JAC Advance Access originally published online on June 22, 2007
Journal of Antimicrobial Chemotherapy 2007 60(3):555-567; doi:10.1093/jac/dkm213
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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
1 Center for Biological Defense, College of Public Health, University of South Florida, 3602 Spectrum Boulevard, Tampa, FL 33612, USA 2 Florida Department of Health, Bureau of Laboratories, 3602 Spectrum Boulevard, Tampa, FL 33612, USA
* Corresponding author. Tel: +1-813-974-3873; Fax: +1-813-974-1479; E-mail: vluna{at}health.usf.edu
Received 2 March 2007; returned 26 April 2007; revised 17 May 2007; accepted 18 May 2007
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Objectives: 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°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°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 ß-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.
Keywords: method comparison , minimum inhibition concentration , trimethoprim , ß-lactams
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In the United States, human cases of anthrax are rare with the most recent cases occurring in 2001 and 2006.1–3 European cases involved travellers who had contact with mammal carcasses.4–6 Bacillus cereus causes gastrointestinal distress, necrotic enteritis, liver failure, bacteraemia, endocarditis, meningitis, pneumonia and skin lesions.7–15 Long considered non-pathogenic and used extensively for insect pest control, Bacillus thuringiensis has been implicated in burn wound infections and food-poisoning.16,17 Of the other B. cereus group members, Bacillus mycoides, Bacillus pseudomycoides and Bacillus weihenstephanensis, only B. mycoides has been implicated in human infection (endophthalmitis).18
Although Bacillus anthracis has been reported as susceptible to a limited number of antimicrobials, resistance to penicillin, erythromycin and quinolones has been noted.19–25 Therefore, it is conceivable that an isolate could be engineered to be resistant to one or more antimicrobials.26–28 Because susceptibility testing of B. anthracis in the sentinel and reference laboratories is not recommended by the Centers for Disease Control and Prevention (CDC) who prefers to perform the testing at the national laboratory, the attending physician will treat a patient with a suspected B. anthracis infection empirically until a report is received from the CDC.29 In contrast, B. cereus, typically resistant only to ß-lactams, can be tested in the clinical laboratory.30,31 Reports of resistance in B. cereus to erythromycin and tetracyclines in the United States and Europe predict the development of further resistance.32–34 B. thuringiensis and B. mycoides can be difficult to distinguish from B. cereus before susceptibility tests are performed. B. pseudomycoides cannot be distinguished from B. mycoides without fatty acid methyl-ester analysis and its antibiogram is unknown.35 Thus, all four species were included in the study.
Mohammed et al.36 at the CDC reported that the Etest® by AB BIODISK (North America Inc., Piscataway, NJ, USA) could be used with B. anthracis and this implies that the method can be used for testing B. cereus. Turnbull et al.25 also compared the Etest® to agar dilution tests for nine antimicrobials and extended this testing to include B. cereus, B. thuringiensis and B. mycoides. The dual purpose of this research was to (i) expand our knowledge of susceptibility patterns of B. anthracis and related Bacillus against a larger number of antimicrobials using the Etest® and (ii) to compare the Etest® method with the Sensititre® automated microbroth dilution method with selected antimicrobials.
