Fecal coliforms and enterococci are indicator organisms used worldwide to monitor water quality. These bacteria are used in microbial source tracking (MST) studies, which attempt to assess the contribution of various host species to fecal pollution in water. Ideally, all strains of a given indicator organism (IO) would experience equal persistence (maintenance of culturable populations) in water; however, some strains may have comparatively extended persistence outside the host, while others may persist very poorly in environmental waters. Assessment of the relative contribution of host species to fecal pollution would be confounded by differential persistence of strains. Here, freshwater and saltwater mesocosms, including sediments, were inoculated with dog feces, sewage, or contaminated soil and were incubated under conditions that included natural stressors such as microbial predators, radiation, and temperature fluctuations. Persistence of IOs was measured by decay rates (change in culturable counts over time). Decay rates were influenced by IO, inoculum, water type, sediment versus water column location, and Escherichia coli strain. Fecal coliform decay rates were significantly lower than those of enterococci in freshwater but were not significantly different in saltwater. IO persistence according to mesocosm treatment followed the trend: contaminated soil > wastewater > dog feces. E. coli ribotyping demonstrated that certain strains were more persistent than others in freshwater mesocosms, and the distribution of ribotypes sampled from mesocosm waters was dissimilar from the distribution in fecal material. These results have implications for the accuracy of MST methods, modeling of microbial populations in water, and efficacy of regulatory standards for protection of water quality.

The antibiotic resistance patterns of fecal streptococci and fecal coliforms isolated from domestic wastewater and animal feces were determined using a battery of antibiotics (amoxicillin, ampicillin, cephalothin, chlortetracycline, oxytetracycline, tetracycline, erythromycin, streptomycin, and vancomycin) at four concentrations each. The sources of animal feces included wild birds, cattle, chickens, dogs, pigs, and raccoons. Antibiotic resistance patterns of fecal streptococci and fecal coliforms from known sources were grouped into two separate databases, and discriminant analysis of these patterns was used to establish the relationship between the antibiotic resistance patterns and the bacterial source. The fecal streptococcus and fecal coliform databases classified isolates from known sources with similar accuracies. The average rate of correct classification for the fecal streptococcus database was 62.3%, and that for the fecal coliform database was 63.9%. The sources of fecal streptococci and fecal coliforms isolated from surface waters were identified by discriminant analysis of their antibiotic resistance patterns. Both databases identified the source of indicator bacteria isolated from surface waters directly impacted by septic tank discharges as human. At sample sites selected for relatively low anthropogenic impact, the dominant sources of indicator bacteria were identified as various animals. The antibiotic resistance analysis technique promises to be a useful tool in assessing sources of fecal contamination in subtropical waters, such as those in Florida.

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Escherichia coli is the most completely characterized prokaryotic model organism and one of the dominant indicator organisms for food and water quality testing, yet comparatively little is known about the structure of E. coli populations in their various hosts. The diversities of E. coli populations isolated from the feces of three host species (human, cow, and horse) were compared by two subtyping methods: ribotyping (using HindIII) and antibiotic resistance analysis (ARA). The sampling effort required to obtain a representative sample differed by host species, as E. coli diversity was consistently greatest in horses, followed by cattle, and was lowest in humans. The diversity of antibiotic resistance patterns isolated from individuals was consistently greater than the diversity of ribotypes. E. coli populations in individuals sampled monthly, over a 7-to 8-month period, were highly variable in terms of both ribotypes and ARA phenotypes. In contrast, E. coli populations in cattle and humans were stable over an 8-h period. Following the cessation of antibiotic therapy, the E. coli population in the feces of one human experienced a rapid and substantial shift, from a multiply antibioticresistant phenotype associated with a particular ribotype to a relatively antibiotic-susceptible phenotype associated with a different ribotype. The high genetic diversity of E. coli populations, differences in diversity among hosts, and temporal variability all indicate complex population dynamics that influence the usefulness of E. coli as a water quality indicator and its use in microbial source tracking studies.The structure of Escherichia coli populations influences several aspects of public health. Pathogenic subtypes of E. coli are known to cause illness around the world (18), and an increased understanding of the genetic variability of populations in animal reservoirs can inform epidemiological studies. E. coli is also one of the standard indicator organisms for fecal pollution in environmental waters (1). The natural host range of E. coli includes all warm-blooded animals, some cold-blooded animals (12), and environmental reservoirs, such as sediments (2, 32) and free-living strains (24); therefore, the source of fecal pollution in water bodies is often ambiguous. Knowledge of indicator organism source is necessary for risk assessment and remediation of polluted waters, including application, such as total maximum daily load assessment. Consequently, the field of microbial source tracking (MST), which seeks to determine the origin of fecal material in water, has emerged (4, 7, 10, 14, 23, 31, 35).Many microbial source tracking methods rely on the premise that, in their gastrointestinal tracts, animal species contain distinct subtypes of E. coli that are shed in their feces. Matching the subtypes of E. coli identified in polluted watersheds to those isolated from known sources would hypothetically allow the identification of the source of the pollution (28). Many MST methods require a library of E. coli subtypes isolated fr...

