Contamination and characterization of multiple pathogens in powdered formula at retail collected between 2014 and 2015 in China

A total of 119 powdered formula samples collected from supermarkets, E-shops and online maternal counters in 16 provinces in China between 2014 and 2015 were analyzed for Cronobacter, Bacillus cereus, Clostridium sporogenes, Salmonella and Staphylococcus aureus. Antimicrobial susceptibility of Cronobacter was also tested by a broth microdilution method. Virulence genes related to emetic and diarrheal toxins production harbored by B. cereus were detected by multiplex PCR. The results showed that the prevalence of Cronobacter, B. cereus, C. sporogenes contamination were 3.4%, 36.1% and 9.2%, respectively. The contamination level of Cronobacter ranged from 0.36 MPN/100 g to 15 MPN/100 g. All Cronobacter isolates cultured from powdered formula tested were susceptible to all antimicrobials agents tested except one isolate which showed intermediate resistance to ciprofloxacin. The prevalence of B. cereus contamination in goat-based powdered formula was higher than that of milk-based powdered formula. A large number of B. cereus isolates (93.0%) carried nhe- and entFM-encoding genes (65.1%). Subtyping results demonstrated that the frequency of nheA, nheB, nheC were 86.1%, 88.4%, 39.5%, while 27.9%, 25.6%, 20.9% were positive for hblA, hblC, hblD, respectively. The cytK gene was detected in 25.6% of B. cereus isolates. There were 5 isolates identified as carrying both hblA/C/D and nheA/B/C and being potentially toxic. These data pointed to the need to improve the hygienic and manufacturing practices during powdered formula production in order to reduce the outbreak burden of foodborne disease risk in China.