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Bacteria and growth conditions
We examined 95 Bacillus isolates: 18 B. anthracis, 42 B. cereus, 5 B. mycoides, 5 B. mycoides/pseudomycoides, 6 B. pseudomycoides and 19 B. thuringiensis. The B. anthracis isolates were received from the Florida Department of Health, Bureau of Laboratories, Tampa, FL, USA (FDOH), the NIH Biodefense and Emerging Infections Research Resources Repository (BEI Resources, Bethesda, MD, USA) or isolated from diverse environment and soil samples. The other Bacillus isolates in the study were received from FDOH, American Type Culture Collection (ATCC, Manassas, VA, USA) or Agriculture Research Service Culture Collection (ARSCC, Peoria, IL, USA), purchased as commercial pesticide products or isolated from various non-replicate environmental, marine and soil samples (one isolate per sample). Only one B. anthracis isolate was known to be from a human culture. Six of the B. thuringiensis isolates were potentially related.37
While all manipulations of B. anthracis isolates were performed in a class 2 biological safety cabinet, B. anthracis Pasteur isolates were stored and handled in a biosafety level 2 laboratory using biosafety level 3 (BSL3) practices and all other B. anthracis isolates were handled in a BSL3 laboratory. This arrangement followed the Institutional Bio-safety Committee requirements at USF. All safety protocols and requirements required by US federal regulation DHHS 42 CFR 73 were strictly met. Prior to susceptibility tests, the bacteria were grown on tryptic soy agar supplemented with 5% sheep red blood cells [blood agar (BA)] (Remel, Lenexa, KS, USA). All plates were incubated at 30 or 35°C (±2) overnight (
18 h) in ambient air before testing.
All Etest® susceptibility tests were set up on Mueller–Hinton agar plates (Remel) and read following the manufacturer's directions. Plates were incubated at 30 or 35°C for 18, 24 and 48 h. Interpretation of the MIC values followed CLSI standards.38–40 Staphylococcus aureus ATCC 29213 was included as a control.
The Sensititre® by TREK Diagnostic Systems (Cleveland, OH, USA) is an automatic system that uses a 96-well plate format with a panel of several antimicrobials that are precision dosed at appropriate dilutions and equates to the classical microbroth dilution method. The instrument detects growth as a fluorescent substrate is utilized by bacterial surface enzymes. The amount of detected fluorescence is proportional to bacterial growth. A data system interprets the MIC values following CLSI recommendations although manual interpretations can be performed with novel antimicrobials. Fail-safe features built into the database preclude interpreting tests read at inappropriate times, correctly interpret manually read tests and automatically flag unusual results. Susceptibility tests were performed following the manufacturer's instructions at both 30 and 35°C and read at 18, 24 and 48 h. S. aureus ATCC 29213 was included as a test control.
Of 24 antimicrobials examined, 16 were tested by both Etest® and Sensititre®: ampicillin, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gatifloxacin, gentamicin, levofloxacin, moxifloxacin, oxacillin, penicillin, quinupristin/dalfopristin, rifampicin, trimethoprim/sulfamethoxazole, tetracycline and vancomycin. Streptomycin and clarithromycin were only tested by the microbroth dilution method because Etest® strips were not available. The remaining six antimicrobials were not available on the Sensititre® format and so were performed by Etest® only: amoxicillin, ceftriaxone, daptomycin, linezolid, meropenem and tigecycline.
In addition, isolates were grown on tryptic soy agar (Fisher Scientific, Suwanee, GA, USA) supplemented with 0.06 mg/L erythromycin (Sigma-Aldrich, St Louis, MO, USA) and retested against clindamycin. Tests for the ß-lactams oxacillin and meropenem were repeated and read at 18, 24 and 48 h.
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The susceptibility tests with Etest® and the Sensititre® microbroth dilution methods, using either 30 or 35°C incubation temperatures, gave identical or near identical MICs (less than a 2-fold dilution difference) for all of the antimicrobials (except for trimethoprim/sulfamethoxazole) at 18, 24 and 48 h readings. This resulted in identical or near identical MIC50s and MIC90s for each antimicrobial. In general, with both methods, the endpoints for the 23 antimicrobials were easier to read at 24 h than 18 h, but we did not see any increase in MICs at the later time point. Even extending the time frame to 48 h did not produce higher MICs. The few times more growth was noted at 48 h with the Etest®, the new MIC values were less than or equal to a 2-fold difference with either temperature (data not shown) and were not considered a true increase in MIC. This agrees with other researchers.25
Because of the reports of trimethoprim/sulfamethoxazole resistance41,42 and the molecular confirmation of trimethoprim resistance in B. anthracis,43 the assumption was made that the other related Bacillus species were also resistant to the drug combination. Therefore, this antimicrobial was not originally planned to be tested. Yet because it is included in the pre-made microtitre plate by Sensititre®, the MICs were recorded. Initial testing at 35°C as recommended by CLSI did not show resistance to the trimethoprim/sulfamethoxazole combination in all of the B. anthracis isolates, the majority of B. cereus or B. thuringiensis. Retesting at 30°C, reading the tests at 24 and 48 h and also testing by Etest® proved that almost all of the isolates were indeed resistant to trimethoprim/sulfamethoxazole. The Sensititre® consistently gave resistant MICs for the B. anthracis at both time points after incubation at either 30 or 35°C while the Etest® produced resistant results for all B. anthracis isolates only at 30°C. For other Bacillus species, both methods yielded more numerous resistant MIC values at the lower temperature at 24 h, but the number of resistant isolates usually increased if the Etest® and 48 h incubation was employed.
