Genetic resistance determinants to fusidic acid and chlorhexidine in variably susceptible staphylococci from dogs

Abstract

Background Concern exists that frequent use of topically-applied fusidic acid (FA) and chlorhexidine (CHX) for canine pyoderma is driving clinically relevant resistance, despite rare description of FA and CHX genetic resistance determinants in canine-derived staphylococci. This study aimed to determine minimum inhibitory concentrations (MICs) and investigate presence of putative resistance determinants for FA and CHX in canine-derived methicillin-resistant (MR) and -susceptible (MS) staphylococci. Plasmid-mediated resistance genes ( fusB, fusC, fusD, qacA/B, smr; PCR) and MICs (agar dilution) of FA and CHX were investigated in 578 staphylococci (50 MR S. aureus [SA], 50 MSSA, 259 MR S. pseudintermedius [SP], 219 MSSP) from Finland, U.S.A., North (NUK) and South-East U.K. (SEUK) and Germany. In all isolates with FA MIC ≥64 mg/L ( n = 27) fusA and fusE were amplified and sequenced. Results FA resistance determinants ( fusA mutations n = 24, fusB n = 2, fusC n = 36) were found in isolates from all countries bar U.S.A. and correlated with higher MICs (≥1 mg/L), although 4 SP isolates had MICs of 0.06 mg/L despite carrying fusC . CHX MICs did not correlate with qacA/B (n = 2) and smr ( n = 5), which were found in SEUK SA, and SP from NUK and U.S.A. Conclusions Increased FA MICs were frequently associated with fusA mutations and fusC, and this is the first account of fusB in SP. Despite novel description of qacA/B in SP, gene presence did not correlate with CHX MIC. Selection pressure from clinical use might increase prevalence of these genetic determinants, but clinical significance remains uncertain in relation to high skin concentrations achieved by topical therapy.

Geographical Variations in Virulence Factors and Antimicrobial Resistance Amongst Staphylococci Isolated From Dogs From the United Kingdom and Romania

“…However, more recently, two equine MRSA isolates from Australia were found to harbor qacA/B genes and the study also showed that some MRSA lineages (i.e., ST71) are more likely to carry qac genes ( 47 ). Although in our study carriage of qacA/B was significantly higher in the CoNS-UK isolates compared to the CoNS-RO isolates, Frosini et al ( 45 ) has shown that carriage of the qacA/B gene tends not to correlate with a high chlorhexidine MIC, which brings into question the clinical significance of qacA/B carriage. Nevertheless, the emergence of biocide resistant S. pseudintermedius strains, particularly if concurrently methicillin resistant, would severely limit therapeutic options and potentiate clinical outbreaks as already demonstrated for mupirocin resistance ( 48 ) and chlorhexidine resistance ( 49 ) amongst S. aureus in humans.…”

“…The prevalence of expB and expA genes reported in the current study was lower than the expB prevalence of 23.2% reported in clinical S. pseudintermedius isolates from dogs with superficial pyoderma (27) and the expA gene prevalence of 31% reported in canine S. pseudintermedius isolates from Spain (5). The expA (formerly known as exi) and expB genes encode exfoliating toxins (43) that were shown to be associated with subcorneal clefts, erythema, vesicles, and erosions when purified and injected into canine skin (27,44).…”

“…Other mechanisms of resistance, such as chromosomal mutations ( fusA ) have been shown to be also involved ( 9 ). More recently, Frosini et al ( 45 ) have shown that increased minimum inhibitory concentrations (MICs) to fusidic acid are frequently associated with carriage of fus C as well as fus A chromosomal mutations. However, fusidic acid is only authorized for topical use in the treatment of canine pyoderma in the UK ( 46 ) and may therefore achieve high concentrations at the site of infection overcoming resistance.…”

Genes on the Move: In Vitro Transduction of Antimicrobial Resistance Genes between Human and Canine Staphylococcal Pathogens

“…MRSA isolates (CC8 and CC22) represented two clonal complexes found worldwide [ 29 ]. Species and respective resistances were confirmed by PCR following previously described methods [ 30 , 31 ] for species-specific thermonuclease ( nuc ), methicillin-resistance ( mecA ), and presence or absence of tet(M), tet(K), fusB, and fusC .…”

“…Donor isolates for FA experiments included two fusB -positive and three fusC -positive MRSP, with resistance genes most likely on transposon-like elements in plasmids ( fusB ) or integrated into the chromosomal DNA in a SCC mec -like cassette ( fusC ). Selection of FA-resistant donors was limited by the infrequent description of these genes in this species [ 30 ]; FA-resistant S. aureus donors were not available for inclusion at the time. Recipient bacteria representing different origins and STs were chosen; all were screened on brain heart infusion agar (BHIA; Oxoid) containing either 30 mg/L tetracycline or 16 mg/L FA to confirm phenotypic susceptibility.…”