Penicillin Resistant Bacillus anthracis Strains Isolated from Farmers

摘要

Considering the severity of anthrax infection, an alternative therapy for the classicalpenicillins should be provided when taking into account the recently isolated B. anthracisstrains resistant to penicillins.There were evaluated the aspects of antibiotic susceptibility of B. anthracis strains intwo 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 respectivestrains, which were resistant to penicillin G, by in agar antibiotic dilution method (usingserial dilutions, from 16?g/ml to 0,0075?g/ml, prepared in saline isotonic solution andincorporated in Mueller-Hinton agar). The antibiosusceptibility aspects were read after 18-20hrs incubation at 35-37C.The penicillin-resistant strains exhibited similar patterns of antibioresistance: topenicillin G, ampicillin, piperacillin and imipenem. Both of B. anthracis strains proved to beresistant to the IIIrd generation cephalosporins, as well as to trimethoprim /sulphamethoxazole. The strains were sensitive to chloramphenicol, gentamycin, tetracyclinesand fluoroquinolones. The MIC levels of penicillin G proved to be for one of the penicillinresistant strains 0.5 ?g/ml, and for the second strain (isolated from a fatal case) 4 ?g/ml,whereas for the standard strain B. anthracis this MIC level was only 0.015 ?g/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, ifadministered a correct therapy.