Sorbitol-fermenting bifidobacteria as indicators of diffuse human faecal pollution in estuarine watersheds

Abstract

Sorbitol fermenting bifidobacteria were evaluated as indicators of non‐point source human faecal pollution to three sub‐estuaries with elevated faecal coliform densities. Human‐specific bifidobacteria correlated with identifiable human sanitary deficiencies in feeder streams to estuarine creeks in two of three watersheds examined, one rural and one moderately developed. Sorbitol‐fermenting bifidobacteria were recovered at densities ranging from 1 to 90 colony‐forming‐units 100 ml−1 in 11 of 258 water samples but were undetected in sediment (n = 68) and scat from resident wildlife (deer, muskrat and raccoon, n = 20). Failure to detect sorbitol‐fermenting bifidobacteria in water samples during the summer months was consistent with laboratory microcosm results showing non‐recoverability of Bifidobacterium adolescentis after 5–9 d in membrane‐filtered estuarine water at 23 and 30 °C, but persistence for 4 weeks at 10 °C. Persistence of sewage‐derived bifidobacteria in membrane‐filtered freshwater at 15 °C was also observed. Recovery of sorbitol‐fermenting bifidobacteria was complicated by high background levels of Gram‐positive rods and cocci. Use of propionic acid and reduced pH (pH = 5·0), or use of a two‐step resuscitation protocol using non‐selective and selective media, did not improve recovery. Although human specific bifidobacteria hold promise as indicators of diffuse faecal contamination, methodological constraints now limit its application to situations of gross contamination, or sampling potential sources during environmental conditions conducive to bifid persistence.

Microbial Source Tracking: Current Methodology and Future Directions

“…The use of these organisms as indicators of human fecal pollution holds some promise due to the above observations; however, the survival of these organisms is highly variable and numbers can decrease by 3 to 4 orders of magnitude after as little as 2 weeks in the environment (66,67). The advantage of using an anaerobic bacterium, however, is its inability to reproduce once deposited in the environment.…”

“…Bifidobacteria are obligate anaerobic, non-spore-forming bacteria that are a major component of the human intestine. These organisms have been investigated as potential candidates for use as indicators of human fecal pollution due to the fact that they are rarely found in animals (52,65), and that certain species, when they are found, tend to be isolated at different frequencies from different animals (23,48,49,67). In addition to their abundance in human feces, the ability of human isolates to ferment sorbitol has been used to further differentiate these organisms as being human-derived (67).…”

A PCR method for detection of bifidobacteria in raw milk and raw milk cheese: comparison with culture-based methods

“…As these species are dominant in human feces, they will indicate a contamination of human origin. Moreover, Rhodes and Kator (1999) enumerated sorbitol-fermenting bifidobacteria to define human fecal pollution in estuarine watersheds. However, in raw milk cheese, the principal contamination was shown to be of animal origin (Beerens et al, 2000), most likely by cow dung on farm, since the same species, B. pseudolongum, was isolated from both kinds of samples.…”

Usefulness of bifidobacteria for the detection of faecal contamination in milk and cheese

“…Bacteroides have been used in several studies to differentiate between human and animal sources [5,9,21]. Another candidate is the genus Bifidobacterium [14,15]. This genus has been suggested as being among the most promising alternative indicators [17,19].…”