Coliform bacteria

Group of bacteria found in the environment, foods, and intestines of people and animals

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Escherichia coli at 10,000x magnification
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Coliform bacteria are a group of Gram-negative bacteria that are commonly found in the environment, including soil, water, and vegetation, as well as in the feces of warm-blooded animals. They are used as indicator organisms to assess the sanitary quality of foods and water. The presence of coliform bacteria in drinking water suggests that there may be a pathway for pathogens to enter the water supply.

Characteristics

Coliform bacteria are rod-shaped, non-spore forming, and motile or non-motile. They are facultative anaerobes, meaning they can survive in both aerobic and anaerobic environments. Coliforms ferment lactose with the production of acid and gas when incubated at 35-37°C.

Types of Coliforms

Coliform bacteria are divided into three groups:

• Total coliforms: This group includes all coliform bacteria, which are found in the environment and feces.
• Fecal coliforms: A subset of total coliforms, fecal coliforms are more specifically associated with fecal contamination. Escherichia coli (E. coli) is the most well-known fecal coliform.
• E. coli: A specific species of fecal coliform bacteria, E. coli is often used as a specific indicator of fecal contamination.

Significance in Water Quality

The presence of coliform bacteria in water is used as an indicator of potential contamination by fecal material and the possible presence of pathogenic organisms. Water quality testing for coliforms is a standard practice in public health to ensure safe drinking water.

Testing for Coliforms

Several methods are used to detect coliform bacteria in water, including:

• Multiple-tube fermentation technique: This method involves inoculating a series of tubes with water samples and observing gas production.
• Membrane filtration: Water is filtered through a membrane that retains bacteria, which are then cultured on selective media.
• Enzyme substrate tests: These tests use substrates that change color or fluoresce in the presence of coliforms.

Health Implications

While coliform bacteria themselves are not typically pathogenic, their presence indicates that other harmful bacteria, viruses, or parasites may be present. This can lead to gastrointestinal illnesses and other health issues.

Also see

• Escherichia coli
• Water quality
• Microbial contamination
• Public health

References

• CDC - Water Quality
• EPA - Drinking Water Regulations