Nineteen strains of Bacillus were isolated and identified from 111 samples of raw milk. The inhibitory effects of Lactobacillus casei and Lactobacillus helveticus on strains of Bacillus were studied. The inhibitory effects were evaluated (using the well diffusion method) on nutrient agar, with NaCl added at concentrations of 40, 45, 50, 55, 60 and 65 g/L. Lactobacillus casei inhibited 16 strains of Bacillus on nutrient agar without salt, and 18 strains in the presence of salt. When the salt concentration was 6.5%, the inhibitory effect decreased, and L. casei inhibited only eight strains of Bacillus ( Bacillus cereus, Bacillus sphaericus, Bacillus licheniformis, Bacillus macerans, Bacillus firmus, Bacillus coagulans, Bacillus polymyxa and Bacillus stearothermophilus). Lactobacillus helveticus formed the inhibitory zones against five strains of Bacillus on nutrient agar without salt, but with 4% NaCl concentration, it showed an inhibitory effect on 13 strains; a further two strains were inhibited in the presence of 4.5 and 5.0% salt. In 5.5% NaCl, the same 15 strains were inhibited by L. helveticus, whilst in 6 and 6.5% salt, the inhibitory effect decreased and only six and seven strains were affected, respectively. The maximum inhibitory effect with both L. casei and L. helveticus was observed in the presence of 4.5–5.5% salt.
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.
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