In vitro antibiotic susceptibility and resistance mechanism of 178 Bacillus anthracis strains isolated in China from 2003 to 2025

Objective To investigate the in vitro antibiotic susceptibility of Bacillus anthracis （B. anthracis）strains isolated in China from 2003 to 2025.

Methods  The drug susceptibility of 178 strains of B. anthracis to 13 antibiotics was tested by using E-test method; the resistance mechanisms to penicillin and ampicillin were investigated through comparative genomic analysis.

Results  The antibiotic susceptibility testing showed that all the tested strains were sensitive to amoxicillin, ciprofloxacin, clarithromycin, clindamycin, doxycycline, levofloxacin, rifampicin, and meropenem. The resistance to penicillin and ampicillin was observed in 1 strain, and 1 strain was resistant to chloramphenicol. The majority of the strains ( 97.19% ) exhibited intermediate sensitivity to ceftriaxone. Genomic analysis suggested that resistance to penicillin and ampicillin might be associated with a nucleotide deletion mutation at position 154 in rsiP gene, representing a novel drug resistance-associated variant.

Conclusion Most B. anthracis isolated in China in recent years remained sensitive to the recommended antibiotics for postexposure prophylaxis and treatment. This study provides updated data for the better understanding of antibiotic resistance of B. anthracis and reasonable selection of antibiotics for treatment and prevention.