When testing the other 23 antimicrobials, all (100%) of the B. anthracis isolates were susceptible to all of the tested therapeutics except erythromycin (Figure 1). Four B. anthracis were intermediately resistant to this antimicrobial: two reported only by Etest®, one reported only by Sensititre® and one by both methods (Table 1). This was due to the MIC values overlapping the susceptible breakpoint of 0.5 mg/L and was not considered a method discrepancy.
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The majority of the B. cereus and all of the B. thuringiensis isolates were resistant to amoxicillin, ampicillin, ceftriaxone, penicillin and oxacillin while susceptible to the remaining antimicrobials (Figure 1). Resistance in B. cereus was uncommon as six (14%) isolates were resistant to meropenem, seven (17%) were intermediate or resistant (inducible and constitutive) to clindamycin and only a single (2%) isolate was resistant to both clarithromycin and erythromycin (Tables 1 and 2). Only one isolate of the seven that were intermediately resistant to erythromycin by Etest® (1 mg/L) was called susceptible by Sensititre® (0.5 mg/L). A single B. thuringiensis had intermediate resistance to clindamycin. The six potentially related B. thuringiensis isolates did not demonstrate identical MIC values for all of the antimicrobials, but since antibiograms can differ within a related population of strains, this did not rule out their possible relatedness.
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One B. mycoides, five B. pseudomycoides and two B. mycoides/pseudomycoides isolates were susceptible to the ß-lactams, whereas the other isolates of these species were resistant (Table 1). The tests were repeated and tests held for an additional 24 h but the MICs remained the same. Sporadic intermediate resistance was seen against meropenem, quinupristin/dalfopristin and clindamycin. All of the B. pseudomycoides were intermediate or resistant to clindamycin, whereas the B. mycoides and B. mycoides/pseudomycoides were generally susceptible.
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When 16 antimicrobials were tested by both Sensititre® and Etest®, the two techniques produced for 15 of the antimicrobials identical or near identical (less than a 2-fold dilution) results at either 30 or 35°C when read after 24 h of incubation. Attempts at discerning growth at < 24 h of incubation rendered unreliable results no matter the method or the antimicrobial tested. This difficulty appeared to be due to the growth traits of the bacteria and not to the particular test method especially for B. mycoides and B. pseudomycoides isolates since they commonly produced their characteristic rhizoid-like branching. Although we were not able to fully compare the two methods with the other eight antimicrobials, we expect that both the Etest® and the microbroth dilution format by Sensititre® will be valid to use.
Like the Etest®, the Sensititre® protocols can be executed within a Bio-Safety Cabinet (BSC). The Sensititre® instrument has a modular design in which the inoculating unit is small enough to move into the BSC while the rest of the instrument can be placed permanently upon a workbench. A standard panel containing 19 antimicrobials is available although customized plates can be requested. The Sensititre® protocol is quick and easy to learn and perform (5–15 min per sample). The results are analysed and interpreted by the manufacturer's computer program. After review by personnel, all reports are automatically printed or sent to a main laboratory computer system. For the Etest®, normally only 5–6 Estrips® are placed onto a large media plate. Yet the choice of strips used can be customized on an as-needed basis and more antimicrobials can be added. More technical hands-on time is required with the Etest® in setting up tests, reading and interpreting the results. In addition, for branching Bacillus species, more expertise is needed to determine the growth line intersecting the MIC value on the Estrip®.
