Antimicrobial Susceptibilities of Diverse Bacillus anthracis Isolates

Abstract

A test of 25 genetically diverse isolates of Bacillus anthracis was conducted to determine their susceptibility to seven clinically relevant antimicrobial agents. Etest strips (AB BIODISK, Solna, Sweden) were used to measure the MICs for the isolates. Using the National Committee for Clinical Laboratory Standards MIC breakpoints for staphylococci, three isolates were found to be resistant to penicillin and five were found to be resistant to cefuroxime. The penicillin-resistant isolates were negative for ␤-lactamase production. Continued surveillance of B. anthracis field isolates is recommended to monitor antimicrobial susceptibility.The etiologic agent of anthrax, Bacillus anthracis, causes an acute disease, primarily of herbivores, that is transmissible to humans. Susceptible animals are primarily infected by the spores formed during the vegetative state of the bacteria. Spores may be found in soil contaminated by diseased animals or in diseased animal products, such as hair, wool, hides, and bones. The importance of treatment of the disease in humans has been underscored by the bioterrorism events of October 2001 in the United States. Ciprofloxacin was the antimicrobial agent of choice for prophylactic treatment after exposure to the spores of B. anthracis that were used in the bioterrorism events. Penicillin, traditionally the drug of choice for treatment, is still recommended in other parts of the world despite reports of penicillin resistance (2, 3). The Centers for Disease Control recommended ciprofloxacin, penicillin, and doxycycline for the treatment of human anthrax and for use as a prophylactic measure prior to and during the October event (1). In the past, streptomycin, penicillin, gentamicin, and chloramphenicol have also been recommended (7).Other articles concerning B. anthracis and antimicrobial susceptibility have been written: two over 10 years ago and one within the past year. The first paper, published in 1990 by Lightfoot et al., determined the antimicrobial susceptibility of 70 isolates of B anthracis to penicillin, amoxicillin, cefuroxime, gentamicin, streptomycin, erythromycin, tretracycline, chloramphenicol, and ciprofloxacin by agar dilution (6). Penicillin resistance and ␤-lactamase production were noted in two isolates. This paper was quickly followed in 1991 by a paper by Doganay and Aydin (2). They tested 22 B. anthracis isolates against 27 antimicrobial agents by agar dilution and reported that 19 isolates showed resistance to the five broad-spectrum cephalosporins tested. The isolates were shown to be sensitive to the other antimicrobials tested. These two papers were very basic in their approach and reporting. The latest paper, by Mohammed et al., tested 65 isolates with nine antimicrobial agents by using the National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution method (7). The results obtained from 50 of the isolates were compared to those obtained with Etest strips. One isolate was penicillin resistant, and no statistically significant difference was ...

Microarray-Based Detection of 90 Antibiotic Resistance Genes of Gram-Positive Bacteria

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Daptomycin exerts rapid bactericidal activity against Bacillus anthracis without disrupting membrane integrity

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The antimicrobial susceptibility and virulence factors of Bacillus anthracis strains isolated in Croatia

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