Enterococci
General description
Intestinal enterococci are a subgroup of the larger group of organisms defined as faecal streptococci, comprising species of the genus Streptococcus.
These bacteria are grampositive and relatively tolerant of sodium chloride and alkaline pH levels. They are facultative anaerobic and occur singly, in pairs or as short chains. Faecal streptococci, including intestinal enterococci, all give a positive reaction with Lancefield’s Group D antisera and have been isolated from the faeces of warm-blooded animals. The subgroup intestinal enterococci consists of the species Enterococcus faecalis, E. faecium, E. durans and E. hirae. This group was separated from the rest of the faecal streptococci because they are relatively specific for faecal pollution. However, some intestinal enterococci isolated from water may occasionally also originate from other habitats, including soil, in the absence of faecal pollution. Source and occurrence Intestinal enterococci are typically excreted in the faeces of humans and other warmblooded animals. Some members of the group have also been detected in soil in the absence of faecal contamination. Intestinal enterococci are present in large numbers in sewage and water environments polluted by sewage or wastes from humans and animals.
Indicator value
The intestinal enterococci group can be used as an indicator of faecal pollution. Most species do not multiply in water environments. The numbers of intestinal enterococci in human faeces are generally about an order of magnitude lower than those of E. coli. Important advantages of this group are that they tend to survive longer in water environments than E. coli (or thermotolerant coliforms), are more resistant to drying and are more resistant to chlorination. Intestinal enterococci have been used in testing of raw water as an indicator of faecal pathogens that survive longer than E. coli and in drinking-water to augment testing for E. coli. In addition, they have been used to test water quality after repairs to distribution systems or after new mains have been laid. Significance in drinking-water The presence of intestinal enterococci provides evidence of recent faecal contamination, and detection should lead to consideration of further action, which could include further sampling and investigation of potential sources such as inadequate treatment or breaches in distribution system integrity.
Methods Enterococci are detectable by simple, inexpensive cultural methods that require basic bacteriology laboratory facilities. Commonly used methods include membrane filtration with incubation of membranes on selective media and counting of colonies after incubation at 35–37°C for 48 hours (as per EN ISO 7899-2). Other methods include a most probable number technique use the ability of intestinal enterococci to hydrolyse 4-methylumbelliferyl-β-D-glucoside at 41°C.
Selected bibliography
Ashbolt NJ, Grabow WOK, Snozzi M (2001). Indicators of microbial water quality. In: Fewtrell L, Bartram J (eds.) Water quality—guidelines, standards and health: assessment of risk and risk management for waterrelated infectious disease. London: IWA Publishing, pp. 289–315. Grabow WOK (1996). Waterborne diseases: update on water quality assessment and control. Water SA 22:193–202. Junco TT et al. (2001).
Identification and antibiotic resistance of faecal enterococci isolated from water samples. International Journal of Hygiene and Environmental Health 203:363–368. Pinto B et al. (1999).
Characterization of “faecal streptococci” as indicators of faecal pollution and distribution in the environment. Letters in Applied Microbiology 29:258–263.
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