我国市售婴儿配方乳粉中蜡样芽胞杆菌污染及其毒力基因调查

目的了解国内市售婴儿配方乳粉中蜡样芽胞杆菌污染及毒力基因分布情况。方法采用MPN法定量检测婴儿配方乳粉中的蜡样芽胞杆菌,在对分离菌株正确鉴定的基础上,开展腹泻型和呕吐型毒素产生相关毒力基因的分布研究。结果 135份婴儿配方乳粉中有57份检出蜡样芽胞杆菌,检出率为42.22%。平均污染水平为7.14 MPN/g。国产产品蜡样芽胞杆菌污染较进口产品重,网售产品较超市销售产品重,差异有统计学意义(P0.05)。共发现24种蜡样芽胞杆菌毒力基因携带模式,其中nhe基因携带率最高,达92.98%(53/57),其次为ent FM基因(71.93%),70.18%(40/57)的菌株同时携带nhe和ent FM基因。亚型分型结果显示nhe A、nhe B和nhe C基因的携带率分别为88.72%、88.72%和49.12%。溶血素BL基因携带率分别为hbl A 24.56%、hbl C 22.81%和hbl D 17.54%,cyt K基因携带率为22.81%。有8株菌既携带nhe的3个基因又携带hbl的3个基因。结论我国市售婴儿配方乳粉蜡样芽胞杆菌污染较重,分离到的蜡样芽胞杆菌菌株普遍携带毒力基因,建议加强对婴儿配方乳粉中蜡样芽胞杆菌污染的监管,并开展膳食暴露该菌对婴儿健康影响的风险评估,为制定婴儿配方乳粉中蜡样芽胞杆菌的限量标准提供依据。

Survey on contamination of Bacillus cereus and its virulence gene profiles isolated from retail infant formula in China

To survey the contamination and virulence gene profiles of B.cereus isolated from retail infant formula in China.Methods Infant formulas were quantitatively detected for B.cereus using MPN method. Virulence genes in relation to emetic and diarrheal toxins production harbored by B.cereus were detected by multiplex PCR. Results Fifty-seven out of 135 infant formula samples were positive for B.cereus with the contamination rate of 42.22% and the mean contamination level of 7.14 MPN/g. The contamination of B.cereus in domestically produced infant formula was more severe than those imported one. B.cereus contamination of infant formula sold online was more serious than that collected from supermarket. A total of 24 toxigenic patterns in B.cereus were found. Most of B.cereus isolates carried nhe gene (92.98%) and entFM gene (71.93%). There were 40 (70.18%) strains that carried both nhe and entFM genes simultaneously. Subtyping results demonstrated that the frequency of nheA, nheB, nheC were 88.72%, 88.72%, 49.12%, and hblA, hblC, hblD were 24.56%, 22.81%, 17.54%, respectively. The frequency of cytK occurrence was 22.81%. There were 8 strains that carried all three subtypes of both nhe and hbl genes, which indicated that these strains may be highly toxic.Conclusion Retail infant formulas were heavily contaminated by B.cereus. Most isolates carried one or more virulence genes. It is recommended to broaden the monitoring for B.cereus in infant formulas. It is necessary to make an assessment of infant dietary exposure to B.cereus in order to establish the national standard of maximal limit for B.cereus in infant formula.