Molecular characterization of Bacillus strains involved in outbreaks of anthrax in France in 1997

A CRISPR/Cas12a-based DNAzyme visualization system for rapid, non-electrically dependent detection of Bacillus anthracis

As next-generation pathogen detection methods, CRISPR-Cas-based detection methods can perform single-nucleotide polymorphism (SNP) level detection with high sensitivity and good specificity. They do not require any particular equipment, which opens up new possibilities for the accurate detection and identification of Bacillus anthracis. In this study, we developed a complete detection system for B. anthracis based on Cas12a. We used two chromosomally located SNP targets and two plasmid targets to identify B. anthracis with high accuracy. The CR5 target is completely new. The entire detection process can be completed within 90 min without electrical power and with single-copy level sensitivity. We also developed an unaided-eye visualization system based on G4-DNAzyme for use with our CRISPR-Cas12a detection system. This visualization system has good prospects for deployment in field-based point-of-care detection. We used the antisense nucleic acid CatG4R as the detection probe, which showed stronger resistance to interference from components of the solution. CatG4R can also be designed as an RNA molecule for adaptation to Cas13a detection, thereby broadening the scope of the detection system.

Colony-Forming Unit Spreadplate Assay versus Liquid Culture Enrichment-Polymerase Chain Reaction Assay for the Detection of Bacillus Endospores in Soils

A liquid culture enrichment-polymerase chain reaction (E-PCR) assay was investigated as a potential tool to overcome inhibition by chemical component, debris, and background biological impurities in soil that were affecting detection assay performance for soil samples containing Bacillus atrophaeus subsp. globigii (a surrogate for B. anthracis). To evaluate this assay, 9 g of matched sets of three different soil types (loamy sand [sand], sandy loam [loam] and clay) was spiked with 0, ~4.5, 45, 225, 675 and 1350 endospores. One matched set was evaluated using a previously published endospore concentration and colony-forming unit spreadplate (CFU-S) assay and the other matched set was evaluated using an E-PCR assay to investigate differences in limits of detection between the two assays. Data illustrated that detection using the CFU-S assay at the 45-endospore spike level started to become sporadic whereas the E-PCR assay produced repeatable detection at the ~4.5-endospore spike concentration. The E-PCR produced an ~2-log increase in sensitivity and required slightly less time to complete than the CFU-S assay. This study also investigated differences in recovery among pure and blended sand and clay soils and found potential activation of B. anthracis in predominately clay-based soils.

Investigation of animal anthrax outbreaks in the human-animal interface at risky districts of Bangladesh during 2016-2017

Objective

The objective of the study was to explore the outbreak situation in terms of animal, place, and time towards minimizing the risk of animal infection at the source in future and subsequent spillover in human in the endemic rural settings.

Methodology

An outbreak investigation team from the Department of Livestock Services visited in each of the outbreak sites to explore the event towards strengthening the control program in the future. Meat samples of the infected slaughtered animals were collected to confirm the causal agent of the animal outbreak using polychrome methylene blue microscopic examination technique. Participatory epidemiology tool such as semi-structured interview had been used in these investigations to realize the knowledge and practices of local people/cattle keepers on anthrax control and prevention in animal and human as well.

Results

All identified affected human cases had been confirmed as a history of contact with the animal carcasses or handling/processing with infected meat. The level of awareness at the community level was not satisfactory for the prevention and control of anthrax at the source and further spillover in human. The infected slaughtered animals found to be in non-vaccinated status during the outbreak investigation and uncontrolled animal movement is considered to be responsible for new outbreaks in a vaccinated zone where enforcement of veterinary legislation is inadequate.

Conclusion

A comprehensive preparedness and response strategy is to be obligatory for prevention, control and respond on anthrax in Bangladesh. Maximum vaccination coverage in the animal, increase community awareness of animal and human anthrax are also demanded for transmission of anthrax from animal to human.

Investigation and control of anthrax outbreak at the human-animal interface, Bhutan, 2010

In 2010, we investigated anthrax outbreak in Bhutan. A total of 43 domestic animals died, and cutaneous anthrax developed in 9 persons, and 1 died. All affected persons had contact with the carcasses of infected animals. Comprehensive preparedness and response guidelines are needed to increase public awareness of anthrax in Bhutan.

