Nocera, Francesca Paola (2018) Staphylococcus pseudintermedius-associated canine skin disorders: isolation, identification, antibiotic resistance patterns, sequence typing and alternative therapeutic strategies. [Tesi di dottorato]

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Sthaphylococcus pseudintermedius (S. pseudintermedius) is the main inhabitant of skin and mucosa of dogs, where it represents the major bacterial pathogen causing skin diseases. Firstly described in 2005, S. pseudintermedius is a member of the Staphylococcus intermedius Group (SIG), together with S. intermedius and S. delphini. The recent emergence and rapid dissemination of multidrug-resistant S. pseudintermedius strains, particulary methicillin-resistant S. pseudintermedius (MRSP), showing more and more often resistance to the antibiotic agents licensed for use in small animal practice, represent a relevant threat to small animal and public health. In the last decade, the antibiotic resistance issue has become increasingly relevant, highlighting the need to control and limit it by the means of a continuous surveillance of both methicillin-resistant and methicillin-susceptible S. pseudintermedius isolates as well as the development of new and alternative therapeutic options. This study aims to describe the phenotypic and genotypic features, the antibiotic resistance patterns, the prevalence of virulence genes of both MRSP and methicillin-susceptible S. pseudintermedius (MSSP) strains, isolated from dogs suffering from otitis externa and pyoderma. MRSP sequence type clones circulating in Southern Italy were also investigated. Moreover, the antimicrobial activity of hydroxypiridone-based iron chelating co-polymer DIBI and abietic acid was analyzed against S. pseudintermedius isolates, as alternative treatment options. From a total of 259 staphylococcal cultures, 126 S. pseudintermedius strains were selected during the years 2015-2017. S. pseudintermedius strains (49%) were identified by proteomic (MALDI-TOF MS) and molecular profiling (nuc and hlb genes). S. pseudintermedius strains were recovered from dogs suffering from otitis externa (84%) and pyoderma (16%), originating from Naples, Campania Region (52%) and Latina, Lazio Region (48%). Amongst the 126 S. pseudintermedius strains, 18% were MRSP, carrying mecA gene. The remaining 82% were classified as MSSP. None of the isolates was positive to mecC gene. Furthermore, all the MRSP showed a complete resistance to amoxicillin-clavulanate and ampicillin (100%), while the highest resistance rates to selected non-β-lactam antibiotics were registered for erythromycin (91%); tetracycline (87%); sulfamethoxazole/trimethoprim (78%); kanamycin (78%); streptomycin (78%); clindamycin (65%) and enrofloxacin (61%). However, there was no resistance to vancomycin and linezolid. It is worth noting that 91% MRSP strains were found to be multidrug-resistant strains. The 82% MSSP isolates, showed interesting antibiotic resistant profiles, but their resistance rates were of about 50% lower than MRSP strains. The phenotypic tetracycline- and erythromycin-resistant MRSP and MSSP strains harbored tetK and tetM genes, alone or in association, and ermB gene. Referring to MRSP isolates, they mainly belonged to multidrug-resistant sequence type ST71 (26%) European clone. In this study, 9 new clones of MRSP were identified and described in Italy and worldwide for the first time. The newly described sequence types (STs) were named from ST1053 up to ST1061. In addition, DIBI and abietic acid resulted to be effective against MRSP and MSSP strains, inhibiting their growth. Thus, they may be considered as valid non-antibiotic alternative treatment approaches for S. pseudintermedius infections.

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