Related Experiment Video
Updated: Nov 8, 2025
Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
Genomic and in vitro pharmacodynamic analysis of rifampicin resistance in multidrug-resistant canine Staphylococcus
Karly Hicks1, Yongjun Tan2, Wenqi Cao3
1Department of Clinical Sciences, Auburn University, Auburn, AL, 36849, USA.
Background:
Antimicrobial resistance is a growing concern in canine Staphylococcus pseudintermedius dermatitis. Treatment with rifampicin (RFP) is considered only in meticillin-resistant and multidrug-resistant S. pseudintermedius (MDR-MRSP).
Hypothesis/Objectives:
To determine an optimal RFP dosing for MDR-MRSP treatment without induction of RFP resistance and identify causal mutations for antimicrobial resistance.
Methods And Materials:
Time-kill assays were performed in a control isolate and three MDR-MRSP isolates at six clinically relevant concentrations [32 to 1,024 × MIC (the minimum inhibitory concentration)]. Whole-genome resequencing and bioinformatic analysis were performed in the resistant strains developed in this assay.
Results:
The genomic analysis identified nine antimicrobial resistance genes (ARGs) in MDR-MRSP isolates, which are responsible for resistance to seven classes of antibiotics. RFP activity against all four isolates was consistent with a time-dependent and bacteriostatic response. RFP resistance was observed in six of the 28 time-kill assays, including concentrations 64 × MIC in MDR-MRSP1 isolates at 24 h, 32 × MIC in MDR-MRSP2 at 48 h, 32 × MIC in MDR-MRSP3 at 48 h and 256 × MIC in MDR-MRSP3 at 24 h. Genome-wide mutation analyses in these RFP-resistant strains discovered the causal mutations in the coding region of the rpoB gene.
Conclusions And Clinical Relevance:
A study has shown that 6 mg/kg per os results in plasma concentrations of 600-1,000 × MIC of S. pseudintermedius. Based on our data, this dose should achieve the minimum MIC (×512) to prevent RFP resistance development; therefore, we recommend a minimum daily dose of 6 mg/kg for MDR-MRSP pyoderma treatment when limited antibiotic options are available.
