Susceptibility of Bacillus anthracis, Bacillus cereus, Bacillus mycoides, Bacillus pseudomycoides and Bacillus thuringiensis to 24 antimicrobials using Sensititre automated microbroth dilution and Etest agar gradient diffusion methods.
OBJECTIVE
To examine susceptibilities of Bacillus anthracis and related species to 24 antimicrobials using and concurrently comparing two methods.


METHODS
Twenty-four antimicrobials were tested against 95 isolates of the Bacillus cereus group including 18 B. anthracis, 42 B. cereus, 5 Bacillus mycoides, 5 Bacillus mycoides/pseudomycoides, 6 Bacillus pseudomycoides and 19 Bacillus thuringiensis to determine their MICs, MIC ranges, MIC50s and MIC90s with Etest and Sensititre at 30 and 35 degrees C for 18, 24 and 48 h.


RESULTS
Both methods yielded near-identical results at both temperatures for all antimicrobials except trimethoprim/sulfamethoxazole. Resistance to trimethoprim/sulfamethoxazole in 97% (92/95) was not always evident until tests were incubated for 48 h at 30 degrees C. All B. anthracis isolates were susceptible to 22 antimicrobials and resistant to trimethoprim/sulfamethoxazole while three isolates were erythromycin-intermediate. Whereas the B. thuringiensis were resistant to the beta-lactams, two B. cereus, one B. mycoides, five B. pseudomycoides and two B. mycoides/pseudomycoides were susceptible. Three B. cereus were solely clindamycin-resistant. Of the seven erythromycin-intermediate or -resistant B. cereus, three were resistant to clindamycin and one was resistant to clarithromycin and clindamycin. One B. mycoides was intermediately resistant to quinupristin/dalfopristin and meropenem and one was clindamycin-resistant. All B. pseudomycoides were clindamycin-resistant with one quinupristin/dalfopristin-resistant. Two B. mycoides/pseudomycoides were intermediately resistant to quinupristin/dalfopristin and clindamycin and a third was intermediately resistant to clindamycin alone. All isolates were susceptible to chloramphenicol, ciprofloxacin, gatifloxacin, gentamicin, levofloxacin, linezolid, moxifloxacin, rifampicin, streptomycin, tetracycline, tigecycline and vancomycin.


CONCLUSIONS
This paper expands the list of therapeutic or prophylactic antimicrobials potentially effective against B. cereus group isolates using two testing methods that produced comparable results.
Luna
Vicki A
VA
Center for Biological Defense, College of Public Health, University of South Florida, 3602 Spectrum Boulevard, Tampa, FL 33612, USA. vluna@health.usf.edu
King
Debra S
DS
Gulledge
Jenny
J
Cannons
Andrew C
AC
Amuso
Philip T
PT
Cattani
Jacqueline
J
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001407:Bacillus / Q000187:drug effects*; D003470:Culture Media; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D013696:Temperature; D013997:Time Factors
D000900:Anti-Bacterial Agents; D003470:Culture Media