Advances in Anthrax Detection: Overview of Bioprobes and Biosensors

Anthrax is an infectious disease caused by Bacillus anthracis. Although anthrax commonly affects domestic and wild animals, it causes a rare but lethal infection in humans. A variety of techniques have been introduced and evaluated to detect anthrax using cultures, polymerase chain reaction, and immunoassays to address the potential threat of anthrax being used as a bioweapon. The high-potential harm of anthrax in bioterrorism requires sensitive and specific detection systems that are rapid, field-ready, and real-time monitoring. Here, we provide a systematic overview of anthrax detection probes with their potential applications in various ultra-sensitive diagnostic systems.

Capsules, toxins and AtxA as virulence factors of emerging Bacillus cereus biovar anthracis

Emerging B. cereus strains that cause anthrax-like disease have been isolated in Cameroon (CA strain) and Côte d’Ivoire (CI strain). These strains are unusual, because their genomic characterisation shows that they belong to the B. cereus species, although they harbour two plasmids, pBCXO1 and pBCXO2, that are highly similar to the pXO1 and pXO2 plasmids of B. anthracis that encode the toxins and the polyglutamate capsule respectively. The virulence factors implicated in the pathogenicity of these B. cereus bv anthracis strains remain to be characterised. We tested their virulence by cutaneous and intranasal delivery in mice and guinea pigs; they were as virulent as wild-type B. anthracis. Unlike as described for pXO2-cured B. anthracis, the CA strain cured of the pBCXO2 plasmid was still highly virulent, showing the existence of other virulence factors. Indeed, these strains concomitantly expressed a hyaluronic acid (HA) capsule and the B. anthracis polyglutamate (PDGA) capsule. The HA capsule was encoded by the hasACB operon on pBCXO1, and its expression was regulated by the global transcription regulator AtxA, which controls anthrax toxins and PDGA capsule in B. anthracis. Thus, the HA and PDGA capsules and toxins were co-regulated by AtxA. We explored the respective effect of the virulence factors on colonisation and dissemination of CA within its host by constructing bioluminescent mutants. Expression of the HA capsule by itself led to local multiplication and, during intranasal infection, to local dissemination to the adjacent brain tissue. Co-expression of either toxins or PDGA capsule with HA capsule enabled systemic dissemination, thus providing a clear evolutionary advantage. Protection against infection by B. cereus bv anthracis required the same vaccination formulation as that used against B. anthracis. Thus, these strains, at the frontier between B. anthracis and B. cereus, provide insight into how the monomorphic B. anthracis may have emerged.

Anthrax is caused by the bacterium Bacillus anthracis that affects all mammals worldwide. It emerged more than 10,000 years ago from a Bacillus cereus precursor. In the past decade, B. cereus bacteria were isolated in the USA from anthrax-like pneumonia cases. They harbour one virulence plasmid very similar to the toxin–encoding plasmid of B. anthracis. Recently, an anthrax-like disease in great apes in Africa was caused by emerging B. cereus strains, named B. cereus biovar anthracis. These strains are atypical as they possess both plasmids coding for toxin and capsule similar to those so far found only in B. anthracis. These unusual pathogenic B. cereus are currently neglected. We explored the virulence of these pathogens and their colonisation and dissemination capacity within the murine host. We found that these toxinogenic strains harbour two capsules, the classical B. anthracis capsule and an additional polysaccharidic capsule. This latter capsule confers virulence alone or in combination with toxins. Both capsules are concomitantly expressed, under the control of a common global regulator and host signals. Our results show that acquisition of new genetic information by these B. cereus clearly gives them a selective advantage, favouring their dissemination within infected hosts and the environment.

Genotyping of French Bacillus anthracis strains based on 31-loci multi locus VNTR analysis: epidemiology, marker evaluation, and update of the internet genotype database

Background

Bacillus anthracis is known to have low genetic variability. In spite of this lack of diversity, multiple-locus variable-number tandem repeat (VNTR) analysis (MLVA) and single nucleotide polymorphisms (SNPs) including the canonical SNPs assay (canSNP) have proved to be highly effective to differentiate strains. Five different MLVA schemes based on a collection of 31 VNTR loci (MLVA8, MLVA15, MLVA20, MLVA25 and MLVA31) with increased resolving power have been described.

Results

MLVA31 was applied to characterize the French National Reference Laboratory collection. The total collection of 130 strains is resolved in 35 genotypes. The 119 veterinary and environmental strains collection in France were resolved into 26 genotypes belonging to three canSNP lineages and four MLVA clonal complexes (CCs) with particular geographical clustering. A subset of seven loci (MLVA7) is proposed to constitute a first line assay. The loci are compatible with moderate resolution equipment such as agarose gel electrophoresis and show a good congruence value with MLVA31. The associated MLVA and SNP data was imported together with published genotyping data by taking advantage of major enhancements to the MLVAbank software and web site.

