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

The research article investigates how Staphylococcus aureus bacteria in horses in Lichuan, China, could potentially transmit to humans. The study’s findings call for an evaluation of the potential risk presented by horse-to-human transmission of the bacteria.

Objective and Methodology

• The main objective of the study was to evaluate the risk of Staphylococcus aureus transmission from horses to humans. The researchers sought to understand this risk by examining samples from the Lichuan horse breed, which lives in a high-altitude area and has limited exposure to antibiotics.
• The researchers collected 111 samples from three horse farms in Lichuan. The samples were obtained from both healthy and infected horses, farm workers, and the environment.
• The biological characteristics of 18 S. aureus isolates obtained from the samples were analyzed. Specific attributes analyzed included the isolates’ genome sequences, antimicrobial susceptibility, virulence, and their capacity for biofilm formation.

Key Findings

• Four sequence types (STs) of S. aureus isolates were identified. These were ST7, ST15, ST6238, and ST7636.
• The most dominant sequence type was ST7636, which was identified for the first time in this study.
• Resistance to antibiotics such as trimethoprim/sulfamethoxazole and penicillin was common among the S. aureus isolates. Despite no methicillin-resistant Staphylococcus aureus (MRSA) being identified in the horse farms, strong resistance to penicillin was confirmed by the frequent occurrence of the blaZ gene in the isolates.
• Virulence factors specific to horses, LukPQ and EqSCIN, were found in ST6238 and ST7636 isolates. Simultaneously, genes linked to human immune evasion were found in ST7 and ST15 isolates.
• All the isolates had the ability to form biofilms, a trait that contributes to S. aureus survival and resistance to antibacterial treatments.

Significance of the Study

• The study provides new insights on the potential risks presented by horse-to-human transmission of S. aureus, given that certain isolates were found to carry human immune evasion genes.
• Furthermore, the finding that all isolates could produce biofilms and had notable resistance to certain antibiotics raises concern for successful treatment of potential cross-transmissions.
• The research findings could help healthcare professionals and policy makers develop necessary prevention and control measures to limit horse-to-human transmission of S. aureus.