Affiliation:
1. Biological Defense Research Directorate, Naval Medical Research Center, Silver Spring, Maryland 20910-7500
Abstract
ABSTRACT
This paper presents Etest determinations of MICs of selected antimicrobial agents for 76 isolates of
Bacillus anthracis
chosen for their diverse histories and 67, 12, and 4 cultures, respectively, of its close relatives
B. cereus
,
B. thuringiensis
, and
B. mycoides
derived from a range of clinical and environmental sources. NCCLS breakpoints are now available for
B. anthracis
and ciprofloxacin, penicillin, and tetracycline; based on these breakpoints, the
B. anthracis
isolates were all fully susceptible to ciprofloxacin and tetracycline, and all except four cultures, three of which had a known history of penicillin resistance and were thought to originate from the same original parent, were susceptible to penicillin. Based on NCCLS interpretive standards for gram-positive and/or aerobic bacteria, all cultures were susceptible to amoxicillin-clavulanic acid and gentamicin and 99% (one with intermediate sensitivity) of cultures were susceptible to vancomycin. No group trends were apparent among the different categories of
B. cereus
(isolates from food poisoning incidents and nongastrointestinal infections and food and environmental specimens not associated with illness). Differences between
B. anthracis
and the other species were as expected for amoxicillin and penicillin, with all
B. anthracis
cultures, apart from the four referred to above, being susceptible versus high proportions of resistant isolates for the other three species. Four of the
B. cereus
and one of the
B. thuringiensis
cultures were resistant to tetracycline and a further six
B. cereus
and one
B. thuringiensis
cultures fell into the intermediate category. There was a slightly higher resistance to azithromycin among the
B. anthracis
strains than for the other species. The proportion of
B. anthracis
strains fully susceptible to erythromycin was also substantially lower than for the other species, although just a single
B. cereus
strain was fully resistant. The Etest compared favorably with agar dilution in a subsidiary test set up to test the readings, and it compared with other published studies utilizing a variety of test methods.
Publisher
American Society for Microbiology
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