Abstract:
Objective To identify the clinical isolates of Brucella by biochemical identification and molecular bio-typing, and test in vitro susceptibility of Brucella melitensis (B. melitensis) isolates to common antibiotics by E-test drug susceptibility test.
Methods Biochemical identification, abortus melitensis ovis suis(AMOS), multiplex polymerase chain reaction (PCR) and multilocus sequence typing (MLST) were performed for 29 B. melitensis strains collected in the Inner Mongolia Autonomous Region form 2022 to 2023. Eight antibiotics, including azithromycin, doxycycline, rifampicin, ciprofloxacin, levofloxacin, streptomycin, gentamicin and ceftriaxone, were selected to test their minimum inhibitory concentration (MIC) to the strains using E-test strips. By comparing with the MIC reports of B. melitensis collected in different areas, the possible change in drug resistance of strains was determined.
Results AMOS multiple fluorescence quantitative PCR and biochemical identification detected 9 strains of B.melitensis biovar 1, 6 strains of B.melitensis biovar 2 and 14 strains of B.melitensis biovar 3. The MLST typing results showed 28 strains of MLST 8 and 1 strain of MLST 12. All the strains were sensitive to doxycycline, streptomycin, ciprofloxacin, levofloxacin and gentamicin, 20.68% of the strains were resistant to ceftriaxone, 6.89% strains were resistant to rifampicin, and 100.00% of the strains were resistant to azithromycin, and the MIC range increased significantly compared with other areas. This resistance might be related to geographic distribution or time factors.
Conclusion Rifampicin is the first choice for the treatment of brucellosis. The emergence of drug-resistant strains reminds us to strengthen the monitoring of rifampicin resistance. Streptomycin, ciprofloxacin, levofloxacin and gentamicin might be candidates for the treatment of rifampicin-resistant brucellosis patients.