Characterization of Staphylococci colonizing healthy equine skin: antibiotic resistance, virulence factors, and biofilm formation.

In order to develop non-antibiotic therapies to treat dermatological diseases it is urgent to spread knowledge on composition and properties of skin bacteria in healthy animals. Since horses are popular companions of humans, it is necessary to know what risk skin bacteria pose to humans. Therefore the aim of this work was to analyse species composition of staphylococci isolated from skin swabs of 50 healthy horses using MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight) spectrometry and to characterize their virulence properties. Swabs were collected from five body areas (neck, dorsal back, abdomen, pastern and muzzle). Among 19 different staphylococcal species identified, the most common species were Staphylococcus succinus, S. xylosus, S. vitulinus and S. warneri. The most frequent antimicrobial resistance in staphylococcal isolates was observed for penicillin G (48%). The blaZ gene was detected in 90% of penicillin resistant isolates while mecA and mecC genes were not observed. Only low level resistance was noted for erythromycin (12%), tetracycline (6%), linezolid (4%) and oxacillin (4%). No multidrug-resistant strain was found, the MAR (multiple antibiotic resistant) index in average was 0.048 ± 0.039. Biofilm production was observed in 90.1% of isolates whereas 62% of them showed strong production. Gelatinase, DNase, protease and lipase activity was found in 50.4%, 41.3%, 22.3% and 46.3% of isolates, respectively. The results of enzyme activities testing using API ZYM kits (BioMérieux) revealed common production of acid and alkaline phosphatase, esterase, esterase lipase and napthtol-AS-BI-phosphohydrolase. The caution when interacting with horses is important especially in the case of injury since their staphylococci showed many virulent characteristics however they were not multi-resistant.