Vibrio
(endorsed 1996)
Guideline
Escherichia coli (or alternatively thermotolerant coliforms) are used to indicate the presence of pathogenic Vibrio spp. If explicitly sought, pathogenic Vibrio spp. should not be detected. If detected, advice should be sought from the relevant health authority or drinking water regulator.
General description
Vibrio species may be waterborne. Cholera (V. cholerae O1 and O139), for example, is usually a water-associated disease and numerous such outbreaks have been documented. Food-borne outbreaks, however, are also common and person-to-person transmission may occur under conditions of extreme crowding and poor hygiene. The transmission of cholera has been extensively reviewed, and although water is undoubtedly an important vehicle for transmission, many aspects of the epidemiology of cholera remain open to debate (Miller et al. 1985). There is evidence to suggest that in some circumstances, V. cholerae, including serotype O1 and O139, may occur naturally in some surface waters.
Australian significance
Vibrio spp. have been isolated from a number of source waters in Queensland, but not from reticulated waters. There are no published associations between the isolation of Vibrios from source water and health effects in the community.
Treatment of drinking water
Standard disinfection procedures eliminate V. cholerae O1 and O139 (the source of the classic cholera epidemics) from reticulated water, provided turbidity is low.
Method of identification and detection
Vibrio spp. are nonsporing, slightly curved Gram-negative rods, motile by a single polar flagellum. Their metabolism is both respiratory and fermentative without the production of gas, while their growth is aerobic and facultatively anaerobic. Both catalase and oxidase are formed and nitrates are reduced to nitrites (APHA method 9260H 1992, AS4276.15 2014).
Health considerations
Vibrio cholerae is a well-defined species frequently found in source waters. While cases of diarrhoea are caused by other types, only the serovars O1 and O139 are associated with the classical cholera symptoms in which a proportion of cases suffer fulminating and severe watery diarrhoea. The O1 serovar has been further divided into ‘classical’ and ‘El Tor’ biotypes, the latter distinguished by (inter alia) the ability to produce a dialysable, heat-labile haemolysin, active against sheep and goat red blood cells.
When present in large numbers in the intestinal mucosa, V. cholerae O1 produces an enterotoxin (cholera toxin) that alters the ionic fluxes across the mucosa with resulting catastrophic loss of water and electrolytes in liquid stools.
Almost all the organisms that are known to cause epidemic cholera are members of the serogroups O1 and O139, though the very similar V. mimicus (sucrose nonfermenter) has been isolated from cases of clinical cholera.
Derivation of guideline
The isolation of V. cholerae O1 and O139 from water used for drinking is of major public health importance. However, other serogroups of V. cholerae are part of the normal flora of some waters. V. cholerae and other pathogenic Vibrio spp. should be absent from drinking water supplies.
References
APHA Method 9260H, (1992). Detection of pathogenic bacteria: Vibrio cholerae. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington DC.
AS4276.15 (2014). Australian Standard. Water microbiology: Examination for Vibrio cholera. Standards Australia, Sydney, NSW.
Miller CJ, Drasar BJ and Feachem RG (1985). Cholera epidemiology in developed and developing countries: New thoughts on transmission, seasonality and control. Lancet, i, 261–263.
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