Three groups of microorganisms are commonly tested for and used as indicators of overall food quality and the hygienic conditions present during food processing, and, to a lesser extent, as a marker or index of the potential presence of pathogens (i.e. food safety): coliforms, Escherichia coli (E. coli; also a coliform) and Enterobacteriaceae.

Index Microorganisms

Microbiological criteria for food safety which defines an appropriately selected microorganism as an index microorganisms suggest the possibility of a microbial hazard without actually testing for specific pathogens. Index organisms signal the increased likelihood of a pathogen originating from the same source as the index organism and thus serve a predictive function. Higher levels of index organisms may (in certain circumstances), correlate with a greater probability of an enteric pathogen(s) being present. The absence of the index organism does not always mean that the food is free from enteric pathogens.

Indicator Microorganisms

The presence of indicator microorganisms in foods can be used to: assess the adequacy of a heating process designed to inactivate vegetative bacteria, therefore indicating process failure or success; assess the hygienic status of the production environment and processing conditions; assess the risk of post-processing contamination; assess the overall quality of the food product.

Enterobacteriaceae

The taxonomically defined family, Enterobacteriaceae, includes those facultatively anaerobic gram-negative straight bacilli which ferment glucose to acid, are oxidase-negative, usually catalase-positive, usually nitrate-reducing, and motile by peritrichous flagella or nonmotile.

E. coli

A gram-negative rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some, such as serotype O157:H7 can cause serious food poisoning in humans. The harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K, and by preventing the establishment of pathogenic bacteria within the intestine. E. coli are easily destroyed by heat, and cell numbers may decline during freezing and frozen storage of foods.

Coliform

The coliform group is defined on the basis of biochemical reactions, not genetic relationships, and thus the term “coliform” has no taxonomic validity. Coliforms are aerobic and facultatively anaerobic, gram-negative, non-sporeforming rods that ferment lactose, forming acid and gas within 48 hours at 35C.

In the case of refrigerated ready-to-eat products, coliforms are recommended as indicators of process integrity with regard to reintroduction of pathogens from environmental sources and maintenance of adequate refrigeration. The source of coliforms in these types of products after thermal processing is usually the processing environment, resulting from inadequate sanitation procedures and/or temperature control.

Coliforms are ubiquitous in nature, therefore a number of factors should be considered when testing for a particular indicator organism such as the native microflora of the food, the extent to which the food has been processed, and the effect that processing would be expected to have on the indicator organisms.