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Published on: March 2, 2020
Investigation of In Vitro Susceptibility and Resistance Mechanisms in Skin Pathogens: Perspectives for
Stefano Azzariti1, Ross Bond2, Anette Loeffler2
1Department of Comparative Biomedical Sciences, Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield AL9 7TA, UK.
Abstract:
Fluoroquinolones (FQ) are commonly used in dogs with bacterial skin infections. Their use as first choice, along with the increased incidence of FQ-resistance, represents a risk to animal and public health. Our study determined minimum inhibitory (MIC) and bactericidal (MBC) concentrations of five FQs in Staphylococcus aureus, Staphylococcus pseudintermedius, and Escherichia coli, together with FQ-resistance mechanisms. MICs, efflux pump (EP) overexpression and MBCs were measured in 249 skin infection isolates following CLSI guidelines (CLSI VET01-A4, CLSI M26-A). Chromosomal and plasmid-mediated resistance genes were investigated after DNA extraction and sequencing. FQ-resistance was detected in 10% of methicillin-susceptible (MS), 90% of methicillin-resistant (MR) staphylococci and in 36% of E. coli. Bactericidal effect was observed except in 50% of MRSA/P for ciprofloxacin and in 20% of MRSPs for enrofloxacin. Highest MICs were associated with double mutation in gyrA (Ser83Leu + Asp87Asn), efflux pumps and three PMQR genes in E. coli, and grlA (Ser80Phe + Glu84Lys) in S. aureus. EP overexpression was high among E. coli (96%), low in S. aureus (1%) and absent in S. pseudintermedius. Pradofloxacin and moxifloxacin showed low MICs with bactericidal effect. Since in vitro FQ resistance was associated with MR, FQ use should be prudently guided by susceptibility testing.
Insights
Fluoroquinolone resistance is high in canine skin infections, especially in methicillin-resistant staphylococci. Prudent use guided by susceptibility testing is crucial to mitigate risks to animal and public health.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Molecular Biology
Background:
- Fluoroquinolones (FQ) are vital for treating canine bacterial skin infections.
- Increasing FQ resistance poses a significant threat to animal and public health.
- Understanding resistance mechanisms is essential for effective treatment strategies.
Purpose of the Study:
- To determine the minimum inhibitory (MIC) and bactericidal (MBC) concentrations of five FQs against key canine skin pathogens.
- To investigate the prevalence and mechanisms of FQ resistance in clinical isolates.
- To evaluate the efficacy of specific FQs and guide their prudent use.
Main Methods:
- Minimum inhibitory and bactericidal concentrations (MIC/MBC) were determined for five FQs against 249 isolates of *Staphylococcus aureus*, *Staphylococcus pseudintermedius*, and *Escherichia coli*.
- Efflux pump (EP) overexpression and the presence of chromosomal and plasmid-mediated resistance genes were analyzed.
- Standardized methods (CLSI guidelines) were employed for all microbiological and molecular analyses.
Main Results:
- High FQ resistance rates were observed: 90% in methicillin-resistant staphylococci and 36% in *E. coli*.
- Specific mutations in *gyrA* and *grlA*, efflux pump overexpression, and plasmid-mediated quinolone resistance (PMQR) genes were associated with high MICs.
- Pradofloxacin and moxifloxacin demonstrated potent bactericidal activity with low MICs.
Conclusions:
- In vitro FQ resistance in canine skin infections is strongly linked to methicillin resistance in staphylococci.
- Judicious use of FQs, guided by susceptibility testing, is imperative to preserve their efficacy.
- Pradofloxacin and moxifloxacin represent promising therapeutic options due to their broad-spectrum activity and bactericidal effects.
