Prevalence, Enterotoxin Production and Antibiotic Resistance of Bacillus cereus Isolated from Milk and Cheese [1] [2]

Bacillus cereus is a type of bacteria that can cause severe food poisoning. The aim of this study was to determine the incidence of B. cereus in various full-fat milk and cheese samples and to assess the HBL (haemolysin BL) and NHE (nonhaemolytic enterotoxin) production and the resistance to several antimicrobial agents of the isolates. A total of 259 samples of full-fat milk (raw, pasteurized and UHT) and cheese obtained from different retail markets in Bursa province between July and December 2013 were analysed. Isolation of B. cereus was performed using Bacara agar according to the method suggested by FDA. Twenty six (10.04%) out of 259 samples were found to be contaminated with presumptive B. cereus based on their colony morphology and microscopic appearance, by counts that ranged from 1x10(1) to 1.1x10(3) CFU/mL in raw and pasteurized milk and from 4x10(1) to 3.8x10(5) CFU/g in cheese. Thirteen isolates of B. cereus were identified by API system. However, further analysis using MALDI-TOF-MS confirmed 19 isolates as B. cereus. Thirteen out of 19 (68.4%) isolates showed evidence of only NHE toxin production while six out of 19 (31.6%) isolates were positive for both NHE and HBL production. All isolates were resistant to penicillin G, although they were susceptible to oleondamycin, erythromycin and streptomycin. There were seven different patterns of multiple antibiotic resistance in this study. In our study, 84.2% (n = 16) of B. cereus isolates exhibited multiple antibiotic resistance.