Comparison of four membrane filter methods for fecal coliform enumeration in tropical waters

Abstract

Four membrane filter methods for the enumeration of fecal coliforms were compared for accuracy, specificity, and recovery. Water samples were taken several times from 13 marine, 1 estuarine, and 4 freshwater sites around Puerto Rico, from pristine waters and waters receiving treated and untreated sewage and effluent from a tuna cannery and a rum distillery. Differences of 1 to 3 orders of magnitude in the levels of fecal coliforms were observed in some samples by different recovery techniques. Marine water samples gave poorer results, in terms of specificity, selectivity, and comparability, than freshwater samples for all four fecal coliform methods used. The method using Difco m-FC agar with a resuscitation step gave the best overall results; however, even this method gave higher false-positive error, higher undetected-target error, lower selectivity, and higher recovery of nontarget organisms than the method using MacConkey membrane broth, the worst method for temperate waters. All methods tested were unacceptable for the enumeration of fecal coliforms in tropical fresh and marine waters. Thus, considering the high densities of fecal coliforms observed at most sites in Puerto Rico by all these methods, it would seem that these density estimates are, in many cases, grossly overestimating the degree of recent fecal contamination. Since Escherichia coli appears to be a normal inhabitant of tropical waters, fecal contamination may be indicated when none is present. Using fecal coliforms as an indicator is grossly inadequate for the detection of recent human fecal contamination and associated pathogens in both marine and fresh tropical waters.

Pseudomonas aeruginosa and other microbial indicators of pollution in fresh and marine waters of rio de janeiro, Brazil

“…The high frequency of occurrence of atypical biotypes of fecal streptococci with doubtful sanitary significance noted by Araujo et al (1990) in these waters supports a n autochtonous origin of fecal streptococci, fecal coliforms (Santiago-Mercado and Hazen, 19871, and P. aeruginosa. These results also agree with reports of high densities of P. aeruginosa in tropical marine and freshwaters of Porto Rico (Santiago-Mercado and Hazen, 1987).…”

In situ survival of Vibrio cholerae and Escherichia coli in a tropical rain forest watershed

“…2). As noted in other studies, however, this locale has higher densities of fecal coliforms, total anaerobes, and Candida albicans than sites immediately below it in the watershed (4,18,22). Densities of V. cholerae and fecal coliforms were not significantly correlated when compared on the basis of site, time, or both site and time.…”

Comparison of standard most probable number method with three alternate tests for detection of bacteriological water quality indicators

“…When less stringent quality criteria are applied to the raw water sources, then an increase in number of potable sam-ples is found (Table VI). Recently several investigators expressed doubt over the validity of coliform and fecal coliform as indicators of water quality in the tropics (Santiago-Mercado and Hazen, 1987;Rivera et al, 1988;Moe et al, 1991;Ramteke et al, 1992a). Also, the coliform counts were found significantly correlated with water temperature (Ramteke et al, 1992a).…”