Conclusions

The present report provides a wide coverage of the genetic diversity of naturally occurring B. anthracis strains in France as can be revealed by MLVA. The data obtained suggests that once such coverage is achieved, it becomes possible to devise optimized first-line MLVA assays comprising a sufficiently low number of loci to be typed either in one multiplex PCR or on agarose gels. Such a selection of seven loci is proposed here, and future similar investigations in additional countries will indicate to which extend the same selection can be used worldwide as a common minimum set. It is hoped that this approach will contribute to an efficient and low-cost routine surveillance of important pathogens for biosecurity such as B. anthracis.

Mapping the epitopes of a neutralizing antibody fragment directed against the lethal factor of Bacillus anthracis and cross-reacting with the homologous edema factor

The lethal toxin (LT) of Bacillus anthracis, composed of the protective antigen (PA) and the lethal factor (LF), plays an essential role in anthrax pathogenesis. PA also interacts with the edema factor (EF, 20% identity with LF) to form the edema toxin (ET), which has a lesser role in anthrax pathogenesis. The first recombinant antibody fragment directed against LF was scFv 2LF; it neutralizes LT by blocking the interaction between PA and LF. Here, we report that scFv 2LF cross-reacts with EF and cross-neutralizes ET, and we present an in silico method taking advantage of this cross-reactivity to map the epitope of scFv 2LF on both LF and EF. This method identified five epitope candidates on LF, constituted of a total of 32 residues, which were tested experimentally by mutating the residues to alanine. This combined approach precisely identified the epitope of scFv 2LF on LF as five residues (H229, R230, Q234, L235 and Y236), of which three were missed by the consensus epitope candidate identified by pre-existing in silico methods. The homolog of this epitope on EF (H253, R254, E258, L259 and Y260) was experimentally confirmed to constitute the epitope of scFv 2LF on EF. Other inhibitors, including synthetic molecules, could be used to target these epitopes for therapeutic purposes. The in silico method presented here may be of more general interest.

Draft genome sequence of Bacillus anthracis BF-1, isolated from Bavarian cattle

Bacillus anthracis BF-1 was isolated from a cow in Bavaria (Germany) that had succumbed to anthrax. Here, we report the draft genome sequence of this strain, which belongs to the European B2 subclade of B. anthracis. The closest phylogenetic neighbor of strain BF-1 is a strain isolated from cattle in France.

Effects of L-alanine and inosine germinants on the elasticity of Bacillus anthracis spores

The surface of dormant Bacillus anthracis spores consists of a multilayer of protein coats and a thick peptidoglycan layer that allow the cells to resist chemical and environmental insults. During germination, the spore coat is degraded, making the spore susceptible to chemical inactivation by antisporal agents as well as to mechanical inactivation by high-pressure or mechanical abrasion processes. While chemical changes during germination, especially the release of the germination marker, dipicolinic acid (DPA), have been extensively studied, there is as yet no investigation of the corresponding changes in the mechanical properties of the spore. In this work, we use atomic force microscopy (AFM) to characterize the mechanical properties of the surface of Bacillus anthracis spores during germination. The Hertz model of continuum mechanics of contact was used to evaluate the Young's moduli of the spores before and after germination by applying the model to load-indentation curves. The highest modulus was observed for dormant spores, with average elasticity values of 197 +/- 81 MPa. The elasticity decreased significantly after incubation of the spores with the germinants L-alanine or inosine (47.5 +/- 41.7 and 35.4 +/- 15.8 MPa, respectively). Exposure of B. anthracis spores to a mixture of both germinants resulted in a synergistic effect with even lower elasticity, with a Young's modulus of 23.5 +/- 14.8 MPa. The elasticity of the vegetative B. anthracis cells was nearly 15 times lower than that of the dormant spores (12.4 +/- 6.3 MPa vs 197.0 +/- 80.5 MPa, respectively). Indeed from a mechanical strength point of view, the germinated spores were closer to the vegetative cells than to the dormant spores. Further, the decrease in the elasticity of the cells was accompanied by increasing AFM tip indentation depths on the cell surfaces. Indentation depths of up to 246.2 nm were observed for vegetative B. anthracis compared to 20.5 nm for the dormant spores. These results provide quantitative information on how the mechanical properties of the cell wall change during germination, which may explain how spores become susceptible to inactivation processes based on mechanical forces during germination and outgrowth. The study of spore elasticity may be a valuable tool in the design of improved antisporal treatments.

