Antimicrobial Resistance, Virulence, and Genetic Lineages of Staphylococci from Horses Destined for Human Consumption: High Detection of Isolates of Lineage ST1640 and Those Carrying the Gene.

This work aimed to determine the frequency and diversity of species carriage in horses intended for human consumption, as well as their resistance and virulence determinants. Eighty samples (30 nasal; 50 faecal) were recovered from 73 healthy horses in a Spanish slaughterhouse. The samples were cultured for staphylococci and methicillin-resistant staphylococci (MRS) recovery. The phenotype/genotype of antimicrobial resistance was analysed for all isolates. The -type and sequence-type (ST) were determined in strains; moreover, the presence of virulence and host-adaptation genes (, , , and ) was studied by PCR. species were detected in 27/30 (90%) and 33/50 (66%) of nasal and faecal samples, respectively. Ninety isolates belonging to eight species were recovered, with predominance of ( = 34), ( = 19), and ( = 19). strains were all methicillin-susceptible (MSSA), 28/34 were susceptible to all the antibiotics tested, and the remaining six showed resistance to (gene-detected) streptomycin ( (6)-), penicillin (), and trimetroprim/sulphametoxazole (SXT) (, ). The lineage ST1640/t2559 was predominant ( = 21). The genes and were present in all but the ST1640 isolates. Three isolates were multidrug-resistant. Healthy horses in Spain seem to be a reservoir for virulent MSSA and the lineage ST1640, although the presence of the latter in horses is described for the first time in this study. Moreover, the equine-adapted leukocidin gene is frequent among strains. A large variety of staphylococcal species with low antibiotic resistance rate were also observed.