Virulence factors of gram negative bacteria isolated from natural aquatic ecosystems

Natural environments contain a variety of microorganisms, of which, a limited number are able to develop in association with higher organisms and of these, a small number are pathogenic bacteria. The ability of pathogenic bacteria to cause disease in a susceptible host is determined by multiple virulence factors acting individually or together at different stages of infection. The main goal of the present paper was to perform microbiological investigations to phenotypically emphasise the virulence factors of Gram negative bacteria isolated from aquatic ecosystem Danube Delta. The experimental study was performed in 2013, on St. Gheorghe Branch, where some areas are used as raw surface water for drinking, representing a risk to human health. The surface water samples were monthly collected from 11 control sections and they were quantitatively assessed for the microbiological contamination with fecal bacteria. Bacteriological technique used for fecal bacteria monitoring was by Membrane Filtration Method according with SR EN ISO 9308-1:2004/AC/2009. The Gram negative strains were isolated and tested for virulence factors. During the experimental study, an increase of the density of fecal bacteria was revealed in July and August 2013. The presence of enzymes that determined virulence factors for bacterial strains from the surface water samples was identifed: DNase, amylase, caseinase, gelatinase, esculinase, lipase, haemolysin and lecitinase.