Coliforms and E. coli Testing

Escherichia coli (E. coli) is a member of the family Enterobacteriaceae and widely distributed in the intestines of humans and warm-blooded animals. It is the predominant facultative anaerobe in the part of the essential intestinal flora and the bowel.

Figure 1. Electron micrograph of coliforms and related contaminated foods

E. coli is commonly used as an indicator of fecal contamination due to its prevalence in the feces of human and animals. Moreover, it is relatively easier to isolate E. coli than other known gastrointestinal pathogens since E. coli is easily cultured and detected by its ability to ferment glucose. Therefore, the presence of E. coli in food and water samples has been used to indicate recent fecal contamination and the possible presence of more pathogenic organisms of fecal origin. However, other enteric bacteria can also exist in the sample and ferment lactose which have similar phenotypic characteristics as E. coli. Then the term "coliform" was introduced to describe this group of enteric bacteria. Coliform is a definition used to describe a group of gram-negative, rod-shaped, and facultative anaerobic bacteria that ferment lactose to produce acid and gas at 35 ℃ within 48 h. Coliforms are generally found in water and soil and prevalent in raw agricultural products. The sanitation issues can be indicated by a high coliform count. Most species of E. coli and coliforms do not cause serious illness. The enumeration of coliforms has been adopted by the U.S. Public Health Service as a more convenient standard of sanitary significance.

Detection of E. coli is used as in indicator of unsanitary processing and recent fecal contamination. Coliforms are used to indicate the sanitary condition in the food processing environment and sanitary quality of water. The presence of coliforms in processed foods with high numbers (>10⁴ CFU/g) indicates that an unacceptable level of contamination. The level of coliforms less than 10² CFU/g is normally regarded as satisfactory. For E. coli, a level of above 10² CFU/g indicates potential contamination of fecal origin from poor hygienic practices or inadequate processing for ready-to-eat foods. A level of less than 3 CFU/g is normally considered as satisfactory.

Coliforms and E. coli of Food at Alfa Chemistry

The standard methods (EN/ISO, FDA BAM and AOAC) that have been widely used to enumerate E. coli and coliforms are culture-based methods using general microbiological testing supplies. Selective mediums or Petrifilm dry rehydratable film based on lactose fermentation are used to incubate E. coli or coliforms for appropriate time. Then it is followed by the plate counting technique or the most probable number (MPN) to determine the level of E. coli and coliforms in samples. Plating method for coliforms uses solid medium of Violet Red Bile Agar with neutral red as pH indicator. MPN method is a multi-step assay including presumptive, confirmed, and completed phases based on statistical analysis.

Alfa Chemistry offer accurate and validated testing platforms for the enumeration and confirmation of E. coli and coliforms in various food samples to meet customers' needs. We also have experience working on different standards and regulations.

Platform: Plate counting or MPN technique

Limit of detection: <10 CFU/g

Sample type: Solid and liquid food samples

Sample size: 50 g