Susceptibility in vitro of canine methicillin-resistant and -susceptible staphylococcal isolates to fusidic acid, chlorhexidine and miconazole: opportunities for topical therapy of canine superficial pyoderma

Abstract

ObjectivesIncreasing multidrug resistance amongst canine pathogenic staphylococci has renewed interest in topical antibacterial therapy for skin infections in the context of responsible veterinary prescribing. We therefore determined the activity in vitro of three clinically relevant topical agents and synergism between two of them against Staphylococcus pseudintermedius and Staphylococcus aureus.MethodsThe MICs of fusidic acid (n = 199), chlorhexidine (n = 198), miconazole (n = 198) and a 1:1 combination of miconazole/chlorhexidine (n = 198) were determined for canine isolates [50 MRSA and 49 methicillin-resistant S. pseudintermedius (MRSP), 50 MSSA and 50 methicillin-susceptible S. pseudintermedius (MSSP)] collected from the UK and Germany using an agar dilution method (CLSI VET01-A4). Fractional inhibitory concentration (FIC) indices were calculated to assess the interaction of miconazole with chlorhexidine.ResultsMICs of each drug/combination were significantly (P < 0.0005) higher for S. aureus when compared with S. pseudintermedius. Most strains (n = 172) had an MIC of fusidic acid of ≤0.03 mg/L (MIC ≥64 mg/L, n = 5 MRSA). All strains had MICs of chlorhexidine of 0.5–4 mg/L, except for one MRSA (MIC = 8 mg/L). All but four strains had MICs of miconazole of 1–4 mg/L (MIC = 16 mg/L, n = 3; MIC = 256 mg/L, n = 1). Miconazole/chlorhexidine (1:1 ratio) had a synergistic effect against 49/50 MRSA, 31/50 MSSA, 12/49 MRSP and 23/49 MSSP.ConclusionsSince the majority of these staphylococci, including methicillin-resistant isolates, had MICs that should be readily exceeded by topical skin application of these agents, their therapeutic efficacy for canine superficial pyoderma should be assessed. The synergistic interaction shown in vitro supports further clinical evaluation of miconazole/chlorhexidine combination therapy for staphylococcal infection.

New insights on the antibacterial efficacy of miconazole in vitro

“…The results are well in line with previous results . As in veterinary medicine, emergence and dissemination of methicillin‐resistant staphylococci are of rising importance.…”

“…However, in this in vitro study fusidic acid was less effective than in the study by Clark et al. and only in a power of ten more effective than miconazole. In a further study Clark et al.…”

“…Clark et al. determined the MICs of fusidic acid (n=99), chlorhexidine (n=98), miconazole (n=198) and a 1:1 combination of miconazole/chlorhexidine (n=98) for canine isolates (50 MRSA, 50 MSSA and 49 MRSP and 50 MSSP) collected from the UK and Germany using an agar dilution method . All but four strains had MICs of miconazole of 1‐4 mg/L (MIC=6 mg/L, n=3; MIC=256 mg/L, n=1).…”

“…Interestingly azole antimycotics have been shown to also exert antibacterial effects and new formulations for skin diseases have been suggested . Especially the broad‐spectrum imidazole antifungal miconazole was found to be effective against skin infections caused by gram‐positive bacteria both in vitro and in vivo . The present investigation aimed to determine the efficacy of miconazole against bacteria currently isolated from superficial skin lesions and infections using a modified standardised agar dilution test in order to show whether miconazole could be a therapeutic alternative even in the management of difficult to treat bacteria, esp.…”

“…6 Especially the broad-spectrum imidazole antifungal miconazole was found to be effective against skin infections caused by gram-positive bacteria both in vitro and in vivo. [7][8][9][10][11][12][13][14][15][16][17] The present investigation aimed to determine the efficacy of miconazole against bacteria currently isolated from superficial skin lesions and infections using a modified standardised agar dilution test in order to show whether miconazole could be a therapeutic alternative even in the management of difficult to treat bacteria, esp. methicillin-and fusidic acidresistant Staphylococcus aureus isolates.…”