The results for penicillin, ciprofloxacin, gentamicin and vancomycin correlate with what other authors have described.33,40 The fact that only 17% of the B. anthracis demonstrated any resistance to erythromycin, which is much lower than that found previously in one study,25 may reflect the smaller number of B. anthracis examined in this work. The lack of resistance to tetracycline by any of the isolates was surprising since many came from environmental samples obtained from rural areas where farm animals may be routinely treated with tetracyclines.33,34
This paper demonstrates that most of the Bacillus isolates (no matter the species) were resistant to trimethoprim/sulfamethoxazole if the test was performed at 30°C and not at the CLSI recommended 35°C. Therefore, we suggest that this therapeutic combination not be tested nor reported for any isolates of the B. cereus group, especially if dealing with a B. cereus or B. thuringiensis causing a life-threatening infection or a suspected B. anthracis. It was interesting to note that all of the B. anthracis isolates were resistant to trimethoprim/sulfamethoxazole when tested in a broth at either 30 or 35°C, whereas most of the other Bacillus species did not reveal their resistance to the antimicrobial until after 48 h of incubation at 30°C. The lag in demonstrating resistance may be due to a low number of resistant individual organisms in a largely susceptible population that takes time to be observable in a well of broth or on an agar plate. Alternatively, there may be a more molecular-based reason for this difference. The actual mechanism for this false susceptibility is unknown, but one reason may be that the two enzyme targets of trimethoprim/sulfamethoxazole have different shapes at the higher temperature. This change in shape could allow the antimicrobials access to the enzymes and thus inhibit or slow their usual activity. The temperature/resistance differences could be useful in distinguishing B. anthracis from its relatives.
This is the first report of B. mycoides and B. pseudomycoides being susceptible to the ß-lactams. The significance of this becomes important when their phenotypic characteristics are reviewed. Although some of the isolates produced enough haemolysin to give a ß-haemolytic pattern, others did not. The latter were weakly haemolytic under the colony, mimicking a haemolysis pattern that has been seen in B. anthracis.30 These latter isolates were non-motile and did not readily display the characteristic spreading of these two species. Therefore, a sentinel laboratory would consider these cultures suspicious for B. anthracis and send them to a reference laboratory. If susceptibility tests were done before realizing that the organism was a potential B. anthracis, the penicillin susceptibility would give weight to the suspicion that they were indeed B. anthracis. In the meantime, the clinician would start prophylactic therapy. Our laboratory is currently exploring different characteristics of these isolates that might help to easily separate them from B. anthracis in the early stages of identification.
Under current guidelines in the United States, ciprofloxacin is the drug of choice for prophylaxis. For therapy, the CDC recommends a combination therapy of ciprofloxacin and at least one other efficacious antibiotic, while the CDC performs the MICs on a limited battery of antimicrobials: ciprofloxacin, clindamycin, erythromycin, penicillin, rifampicin, tetracycline and vancomycin.3,44 And although B. anthracis can produce penicillinase and cephalosporinase, penicillin historically has been useful for treatment, especially when combined with streptomycin.45 Because ciprofloxacin is the drug of choice for both prophylaxis and treatment, it is possible that in the event of a biothreat or accidental exposure to B. anthracis, the ciprofloxacin supply could be seriously depleted. To help ease the burden, the newer quinolones could be used in the place of ciprofloxacin with successful expectations since B. anthracis isolates were fully susceptible to all of the quinolones. The newer antimicrobials such as linezolid, daptomycin and tigecycline also offer newer choices for therapy against any of the Bacillus species (Table 2).
For the treatment of B. cereus, B. thuringiensis and other Bacillus infections, there is little advice found for treatment. B. cereus is usually susceptible to aminoglycosides, chloramphenicol, clindamycin, erythromycin, tetracycline and vancomycin.30 Yet various Bacillus species in this study demonstrated small populations with some form of resistance to clindamycin and erythromycin. Therefore the wider choice of newer antimicrobials can be useful in treating an infection.
