The inhibitory effects of Lactobacillus casei and Lactobacillus helveticus on Bacillus species isolated from raw milk in various salt concentrations

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.