sheep, and goats. While most strains are harmless and aid in digestion, certain types can cause serious illness, including food poisoning.

E. coli belongs to the Enterobacteriaceae family and is characterized as a gram-negative rod, up to 3 micrometers long. It ferments glucose and various sugars, producing pink colonies on McConkey agar. Certain strains exhibit hemolytic activity on blood agar and are motile with peritrichous flagella, often featuring fimbriae (hair-like structures). E. coli 0157:H7 is an important serotype and seems to be predominate in most areas. The strains producing verotoxin are shiga-like toxin (SLT) which causes diarrhoea in humans and animals.

Source of infection​

Contamination of food by human and animal faeces. The organism can persist in manure, water trough and other farm location. The association of E. coli 0157:H7 with raw meat, under cooked ground beef and raw milk lead to investigation of the role of cattle as a reservoir of the pathogens (Buchanan & Doyle, 1997).

Pathogenesis​

Enterohemorrhagic E. coli (EHEC) strain, particularly the serotype E. coli O157:H7, may produce one or more types of cytotoxins which are collectively referred as shiga-like toxins (SLTs) since they are antigenically and functionally similar to shiga toxin produced by Shigella dysenteriae.

However, new terminology has been applied, and what was SLT is now Stx. All Stxs consists of a single enzymatically active A subunits and multiple B subunits. Stx-sensitive cells possess the toxin receptor, globotriaosyceramide (Gb3), and sodium butyrate appears to play a role in sensitizing cells to Stxs.

Once toxins bind toGb3, internalization follows with transport to the trans-Golgi network. Inside the host cells, the A subunits bind to and release and adenine residue that inhibits protein synthesis. The B subunits form pentamers in association with a single A subunit and thus are responsible for the binding of the toxin to the neutral glycolipid receptors. E. coli O157:H7 thrives in diverse conditions (7°C to 50°C) and acidic environments but is sensitive to heat.

Symptoms​

Infection with E. coli O157:H7 typically manifests after an incubation period of 72-120 hours (3-5 days). Symptoms include:

• Diarrhea: Initially watery, often progressing to bloody
• Abdominal cramps: Severe and persistent
• Vomiting: Occasional
• Absence of fever, unlike many bacterial infections

Most cases resolve within a week, but severe infections can lead to hemolytic uremic syndrome (HUS), a life-threatening condition affecting the kidneys, especially in children and the elderly. Seek medical attention immediately if bloody diarrhea or intense abdominal pain occurs. Antibiotics are generally avoided, as they may worsen HUS risk.

Sources and Transmission​

E. coli spreads through:

• Contaminated food: Undercooked ground beef, raw meat, raw milk, or produce exposed to human or animal faeces
• Water: Drinking or swimming in contaminated sources
• Cross-contamination: Improper handling of raw and cooked foods
• Person-to-person: Poor hygiene after contact with infected individuals
• Animal contact: Interaction with farm animals or petting zoos

Cattle serve as a primary reservoir for E. coli O157:H7, with the bacteria persisting in manure, water troughs, and farm environments. Common outbreak sources include undercooked burgers, unpasteurized cider, and leafy greens.

Detection of toxin​

Diagnosis involves:

• Culturing: Growth on McConkey or sorbitol McConkey agar (specific for O157:H7)
• Serotyping: Identifying strains with antisera
• ELISA: Detecting Stx toxins
• DNA hybridization: Identifying toxin-encoding genes

Sorbitol McConkey agar is especially useful for isolating E. coli O157:H7 from food and fecal samples.

Who’s at Risk?​

While anyone can contract E. coli, higher-risk groups include:

• Children under 5
• Adults over 65
• Pregnant women and immunocompromised individuals
• Travelers to regions with poor sanitation

Occurrence is global, with higher case fatality rates in developing countries, particularly among infants and the elderly (up to 2% for EHEC infections vs. <0.1% for other types in industrialized nations). Most EHEC cases peak in summer.

Control and Prevention​

Preventing E. coli infection relies on straightforward measures:

• Cook thoroughly: Ensure ground beef reaches 70°C (160°F) and steaks hit 62.6°C (145°F) with a 3-minute rest. Heat sensitivity makes proper cooking effective.
• Maintain hygiene: Wash hands, utensils, and surfaces after handling raw meat.
• Separate foods: Use distinct cutting boards for raw meat and other items.
• Store safely: Refrigerate perishables promptly.
• Use safe ingredients: Rinse produce thoroughly and avoid raw milk or undercooked products.

Additional precautions include handwashing after animal contact and avoiding untreated water while swimming or traveling.

Why Awareness Matters​

Global health bodies like the WHO promote food safety standards to curb E. coli outbreaks. Understanding its spread and applying preventive habits can safeguard communities.

References​

1. Buchanan, R., & Doyle, M. (1997). Food Borne Disease: Significance oof E. coli O157:H7 and other Enterohaemorrhagic E. coli. Food Technology, 5, 69-76.
2. Jay, J. (2000). Modern Food Microbiology (6th ed.). Gaithersburg, Maryland: Aspen Publications.
3. Quinlan, J. J. (2013). Foodborne Illness Incidence Rates and Food Safety Risks for Populations of Low Socioeconomic Status and Minority Race/Ethnicity: A Review of the Literature. International Journal of Environmental Research and Public Health, 10, 3634-52.