Occurrence and molecular characterization of different virulence-associated genes of Cronobacter sakazakii isolates from some foods and dust samples

ABSTRACT: Among the Cronobacter genus, Cronobacter sakazakii is the most common species posing a severe health risk for newborns, infants and children. Some infant formulas, cereal-based foods, and food production environments may be the potential reservoirs of C. sakazakii. This pathogen possesses different virulence factors encoded by different virulence genes. Therefore, characterizing these genes is important for distinguishing pathogenic strains from nonpathogenic ones. The objective of this study was to characterize some virulence genes [OmpA, OmpX, zpx, and Cpa] by real-time polymerase chain reaction (PCR) in C. sakazakii isolates from a total of 120 samples (20 each of milk powder, starch, rice flour, semolina, infant formula and dust samples from food production environments). Overall, 13 isolates (7 from milk powder, 2 rice flour, 1 semolina, and 3 dust) were cultured, identified by bioMérieux API® 20E test kit, and then subjected to real-time PCR application for screening the target virulence-associated genes. Our results showed that all of 13 isolates were positive for the virulence genes OmpA, OmpX, zpx, and Cpa. In summary, our study revealed that some of the analyzed foods and environmental samples were contaminated with pathogenic C. sakazakii with its virulence-associated markers, far above the allowable limit; and therefore, this level of contamination may pose a severe health threat for newborns, infants, and children.

摘要：在克罗诺杆菌属（Cronobacter genus）中，阪崎克罗诺杆菌（Cronobacter sakazakii）是最常见的可对新生儿、婴儿及儿童造成严重健康风险的菌种。部分婴儿配方食品、谷物基食品及食品生产环境可能是阪崎克罗诺杆菌的潜在储存库。该病原菌携带多种由不同毒力基因编码的毒力因子，因此对这些基因进行表征，对于区分致病菌株与非致病菌株具有重要意义。
本研究旨在通过实时聚合酶链反应（real-time polymerase chain reaction, PCR），对取自共计120份样本的阪崎克罗诺杆菌分离株的部分毒力基因[OmpA、OmpX、zpx及Cpa]进行表征，上述120份样本分别为奶粉、淀粉、米粉、粗粒小麦粉、婴儿配方食品及食品生产环境尘埃样本各20份。
最终共培养得到13株分离株（其中7株来自奶粉、2株来自米粉、1株来自粗粒小麦粉、3株来自尘埃样本），采用生物梅里埃API® 20E鉴定试剂盒完成菌株鉴定后，通过实时PCR技术对靶标毒力相关基因进行筛查。结果显示，13株分离株的OmpA、OmpX、zpx及Cpa毒力基因均呈阳性。
综上，本研究表明部分受检食品及环境样本被携带毒力相关标记的致病型阪崎克罗诺杆菌污染，污染水平远超允许限值；该程度的污染或可对新生儿、婴儿及儿童构成严重健康威胁。