High prevalence of multidrug resistant S. aureus-CC398 and frequent detection of enterotoxin genes among non-CC398 S. aureus from pig-derived food in Spain

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) CC398 is a livestock-associated (LA) lineage, mainly detected in swine. Its dissemination via the food-chain could be a food-safety issue. This work aimed to study the diversity of S. aureus lineages in pork-products, to determine the prevalence of MRSA and methicillin-susceptible S. aureus (MSSA) of lineage CC398, and to study the antimicrobial resistance phenotype/genotype and the virulence traits of recovered isolates. One hundred and one samples of pig-derived food were collected in Northern Spain for S. aureus isolation. Antibiotic resistance profile was analysed, and associated resistance genes were screened by PCR. Detection of CC398 lineage, spa-type, multilocus sequence-type, virulence factors, immune evasion cluster (IEC) genes, and phage ΦSa3 integrase was performed by PCR/sequencing. The prevalence of S. aureus and MRSA among pig-derived food was 33.6% and 21.8%, respectively. Thirty-nine S. aureus isolates were recovered and attributed to 19 spa-types and 12 STs, ST398 being the predominant lineage (n = 25; 64%). MRSA-CC398 isolates (n = 23) were mainly spa-t011 (n = 16) and 82.6% were multidrug-resistant (MDR). All MRSA-CC398 were tetracycline-resistant and IEC-negative and four hosted either eta, tst or sea gene. The two MSSA-CC398 isolates detected were spa-t5452, IEC-positive, and were resistant to penicillin (blaZ) and erythromycin/clindamycin (inducible) (ermT with/without ermC + msrA). Among the 14 non-CC398 isolates, only two were MRSA (ST8, PVL-positive, enterotoxin-positive, IEC-negative). The 12 MSSA isolates included two of lineage CC45 and IEC-positive. CC398 lineage is prevalent among S. aureus of pig-derived food (both MRSA and MSSA), LA-MRSA-CC398/t011 being the clone most represented. The presence of the IEC-positive MSSA-CC398 and MSSA-CC45 isolates in food products highlights the potential implication of handlers in transmission of foodborne pathogens. Moreover, given the high frequency of MDR isolates and virulence genes detected, hygienic practices should be improved to limit the dissemination risk of S. aureus via the food chain.

Keywords: CC398; Enterotoxins; IEC; MRSA; MSSA; Multidrug-resistance.