Detection And Pathogenic Analysis Of Food-borne Pathogen-Bacillus Cereus In Chinese Rice

Bacillus cereus is a endospore froming pathogenic bacterium that is ubiquitous in the environment and is frequently associated emetic and diarrheal types of foodborne illness.In this paper,138samples of rice from retail or supermarket were analyzed for the examination,the separation and the appraisal,with MPN test, chromogenic medium and ITS sequence analysis. Bacillus species were found in109(81.3%)134of the rice samples from domestic district. Of the109rice samples analyzed107(79.9%)samples were positive for B.cereus(3.0～>1100CFU/g) with an mean value of39.1CFU/g,7(5.2%)samples were positive for Bacillus thuringiensis with an mean value of3.8CFU/g,1(0.7%)samples was positive for B.mycoides with7.2CFU/g.The three rice samples from Thailand were all positive for B.cereus with an mean value of16.9CFU/g,and two samples were detected B. thuringiensis with an mean value of4.7CFU/g. And in one sample from Vietnam only B. thuringiensiswas found with150.0CFU/g.268of the285Bacillus species isolates were identified as B.cereus,16were identified as B. thuringiensis and one was identified as B.mycoides.The amounts of B.cereus in different cilmate regions and in different rice processing technology were statistically significant(P<0.05).B.cereus maybe have certain selectivity to favorable cilmate region for the growth and reproduction.Useing PCR the isolates were checked for the presence of the cereulide synthetase gene(ces),the cytK1and cytK2gens of cytotoxin K,the nhe B gene of the nonhemolytic(NHE) enterotoxin complex and the hbl C gene of the hemolysin BL(HBL) complex.Different distinct had different detcetion rate of the B.cereus toxin genes. The toxins distribution of B.cereus in different cilmate regions were statistically significant(P<0.0001).The nhe B gene (75.0%) are generally common,followed by cytK2(55.2%) and hblC(43.3%),and cytK1of all isolates were negative.Whereas90.3%(242/268)isolates were positive for at least one enterotoxin gene, that is to say, B.cereus generally produced enterotoxin genes everywhere.B.cereus isolates were able to grow at8℃～48℃.The majority of B.cereus(82.%%) were strongly beta hemolytic or weakly hemolytic,and also46isolates (17.2%)were non-hemolytic.The ces and cytK1genes of16B. thuringiensis isolates were negative,while the cytK2, nhe B and hbl C genes simultaneously of87.5%B.thuringiensis isolates were positive.The toxin genes of B.mycoides were all negative,but was strongly beta hemolytic.37(13.8%)B.cereus isolates produced ces gene,widely distributed in15regions,obviously had higher detection rate than other counties.These isolates were only capable of cytK2and/or nhe B genes.It is worth noting that94.6%ces positive isolates were also capable of nhe B,more than the detection rate75%of nhe B that in all B.cereus isolates.Most of isolates grew well at10～48℃.Using HPLC-MS, all strains carried ces gene had high concentration of cereulide,whereas the strains not carried ces gene did not detect cereulide.The HPLC-MS result coincided exactly with the PCR detection.