Study population. We addressed attendees of the veterinary conference VETclasses 2017, held in Hradec Kralove, Czech Republic, 23. - 24. 9. 2017. The target groups were both small-animal and livestock practitioners. Among 436 participants, there were 334 practicing veterinarians, and 102 nurses, technicians and other personnel involved in industry or research. Most of them were from the Czech Republic, but a few representatives from Slovakia and Belgium were also represented. Total of 134 volunteers agreed to be screened, which is approximately 3% of the practicing veterinarians in Czech Republic. According to the Chamber of Veterinary Surgeons of the Czech Republic, there were 4205 private veterinarians registered, which forms the majority of practicing professionals in the Czech Republic (accessed 26 August 2019). In our country small animal veterinary practitioners make up 70%, the rest are involved in mixed animal practice, livestock specialized veterinarians have minimal representation. The Ethics Committee of the Faculty Hospital in Hradec Kralove gave permission to carry out the study on human volunteers.
Sample collection. Bilateral nasal swab specimens (~ 1 cm into each nostril) were collected with sterile cotton-tipped swabs, stored in transport medium (Copan Transystem®) and transported immediately for laboratory processing. The sample collection was voluntary and anonymous, and additional data were obtained: demographic data, data on exposure to animals or a hospital environment, place of work, job description, type of clinical practice (small animals, mostly dogs, cats or large animals, horses, pigs, ruminants), known exposure to an MRSA positive-animal, previous hospitalization within 30 days, residence with a healthcare worker. The questionnaire was developed for the purposes of this study (Additional file 1).
Bacterial strains. Nasal swabs were cultured for 18 hours on Sheep Blood Agar (OxoidTM Columbia Blood Agar Base, Thermo ScientificTM) and chromogenic agar MRSA SelectTM (Bio-Rad). S. aureus was identified morphologically, identification was confirmed by Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS, Bruker Microflex LTTM, Bruker Daltonics). MRSA was detected by cefoxitin resistance  and confirmed by detection of mecA and mecC genes by PCR .
Antibiotic susceptibility testing. Testing and evaluation of Minimal Inhibitory Concentrations (MIC) in MRSA strains was performed by broth microdilution method according to standard ISO 20776-1 . Susceptibility to erythromycin, clindamycin, linezolid, chloramphenicol, tetracycline, ciprofloxacin, trimethoprim/sulfamethoxazole, gentamicin and vancomycin was tested.
Spa typing and Based Upon Repeat Pattern (BURP) analysis. The typing was performed with primers spa-1113f (5´TAA AGA CGA TCC TTC GGT C -3´) and spa-1514r (5´-CAG CAG TAG TGC CGT TTG CTT -3´) . The software Ridom StaphTypeTM (ver. 2.2.1; Ridom GmbH) was used for sequence and BURP analysis. Resulting clonal clusters (spa-CCs) were composed of ≥ 2 related spa types and clustered only if their cost value was ≤ 4 and had at least 5 repeats . The algorithm counts with repeat duplication, deletion and point mutation when assessing if different spa types are related.
Multilocus Sequence Typing (MLST) was performed as described previously ; the allele types and the resulting STs were assigned using software BioNumerics (ver.7.0; Applied Maths).
SCCmec typing. The SCCmec types were identified using multiplex PCR based on identification of specific genes within J regions of particular cassettes (I to V) as described previously .
Statistical analysis. The statistical analyses (Confidence Interval, Fisher test) was performed using NCSS 11 Statistical Software (2016). NCSS, LLC. Kaysville, Utah, USA, ncss.com/software/ncss.