In conclusion, this paper has broadened the number of antimicrobials potentially useful against B. anthracis, B. cereus, B. mycoides, B. pseudomycoides and B. thuringiensis. In vitro testing by Etest® and Sensititre® methods produced comparable results. Resistance in these species to trimethoprim/sulfamethoxazole was confirmed by using a lower testing temperature and longer incubation time during testing.
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This work was supported by the United States Department of Defense, DOD Contract Number W911SR-06-C-0020.
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None to declare.
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We thank Dr Peter Turnbull for reading the manuscript and suggesting improvements. We also thank Drs Loree Heller and Dale Griffin for obtaining soil samples from Oregon and Colorado, and Louisiana, respectively. The B. anthracis isolates from NIH were graciously contributed by the NIH Biodefense and Emerging Infections Research Resources Repository, NIAID, NIH. Isolates obtained by the Florida Department of Health were generously donated by Lea Larson and Frank Reeves. The non-anthracis isolates were identified and with the B. anthracis Pasteur are phenotypically characterized and maintained in the Center for Biological Defense Culture Collection by K. Kealy Peak and William Veguilla.
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1 Centers for Disease Control, Prevention. Health Alert Network. Health Update: Inhalation anthrax case investigation, Pennsylvania, New York City - Update, 2/24/06. CDC website: http://www2a.cdc.gov/HAN/ArchiveSys/ViewMsgV.asp?AlertNum=00242 (7 February 2007, date last accessed).
2 Centers for Disease Control and Prevention. Inhalation anthrax associated with dried animal hides—Pennsylvania and New York City, 2006. MMWR Morb Mortal Wkly Rep (2006) 55:280–2.[Medline]
3 Jernigan JA, Raghunathan PL, Bell BP, et al. Investigation of bioterrorism-related anthrax, United States, 2001: epidemiologic findings. Emerg Infect Dis (2002) 8:1019–28.[Web of Science][Medline]
4 Clegg S, Wildlife Anthrax Epizootic Workshop Working Group. Preparedness for anthrax epizootics in wildlife areas [conference summary]. Emerg Infect Dis [serial on the Internet] 2006 July. http://www.cdc.gov/ncidod/EID/vol12no07/06-0458.htm (7 February 2007, date last accessed).
5 Rabinowitz P, Gordon A, Chudnov D, et al. Animals as sentinels of bioterrorism agents. Emerg Infect Dis (2006) 12:647–52.[Web of Science][Medline]
6 Van den Enden E, Van Gompel A, Van Esbroeck M. Cutaneous anthrax Belgian traveler. Emerg Infect Dis (2006) 12:523–4.[Web of Science][Medline]
7 Colpin GG, Guiot HFL, Simonis RFA, et al. Bacillus cereus meningitis in a patient under gnotobiotic care. Lancet (1981) ii:694–5.
8
Craig CP, Lee WS, Ho M. Bacillus cereus endocarditis in an addict. Ann Intern Med (1974) 80:418–9.
9
Dierick K, Van Coillie E, Swiecicki I, et al. Fatal family outbreak of Bacillus cereus-associated food poisoning. J Clin Microbiol (2005) 43:4277–9.
10 Ghelardi E, Celandroni F, Salvetti S, et al. Identification and characterization of toxigenic Bacillus cereus isolates responsible for two food-poisoning outbreaks. FEMS Microbiol Lett (2002) 208:129–34.[CrossRef][Web of Science][Medline]
11 Ginsburg AS, Salazar LG, True LD, et al. Fatal Bacillus cereus sepsis following resolving neutropenic entercolitis during the treatment of acute leukemia. Am J Hematol (2003) 72:204–9.[CrossRef][Web of Science][Medline]
12 Lund T, De Buyser MI, Granum PE. A new cytotoxin from Bacillus cereus that may cause necrotic enteritis. Mol Microbiol (2005) 38:254–61.[CrossRef]
13
Mahler H, Pasi A, Kramer JM, et al. Fulminant liver failure in association with the emetic toxin of Bacillus cereus. N Engl J Med (1997) 336:1142–8.
