ABSTRACTWe investigated the abundance, distribution, and virulence gene content ofVibrio cholerae,V. parahaemolyticus, andV. vulnificusin the waters of southern Lake Pontchartrain in Louisiana on four occasions from October 2005 to September 2006, using selective cultivation and molecular assays. The three targeted pathogenic vibrios were generally below the detection level in January 2006, when the water was cold (13°C), and most abundant in September 2006, when the lake water was warmest (30°C). The maximum values for these species were higher than reported previously for the lake by severalfold to orders of magnitude. The only variable consistently correlated with total vibrio abundance within a single sampling was distance from shore (P= 0.000). Multiple linear regression of the entire data set revealed that distance from shore, temperature, and turbidity together explained 82.1% of the variability in total vibrio CFU. The log-transformed mean abundance ofV. vulnificusCFU in the lake was significantly correlated with temperature (P= 0.014), but not salinity (P= 0.625). Virulence-associated genes ofV. cholerae(ctx) andV. parahaemolyticus(trhandtdh) were not detected in any isolates of these species (n= 128 andn= 20, respectively). In contrast, 16S rRNA typing ofV. vulnificus(n= 298) revealed the presence of both environmental (type A) and clinical (type B) strains. The percentage of the B-typeV. vulnificuswas significantly higher in the lake in October 2005 (35.8% of the total) than at other sampling times (P≤ 0.004), consistent with the view that these strains represent distinct ecotypes.
Bacteriological water quality in and around Lake Pontchartrain following Hurricanes Katrina and Rita
