Isolation of Enterococcus from powdered infant and follow-on formulas, and their antibiotic susceptibilites

Abstract

Enterococcus spp. from powdered infant formula and follow-on formulas were identified and characterized for antibiotic susceptibility to confirm the enterococcal safety. Seventy-three Enterococcus from 96 powdered infant formulas and 26 strains from 33 follow-on formulas were isolated. More than 90% of Enterococcus in the foods were E. faecium. E. casseliflavus, and E. faecalis were also isolated. All Enterococcus were sensitive to ampicillin, penicillin, tetracycline, and vancomycin. However, 2 E. casseliflavus showed low resistance to vacomycin by minimum inhibitory concentration 4.0 mu g/mL. Multiplex PCR indicated no existence of highly hazardous vancomycinresistant vanA and vanB genes. The isolates also showed the broad susceptibilities to erythromycin, ripampin, and streptomycin. Major strains of about 60% were intermediately and highly resistant to erythromycin and streptomycin, respectively. However, Enterococcus resistances to those antibiotics were not high and similar to those of Enterococcus from the other evaluated foods. Therefore, it appeared that powdered infant formula and follow-on formula might be safe to Enterococcus with regard to vancomycin and the antibiotics.