14 Miller JM, Hair JG, Hebert M, et al. Fulminating bacteremia and pneumonia due to Bacillus cereus. J Clin Microbiol (1997) 35:534–7.
15 Centers for Disease Control and Prevention. Outbreak of cutaneous Bacillus cereus infections among cadets in a university military program—Georgia, August 2004. MMWR Morb Mortal Wkly Rep (2005) 54:1233–5.[Medline]
16 Damgaard PH, Granum PE, Bresciani J, et al. Characterization of Bacillus thuringiensis isolated from infections in burn wounds. FEMS Immunol Med Microbiol (1997) 18:47–53.[CrossRef][Web of Science][Medline]
17 Jackson SG, Goodbrand RB, Ahmed R, et al. Bacillus cereus and Bacillus thuringiensis isolated in a gastroenteritis outbreak investigation. Lett Appl Microbiol (1995) 21:103–5.[Web of Science][Medline]
18 Ansell SE, Lawton EB, McRae S, et al. Endophthalmitis due to Bacillus cereus: case report. N Z Med J (1980) 92:12–3.[Web of Science][Medline]
19
Bast DJ, Athamna A, Duncan CL, et al. Type II topoisomerase mutations in Bacillus anthracis associated with high-level fluoroquinolone resistance. J Antimicrob Chemother (2004) 54:90–4.
20 Brook I, Elliott TB, Pryor HI 2nd, et al. In vitro resistance of Bacillus anthracis Sterne to doxycycline, macrolides and quinolones. Int J Antimicrob Agents (2001) 18:559–62.[CrossRef][Web of Science][Medline]
21
Cavallo JD, Ramisse F, Girardet M, et al. Antibiotic susceptibilities of 96 isolates of Bacillus anthracis isolated in France between 1994 and 2000. Antimicrob Agents Chemother (2002) 46:2307–9.
22
Coker PR, Smith KL, Hugh-Jones ME. Antimicrobial susceptibilities of diverse Bacillus anthracis isolates. Antimicrob Agents Chemother (2002) 46:3843–5.
23
Drago L, De Vecchi E, Lombardi A, et al. Bactericidal activity of levofloxacin, gatifloxacin, penicillin, meropenem and rokitamycin against Bacillus anthracis clinical isolates. J Antimicrob Chemother (2002) 50:1059–63.
24 Lalitha MK, Thomas M. Penicillin resistance in Bacillus anthracis. Lancet (1997) 349:1522.[CrossRef][Web of Science][Medline]
25
Turnbull PCB, Sirianni NM, LeBron CI, et al. MICs of selected antibiotics for Bacillus anthracis, Bacillus cereus, Bacillus thuringiensis and Bacillus mycoides from a range of clinical environmental sources as determined by the Etest. J Clin Microbiol (2004) 42:3626–34.
26
Athamna A, Athamna M, Abu-Rashed N, et al. Selection of Bacillus anthracis isolates resistant to antibiotics. J Antimicrob Chemother (2004) 54:424–8.
27 Jones ME, Goguen J, Critchley IA, et al. Antibiotic susceptibility of isolates of Bacillus anthracis, a bacterial pathogen with the potential to be used in biowarfare. Clin Microbiol Infect (2003) 9:984–6.[CrossRef][Web of Science][Medline]
28
Stephenson J. Experts focus on infective agents of bioterrorism. JAMA (2002) 287:575–6.
29 Weyant RS, Ezzell JW, Popovic T, et al. Level B. Laboratory procedure for the identification of Bacillus anthracis. In: Laboratory Protocols for Bioterrorism Response Laboratories for the Identification of Bacillus anthracis—Lindsey KQ, Morse SA, eds. 27 June 2005 last revision date. Atlanta, GA: Centers for Disease Control and Prevention. 47–64. www.cdc.gov (8 February 2007, date last accessed).
