Reservoir of Bacterial Exotoxin Genes in the Environment

Many bacteria produce secreted virulence factors called exotoxins. Exotoxins are often encoded by mobile genetic elements, including bacteriophage (phage). Phage can transfer genetic information to the bacteria they infect. When a phage transfers virulence genes to an avirulent bacterium, the bacterium can acquire the ability to cause disease. It is important to understand the role played by the phage that carry these genes in the evolution of pathogens. This is the first report of an environmental reservoir of a bacterial exotoxin gene in an atypical host. Screening bacterial isolates from the environment via PCR identified an isolate with a DNA sequence >95% identical to the Staphylococcus aureus enterotoxin A gene (sea). 16S DNA sequence comparisons and growth studies identified the environmental isolate as a psychrophilic Pseudomonas spp. The results indicate that the sea gene is present in an alternative bacterial host, providing the first evidence for an environmental pool of exotoxin genes in bacteria

Bacteriophage-encoded shiga toxin gene in atypical bacterial host

<p>Abstract</p> <p>Background</p> <p>Contamination from fecal bacteria in recreational waters is a major health concern since bacteria capable of causing human disease can be found in animal feces. The Dog Beach area of Ocean Beach in San Diego, California is a beach prone to closures due to high levels of fecal indicator bacteria (FIB). A potential source of these FIB could be the canine feces left behind by owners who do not clean up after their pets. We tested this hypothesis by screening the DNA isolated from canine feces for the bacteriophage-encoded <it>stx </it>gene normally found in the virulent strains of the fecal bacterium <it>Escherichia coli</it>.</p> <p>Results</p> <p>Twenty canine fecal samples were collected, processed for total and bacterial fraction DNA, and screened by PCR for the <it>stx </it>gene. The <it>stx </it>gene was detected in the total and bacterial fraction DNA of one fecal sample. Bacterial isolates were then cultivated from the <it>stx</it>-positive fecal sample. Eighty nine of these canine fecal bacterial isolates were screened by PCR for the <it>stx </it>gene. The <it>stx </it>gene was detected in five of these isolates. Sequencing and phylogenetic analyses of 16S rRNA gene PCR products from the canine fecal bacterial isolates indicated that they were <it>Enterococcus </it>and not <it>E. coli</it>.</p> <p>Conclusions</p> <p>The bacteriophage-encoded <it>stx </it>gene was found in multiple species of bacteria cultivated from canine fecal samples gathered at the shoreline of the Dog Beach area of Ocean Beach in San Diego, California. The canine fecal bacteria carrying the <it>stx </it>gene were not the typical <it>E. coli </it>host and were instead identified through phylogenetic analyses as <it>Enterococcus</it>. This suggests a large degree of horizontal gene transfer of exotoxin genes in recreational waters.</p