Characterization and antibiotic resistance of S. aureus isolated from rabbits (Oryctolagus cuniculus)

Introduction The epidemiology of Staphylococcus aureus (SA) infections has gained interest in the last years for their importance in veterinary medicine, the emergence of some clonal animal lineages, and their increasingly evidenced zoonotic potential. The discovery of emergent mecC MRSA in farmed rabbits together with the sporadic reports of MRSA in companion rabbits, including livestock-associated clonal complex 398 MRSA and the Panton-Valentine Leucocidin-positive isolates have raised concern about the SA population in rabbits. Phenotypic and genotypic investigations were carried out on SA strains isolated from skin and lesion swabs of different rabbit categories and farm workers in order to evaluate the prevalence, the zoonotic infection risk, the predominant clonal lineages and the antibiotic resistance profiles. Materials and Methods In June 2015, 2200 swabs were collected from 400 rabbits belonging to different categories (young rabbits, adults, reproducers), randomly selected from a large farm in the Lazio region. Ear, nasal, axillary, inguinal, perineum areas, and additional skin lesions were tested for the presence of SA. A random selected number of strains (n=98) isolated from nasal swabs and skin lesions were characterized in order to assess the presence of nuc and mecA, bbp, selm, flank genes, to assign the spa-type and evaluate the antibiotic resistance by Kirby-Bauer and E-test methods (EUCAST 2017). The statistical analysis was performed by Software STATA version 13.0. Results SA was detected with a frequency of 592 isolates (17%, n=3376). All areas were infected, recording a significant difference between skin areas and lesions (P<0.05), while relevant numbers were detected both in the ear (38%) and the nasal cavity (41%, P=0.925). A significant difference was recorded in relation to the age ranges (P<0.05), except for youngs (5%) and reproducers (4%; P=0.785). All strains resulted MSSA but showed some multi-resistance profiles, ranging from 3 to 7 antibiotic classes: in particular tetracyclines (96%), macrolides (94%), diterpenes (84%), fluoroquinolones (64%), aminoglycosides B-C grades (48%, 5%), and glycopepetides (teicoplanin: 73%; hVISA: 4%; VISA: 5%). All the strains were negative for the presence of virulence genesand therefore were classified as low virulence strains. Five different spa-types were identified, belonging to two different clonal complexes (CC97, CC15). The most frequently recovered spa-type has been t2802 (55%), also detected in human samples. Conclusions In this study a high frequency of multiresistant SA strains was observed in rabbits, although none could be classified as MRSA. Clonal lineages were not correlated to the sampling site, while an association was recorded with the antibiotic-resistance profiles.