Isolation and molecular typing of Cronobacter spp. in commercial powdered infant formula and follow-up formula

Cronobacter spp. (Enterobacter sakazakii) are important foodborne pathogens. Infections with this pathogen can lead to neonatal meningitis, necrotizing enterocolitis, and bacteremia. This study examined Cronobacter spp. contamination in commercial powdered infant formulas (PIFs) and follow-up formulas (FUFs) in China. Forty-nine of 399 samples were contaminated with Cronobacter spp. and 10.2% of the isolates were resistant to cefotaxime; in contrast, all of the tested isolates were susceptible to amikacin, amoxicillin/clavulanic acid, cefepime, ciprofloxacin, imipenem, and meropenem. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) analyses produced a total of 16 PFGE banding patterns and 11 sequence types (STs), including 7 novel STs. In summary, the rates at which Cronobacter spp. were isolated from commercial PIF and FUF samples in China were relatively high, and the isolated strains exhibited high susceptibility in vitro to most antibiotics. The PFGE method exhibited higher typing capability than the MLST method, and molecular typing results revealed that the contamination of PIF and FUF with Cronobacter spp. in China may be mainly due to the addition of contaminated materials. Thus, the development of more effective control strategies during the manufacturing process is needed.