| Bacillus cereus is a Gram-positive, spore-forming rod that grows well, which is one of the most important food-borne pathogens, which may cause an emetic or a diarrhoeal type of food-associated illness. The emetic disease is a food intoxication caused by cereulide, while the diarrhoeal type of food poisoning is caused by complex enterrotoxins.This study assessed 238 food-borne Bacillus cereus from 427 suspected strains isolated in China and investigated the distribution of biochemical Type, virulence genes and antibiotic susceptibility, aimed to characterize the epidemiological and virulence features, supplying more data, technology and theory to guarantee food security and control of food poisoning.1. Biochemical type characterization238 Bacillus cereus isolated from food in five different areas of China (North China, East China, South Central China, Southwest China and North-West District) was confirmed and biochemical typing following "Microbiological examination of food hygiene Examination of Bacillus cereus". Biochemical type 1～type 13 were identified for 195 B.cereus isolates, of which type 1,2,3,8 were dominant Biochemical types, accounting for 28.6%,11.0%,16.4% and 10.5% in the isolates,respectively. Different regions have different major biochemical types. Type 1,2,3,8 should arouse our attention and close observation.2. Virulent Gene distributionMolecular investigation on the genes encoding virulence determinants NRPS、hblA、 hblC、hblD、nheA、nheB、nheC、entFM、bceT、and cytK were conducted within 238 strains of Bacillus cereus by means of PCR. The results reveals that the positive rate in se-quence from high to low is:nheC、cytK、hblC、hblA、hblD、bceT、nheB、entFM、nheA and NRPS. The finding rates were 63.9%、50.4%、50.4%、48.7%、41.6%、40.3%、24.8%、 23.1%、13.4%、7.1%,respectively. The nheC, cytK, hblA, hblC, hblD, bceTare predominant virulence determinants, which were more than 40.3% higher. There were lower prevalence of nheA, nheB,entFM and NRPS. Genotypes are multifarious. There are 58 genotypes, of which carried up to 9 virulence genes. None carry 10 virulence genes.12.6% have no virulence gene. Study found that 208 strains(87.4%) carried at least one virulent gene.95 (39.9%) strains carried entire genetic makeups of hemolysin BL (HBL) gene (hblA,C,D),while 29 (12.2%) strains carried entire genetic makeups of nonhemolytic enterotoxin (NHE) gene (nheA,B,C). High carriage rate of virulence genes and genotypic diversity pose a potential food safety and public health threat.3. Virulent gene characteristic in major biochemical typesThe analysis of experimental data shows that hblA、hblC、hblD and entire hblA, C, D had higher incidence in strains of biochemical type 1 and type 2 than type 3 or type 8.Higer rate of entire nheABC appeared in typel and type 3 than type 2 or type 8. The positive rate of entFM、bceT and cytK in typel, type 2 and type 3 were high. The proportions for at least one virulent gene were all above 72.0% in type 1,2,3 and 8, which indicated the potential risk in major biochemical types.4. Antibiotic susceptibility characterization of food-borne Bacillus cereusThe susceptibility of 238 isolates of food-borne Bacillus cereus to antibiotics was deter-mined by Broth Microdilution Susceptibility Testing by Clinical and Laboratory Standards Institute.The antibiotics include ampicillin, cefotaxime, gentamicin, vancomycin, erythromy-cin, tetracycline, ciprofloxacin, trimethoprim-sulfamethoxazole, chloramphenicol and clindamycin. We found the sensitive rate of the Bacillus cereus strains to gentamicin, vanco-mycin, ciprofloxacin and trimethoprim-sulfamethoxazole were all 100%, the sensitiveness to erythromycin, tetracycline, chloramphenicol, clindamycin were 88.8%、90.2%、99.6% and 87.1%,respectively, while that of ampicillin and cefotaxime was only 0.4% and 5.4%. There is no significant difference in different regions, the sensitiveness to erythromycin and clindamycin revealed biochemical types difference. |
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