Hemolytic and nonhemolytic enterotoxin genes are broadly distributed among Bacillus thuringiensis isolated from wild mammals

The presence of cytotoxin K (cytK), nonhemolytic (NHE), and hemolytic (HBL) enterotoxin genes was investigated in 74 Bacillus thuringiensis strains recovered from the intestines of wild mammals from northeast Poland, using polymerase chain reaction amplification and Southern hybridization. All the isolates harbored genes coding for toxin(s) that could cause diarrhea. The B. thuringiensis strains containing the nhe genes were found more frequently (nheA 100%, nheB 77%, nheC 96%) than those with the hblACD (74%) and cytK (73%) genes. The presence/absence of the nheA, hblA, and cytK genes was confirmed in all of the B. thuringiensis strains by Southern hybridization. Interestingly, these experiments also indicated that the nheA locus is located on a more variable chromosome region compared with hblA and, to a lesser degree, cytK. Detection of the 41-kDa component of NHE enterotoxin by the TECRA assay revealed various protein levels by B. thuringiensis strains. These results indicate the existence of environmental B. thuringiensis strains bearing the potential virulence arsenal for the production of diarrheal toxins, and emphasize the importance of small animals in the spread of B. cereus-like enterotoxin genes in nature. However, further investigation is needed to clarify any possible involvement of environmental B. thuringiensis strains in human health issues.