Three related cases of cutaneous anthrax in France: clinical and laboratory aspects

Anthrax is an acute bacterial infection caused by Bacillus anthracis. The infection is cutaneous in about 95% of human cases and respiratory in about 5%. Approximately 2000 cases of cutaneous anthrax are reported annually worldwide. This disease became exceptional in Europe thanks to strict veterinarian monitoring. The last human cases of anthrax indicated in France were in 1997. We report 3 new related cases of naturally acquired cutaneous anthrax that occurred in France in 2008. The unique features of these cases include the atypical clinical presentation and the contribution of the rapid and specific diagnosis techniques by polymerase chain reaction.In cutaneous forms of anthrax, although the local course is not influenced by the treatment, antibiotic therapy is necessary to control any bacterial distribution. A case of exposure similar to that of a confirmed human case or an exposure identified by epidemiologic inquiry should usually result in chemoprophylaxis. Chemoprophylaxis for the close relations of a patient or for health workers is unnecessary since person-to-person transmission has not been reported.

The secret life of the anthrax agent Bacillus anthracis: bacteriophage-mediated ecological adaptations

Ecological and genetic factors that govern the occurrence and persistence of anthrax reservoirs in the environment are obscure. A central tenet, based on limited and often conflicting studies, has long held that growing or vegetative forms of Bacillus anthracis survive poorly outside the mammalian host and must sporulate to survive in the environment. Here, we present evidence of a more dynamic lifecycle, whereby interactions with bacterial viruses, or bacteriophages, elicit phenotypic alterations in B. anthracis and the emergence of infected derivatives, or lysogens, with dramatically altered survival capabilities. Using both laboratory and environmental B. anthracis strains, we show that lysogeny can block or promote sporulation depending on the phage, induce exopolysaccharide expression and biofilm formation, and enable the long-term colonization of both an artificial soil environment and the intestinal tract of the invertebrate redworm, Eisenia fetida. All of the B. anthracis lysogens existed in a pseudolysogenic-like state in both the soil and worm gut, shedding phages that could in turn infect non-lysogenic B. anthracis recipients and confer survival phenotypes in those environments. Finally, the mechanism behind several phenotypic changes was found to require phage-encoded bacterial sigma factors and the expression of at least one host-encoded protein predicted to be involved in the colonization of invertebrate intestines. The results here demonstrate that during its environmental phase, bacteriophages provide B. anthracis with alternatives to sporulation that involve the activation of soil-survival and endosymbiotic capabilities.

Diversity of Bacillus anthracis strains in Georgia and of vaccine strains from the former Soviet Union

Despite the increased number of anthrax outbreaks in Georgia and the other Caucasian republics of the former Soviet Union, no data are available on the diversity of the Bacillus anthracis strains involved. There is also little data available on strains from the former Soviet Union, including the strains previously used for vaccine preparation. In this study we used eight-locus variable-number tandem repeat analyses to genotype 18 strains isolated from infected animals and humans at different sites across Georgia, where anthrax outbreaks have occurred in the last 10 years, and 5 strains widely used for preparation of human and veterinary vaccines in the former Soviet Union. Three different genotypes affiliated with the A3.a cluster were detected for the Georgian isolates. Two genotypes were previously shown to include Turkish isolates, indicating that there is a regional strain pattern in the South Caucasian-Turkish region. Four of the vaccine strains were polymorphic, exhibiting three different patterns of the cluster A1.a genotype and the cluster A3.b genotype. The genotype of vaccine strain 71/12, which is considered an attenuated strain in spite of the presence of both of the virulence pXO plasmids, appeared to be a novel genotype in the A1.a cluster.

