Genetic Relatedness, Antimicrobial and Biocide Susceptibility Comparative Analysis of Methicillin-Resistant and -Susceptible Staphylococcus pseudintermedius from Portugal

Forty methicillin-resistant and -susceptible Staphylococcus pseudintermedius (MRSP and MSSP, respectively) from colonization and infection in dogs and cats were characterized for clonality, antimicrobial, and biocide susceptibility. MSSP were genetically more diverse than MRSP by multi-locus sequence typing and pulsed-field gel electrophoresis. Three different spa types (t06, t02, t05) and two SCCmec types (II-III and V) were detected in the MRSP isolates. All MRSP and two MSSP strains were multidrug-resistant. Several antibiotic resistance genes (mecA, blaZ, tet(M), tet(K), aac(6')-Ie-aph(2')-Ia, aph(3')-III, ant(6)-Ia, sat4, erm(B), lnu(A), dfr(G), and catpC221) were identified by microarray and double mutations in the gyrA and grlA genes and a single mutation in the rpoB gene were detected by sequence analysis. No differences were detected between MSSP and MRSP in the chlorhexidine acetate (CHA) minimum inhibitory concentrations (MICs). However, two MSSP had elevated MIC to triclosan (TCL) and one to benzalkonium chloride and ethidium bromide. One MSSP isolate harboured a qacA gene, while in another a qacB gene was detected. None of the isolates harboured the sh-fabI gene. Three of the biocide products studied had high bactericidal activity (Otodine(®), Clorexyderm Spot Gel(®), Dermocanis Piocure-M(®)), while Skingel(®) failed to achieve a five log reduction in the bacterial counting. S. pseudintermedius have become a serious therapeutic challenge in particular if methicillin- resistance and/or multidrug-resistance are involved. Biocides, like CHA and TCL, seem to be clinically effective and safe topical therapeutic options.

Significant Differences Characterise the Correlation Coefficients between Biocide and Antibiotic Susceptibility Profiles in Staphylococcus aureus.

There is a growing concern by regulatory authorities for the selection of antibiotic resistance caused by the use of biocidal products. We aimed to complete the detailed information on large surveys by investigating the relationship between biocide and antibiotic susceptibility profiles of a large number of Staphylococcus aureus isolates using four biocides and antibiotics commonly used in clinical practice. The minimal inhibitory concentration (MIC) for most clinically-relevant antibiotics was determined according to the standardized methodology for over 1600 clinical S. aureus isolates and compared to susceptibility profiles of benzalkonium chloride, chlorhexidine, triclosan, and sodium hypochlorite. The relationship between antibiotic and biocide susceptibility profiles was evaluated using non-linear correlations. The main outcome evidenced was an absence of any strong or moderate statistically significant correlation when susceptibilities of either triclosan or sodium hypochlorite were compared for any of the tested antibiotics. On the other hand, correlation coefficients for MICs of benzalkonium chloride and chlorhexidine were calculated above 0.4 for susceptibility to quinolones, beta-lactams, and also macrolides. Our data do not support any selective pressure for association between biocides and antibiotics resistance and furthermore do not allow for a defined risk evaluation for some of the compounds. Importantly, our data clearly indicate that there does not involve any risk of selection for antibiotic resistance for the compounds triclosan and sodium hypochlorite. These data hence infer that biocide selection for antibiotic resistance has had so far a less significant impact than feared.