Identification and molecular characteristics of Staphylococcus aureus isolated from horses in Lichuan, China.

Staphylococcus aureus can transfer from animals to humans. Lichuan horse is an isolated breed living in a high-altitude area with limited use of antibiotics and is bred for use in tourism. To evaluate the risk of human-animal cross-transmission, the S. aureus was isolated from three horse farms in Lichuan, including healthy horses and horses with skin infections, farm workers and environment. From a collection of 111 samples, 18 S. aureus isolates were obtained. All the isolates were genome sequenced and their biological characteristics including antimicrobial susceptibility, virulence and biofilm formation were determined. Eighteen isolates were grouped into four sequence types (STs) including ST7 (n = 1), ST15 (n = 1), ST6238 (n = 5) and ST7636 (n = 11). The predominate sequence type, ST7636, was first reported in this study. No MRSA was found in horse farms, but most isolates were resistant to trimethoprim/sulfamethoxazole and penicillin. High frequency of blaZ also supported the strong resistance to penicillin. Horse-specific virulence factors LukPQ and EqSCIN were detected in both ST6238 and ST7636, while human immune evasion cluster (IEC) genes were found in the ST7 and ST15 isolates. All the isolates could produce biofilms. These results indicated that Lichuan horses may carry the S. aureus lineage that originated from human, posing a potential risk for animal-to-human transmission.