The Population Dynamic Changesof Bacillus Cereus In Infant Formulaand Dissolving Infant Formula

Bacillus cereus is a commonconditioned pathogen,almost all kinds of food have been reported that are related to food poisoning caused by B.cereus.Infant formula is the main food supplement to infants,once B.cereus contamination,will pose a serious threat of infection to infants.This paper studied the contamination of B.cereus in infant formula in Beijing,while the virulence genes and drug susceptibility of the strains isolated were detected and analysied.For further,the population dynamic changes of B.cereus in infant formula were studied to provide technical support to reduce the harm of the bacteria in the consumption of infant formula The results are as fllows:1.Investigation of B.cereus in infant formula in BeijingWith regard to the incidence and population levels of B.cereus in infant formula,68 samples involved 19 brands were collected in Beijing and examined.48.5%(39/68)of the samples were contaminated with B.cereusreaching levels from 0.36 to 46 MPN/g.The incidences of various enterotoxigenic genes hblA,hblC,hblD,nheA,nheB,nheC,cytK,bceT and entFM in the 88 isolates was 5.68%,9.09%,5.68%,54.54%,63.64%,86.36%,21.59%,21.59%and 21.59%,respectively.All of the B.cereus isolates were observed?-haemolytic activity on blood agar.For the antibiotic susceptibility,the strains were highly resistant to penicillin as expected,and showed great susceptibility to the non-?-lactam antibiotics used in this study except rifampin.The results of this study indicated that B.cereus had high prevalence in infant formula.Most of the strans isolated in infant formula were potentially or actually toxigenic and susceptible to the non-?-lactam antibiotics.2.The study of the population dynamic changes of B.cereus in infant formulaAfter being opened,the infant formula need to sealed and avoid light preservation,the preservation time should not be more than 1 months.The study is mainly on the population dynamic changes of B.cereus in infant formula in the 30 day storage period.The results showed that B.cereus could not growth in the infant formula,cells stayed in the sub damage state,this damage could be repaired in suitable conditions.The recombination temperature of infant formula does not exceed 60?,therefore,the growth characteristics of B.cereus in dissolving infant formula was studied at 25-60?.The research results show that?the B.cereus in dissolving infant formula has obvious growth/inactivation boundaries,25-48? showed growth,49-60? showed inactivation.25-48?:The growth prediction models of B.cereus in dissolving infant formula at 25,28,33,37,40,45 and 48 ? were built by using the modified Gompertz model,Logistic model and Baranyi model.The models were evaluated,and the modified Gompertz model was optimal.The results showed that the models were effective.The secondary models showed that the maximum specific growth rate first increases and then decreased,the lag period shortened first and then decreased with the increase of temperature,49-60?:The thermal inactivation models of B.cereus in dissolving infant formula at 49,52,55,57 and 60? were built by using the Log-logistic model.The models were evaluated.The results showed that the models were effective.By comparing the logarithmic time of maximum inactivation rate,maximum inactivation rate and the log reduction value of the thermal inactivation models at 49-55? and 57?60?,it is not conducive to the inactivation of B.cereus in dissolving infant formula.