Escherichia coli O157 can grow in natural freshwater at low carbon concentrations

Abstract

Whereas much information on the die-off of Escherichia coli in the aquatic environment is available, only few data support its growth under such conditions. We therefore investigated batch growth in microcosms containing different types of sterile freshwater. The water samples were inoculated with low starting cell concentrations of E. coli O157 (3 x 10(3) cells ml(-1)) and growth was followed using nucleic acid staining combined with flow cytometry. We demonstrated that E. coli O157 is able to grow in sterile freshwater at low carbon concentrations, which is against the common view that cell numbers decline over time when added to freshwater samples. A correlation between apparent assimilable organic carbon (AOC(app)) concentration and the final cell concentration reached by E. coli O157 was established (P < 0.01). A considerable fraction of the AOC(app) (34 +/- 13%) was used by E. coli O157 but the numerical cell yield was about five-times lower in comparison with the bacterial AOC-test community, which originated from natural freshwater. On average, the maximum specific growth rate (mu(max)) of E. coli O157 growing in sterile freshwater at 30 degrees C was 0.19 +/- 0.07 h(-1). Batch growth assays at five different temperatures revealed a positive influence of temperature on mu(max) of E. coli O157. The results give new information on the behaviour of this common pathogen in the aquatic environment and contribute to microbial risk assessment in order to prevent spreading of water-borne diseases.

Survival of Escherichia coli in the environment: fundamental and public health aspects

“…Furthermore, E. coli was also found to exhibit a high degree of catabolic flexibility, which conferred a clear fitness advantage in its secondary habitats such as soil and water (Ihssen and Egli, 2005). E. coli O157:H7 may survive and even grow in sterile freshwater at low carbon concentrations, which stands in contrast to the common conception that the organism will die out over time in such strongly carbon-limited environments (Vital et al, 2008). Moreover, because of the production of RpoS (subunit of RNA polymerase, represents a major factor involved in starvation survival), E. coli is able to rapidly adapt to, and tolerate, diverse stress conditions (Lange and Hengge-Aronis, 1991).…”

“…General observations on E. coli survival E. coli can, to varying extents, survive in different open environments such as soil, manure and water (Kudva et al, 1998;Jiang et al, 2002;Vital et al, 2008). There are also possibilities for migration between these habitats.…”

Survival of Host-Associated Bacteroidales Cells and Their Relationship with Enterococcus spp., Campylobacter jejuni, Salmonella enterica Serovar Typhimurium, and Adenovirus in Freshwater Microcosms as Measured by Propidium Monoazide-Quantitative PCR

“…Another possible explanation is the release of extracellular DNA from particulate material during this initial period, which then becomes available for qPCR later. The increase in DNA amplified by both PMA-qPCR and qPCR under dark conditions was not surprising because the availability of dissolved organic carbon can trigger the growth of Enterococcus, which subsequently ceases when the nutrients are depleted, as reported for the growth of Enterococcus in beach sands (51) and of E. coli O157 in natural freshwater at low carbon concentrations (43). The slopes from the cultivation-dependent method and PMA-qPCR were significantly different (P values ϭ 0.001 and 0.02 for sunlight exposure and dark condition, respectively), which was likely due to the presence of intact but noncultivable Enterococcus cells.…”

Modeling the Complexities of Water, Hygiene and Health in Limpopo, South Africa

“…Vital et al (2008) similarly found a positive correlation between AOC and final concentration after a 3 day incubation.…”

“…AOC concentrations above 100 µg/mL are significant because they can lead to biological growth of harmful pathogens such as cholera (Vital et al , 2007) or E. coli (Vital et al , 2008). 50% (n = 8) of the samples had AOC concentrations higher than this value.…”