Phenotypic and Genotypic Characterization of Encapsulated Escherichia coli Isolated From Blooms in Two Australian Lakes

Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia.
Environmental Microbiology (Impact Factor: 6.2). 06/2005; 7(5):631-40. DOI: 10.1111/j.1462-2920.2005.00729.x
Source: PubMed


Escherichia coli has long been used as an indicator organism for water quality assessment. Recently there has been an accumulation of evidence that suggests some strains of this organism are able to proliferate in the environment, a characteristic that would detract from its utility as an indicator of faecal pollution. Phenotypic and genotypic characterization of E. coli isolated from blooms in two Australian lakes, separated by a distance of approximately 200 km, identified that the blooms were dominated by three E. coli strains. A major phenotypic similarity among the three bloom strains was the presence of a group 1 capsule. Genetic characterization of a conserved region of the cps gene cluster, which encodes group 1 capsules, identified a high degree of genetic variation within the bloom isolates. This differs from previously described encapsulated E. coli strains which are highly conserved at the cps locus. The phenotypic or genotypic profiles of the bloom strains were not identified in 435 E. coli strains isolated from vertebrates. The occurrence of these encapsulated strains suggests that some E. coli have evolved a free-living lifestyle and do not require a host in order to proliferate. The presence of the same three strains in bloom events in different geographical regions of a temperate climate, and at different times, indicates that free-living E. coli strains are able to persist in these water reservoirs. This study provides further evidence of circumstances where caution is required in using E. coli as an indicator organism for water quality.

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    • "Consequently , contamination of harvested rainwater by enteric bacteria including faecal coliforms, Escherichia coli, and enterococci spp which are commonly found in the guts of warm blooded animals has been reported (Sung et al. 2010; Young et al. 2010; Ahmed et al. 2011a). These bacteria have a wide natural host range, which includes all warm blooded animals, some coldblooded animals and environmental reservoirs, such as sediments and free-living strains (Harwood et al. 1999; Power et al. 2005) Although several enteric bacteria can be used to monitor faecal contamination, E. coli is the most used indicator bacteria as well as a regulatory organism of faecal pollution in aquatic environments (Clesceri et al. 1998). The detection of E. coli in water primarily provides evidence of faecal pollution and secondarily reflect the possible presence of bacterial, viral and parasitic enteric pathogens (Mohapatra et al. 2007). "
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    ABSTRACT: The objective of this study was to investigate the risks associated with the use of roof-harvested rainwater (RHRW) and the implication of pigeons as the most likely source of contamination by testing for antibiotic resistance profiles of Escherichia coli. A total of 239 E. coli were isolated from thirty fresh pigeon faecal samples (130 isolates), 11 RHRW tanks from three sites in Pretoria (78) and two in Johannesburg (31). E. coli isolates were tested against a panel of 12 antibiotics which included ampicillin, amoxicillin, amikacin, cefoxitin, ceftriaxone, chloramphenicol, ciprofloxacin, cotrimoxazole, enrofloxacin, gentamicin, nalidixic acid and tetracycline. In all samples, resistance to ampicillin (22.7.9 %), gentamicin (23.6 %), amikacin (24 %), tetracycline (17.4) and amoxicillin (16.9 %) were the most frequently encountered form of resistance. However, a relatively higher proportion of isolates from pigeon faeces (67.3 %) were antibiotic resistant than those from RHRW (53.3 %). The highest number of phenotypes was observed for single antibiotics, and no single antibiotic resistance was observed for chloramphenicol, ceftriaxone, gentamicin, cefoxitin, cotrimoxazole, although they were detected in multiple antibiotic resistance (MAR) phenotypes. The highest multiple antibiotic resistance (MAR) phenotypes were observed for a combination of four antibiotics, on isolates from JHB (18.8 %), pigeon faeces (15.2 %) and Pretoria (5.1 %). The most abundant resistance phenotype to four antibiotics, Ak-Gm-Cip-T was dominated by isolates from pigeon faeces (6.8 %) with Pretoria and Johannesburg isolates having low proportions of 1.3 and 3.1 %, respectively. Future studies should target isolates from various environmental settings in which rainwater harvesting is practiced and the characterisation of the antibiotic resistance determinant genes among the isolates.
    Environmental Monitoring and Assessment 07/2015; 187(7):4636. DOI:10.1007/s10661-015-4636-x · 1.68 Impact Factor
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    • "This is due to its ease of culturability, the specificity and sensitivity of the available methods of detection and quantification [2] [3]. E. coli is still the choice indicator for faecal pollution assessment [4] although it still has the limitation of growing and establishing populations in some natural environments, including lakes [5]. Parallel conclusions of the behavior of E. coli as an extension of that of pathogens are done with caution as a result. "
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    ABSTRACT: The mechanisms by which oligotrophic and eutrophic lakes rid itself of Escherichia coli or faecal coliforms are still not clearly understood. This study sought to review the various means by which E. coli or faecal coliforms are inactivated or removed in lakes. The review cited temperature, solar radiation, predation, starvation, attachment and sedimentation as key factors that aid the removal of E. coli in lakes. In eutrophic lakes additional factors such as the role of algal biomass may play a role due to increased pH and dissolved oxygen levels attributed to algal presence. Algal toxins or exudates may also play a role although this is still under debate. The interactive effect of two or more of these factors on E. coli inactivation and the relative importance of these mechanisms on E. coli removal are still not known. Areas for further research include the role of algae in sedimenting E. coli or faecal coliforms and the possible role of algal exudates on E. coli inactivation.
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    • "Thus, a clear phylogenetic signal delineates members of this species into four major phylogenetic groups (A + B1, B2, D and E) (Selander et al., 1987; Goullet and Picard, 1989; Herzer et al., 1990; Escobar-Páramo et al., 2004; Gordon et al., 2008). It has been assumed that each one of these lineages could be associated with a particular niche, suggesting an ecological component in E. coli evolution (Picard et al., 1999; Duriez et al., 2001; Gordon and Cowling, 2003; Power et al., 2005; Gordon et al., 2008). Recent studies however, have questioned the existence of such ecological specificity coupled to phylogenetic origin (Tenaillon et al., 2010; Clermont et al., 2011; Sabarly et al., 2011; White et al., 2011). "
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    ABSTRACT: Escherichia coli occur as either free-living microorganisms, or within the colons of mammals and birds as pathogenic or commensal bacteria. Although the Mexican population of intestinal E. coli maintains high levels of genetic diversity, the exact mechanisms by which this occurs remain unknown. We therefore investigated the role of homologous recombination and point mutation in the genetic diversification and population structure of Mexican strains of E. coli. This was explored using a multi locus sequence typing (MLST) approach in a non-outbreak related, host-wide sample of 128 isolates. Overall, genetic diversification in this sample appears to be driven primarily by homologous recombination, and to a lesser extent, by point mutation. Since genetic diversity is hierarchically organized according to the MLST genealogy, we observed that there is not a homogeneous recombination rate, but that different rates emerge at different clustering levels such as phylogenetic group, lineage and clonal complex (CC). Moreover, we detected clear signature of substructure among the A+B1 phylogenetic group, where the majority of isolates were differentiated into four discrete lineages. Substructure pattern is revealed by the presence of several CCs associated to a particular life style and host as well as to different genetic diversification mechanisms. We propose these findings as an alternative explanation for the maintenance of the clear phylogenetic signal of this species despite the prevalence of homologous recombination. Finally, we corroborate using both phylogenetic and genetic population approaches as an effective mean to establish epidemiological surveillance tailored to the ecological specificities of each geographic region.
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