Penicillin Resistant Bacillus anthracis Strains Isolated from Farmers

Abstract

Considering the severity of anthrax infection, an alternative therapy for the classical penicillins should be provided when taking into account the recently isolated B. anthracis strains resistant to penicillins. There were evaluated the aspects of antibiotic susceptibility of B. anthracis strains in two patients (farmers) by Kirby-Bauer method, using Oxoid disks: penicillin G, ampicillin, oxacillin, piperacillin, imipenem, ceftazidime, ceftriaxone, cefuroxime, chloramphenicol, trimethoprim/sulphamethoxazole, erythromycin, clarithromycin, tetracycline, doxycycline, rifampicin, gentamycin, ofloxacin, norfloxacin, ciprofloxacin, metronidazole. Subsequently, there were determined the minimum inhibitory concentrations (MICs) of the respective strains, which were resistant to penicillin G, by “in agar” antibiotic dilution method (using serial dilutions, from 16μg/ml to 0,0075μg/ml, prepared in saline isotonic solution and incorporated in Mueller-Hinton agar). The antibiosusceptibility aspects were read after 18-20 hrs incubation at 35-37°C. The penicillin-resistant strains exhibited similar patterns of antibioresistance: to penicillin G, ampicillin, piperacillin and imipenem. Both of B. anthracis strains proved to be resistant to the IIIrd generation cephalosporins, as well as to trimethoprim / sulphamethoxazole. The strains were sensitive to chloramphenicol, gentamycin, tetracyclines and fluoroquinolones. The MIC levels of penicillin G proved to be for one of the penicillin resistant strains 0.5 μg/ml, and for the second strain (isolated from a fatal case) 4 μg/ml, whereas for the standard strain B. anthracis this MIC level was only <0.015 μg/ml. Although the most B. anthracis strains remain still sensitive to penicillin, however, fluoroquinolones remain the antibiotics of choice in the treatment of anthrax infection, if administered a correct therapy.