Enterococci are a subgroup of fecal streptococci and are characterized by their ability to grow at low and elevated temperatures (10°C and 45°C) and at elevated pH (9.5). These microorganisms have been used as indicators of fecal pollution for many years especially in water samples.
Enterococci are benign bacteria when they reside in their normal habitat such as the gastrointestinal tracts of humans or animals. Outside of their normal habitat, enterococci are pathogenic causing urinary tract and wound infections, and life-threatening diseases such as meningitis. Enterococci easily colonize open wounds.
Compounding their pathogenesis, enterococci are also some of the most resistant bacteria, particularly from human sources. Studies have shown that certain strains of enterococci are resistant to expensive and potent antibiotics such as vancomycin. Several intrinsic features of the enterococcus genus allow it to survive for extended periods of time. These bacteria have been shown to survive for 30 minutes at 60°C and persist in the presence of detergents. Enterococci may remain viable on surfaces for days or weeks because the organisms are resistant to desiccation.
Fortunately the bacteria are easily killed by disinfectants used in the bottling plant, such as peracetic acid and hydrogen peroxide. However, the main reason for enterococci to be mentioned in quality standards for water is the link with possible fecal contamination. Sources of enterococci can be from toilet flushes, animal faeces brought in on shoes or boots or poor hand hygiene.
Enterococcus faecalis is a Gram-positive bacterium and it is interesting to note that Gram-positive strains are very common in indoor environments and have been measured in one study to represent 40% of the species recovered from airborne bacteria.
Weekly testing for enteroccoci is recommended while bottling water. An easy-to-use test from IDEXX called Enterolert makes measurement of presence/absence possible in the bottling plant in 24hrs.