Prevalence and characterization of Salmonella enterica in dried milk-related infant foods in Shaanxi, China

The aim of this study was to investigate the existence and characteristics of Salmonella enterica in dried milk-related infant foods. Twenty-four (3.4%) of 705 samples, including 5 (2.0%) of 246 powdered infant formula, 18 (4.0%) of 445 infant rice cereal, and 1 (7.1%) of 14 other infant foods, were positive for Salmonella. Fifteen serotypes were identified in 40 Salmonella isolates; Salmonella Duesseldorf (15.0%) and Salmonella Indiana (15.0%) were more frequently detected than other serotypes. Resistance to chloramphenicol (82.5%) was most common, followed by tetracycline (57.5%), ceftiofur (52.5%), kanamycin (52.5%), streptomycin (50.0%), gentamycin (45.0%), nalidixic acid (35.0%), ceftriaxone (32.5%), ciprofloxacin (25.0%), amikacin (20.0%), and cefoxitin (15.0%). Twenty-eight (70.0%) isolates were resistant to ≥8 antimicrobials, with 5 (12.5%) being resistant to 14 antimicrobials. Amino acid substitutions in gyrase A (GyrA) were most frequently detected as Ser83Arg/Asp87Glu and in p53-associated Parkin-like cytoplasmic protein (ParC), they were all Ser80Arg; the quinolone resistance gene qnrS (47.5%) was commonly detected as well as aminoglycoside acetyltransferase [aac(6′)-Ib; 25.0%], qnrA (17.5%), and qnrB (15.0%) genes. Thirty distinct pulsed-field gel electrophoresis patterns were identified among 40 isolates; no identical pulsed-field gel electrophoresis pattern was detected among Salmonella isolates with the same serovar that was recovered in 2010 and 2012. Our results suggest that dried milk-related infant foods could be contaminated with Salmonella and highlight that the dangers to infant health should not be neglected.