30 Logan N, Turnbull PCB. Bacillus and other aerobic endospore-forming bacteria. In: Manual of Clinical Microbiology, Eighth Edition—Murray PR, Baron EJ, Jorgensen JH, et al, eds. (2003; 445–60) Washington, DC: American Society for Microbiology.
31
Weber DJ, Saviteer SM, Rutala WA, et al. In vitro susceptibility of Bacillus spp. to selected antimicrobial agents. Antimicrob Agents Chemother (1988) 32:642–5.
32
Citron DM, Appleman MD. In vitro activities of daptomycin, ciprofloxacin and other antimicrobial agents against the cells and spores of clinical isolates of Bacillus species. J Clin Microbiol (2006) 44:3814–8.
33 Jensen LB, Baloda S, Boye M, et al. Antimicrobial resistance among Pseudomonas spp. and the Bacillus cereus group isolated from Danish agricultural soil. Environ Int (2001) 26:581–7.[CrossRef][Web of Science][Medline]
34 Sengelov G, Agerso Y, Halling-Sorensen B, et al. Bacterial antibiotic resistance levels in Danish farmland as a result of treatment with pig manure slurry. Environ Int (2003) 28:587–95.[CrossRef][Web of Science][Medline]
35
Nakamura LK, Jackson MA. Clarification of the taxonomy of Bacillus mycoides. Int J Syst Evol Bacteriol (1995) 45:46–9.
36 Mohammed MJ, Marston CK, Popovic T, et al. Antimicrobial susceptibility testing of Bacillus anthracis: comparison of results obtained by using the National Committee for Clinical Laboratory Standards broth microdilution reference and Etest agar gradient diffusion methods. J Clin Microbiol (2002) 6:1902–7.
37 Skibicka KP, Tatavarthy A, Luna VA, et al. Identification and typing of Bacillus thuringiensis using real-time PCR, pulsed field gel electrophoresis and riboprinting. In: Abstracts of the One Hundred and Third General Meeting, Washington, DC, 2003. Washington, DC, USA. Abstract Y029, p. 669. American Society for Microbiology.
38 Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing: Sixteenth Informational Supplement M100-S16 (2006) Wayne, PA, USA: CLSI.
39 Clinical and Laboratory Standards Institute. Methods for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria: Proposed Guideline M45-P (2005) Wayne, PA, USA: CLSI.
40 Clinical and Laboratory Standards Institute. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically—Seventh Edition: Approved Standard M7-A7 (2006) Wayne, PA, USA: CLSI.
41 Bakici MZ, Elaldi N, Bakir M, et al. Antimicrobial susceptibility of Bacillus anthracis in an endemic area. Scand J Infect Dis (2002) 34:564–6.[CrossRef][Web of Science][Medline]
42 Odendaal MW, Pieterson PM, deVos V, et al. The antibiotic sensitivity patterns of Bacillus anthracis isolated from the Krueger National Park. Onderstepoort J Vet Res (1991) 58:17–9.[Web of Science][Medline]
43
Barrow EW, Bourne PC, Barrow WW. Functional cloning of Bacillus anthracis dihydrofolate-reductase and confirmation of natural resistance to trimethoprim. Antimicrob Agents Chemother (2004) 48:4643–9.
44 Centers for Disease Control and Prevention. Investigation of bioterrorism-related anthrax and interim guidelines for exposure management and antimicrobial therapy. MMWR Morb Mortal Wkly Rep (2001) 50:909–19.[Medline]
45 Lincoln RE, Klein F, Walker JS, et al. Successful treatment of rhesus monkeys for septicemic anthrax. Antimicrob Agents Chemother (2006) 4:759–63.
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 B. J. Wiskur, M. L. Robinson, A. J. Farrand, B. D. Novosad, and M. C. Callegan Toward Improving Therapeutic Regimens for Bacillus Endophthalmitis Invest. Ophthalmol. Vis. Sci., April 1, 2008; 49(4): 1480 - 1487. [Abstract] [Full Text] [PDF]
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