Prevalence, molecular characterization, and antibiotic susceptibility of Cronobacter spp. in Chinese ready-to-eat foods

Cronobacter spp. are foodborne pathogens that cause rare but life-threatening diseases in neonates and infants; they can also cause disease in adults. Cronobacter spp. contamination of ready-to-eat (RTE) foods has been reported previously. However, to date, the prevalence and contamination levels of these bacteria in RTE foods in China have not yet been determined. Therefore, the aim of this study was to investigate the prevalence of Cronobacter spp. in RTE foods marketed in China. Two-hundred and eighty RTE food samples were collected from different producers and retailers and analyzed using quantitative methods. The isolates obtained were identified to the species level based on fusA sequences, and were subtyped using a PCR-based serotyping technique. Selected isolates were further characterized by multilocus sequence typing (MLST) and antimicrobial sensitivity determination. Of 280 samples tested, 52 (18.6%) were positive for Cronobacter spp. The contamination levels were less than 110 MPN/g for 78.8% (41/52) of the samples. The results of the O-antigen serotyping for 111 isolates showed that Cronobacter sakazakii serogroup O2 (28 isolates) was the most prevalent serotype. MLST analyses produced 41 sequence types (STs), including 20 novel STs. ST8 was the most prevalent ST (9 isolates) followed by ST4 (5 isolates). Antimicrobial sensitivity testing showed that 84.5% and 46.5% of the isolates were resistant to penicillin G and cephalothin, respectively; in contrast, all of the tested isolates were susceptible to cefotaxime, ciprofloxacin, tetracycline, and nalidixic acid. To the best of our knowledge, this is the first report on Cronobacter spp. prevalence in RTE foods in China, and the findings of our study nonetheless suggested that Cronobacter spp. contamination of Chinese RTE foods poses a potential risk for the consumer. Thus, the study highlights the significance of developing more effective control strategies during the manufacturing process.