Prevalence, Antimicrobial Resistance, and Molecular Characteristics of Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus from Retail Ice Cream in Shaanxi Province, China.

Staphylococcus aureus (S. aureus) is one of the major opportunistic foodborne pathogens as well as a source of human and animal infections. As surveillance of S. aureus and methicillin-resistant Staphylococcus aureus (MRSA) is limited in ice cream, a total of 240 ice cream samples were collected from three cities in Shaanxi province, China, and screened for S. aureus. All isolates were characterized by antimicrobial susceptibility testing, staphylococcal protein A typing, multilocus sequence typing, enterobacterial repetitive intergenic consensus typing, virulence, and resistance genes. S. aureus was recovered from 10 (4.2%) ice cream samples (13 isolates) with average count from 10 to 100 colony-forming units per gram in all cases. Resistance to amoxicillin/clavulanic acid, penicillin, and trimethoprim/sulfamethoxazole (each 100.0%) was most frequently observed, followed by ampicillin (76.9%), erythromycin (46.2%), ceftriaxone (30.8%), and cefoxitin (15.4%). A total of five types of antimicrobial resistance genes were detected, including β-lactam (blaZ and mecA), macrolide (ermB and ermC), tetracycline (tetK), aminoglycoside [aac(6')/aph(2') and aph(3')-III], and trimethoprim (dfrG). All of the strains harbored at least one staphylococcal enterotoxins gene. The commonly detected virulence genes were selw and hld (100.0%), followed by selx (92.3%); hla (84.6%); pvl (76.9%); seg, sem, and sen (each 38.5%); sei, seo, and hlb (each 30.8%); sea, seb, selu, and sely (each 23.1%); sed, sej, sek, sep, and seq (each 15.4%); and ser (7.7%). ST5-t002, ST7-t091, and ST5225-t4911 (each 15.4%) were the predominant clones, followed by ST5-t045/t105, ST6-t701/t15417, ST25-t078, ST188-t189, and ST398-t034 (each 7.7%). Among the 13 strains of S. aureus, 2 isolates were detected as MRSA (15.4%), and the molecular type belonged to ST5225-IVa-t4911. Using a 98.8% similarity cutoff, the 13 isolates were divided into 5 clusters (I-1 to I-5). These results demonstrated that the prevalence of S. aureus and MRSA was low in ice cream. However, these isolates exhibited a high level of potential pathogenicity, which represents a potential health hazard for consumers.