Citrobacter freundii is a species of facultative anaerobic gram-negative bacteria of the family Enterobacteriaceae. The bacteria have a long rod shape with a typical length of 1–5 μm. Most C. freundii cells generally have several flagella used for locomotion, but some do not and are non-motile.
Citrobacter is a genus of Gram-negative coliform bacteria in the Enterobacteriaceae family. The species C. amalonaticus, C. koseri, and C. freundii can use citrate as a sole carbon source. Citrobacter species are differentiated by their ability to convert tryptophan to indole (C. koseri is the only citrobacter to be commonly indole-positive), ferment lactose (C. koseri is a non-lactose fermentor), and use malonate.
Total Coliforms, Fecal Coliforms, and E. Coli The most basic test for bacterial contamination of a water supply is the test for total coliform bacteria. Total coliform counts give a general indication of the sanitary condition of a water supply.
Escherichia coli (E. coli) is the major species in the fecal coliform group. Of the five general groups of bacteria that comprise the total coliforms, only E. coli is generally not found growing and reproducing in the environment. Consequently, E. coli is considered to be the species of coliform bacteria that is the best indicator of fecal pollution and the possible presence of pathogens.
The coliform group is not a distinct valid taxonomic group, but is defined functionally as organisms that ferment lactose with both gas and acid production at 35°C. The coliform members include Citrobacter, Enterobacter, Escherichia, and Klebsiella. Some also add to the group Serratia and Hafnia to the coliform group.
Some Klebsiella bacteria have become highly resistant to antibiotics. When bacteria such as Klebsiella pneumoniae produce an enzyme known as a carbapenemase (referred to as KPC-producing organisms), then the class of antibiotics called carbapenems will not work to kill the bacteria and treat the infection.