Requirements for the Development of Bacillus Anthracis Spore Reference Materials Used to Test Detection Systems

Bacillus anthracis spores have been used as biological weapons and the possibility of their further use requires surveillance systems that can accurately and reliably detect their presence in the environment. These systems must collect samples from a variety of matrices, process the samples, and detect the spores. The processing of the sample may include removal of inhibitors, concentration of the target, and extraction of the target in a form suitable for detection. Suitable reference materials will allow the testing of each of these steps to determine the sensitivity and specificity of the detection systems. The development of uniform and well-characterized reference materials will allow the comparison of different devices and technologies as well as assure the continued performance of detection systems. This paper discusses the special requirements of reference materials for Bacillus anthracis spores that could be used for testing detection systems. The detection of Bacillus anthracis spores is based on recognition of specific characteristics (markers) on either the spore surface or in the nucleic acids (DNA). We have reviewed the specific markers and their relevance to characterization of reference materials. We have also included the approach for the characterization of candidate reference materials that we are developing at the NIST laboratories. Additional applications of spore reference materials would include testing sporicidal treatments, techniques for sampling the environment, and remediation of spore-contaminated environments.

Bacillus anthracis: toxicology, epidemiology and current rapid-detection methods

B. anthracis, the causative agent for anthrax, has been well studied for over 150 years. Due to the genetic similarities among various Bacillus species, as well as its existence in both a spore form and a vegetative state, the detection and specific identification of B. anthracis have been proven to require complex techniques and/or laborious methods. With the heightened interest in the organism as a potential biological threat agent, a large number of interesting detection technologies have recently been developed, including methods involving immunological and nucleic acid-based assay formats. The technologies range from culture-based methods to portable Total Analysis Systems based on real-time PCR. This review with 170 references provides a brief background on the toxicology and epidemiology of B. anthracis, discusses challenges associated with its detection related to genetic similarities to other species, and reviews immunological and, with greater emphasis, nucleic acid-based detection systems.

Molecular characterization of Korean Bacillus anthracis isolates by amplified fragment length polymorphism analysis and multilocus variable-number tandem repeat analysis

We analyzed the genetic relationships and molecular characteristics of 34 Bacillus anthracis isolates from soil and clinical samples in various regions of Korea and 17 related Bacillus species, using the amplified fragment length polymorphism (AFLP) and multilocus variable-number tandem repeat (MLVA) approaches. Triplicate AFLP profiles of these strains showed high reproducibility and identified 376 polymorphisms. AFLP phylogenetic analysis of B. anthracis isolates showed a high level of similarity, 0.93, and this monomorphic fragment profile proved to be useful to differentiate B. anthracis strains from other Bacillus species. The B. cereus group was separated from other Bacillus species at a level of similarity of 0.68. Among them, some B. cereus strains showed genetic interspersion with B. thuringiensis strains. The evolutionary pattern of nucleotide differences among B. anthracis strains with the eight MLVA markers showed nine MLVA types. Three MLVA types, M1 to M3, were pathogenic B. anthracis isolates and were assigned as new genotypes belonging to the A4 and B3 clusters, compared with 89 genotypes deduced from previous data. This indicates that differences in cluster prevalence and distribution may be influenced more by MLVA markers on two plasmids loci and human activity. Consequently, we suggest that the novel MLVA type may represent significant evidence for historic adaptation to environmental conditions of the Asian continent, particularly Korea. Therefore, MLVA techniques may be available for molecular monitoring on anthrax-release-related bioterrorism and further study is required for the continuous epidemiological study of variable anthrax collections.

Rapid genotypic detection of Bacillus anthracis and the Bacillus cereus group by multiplex real-time PCR melting curve analysis

Bacillus anthracis has four plasmid possible virulence genotypes: pXO1+/pXO2+, pXO1+/pXO2-, pXO1-/pXO2+ or pXO1-/pXO2-. Due to the lack of a specific chromosomal marker for B. anthracis, differentiation of the pXO1-/pXO2- form of B. anthracis from closely related Bacillus cereus group species is difficult. In this study, we evaluate the ability of sspE, pXO1 and pXO2 primers to discriminate individual B. anthracis and the B. cereus group genotypes using multiplex real-time PCR and melting curve analysis. Optimal conditions for successful multiplex assays have been established. Purified DNAs from 38 bacterial strains including 11 strains of B. anthracis and 18 B. cereus group strains were analyzed. Nine of the B. cereus group near-neighbor strains were shown by multilocus sequence typing to be phylogenetically proximate to the B. anthracis clade. We have demonstrated that the four plasmid genotypes of B. anthracis and B. cereus group near-neighbors were differentially and simultaneously discriminated by this assay.

