Determination of the prevalence and virulence properties of aerobic endospore-forming bacteria isolated from commercial packaged foods in Dhaka city

Abstract

Endospore forming bacteria in packaged foods can lead to gastrointestinal disease and food spoilage upon germination in the GI tract or favourable storage conditions. In the current study,14 samples of packaged foods from 4 categories – UHT milk, milk powder, processed honey and fruit juice – were sampled for isolation of aerobic endospore forming bacteria, namely Bacillus spp., with a focus on theBacillus cereus group. A total of 77 isolates were found; 24 isolates were presumptively identified as B. cereus group, amongst which 4 isolates were classified as B. thuringiensis and 2 isolates were presumed to be B.anthracis. The remaining 52 were classified as B. spp. It was found that UHT milk had the lowest prevalence of endospore forming bacteria, while milk powder had the highest. All isolates were tested for production of hydrolytic exoenzymes that hydrolyze starch, casein, lipid and gelatin, while antimicrobial susceptibility of the 24 B. cereus isolates were tested against 25 antibiotics using disk diffusion method. B. cereus isolates were also screened for production of HBL toxin via discontinuous haemolysis on HBL agar. 15 out of 24 isolates showed production of HBL toxin in vitro, showing potential to cause diarrheal syndrome.