Coliform germs in drinking water - what does that mean?

Coliforms are a bacterial group that serves as a hygiene indicator for drinking water. What germs belong to this group, which limit values ​​apply in drinking water, and what is the danger of coliform bacteria is explained in this article.


Coliforms are named because of their similarity to Escherichia coli, the coliform bacteria. They are gram-negative, have a rod shape and produce various harmful acids and gases within 48 hours of infection. They are considered enterobacteria and split lactose.

The most important strains belonging to the group are:

  • Citrobacter
  • Enterobacter
  • Escherichia and
  • Klebsiella


Citrobacter requires only citrate as the only source of energy. It occurs as a natural intestinal germ and splits various organic substances and also supports fermentation processes. As a pathogen, he is not very potent. Citrobacter rarely causes very mild urinary tract infections.


Enterobacter are also naturally occurring intestinal germs. They oxidize organic substances to water and CO2, but can also be nourished by acidification. Some strains are potential pathogens that can cause urinary tract infections, meningitis and respiratory infections.


Escherichia is a germ that can move itself. Escherichia coli also belongs to this bacterial strain. Similar to Enterobacter, they can use both oxidation for nutrition and acid fermentation.

Escherichia coli is a normally non-pathogenic germ that is also part of the human intestinal flora. However, some types can cause serious illnesses - such as complicated urinary tract infections or neonatal meningitis.

In developing countries, E. coli is one of the most common pathogens, causing around 160 million diarrheal diseases worldwide. About one million deaths per year are due to an infection of E. coli.

In addition, some strains can cause bacterial disturbances, here kidney failure is a common complication. Involvement of E. coli in chronic inflammatory bowel disease such as Mb.Crohn is contemplated.

In order for Escherichia to have a morbid effect, however, a weakening of the patient must first be present. Children are particularly affected.


Klebsiella are important pathogens of venereal diseases. Some strains produce a picture similar to syphilis. Most Klebsiella are penicillin resistant.

Limits for coliform bacteria

According to the Drinking Water Ordinance, the limit value for coliform bacteria is 0/250 mL.

Drinking water pollution by coliform bacteria is very dangerous and common in tropical countries. It indicates a fecal load.

Tips & Tricks

So-called traveler's diarrhea (Montezuma's revenge) is almost always triggered by drinking water contaminated with coliform bacteria.

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