Incidence and characterization of Bacillus cereus isolates contaminating dairy products

Abstract

A total of 293 dairy products purchased from local markets were examined to determine the incidence of and characterize Bacillus cereus. Isolations were made on mannitol-egg yolk-polymyxin B agar medium and confirmed by several staining and biochemical tests. B. cereus occurred in 17% of fermented milks, 52% of ice creams, 35% of soft ice creams, 2% of pasteurized milks and pasteurized fruitor nut-flavored reconstituted milks, and 29% of milk powders, mostly in fruitor nut-flavored milk mixes. The average population of B. cereus in these dairy products was 15 to 280 CFU/ml or CFU/g (range, 5 to 800). The characteristics of these B. cereus isolates in terms of heat resistance, biochemical reactions, and antibiotic susceptibility were similar to previously reported data except for a higher utilization of sucrose. Some isolates were especially resistant to carbenicillin, nalidixic acid, streptomycin, and tetracycline. The MICs for the isolates were also determined. All of the tested isolates lysed rabbit erythrocytes; 98% showed verotoxicity, 68% showed cytotonic toxicity for CHO cells, and 3 of 11 selected isolates that showed strong hemolysin activity killed adult mice.

Occurrence, heat and antibiotic resistance profile of Bacillus cereus isolated from raw cow and processed milk in Mezam Division, Cameroon

“…However, our prevalence of 8.2% in raw milk is lower than 25% reported by Larsen and Jorgensen (1997), 29% reported by Wong et al (1988) and 34.5% Reyes et al (2007). Sample collection in these studies was carried out for a longer duration compared to our study increasing their chances of detecting B. cereus.…”

“…Ahmed et al (1983) reported similar findings. However, Wong et al (1988) reported a prevalence of 17% in Z-values with the same superscript (a-f) for different strain were not significantly different at 5% level.…”

“…A majority of the isolates were susceptible to kanamycin (80%) and vancomycin (70%) with the remaining 20 and 30%, respectively, showing intermediate reactions. Wong et al (1988) also reported a high susceptibility to chloramphenicol, nalidixic acid and kanamycin, and a high resistance to penicillin among B. cereus isolates, but their susceptibility to tetracycline was lower (19%) and higher (78%) for trimethoprim/sulphamethoxazole. All isolates also demonstrated resistance to penicillin, ampicillin and trimethoprim/sulphamethoxazole.…”

“…and the differences in time and geographic location. Certain B. cereus isolates may acquire these drug resistance phenotypes, as antibiotics are frequently used in animal feeds and in chemotherapy (Wong et al 1988). Penicillin G and ampicillin are commonly used in Mezam division by farmers in the treatment of some diseases of cattle.…”

Occurrence and significance ofBacillus cereusandBacillus thuringiensisin ready-to-eat food

“…Hence, potential infections caused by the B. cereus-like organisms deriving from the present study may be treated with antimicrobial agents. Antimicrobial resistance among B. cereus has Table 3 Distribution of Minimum Inhibitory Concentration (MIC) and occurrence of resistance to eight antimicrobial agents among 40 randomly selected isolates of B. cereus-like organisms isolated from ready-to-eat food previously been reported in milk [44] and dairy products [45]. Phenotypic characterisation of the isolates based on antibiotic resistance profiles was not possible in this investigation, though other studies have shown that the resistance patterns of different Bacillus spp., in part, are species related [46][47][48].…”