Determination of β-Lactamase Activities and Antibiotic Susceptibility of Some Bacillus Strains Causing Food Poisoning

Some Bacillus species are important food pathogens. For example, B. cereus is an opportunistic pathogen found in raw milk that is a common cause of food poisoning. It is of interest to investigate the virulant profiles of Bacillus strains isolated from foods and samples associated with food-poisoning outbreaks. Nineteen Bacillus strains were isolated from various milk samples. Beta-lactamase enzyme activities of these Bacillus strains were evaluated with iodometric and chromogenic cephalosporin (nitrocefin) test methods. Five of 19 Bacillus strains isolated were positive for beta-lactamase activity. Clavulanate-amoxycillin and cephazolin were chosen to test the antibiotic susceptibilities of the beta-lactamase positive and negative Bacillus strains. Of the five beta-lactamase positive Bacillus strains, three were susceptible, and two strains intermediate to clavulanate-amoxycillin; one was susceptible, and four strains were intermediate to cephazolin. None of the beta-lactamase positive Bacillus strains was resistant to both antibiotics. Of the 14 beta-lactamase negative strains, five were susceptible to clavulanate-amoxycillin, four strains were intermediate, and five strains were resistant; three were susceptible, one intermediate, and ten beta-lactamase negative strains were resistant to cephazolin.