The effects of temperature, pH, and iron on biofilm formation by clinical versus environmental strains of Vibrio vulnificus

Due to the nature of Vibrio vulnificus infections (i.e., gastroenteritis and septicemia), only very few studies of a biofilm-associated form in this pathogen's life cycle have been conducted. We proposed that biofilm production by clinical strains of V. vulnificus would be higher than by environmental strains. Biofilm formation by clinical and environmental reference strains was tested under different temperatures (24, 30, and 37 degrees C), pH (5.5, 7.5, and 8.5) and iron concentrations (18, 30, 50, 100, and 200 mu M). Biofilm production by clinical strains was consistently higher (p < 0.001) at 24 degrees C than by environmental strains. Higher biofilm production was observed at pH 5.5 by all strains. Growth rates were lowest at pH 5.5 for environmental strains but for clinical strains there were no differences at pH 5.5, 7.5, and 8.5, demonstrating a tolerance to acidic and alkaline conditions. There was a strong, direct correlation between iron concentration in the growth medium and biofilm production by all strains tested. The current study indicates that biofilm formation might be important for the survival of V. vulnificus in vivo as well as in the marine environment. With regard to temperature and pH, higher biofilm production appears to be a trait of clinical strains and could be considered a virulence determinant in V. vulnificus.