An investigation of the cytotoxic effect of Bacillus spp. isolated from raw milk on vero cell cultures
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Members of the genus Bacillus are often present as contaminants in raw milk. The sources of milk contamination are in the environment. The average level of raw milk contamination with Bacillus spp. is 3.42 × 10 2 |ml during the winter and 1.03×10 2 /ml in the summer. Reduction of the number of Bacillus in thermally processed milk directly depends on the applied treatment. The thermic treatments which are used for pasteurization do not lead to a reduction of Bacillus number. Thermic treatments aimed at sterilization, decrease Bacillus numbers in direct cerrelation with their thermoresistance (D-values). Bacillus cureus is known as a cause of food poisoning. Intensive examination in the last ten years has shown that other Bacillus spp. can also produce toxins. Besides biological assays and immunological methods toxin production has been measured by determine cytotoxicity to suitable cell cultures. Thus, 15 strains of Bacillus spp. have been screened for cytotoxicity to Vero cell cultures.... Out of this 13 were from the mesophyl group and 2 from the psychrotrophic group. All the examined strains were lecithinase positive, haemolytic and hydrolysed casein. The strains were cultivated in brain-heart infusion broth, supplemented with 0.1% glucose (BHIG broth) at 20±1°C and 30±1°C for 24-96 hours. Cytotoxicity was estimated after incubation for 1-48 h of the broth culture supernatant inoculum on Vero cells. It was found that the Bacillus spp. population after 24 h of incubation at 20±1°C achieved a level of log 9.888±0.909 and at 30±1°C a level of log 9.739±1.001. There was no statistically significant difference in the Bacillus spp. numbers during incubation for 96 hours at 30±1°C. A statistically significant difference in Bacillus spp. numbers (p<0.05) occurred between the first and the fourth day during the incubation for 96 hours at 20+1°C. The appearance of a cytotoxic effect on Vero cells was found in 8 of the 15 investigated broth culture supernatants obtained after the first day of incubation of Bacillus strains at 30±1°C in 9 after the second day and in 11 strains affter the third and fourth day. After incubation of Bacillus strains in BHIG broth for 24-96 h at 20±1°C, cytotoxicity of supernatants on Vero cells was noted in 7 out of 15 strains after the first day and in 10 strains after the second, third and the fourth days.
Keywords:raw milk / Bacillus spp. / cytotoxic effect
Source:Acta veterinaria - Beograd, 1999, 49, 5-6, 353-361
- Univerzitet u Beogradu - Fakultet veterinarske medicine, Beograd