Evidence for coexistence of distinct Escherichia coli populations in various aquatic environments and their survival in estuary water

Abstract

Escherichia coli, a commensal bacterium from the intestinal tracts of humans and vertebrate animals, has been used as one of two bacterial indicators of fecal contamination, along with intestinal enterococci, to monitor the microbiological quality of water. However, water environments are now recognized as a secondary habitat where some strains can survive. We investigated the survival of E. coli isolates collected from bodies of water in France exhibiting distinct profiles of contamination, defined according to the following criteria: vicinity of the point sources of contamination, land use, hydrology, and physicochemical characteristics of the receiving water. We selected 88 E. coli strains among a collection of 352 strains to carry out a microcosm experiment in filtered estuarine water for 14 days at 10°C. The relationship between the survival of E. coli strains and genotypic and phenotypic characteristics was analyzed. This work showed that distinct E. coli survival types, able to survive from between 7 and 14 days to less than 2 days, coexisted in the water. E. coli isolates that rapidly lost their culturability were more frequently isolated in water recently contaminated by fecal bacteria of human origin, and most were multiresistant to antibiotics and harbored several virulence factors. In contrast, persistent strains able to survive from 4 to 14 days were more often found in water with low levels of fecal bacteria, belonged mainly to the B1 phylogroup, often harbored only one virulence factor, kspE or ompT, and were able to grow at 7°C.

Fig 1

Survival of 88 E. coli and Escherichia clade strains in a water microcosm related to water contamination profile origin. Strains were isolated from bodies of water (A) and human and bovine feces (B). S1 to S4 correspond to the four survival groups described in Results: black bars, S1 survival group (between 7 to 14 days); light-gray bars, S2 survival group (between 4 to 6 days); dark-gray bars, S3 survival group (between 2 to 4 days); striped bars, S4 survival group (less than 2 days). The water contamination profiles (from 1 to 4) correspond to those described in Materials and Methods.

Fig 2

Antibiotic resistance according to origin and survival abilities of 88 E. coli and Escherichia clade strains. Strains were isolated from bodies of water (A) and human (B) and bovine (C) feces. S1 to S4 correspond to the four survival groups described in Results. Antibiotic susceptibility: strains susceptible to the 17 antibiotics tested (light-gray bars), resistant to one or two antibiotics (dark-gray bars), and resistant to at least 3 antibiotics (multiresistant strains) (black bars).

Fig 3

Correspondence factorial analysis of 58 E. coli and Escherichia clade water sample strains. Projection on the F1/F2 plane of the 17 bacterial traits (black diamonds) and 4 survival groups (gray circles): S1, 7 to 14 days; S2, 4 to 6 days; S3, 2 to 3 days; S4, <2 days. Phylogroups A, B1, B2, and D and clade V (Escherichia clade V); minimal growth temperatures, ≥ 20°C and ≥ 7°C. VF: 0, absence of virulence factor; VF: 1, presence of only one virulence factor; VF: 2 to 3, presence of 2 and 3 virulence factors; VF: 4 to 8, presence of 4 to 8 virulence factors; Atb_R3-8, strains resistant to at least 3 antibiotics (multiresistant strains); Atb_R1-2, resistant to one or two antibiotics; Atb_S, susceptible to the 17 antibiotics tested; M: 1, degradation of one macromolecule; M: 2, degradation of two macromolecules; M: 3, degradation of three macromolecules.