Plasmid-encoded regulator of extracellular proteases in Bacillus anthracis

Bacillus anthracis Sterne cured of the pXO1 plasmid had enhanced secreted protease activity during the postexponential phase but no change in hemolytic or lecithinase activities. A zymogen profile revealed at least six proteases, including serine, metal, and perhaps cysteine types. There were similar amounts of protease secreted by the closely related species Bacillus cereus and Bacillus thuringiensis, but the patterns differed. Among the pXO1 plasmid-encoded proteins, there is a tetratricopeptide protein designated Cot43 that is related to the Rap proteins of Bacillus subtilis and the PlcR pleiotropic regulator of secreted enzymes and toxins in B. thuringiensis. A disruption of the cot43 gene resulted in overproduction of several proteases to a somewhat greater extent than in the plasmid-cured strain. Transformation of either of these strains with a clone of the cot43 gene resulted in the inhibition of accumulation of some of the proteases and induction of at least one. On the basis of lacZ fusions, transcription of the cot43 gene increased in late exponential cells at the time of protease accumulation. The expression of lacZ fusions to the upstream regions of two B. anthracis extracellular protease genes was greater in the strain with the disruption of cot43 than in the Sterne strain, indicating regulation at the level of transcription. In B. anthracis, a pXO1 plasmid-encoded protein directly modulates or indirectly regulates the transcription of genes for several chromosomally encoded extracellular proteases.

Comparative secretome analyses of three Bacillus anthracis strains with variant plasmid contents

Bacillus anthracis, the causative agent of anthrax, secretes numerous proteins into the extracellular environment during infection. A comparative proteomic approach was employed to elucidate the differences among the extracellular proteomes (secretomes) of three isogenic strains of B. anthracis that differed solely in their plasmid contents. The strains utilized were the wild-type virulent B. anthracis RA3 (pXO1(+) pXO2(+)) and its two nonpathogenic derivative strains: the toxigenic, nonencapsulated RA3R (pXO1(+) pXO2(-)) and the totally cured, nontoxigenic, nonencapsulated RA3:00 (pXO1(-) pXO2(-)). Comparative proteomics using two-dimensional gel electrophoresis followed by computer-assisted gel image analysis was performed to reveal unique, up-regulated, or down-regulated secretome proteins among the strains. In total, 57 protein spots, representing 26 different proteins encoded on the chromosome or pXO1, were identified by peptide mass fingerprinting. S-layer-derived proteins, such as Sap and EA1, were most frequently observed. Many sporulation-associated enzymes were found to be overexpressed in strains containing pXO1(+). This study also provides evidence that pXO2 is necessary for the maximal expression of the pXO1-encoded toxins lethal factor (LF), edema factor (EF), and protective antigen (PA). Several newly identified putative virulence factors were observed; these include enolase, a high-affinity zinc uptake transporter, the peroxide stress-related alkyl hydroperoxide reductase, isocitrate lyase, and the cell surface protein A.

Identification and characterization of Bacillus anthracis by multiplex PCR on DNA chip

Bacillus anthracis can be identified by detecting virulence factor genes located on two plasmids, pXO1 and pXO2. Combining multiplex PCR with arrayed anchored primer PCR and biotin-avidin alkaline phosphatase indicator system, we developed a qualitative DNA chip method for characterization of B. anthracis, and simultaneous confirmation of the species identity independent of plasmid contents. The assay amplifies pag gene (in pXO1), cap gene (in pXO2) and Ba813 gene (a B. anthracis specific chromosomal marker), and the results were indicated by an easy-to-read profile based on the color reaction of alkaline phosphatase. About 1 pg of specific DNA fragments on the chip wells could be detected after PCR. With the proposed method, the avirulent (pXO1+/2-, pXO1-/2+ and pXO1-/2-) strains of B. anthracis and distinguished 'anthrax-like' strains from other B. cereus group bacteria were unambiguously identified, while the genera other than Bacillus gave no positive signal.

Mass spectrometry provides accurate characterization of two genetic marker types in Bacillus anthracis

Epidemiological and forensic analyses of bioterrorism events involving Bacillus anthracis could be improved if both variable number tandem repeats (VNTRs) and single nucleotide polymorphisms (SNPs) could be combined on a single analysis platform. Here we present the use of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) to characterize 24 alleles from 6 VNTR loci and 11 alleles from 7 SNP loci in B. anthracis. The results obtained with ESI-FTICR-MS were consistent with independent results obtained from traditional approaches using electrophoretic detection of fluorescent products. However, ESI-FTICR-MS improves on the traditional approaches because it does not require fluorescent labeling of PCR products, minimizes post-PCR processing, obviates electrophoresis, and provides unambiguous base composition of both SNP and VNTR PCR products. In addition, ESI-FTICR-MS allows both marker types to be examined simultaneously and at a rate of approximately 1 sample per min. This technology represents a significant advance in our ability to rapidly characterize B. anthracis isolates using VNTR and SNP loci.

