Bacteroides
(endorsed 2011)
Guideline
No guideline value has been established for Bacteroides in drinking water. If used as an indicator and detected in drinking water, immediate action should be taken including investigation of potential sources of faecal contamination. The primary value of these organisms is as a tool for tracking and identifying sources of contamination.
General description
Bacteroides is an anaerobic Gram-negative, non-spore-forming rod from the family Bacteroidaceae. Bacteroides is primarily found in the intestinal tract of humans and other animals, comprising up to one third of faecal flora and far outnumbering concentrations of Escherichia coli (Finegold et al. 1983, Layton et al. 2006). Bacteroides can be present at concentrations of up to to per gram of faeces. It is involved primarily in digestion and plays a role in excluding potential pathogens from the human gut. Due to its anaerobic nature, Bacteroides does not survive or grow in aerobic conditions, including in water supplies.
Although Bacteroides is not a frank pathogen, some species, for example B. fragilis, are opportunistic pathogens and can cause bacteraemias and abscess formation at multiple body sites (Wexler 2007).
Recent advances in molecular technology have resulted in the development of several human- and animal-specific genetic markers for Bacteroides. These methods have the potential not only to identify faecal contamination but also to discriminate between sources of contamination. Specific Bacteroides markers for humans and ruminants have been developed (Layton et al. 2006) and work is in progress on a marker specific to birds.
Source and occurrence
Bacteroides is present in very high numbers in faecal material from animals and humans. It does not grow or survive in oxygenated water. There appears to be a high degree of host specificity.
Method of identification and detection
Bacteroides can be cultured using anaerobic media (Kator and Rhodes 2003). In addition there is a rapid fluorescent antibody technique that can be used (Fiksdal and Berg 1987).
Specific molecular methods can distinguish various specific markers within Bacteroides. These techniques have been published but are not yet available as routine diagnostic methods. Most Bacteroides methods involve quantitative PCR of the 16SrRNA of the organism (Bernard and Field 2000, Layton et al. 2006, Reischer et al. 2007, Kildare et al. 2007, Ahmed et al. 2009).
Indicator value and application in practice
Bacteroides has been proposed as a suitable indicator of contamination of water supplies. It is present in high numbers in faeces and does not grow in water supplies. In addition, Bacteroides can be used as a tool in faecal source tracking (USEPA 2005). Understanding sources of contamination in source waters is important in developing sound risk management plans. Bacteroides can be used to assess source water quality and the relative impacts of human and livestock waste. Such information can improve the accuracy of microbial risk assessments and identification of appropriate control measures. Faecal source tracking can also be used to investigate sources of post-treatment ingress of human and animal waste into distribution systems.
The presence of Bacteroides provides evidence of recent faecal contamination. Detection in drinking water should always lead to investigation of the cause, which could include inadequate treatment or ingress of contamination.
NOTE: Important general information is contained in PART II, Chapter 5
References
Ahmed W, Goonetilleke A, Powell D, Gardner T (2009) Evaluation of multiple sewage-associated Bacteroides PCR markers for sewage pollution tracking. Water Research 43:4872-4877.
Bernhard AE, Field KG (2000). Identification of non-point sources of faecal pollution in coastal waters by using host-specific 16S ribosomal DNA genetic markers from faecal anaerobes. Applied and Environmental Microbiology, 66:1587-1594.
Finegold SM, Sutter VL, Mathisen GE (1983). Normal indigenous intestinal flora. In: Human Intestinal Microflora in Health and Disease. Academic Press, London, pp. 3-31.
Fiksdal L, Berg JD (1987). Evaluation of a fluorescent antibody technique for the rapid enumeration of Bacteroides fragilis group of organisms in water. Journal of Applied Microbiology, 62(4):377-383.
Kator H, Rhodes M (2003). Detection enumeration and identification of environmental microorganisms of public health significance. In: Mara D, Horan N (eds), The Handbook of Water and Wastewater Microbiology. Academic Press London.
Kildare BJ, Leutenegger CM, McSwain BS, Bambic DG, Rajal VB, Wuertz S (2007). 16s rRNA-based assays for quantitative detection of universal, human-, cow-, and dog-specific faecal Bacteroides: A Bayesian approach. Water Research 41:3701-3715.
Layton A, McKay L, Williams D, Garrett V, Gentry R, Sayler G (2006). Development of Bacteroides 16S rRNA gene TaqMan-based real-time PCR assays for estimation of total, human and bovine faecal pollution in water. Applied and Environmental Microbiology, 72:4214-4224.
Reischer GH, Kasper DC, Steinborn R, Farnleitner AH, Mach RL (2007). A quantitative real-time PCR assay for the highly sensitive and specific detection of human faecal influence in spring water from a large alpine catchment area. Letters in Applied Microbiology, 44:351-356.
USEPA (United States Environmental Protection Agency) (2005). Microbial source Tracking Guide Document. EPA 600/R-05/064, USEPA, Cincinatti, USA.
Wexler H (2007). Bacteroides: the good, the bad, and the nitty-gritty. Clinical Microbiology Reviews, 20(4):593-621
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