Indicator organisms are used as a proxy to monitor conditions in a particular environment, ecosystem, area, habitat, or consumer product. Certain bacteria, fungi and helminth eggs are being used for various purposes.
Indicator bacteria:
Certain bacteria can be used as indicator organisms in particular situations. The presence of bacteria commonly found in human feces, termed coliform bacteria (e.g. E. coli), in surface water is a common indicator of faecal contamination. For this reason, sanitation programs often test water for the presence of these organisms to ensure that drinking water systems are not contaminated with feces. This testing can be done using several methods which generally involve taking samples of water, or passing large amounts of water through a filter to sample bacteria, then testing to see if bacteria from that water grow on selective media such as MacConkey agar. Alternatively, the sample can be tested to see if it utilizes various nutrients in ways characteristic of coliform bacteria.
Coliform bacteria selected as indicators of faecal contamination must not persist in the environment for long periods of time following efflux from the intestine, and their presence must be closely correlated with contamination by other faecal organisms. Indicator organisms need not be pathogenic. Non-coliform bacteria, such as Streptococcus bovis and certain clostridia may also be used as an index of faecal contamination
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. The Enterobacteriaceae group does include many coliforms, with the addition of other microorganisms which ferment glucose instead of lactose (i.e. Salmonella). Common foodborne genera of the Family Enterobacteriaceae include Citrobacter, Enterobacter, Erwinia, Escherichia, Hafnia, Klebsiella, Proteus, Providencia, Salmonella, Serratia, Shigella, and Yersinia. Psychrotrophic strains of Enterobacter, Hafnia, and Serratia may grow at temperatures as low as 0C. If the meat ecosystem favors their growth, genera in the family Enterobacteriaceae may be important in muscle food spoilage. Conditions allowing growth of Enterobacteriaceae include limited oxygen and low temperature. Members of this family produce ammonia and volatile sulfides, including hydrogen sulfide and malodorous amines, from amino acid metabolism The Enterobacteriaceae have been used for years in Europe as indicators of food quality and indices of food safety. The use of coliforms as indicators of food quality or insanitation in food processing environments is based upon tradition in the United States. This practice arbitrarily bases judgment on food quality or manufacturing plant insanitation upon recovery of those members of the Enterobacteriaceae group (i.e. coliforms) which ferment lactose, thus ignoring the presence of non-lactose fermenting members..
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 be heat, and cell numbers may decline during freezing and frozen storage of foods. E. coli is the only member of the coliform group that unquestionably is an inhabitant of the intestinal tract and it has become the definitive organism for the demonstration of fecal pollution of water and food not undergoing any processing which would kill the organism. In cases where it is desirable to determine whether fecal contamination may have occurred, at present, E. coli is the most widely used indicator of such, the presence of which implies a risk that other enteric pathogens may be present in the food. In many raw foods of animal origin, small number of E. coli can be expected because of the close association of these foods with the animal environment and the likelihood of contamination of carcasses from fecal material, hides, or feathers during slaughter-dressing procedures. The failure to detect E. coli in a food, however, does not assure the absence of enteric pathogens , However, criteria involving E. coli are generally not useful for detecting likely fecal contamination for foods that have been processed sufficiently to destroy this bacterium.
E. coli are not always confined to the intestine; they have the ability to survive in the food processing plant environment and re-contaminate processed foods (E. coli found in environmental swabs is a good indication of fecal contamination). Hence, the presence of E. coli in a heat-processed food does not necessarily indicate fecal contamination, but indicates either process failure or, more commonly, post-processing contamination from equipment or employees or from contact with contaminated raw foods.
Dairy microbiologists use E .coli as a true indicator organism to assess post-pasteurization contamination in milk. The presence of E. coli in pasteurized milk may indicate inadequate pasteurization, poor hygienic conditions in the processing plant, and/or post-processing contamination because proper pasteurization inactivates levels of E. coli anticipated in raw milk.
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.
Indicator fungi:
Penicillium species, Aspergillus niger and Candida albicans are used in the pharmaceutical industry for microbial limit testing, bioburden assessment, method validation, antimicrobial challenge tests, and quality control testing., When used in this capacity, Penicillium and A. niger are compendial mold indicator organisms,
Molds such as Trichoderma, Exophiala, Stachybotrys, Aspergillus fumigatus, Aspergillus versicolor, Phialophora, Fusarium, Ulocladium and certain yeasts are used as indicators of indoor air quality
Referances:
- Warner NR, Levy J, Harpp K, et al. Drinking water quality in Nepal’s Kathmandu Valley: A survey and assessment of selected controlling site characteristics (2007) Hydrogeology Journal. 2008;16:321–334.
- http://www.sciencedomain.org/
- Rai SK, Ono K, Yanagida J, Ishiyama S, Kurokawa M, Rai CK. A large-scale study of bacterial contamination of drinking water and its public health impact in Nepal. Nepal Med Coll J. 2012;14(3):234-240.
- Standard methods for the examination of water and wastewater. American Public Health Association, American Water Works Association, and Water Pollution Control Federation. American Public Health Association, Inc., 13th ed., New York. 1971;875.
Presented by
Assist prof Dr .Manal Abd Alssirag
Collage of Agriculture
Kerbala university