Intriguing diversity ofBacillus anthracisin eastern Poland – the molecular echoes of the past outbreaks

The multiple locus VNTRs analysis (MLVA) revealed the presence of five genotypes in a group of 10 Bacillus anthracis isolates from epidemiologically unrelated cases of bovine-anthrax in eastern Poland. Eight tested isolates possessed the pagA and capB genes indicating the presence of both virulence plasmids, while two isolates revealed only pagA and lacked pXO2. The MLVA and DNA sequence analysis indicated that seven tested isolates represent four novel genotypes. Five tested strains revealed a unique 144 bp vrrB2 variant as well as 220 bp variant of vrrB1, implying the relatedness to the lineage B2. Consequently, we propose establishing of novel B2 strains sub-lineage. Multiple anthrax outbreaks, which took place in Poland several decades ago were proposed as a cause of intriguing diversity of B. anthracis observed in this study.

Electrogenerated Chemiluminescence. 77. DNA Hybridization Detection at High Amplification with [Ru(bpy)3]2+-Containing Microspheres

An ultrasensitive DNA hybridization detection method based on electrogenerated chemiluminescence (ECL) using polystyrene microspheres/beads (PSB) as the carrier of the ECL labels, namely, tris(2,2'-bipyridyl)ruthenium(II) tetrakis(pentafluorophenyl)borate (Ru(bpy)3[B(C6F5)4]2), is reported. Probe single-stranded DNA (p-ssDNA) was attached to the surface of magnetic beads (MB) and hybridized with target-ssDNA (t-ssDNA) with immobilized PSB containing a large number of water insoluble Ru(bpy)3[B(C6F5)4]2 species (approximately 7.5 x 10(9) molecules/bead). With this approach a large amplification factor of Ru(bpy)3[B(C6F5)4]2 molecules for each t-ssDNA can be achieved, when each PSB is attached to a limited number of t-ssDNA. The p-ssDNA-MB <--> t-ssDNA-PSB/Ru(bpy)3(2+) conjugates formed were magnetically separated from the reaction media and dissolved in MeCN containing tri-n-propylamine (TPrA) as an ECL coreactant. ECL was produced with a potential scan from 0 to 3.0 V versus Ag/Ag+, and the integrated ECL intensity was found to be linearly proportional to the t-ssDNA concentration in a range of 1.0 fM to 10 nM under optimized conditions. ECL signals associated with two base pair mismatched ssDNA and noncomplementary ssDNA can be distinguished well from the ECL signal related to the complementary DNA hybridization. A Poisson distribution is followed when a large number of MB reacts with PSB, and the minimum number of 1.0- and 2.8-microm diameter MB required to bind and magnetically separate a single 10-microm diameter PSB from the reaction solution was estimated to be three and one, respectively. The principle described in this paper could be also applied to many other ECL analyses, such as immunoassays.

MICs of selected antibiotics for Bacillus anthracis, Bacillus cereus, Bacillus thuringiensis, and Bacillus mycoides from a range of clinical and environmental sources as determined by the Etest

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.

US Food and Drug Administration Approval of Ciprofloxacin Hydrochloride for Management of Postexposure Inhalational Anthrax

In August 2000, the US Food and Drug Administration (FDA) approved ciprofloxacin hydrochloride (Cipro; Bayer) for management of postexposure inhalational anthrax. This was the first antimicrobial drug approved by the FDA for use in treating an infection due to a biological agent used intentionally. The terrorist attacks of 2001 involving anthrax underscore the imperative that safe and effective drugs to manage such infections be readily available in the United States. The approval of ciprofloxacin hydrochloride, which was made on the basis of a surrogate human marker of efficacy, made extensive use of data from an animal model of disease. This represents a new direction in the development of efficacy data in support of drug approval and facilitates the availability of those drugs for which there is an urgent need. This article presents the scientific data and regulatory mechanism that supported the approval of ciprofloxacin hydrochloride for management of postexposure of inhalational anthrax.

