Objective To investigate the pollution, molecular types, and drug resistance of Enterobacter sakazakii isolated from infant food products in Songjiang District of Shanghai, and to provide a scientific basis for baby food safety management, prevention of foodborne diseases, and clinical medication.
Methods All samples of infant formulas (milk-based and soy-based), cereal-based infant food supplement, and powdered in fant drinks were collected from 19 supermarkets or grocery stores from 3 subdistrict and 4 villages of Songjiang District in 2016. Isolation, identification, and serotyping of Enterobacter sakazakii were performed according to the protocol stipulated in the National food safety standard Food microbiological examination:Enterobacter sakazakii (GB 4789.40-2010) and fluorescence quantitative PCR method. Antibiotic susceptibility test and pulsed-field gel electrophoresis were also carried out.
Results There were 124 food samples. Eleven strains of Enterobacter sakazakii were isolated from 51 cereal-based infant food supplement samples, in which two strains were not preserved, and the positive rate of Enterobacter sakazakii was 21.6%; no strains were isolated from 53 infant formulas samples and 20 powdered drinks samples; and the difference was statistically significant among the three types of baby foods (P < 0.01). The results of PCR method obtained were coincident with the above results. Of the 9 strains with positive Enterobacter sakazakii, serotyping results showed three strains of O1 type and six strains of O2 type. All strains were resistant or moderately resistant to cefazolin among 16 selected antibiotics, and were susceptible for other antibiotics. Pulsedfield gel electrophoresis typing results showed five groups with similarity ranged from 50% to 100%, including four strains of type A and two strains of type B whose similarities were both 100%.
Conclusion The positive rate of Enterobacter sakazakii is significantly higher in cereal-based infant food supplement than in other infant food products. All strains are susceptible to selected antibiotics except cefazolin. O1 and O2 are main serotypes. Pulsedfield gel electrophoresis typing results show Enterobacter sakazakii isolated from infant food products are homologous, and the method can be used for molecular typing and source tracing of Enterobacter sakazakii.
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