Vancomycin-resistant Enterococcus spp. (VRE) were isolated from sewage and chicken feces but not from other animal fecal sources (dog, cow, and pig) or from surface waters tested. VRE from hospital wastewater were resistant to >20 g of vancomycin/ml and possessed the vanA gene. VRE from residential wastewater and chicken feces were resistant to 3 to 5 g of vancomycin/ml and possessed the vanC gene.Vancomycin resistance in Enterococcus species is becoming a major concern in clinical settings as the rate of occurrence of vancomycin-resistant Enterococcus spp. (VRE) implicated in disease increases. For example, by 1999 the incidence of VREmediated nosocomial infections in intensive care units had increased 43% from that of the period of 1994 to 1998 (23). Enterococcus faecalis and E. faecium are reported more frequently as etiological agents of disease than are other enterococci (14, 15), but other species, such as E. avium (25), occasionally cause disease.Several operons that mediate vancomycin resistance in Enterococcus spp. have been identified. Perhaps the most significant from an epidemiological standpoint is vanA-mediated vancomycin resistance, as these genes are carried on transposon Tn1546 (4) and confer inducible high-level resistance to vancomycin and teicoplanin (19). The chromosomally encoded phenotype mediated by the vanC gene is marked by low-level resistance to vancomycin (20) and is an intrinsic characteristic of E. gallinarum (11), E. casseliflavus, and E. flavescens (24).VRE that are resistant to high levels of vancomycin can be readily isolated from the feces of domestic animals in Europe (2, 10) and from humans with no exposure to hospitals (17, 31). There has been no report of high-level vancomycin resistance (Ͼ32 g/ml) in Enterococcus spp. from animal feces or from humans without hospital exposure in the United States. In spite of a 1997 call for the investigation of sources of VRE outside the health care setting in the United States (21), there are remarkably few publications containing such data (8). VRE that are intrinsically resistant to low levels of vancomycin, such as E. gallinarum, E. casseliflavus, and E. flavescens, have been isolated from bird feces (30), and E. gallinarum containing the vanC gene has been isolated from chickens and farm lagoons (8).As part of another study (18), our laboratory isolated thousands of fecal streptococci (a group that includes Enterococcus spp. and other group D Streptococcus spp.) from animal feces, wastewater, and surface waters. Some of these isolates were resistant to high levels (Ͼ32 g/ml) of vancomycin. In order to investigate the presence of VRE in wastewater, animal feces, and surface waters, all VRE were identified to the genus and species level.Isolation of vancomycin-resistant fecal streptococci. Fecal streptococcus isolates were obtained from the feces of cattle, chickens, dogs, pigs, and wild animals (birds and raccoons). Fecal streptococci were also isolated from wastewater samples collected at a central sewer lift station (designated LF)...