Bacteriophage-encoded shiga toxin gene in atypical bacterial host

Abstract

BackgroundContamination 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 stx gene normally found in the virulent strains of the fecal bacterium Escherichia coli.ResultsTwenty canine fecal samples were collected, processed for total and bacterial fraction DNA, and screened by PCR for the stx gene. The stx gene was detected in the total and bacterial fraction DNA of one fecal sample. Bacterial isolates were then cultivated from the stx-positive fecal sample. Eighty nine of these canine fecal bacterial isolates were screened by PCR for the stx gene. The stx 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 Enterococcus and not E. coli.ConclusionsThe bacteriophage-encoded stx 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 stx gene were not the typical E. coli host and were instead identified through phylogenetic analyses as Enterococcus. This suggests a large degree of horizontal gene transfer of exotoxin genes in recreational waters.

Genomic and Metagenomic Approaches for Predicting Pathogen Evolution

“…Acquisition or enhancement of virulence traits is facilitated by the presence of environmental reservoirs of virulence genes. For example, metagenomics has revealed that a reservoir of exotoxin-encoding genes exists in the environment (5)(6)(7). As the temperature increases, there is increased stress on ecosystems such as coral reefs, and this stress makes organisms more susceptible to infectious disease.…”

“…Moreover, if these genes are found in alternative, noncognate environmental hosts, they serve as the genetic "raw material" for evolution of novel animal and human pathogens. As described below, the phage-encoded genes for Shiga toxin and staphylococcal enterotoxin A have been found in alternative hosts cultivated from environmental samples (5,6).…”

Validation of the Enterococci indicator for bacteriological quality monitoring of beaches in Malaysia using a multivariate approach

“…In Western nations, beach water and sand quality monitoring has attracted significant attention in recent years owing to improved legislation (Casas et al, 2011). This development partly may be due to the availability of institutional frameworks-scientific, managerial and engineering competencies, considerable budgetary allocations and relevant political and stakeholder willpower that concertedly work to ensure the functionality of robust surveillance systems.…”

“…Yet in these countries, there have been accounts reported of alarming levels of bacteria found in faeces and dangerous heavy metals in contaminated storm water flowing into beaches (Oshiro and Fujioka, 1995;Olapade et al, 2006;Grant et al, 2001;Novais et al, 2005;Yoder et al, 2004;Debacker et al, 2000). This often results in a number of public health advisories and beach closures (Graham et al, 2009;Casas et al, 2011). Furthermore, epidemiological research on the effects on health of swimming at bathing beaches has shown that swimming in bathing beaches carries some risk of illness even when these beaches comply with existing legislative standards (Barrell et al 2000).…”

An In Vitro Combined Antibiotic-Antibody Treatment Eliminates Toxicity from Shiga Toxin-Producing Escherichia coli

“…The stx genes are carried by lambdoid phages, and these phages have disseminated stx genes among a wide variety of bacterial species, including E. coli (i.e., enterohemorrhagic E. coli [EHEC] and enteroaggregative hemorrhagic E. coli [EAHEC]) (10), Enterobacter cloacae (9,11), Escherichia albertii (12), and even Grampositive Enterococcus (13). EHEC, so named because it frequently causes hemorrhagic colitis (bloody diarrhea), often harbors one or several stx genes.…”