[Comparative study of survival Vibrio parahaemolyticus with Escherichia coli and Salmonella typhimurium in seawater]. / Etude comparative de la survie en eau de mer de Vibrio parahaemolyicus avec Escherichia coli et Salmonella typhimurium.

In this work, survival tests are conducted in oligotrophic seawater using pathogenic bacterial strains: Escherichia coli entéroagrégative, Salmonella Typhimurium and Vibrio parahaemolyticus. After 26 days of incubation in seawater, the three bacterial strains are exposed to sunlight for nine hours. Bacterial cells of the three strains, recovered at the end of the experiment by centrifugation were tested for their sensitivity to antibiotics and their enzymatic and metabolic profile (API 20E and 20NE). The results showed a decline in the culturability of ascending chronological order: first enteroaggregative Escherichia coli (T90 = 7 days), followed by Salmonella Typhimurium (T90 = 12 days) and finally Vibrio parahaemolyticus (T90 = 43 days). Vibrio parahaemolyticus strain showed better survival under seawater conditions before and after exposure to sunlight compared to other strains tested. On the other hand, the most reduced survival time is observed for Escherichia coli, which then becomes inadequate to predict halophilic pathogenic bacteria. Also, we noted that the solar radiation in this study would be the most important factor affecting the survival of three bacterial strains incubated in oligotrophic seawater. Changes of the enzymatic and metabolic profile are more pronounced in Escherichia coli and Salmonella, which reflect a form of resistance and a response to the passage in a hostile environment. However, the rate of antibiotic susceptibility is more apparent in Vibrio (100%) compared to the wild type Escherichia coli (60%) although the latter has completely lost its power to cultivate. This result underlines the relationship between the antibiotics resistance power of VNC cells and the history of the bacterial strain.

Survival study of enterotoxigenic Escherichia colistrain in seawater and wastewater microcosms.

In order to survey osmotic and oligotrophic stress consequence on pathogenic enterobacteria discharged in marine areas, we examined enterotoxigenic Escherichia coli (ETEC) and a reference (Ecoli O126:B16) strains during their survival (47 days) in wastewater microcosms, submerged in natural seawater and maintained in laboratory conditions. The results revealed that the survival time for the two strains was prolonged when bacterial cells were previously incubated in wastewater, with less cellular membrane damage. In addition, the wild clinical E. coli strain showed a better survival capacity than the reference E. coli strain one. For both, we noted some modifications in biochemical profiles relatively to the initial state, notably when they were previously incubated in wastewater microcosm.

Survival of Escherichia coli strains in Mediterranean brackish water in the Bizerte lagoon in northern Tunisia.

This study investigated survival and virulence of Escherichia coli strains exposed to natural conditions in brackish water. Two E. coli strains (O126:B16 and O55:B5) were incubated in water microcosms in the Bizerte lagoon in northern Tunisia and exposed for 12 days to natural sunlight in June (231 to 386 W/m2, 26 +/- 1 degrees C, 30 g/L) and in April (227 to 330 W/m2, 17 +/- 1 degrees C, 27 g/L) or maintained in darkness for 21 days (17 +/- 1 degrees C, 27 g/L). The results revealed that sunlight was the most significant inactivating factor (decrease of 3 Ulog within 48 hours for the two strains) compared to salinity and temperature (in darkness). Survival time of the strains was prolonged as they were maintained in darkness. Local strain (E. coli O55:B5) showed better survival capacity (T90 = 52 hours) than E. coli O126:B16 (T90 = 11 h). For both, modifications were noted only for some metabolic activities of carbohydrates hydrolysis. Cytotoxicity of the two strains, tested on Vero cell, was maintained during the period of survival.

[Preliminary study of the environmental effect on Aeromonas hydrophila's survival]. / Etude préliminaire de l'effet des facteurs environnementaux sur la survie d'Aeromonas hydrophila.

A survival of A. hydrophila B3 has been conducted in different conditions (mineral water, seawater exposed or not to the sunlight). Also, unculturable forms have been detected by using epifluorescence microscopy. Thus, different kinds of microcosms were prepared using filtered and autoclaved marine water or mineral water, inoculated by A. hydrophila B3 and maintained or not in room light. Further, we tested the survival of A. hydrophila B3 incubated in seawater and exposed to sunlight. Our results revealed that the culturable count of A. hydrophila B3 incubated in different conditions declined. Nevertheless, no variations were obtained for the total bacterial cells. Morphological, biochemical and antimicrobial modifications were noted.