A. Derrien

Occurrence of pathogenic vibrios in coastal areas of France

Aims: This study was carried out to investigate the occurrence of potentially pathogenic species of Vibrio in French marine and estuarine environments.

Responses of enteric bacteria to environmental stresses in seawater

Abstract The effects of different environmental factors (nutrient deprivation, hyperosmotic shock, exposure to light) on enteric bacteria which have been transferred into the marine environment, have been studied experimentally (microcosms) by considering demographic, physiological and genetic responses in Escherichia coli or Salmonella typhimurium populations. Short-term experiments (≤ 48 h) showed that nutrient deprivation induced limited changes in measured bacteriological variables, but when combined with hyperosmotic shock, it results in an energy charge decrease and inactivation of membrane transport. Light exposure mainly affects the colony-forming capacity of bacterial populations. Combining different stress factors confirmed the rapid appearance of a viable, but nonculturable state (VBNC) in populations of E. coli and S. typhimurium. It has been shown that cellular forms other than those previously described in the literature can be generated following incubation in seawater. It was also established that pre-adaptation phenomena may occur, leading to better survival (e.g. pre-incubation in seawater in darkness enhanced survival under light exposure). An explanation concerning these phenomena can be found by looking at the rpoS gene which controls the expression of numerous genes and can trigger a general anti-stress response under different adverse conditions. Although the results provide better comprehension of the fate of enteric bacteria in the marine environment, they also raise numerous questions related to fundamental and applied problems, given in the conclusion of this paper.

Salmonella DNA persistence in natural seawaters using PCR analysis

The risks of false‐positive responses were examined when using the polymerase chain reaction (PCR) method for the detection of Salmonella in the marine environment (water and shellfish). The degradation rates of DNA, both free and from dead Salmonella, were evaluated in natural seawaters maintained at 10° and 20°C, using PCR with Vir and invA primers. The DNA of dead Salmonella was detected up to 55 d in seawater collected in winter and stored at 10°C. But in summer, the persistence was shorter: 10 d or even 2 d for a smaller inoculum (3 × 103Salmonella ml−1). The role of the planktonic organisms present in spring and summer was pinpointed. For free DNA, the persistence times were shorter: from 2 to 4 d at 20°C, and from 3 to 8 d at 10°C showing that the nuclease activity of marine organisms is higher at warm temperatures. These data led us to recommend careful interpretations of direct PCR results, especially during cold periods and for samples collected close to terrestrial discharges of high concentrations of live, dead or lysed Salmonella. PCR is a rapid, specific and sensitive method, but should be applied with care to marine samples, in order to avoid false‐positive responses.

Chlorophyll a might structure a community of potentially pathogenic culturable Vibrionaceae. Insights from a one‐year study of water and mussels surveyed on the French Atlantic coast

The present study focused on the isolation of culturable bacteria from mussels and sea water to identify Vibrionaceae potentially pathogenic for humans. Three sites located on the French Atlantic coast were monitored monthly (twice each month during summer) for 1 year. Environmental parameters were surveyed (water temperature, salinity, turbidity, chlorophyll a) and bacteria were detected by culture and identified by API 20E(®) systems (BioMérieux) and PCR. A total of seven species were detected (Grimontia hollisae, Photobacterium damselae, Vibrio alginolyticus, V. cholerae, V. fluvialis, V. vulnificus and V. parahaemolyticus) and species diversity was higher at the end of summer. Surprisingly, V. cholerae non-O1/non-O139 was detected in spring. No site effect was detected. Using Sørensen similarity indices and statistical analyses, we showed that chlorophyll a had a significant influence on the bacterial community detected in mussels and assemblages were more similar to one another when chlorophyll a values were above 20 µg l(-1) . No significant effect of any parameter was found on the community detected in water samples. Such surveys are essential for the understanding of sanitary crises and detection of emerging pathogens.