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Proposal of Epidemiological Cutoff Values for Apramycin 15 μg and Florfenicol 30 μg Disks Applicable to
Sofia Santos Costa1, Carolina Ferreira1, Rute Ribeiro1
1Global Health and Tropical Medicine (GHTM), Unit of Medical Microbiology, Instituto de Higiene e Medicina Tropical (IHMT), Universidade NOVA de Lisboa (UNL), Lisbon, Portugal.
Abstract:
Apramycin and florfenicol are two antimicrobial agents exclusively used in veterinary medicine. Resistance determinants to these antimicrobial agents have been described in several staphylococci, yet no inhibition zone-based epidemiological cutoff (ECOFF) values are available to detect populations harboring resistance mechanisms. In this study, we propose disk diffusion inhibition zone ECOFF values of Staphylococcus aureus for apramycin and florfenicol. The susceptibility to apramycin and florfenicol was evaluated by disk diffusion of five S. aureus collections, comprising 352 isolates of animal (n = 265) and human (n = 87) origin. The aggregated distributions of inhibition zone diameters were analyzed by the normalized resistance interpretation method to obtain normalized wild-type (WT) population distributions and corresponding ECOFF values. The putative WT populations of S. aureus were characterized by an inhibition zone ≥15 mm (ECOFF = 15 mm) for apramycin and ≥21 mm for florfenicol (ECOFF = 21 mm). Five nonwild-type (NWT) isolates were detected for apramycin, all without inhibition zone and harboring the apmA gene, whereas five NWT isolates were identified for florfenicol, all carrying the fexA gene. The proposed ECOFF values for apramycin and florfenicol may be a valuable tool in future antimicrobial resistance monitoring and surveillance studies to identify S. aureus NWT populations toward these antimicrobial agents.
Insights
This study establishes new epidemiological cutoff (ECOFF) values for apramycin and florfenicol in Staphylococcus aureus. These values will aid in detecting antimicrobial resistance in veterinary medicine.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Molecular Epidemiology
Background:
- Apramycin and florfenicol are veterinary antimicrobials.
- Resistance mechanisms exist in staphylococci, but established disk diffusion ECOFF values are lacking.
- Accurate detection of antimicrobial resistance is crucial for effective treatment and surveillance.
Purpose of the Study:
- To propose disk diffusion inhibition zone epidemiological cutoff (ECOFF) values for apramycin and florfenicol in Staphylococcus aureus.
- To establish a standardized method for detecting resistance to these agents in veterinary isolates.
- To facilitate future antimicrobial resistance monitoring and surveillance studies.
Main Methods:
- Disk diffusion susceptibility testing was performed on 352 Staphylococcus aureus isolates (265 animal, 87 human).
- Normalized resistance interpretation method was used to analyze inhibition zone diameters.
- Wild-type (WT) population distributions and ECOFF values were determined.
Main Results:
- Proposed ECOFF values: apramycin ≥15 mm, florfenicol ≥21 mm.
- Five non-wild-type (NWT) apramycin-resistant isolates harbored the 'apmA' gene.
- Five NWT florfenicol-resistant isolates carried the 'fexA' gene.
Conclusions:
- The proposed ECOFF values provide a tool for identifying Staphylococcus aureus populations with resistance mechanisms to apramycin and florfenicol.
- These ECOFF values are valuable for future antimicrobial resistance surveillance in veterinary settings.
- This research contributes to the ongoing efforts to combat antimicrobial resistance in animal health.
