1. Importance of E. coli in Food Safety
Escherichia coli (E. coli) is a crucial bacterium in food safety due to its role as an indicator of fecal contamination and its potential to cause severe foodborne illnesses. The presence of E. coli in food suggests possible contamination with pathogens that originate from human or animal waste, making it a significant marker for assessing sanitation and hygiene in food production (Racine, 2024). While most E. coli strains are harmless and even beneficial in the human gut, pathogenic variants, such as E. coli O157:H7, can cause severe diseases, including hemolytic uremic syndrome (HUS) and hemorrhagic colitis (Samad, 2024). Contamination is common in raw meats, unpasteurized dairy products, and fresh produce due to inadequate handling, cross-contamination, or irrigation with contaminated water. Understanding E. coli is vital to preventing outbreaks and ensuring food safety.
2. Introduction to E. coli
coli is a gram-negative, facultative anaerobic, rod-shaped bacterium belonging to the Enterobacteriaceae family. It is classified into several pathotypes, including enteropathogenic (EPEC), enterotoxigenic (ETEC), enterohemorrhagic (EHEC), enteroinvasive (EIEC), and enteroaggregative (EAEC) E. coli, each with distinct pathogenic mechanisms (Racine, 2024). Morphologically, E. coli forms smooth, moist, and circular colonies on MacConkey agar, fermenting lactose to produce pink colonies. Pathogenic strains produce toxins such as Shiga toxins (Stx) in EHEC, heat-labile (LT), and heat-stable (ST) toxins in ETEC that contribute to severe diarrheal diseases. Among these, E. coli O157:H7 is the most notorious due to its association with major foodborne outbreaks.
3. Laboratory Identification Methods
Several microbiological, biochemical, and molecular methods are used for the identification of E. coli in food and clinical samples. Standard microbial tests include culturing on selective media such as MacConkey agar and Eosin Methylene Blue (EMB) agar, where E. coli exhibits metallic green sheen colonies. Biochemical identification relies on tests such as the indole test (positive for E. coli), methyl red test, Voges-Proskauer test, and citrate utilization test (Samad, 2024). DNA-based detection methods, including polymerase chain reaction (PCR), are highly specific for detecting pathogenic E. coli strains by targeting virulence genes such as stx1, stx2, and eaeA. RNA-based methods such as reverse transcription PCR (RT-PCR) are effective in detecting viable E. coli in food samples.
4. Sources and Life Cycle of Contamination
coli contamination originates from fecal matter, contaminated water, and improper food handling. The most potent food sources include raw or undercooked meats, unpasteurized milk and juices, fresh produce, and contaminated water (Racine, 2024). Modes of contamination include cross-contamination during processing, irrigation of crops with contaminated water, and poor personal hygiene among food handlers. The life cycle of E. coli involves entry through ingestion, colonization of the intestinal tract, production of toxins (in pathogenic strains), and excretion through feces, perpetuating environmental contamination.
5. Major Outbreaks and Regulatory Limits
Several E. coli outbreaks have been recorded globally. In the United States, the 1993 Jack in the Box outbreak of E. coli O157:H7 resulted in four deaths and over 700 infections due to undercooked beef patties (Samad, 2024). Similarly, the 2006 spinach outbreak caused by E. coli O157:H7 led to multiple deaths and prompted stricter agricultural water regulations. The regulatory limits for E. coli in drinking water are 0 CFU/100 mL, while in milk and packaged food, strict limits apply depending on the product type. In raw meats, a non-zero limit is permitted since cooking effectively eliminates bacteria.
6. Prevention and Control Measures
Preventing E. coli contamination requires a combination of hygiene, food processing controls, and consumer awareness. The bacterium is heat-labile, meaning thorough cooking (above 70°C) effectively kills it. Freezing can slow bacterial growth but does not eliminate E. coli entirely. Basic hygiene practices, including handwashing, proper sanitation of food processing equipment, and avoidance of cross-contamination, are essential preventive measures (Racine, 2024). The implementation of Hazard Analysis and Critical Control Points (HACCP) in food production further enhances food safety by identifying and mitigating risks.
References
- Racine, J. R. (2024). The Examination of Escherichia coli Contamination via Agricultural Water Applications and Survival During Pre-Harvest Field Curing of Dry Bulb Onions. Oregon State University. Retrieved from https://ir.library.oregonstate.edu/downloads/4t64gx220.
- Samad, M. A. (2024). A Systematic Review of Bacterial Zoonotic Diseases in the Light of ‘One Health’ Approach with Multidrug Resistance Status in Escherichia coli. lepvmbj.org. Retrieved from http://www.lepvmbj.org/public/files/file_manager/1736077391.pdf.
About Author
Name : Pratiksha Shrestha
pratiksha.shrestha2001@gmail.com
Ms. Shrestha is currently a Graduate Research Assistant at Louisiana State University, USA and holds a Master’s degree in Food Engineering and Bioprocess Technology from the Asian Institute of Technology (AIT), Thailand. She previously, she worked for the Government of Nepal at the Department of Food Technology and Quality Control (DFTQC), Kathmandu, and also served as a teaching faculty at the College of Applied Food and Dairy Technology (CAFODAT) affiliated with Purbanchal University, Nepal.