Distinct mutations in PlcR explain why some strains of the Bacillus cereus group are nonhemolytic

Bacillus thuringiensis, Bacillus cereus, and Bacillus anthracis are closely related species belonging to the Bacillus cereus group. B. thuringiensis and B. cereus generally produce extracellular proteins, including phospholipases and hemolysins. Transcription of the genes encoding these factors is controlled by the pleiotropic regulator PlcR. Disruption of plcR in B. cereus and B. thuringiensis drastically reduces the hemolytic, lecithinase, and cytotoxic properties of these organisms. B. anthracis does not produce these proteins due to a nonsense mutation in the plcR gene. We screened 400 B. thuringiensis and B. cereus strains for their hemolytic and lecithinase properties. Eight Hly- Lec- strains were selected and analyzed to determine whether this unusual phenotype was due to a mutation similar to that found in B. anthracis. Sequence analysis of the DNA region including the plcR and papR genes of these strains and genetic complementation of the strains with functional copies of plcR and papR indicated that different types of mutations were responsible for these phenotypes. We also found that the plcR genes of three B. anthracis strains belonging to different phylogenetic groups contained the same nonsense mutation, suggesting that this mutation is a distinctive trait of this species.

Electrogenerated chemiluminescence. 72. Determination of immobilized DNA and C-reactive protein on Au(111) electrodes using tris(2,2'-bipyridyl)ruthenium(II) labels

Anodic electrogenerated chemiluminescence (ECL) with tri-n-propylamine (TPrA) as a coreactant was used to determine DNA and C-reactive protein (CRP) by immobilizations on Au(111) electrodes using tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) labels. A 23-mer synthetic single-stranded (ss) DNA derived from the Bacillus anthracis with an amino-modified group at the 5' end position was covalently attached to the Au(111) substrate precoated with a self-assembled thiol monolayer of 3-mercaptopropanoic acid (3-MPA) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) and then hybridized with a target ssDNA tagged with Ru(bpy)(3)(2+) ECL labels. Similarly, biotinylated anti-CRP species were immobilized effectively onto the Au(111) substrate precovered with a layer of avidin linked covalently via the reaction between avidin and a mixed thiol monolayer of 3-MPA and 16-mercaptohexadecanoic acid on Au(111) in the presence of EDAC and N-hydroxysuccinimide. CRP and anti-CRP tagged with Ru(bpy)(3)(2+) labels were then conjugated to the surface layer. ECL responses were generated from the modified electrodes described above by immersing them in a TPrA-containing electrolyte solution. A series of electrode treatments, including blocking free -COOH groups with ethanol amine, pinhole blocking with bovine serum albumin, washing with EDTA/NaCl/Tris buffer, and spraying with inert gases, were used to reduce the nonspecific adsorption of the labeled species. The ECL peak intensity was linearly proportional to the analyte CRP concentration over the range 1-24 microg/mL. CRP concentrations of two unknown human plasma/serum specimens were measured by the standard addition method based on this technique.

Antibiotic susceptibility of isolates of Bacillus anthracis, a bacterial pathogen with the potential to be used in biowarfare

Bacillus anthracis is a bacterial species that could be used in a bioterrorist attack. We tested a collection of isolates with a range of relevant antimicrobial compounds. All isolates tested were susceptible to ciprofloxacin and doxycycline. Penicillin and amoxicillin, with or without clavulanate, showed in vitro activity against all B. anthracis isolates. Ceftriaxone demonstrated lower-level in vitro activity compared to penicillin-related compounds against B. anthracis. In vitro data from this study are in keeping with available guidelines.

Identification of Bacillus anthracis specific chromosomal sequences by suppressive subtractive hybridization

Background

Bacillus anthracis, Bacillus thuringiensis and Bacillus cereus are closely related members of the B. cereus-group of bacilli. Suppressive subtractive hybridization (SSH) was used to identify specific chromosomal sequences unique to B. anthracis.

Results

Two SSH libraries were generated. Genomic DNA from plasmid-cured B. anthracis was used as the tester DNA in both libraries, while genomic DNA from either B. cereus or B. thuringiensis served as the driver DNA. Progressive screening of the libraries by colony filter and Southern blot analyses identified 29 different clones that were specific for the B. anthracis chromosome relative not only to the respective driver DNAs, but also to seven other different strains of B. cereus and B. thuringiensis included in the process. The nucleotide sequences of the clones were compared with those found in genomic databases, revealing that over half of the clones were located into 2 regions on the B. anthracis chromosome.

Conclusions

Genes encoding potential cell wall synthesis proteins dominated one region, while bacteriophage-related sequences dominated the other region. The latter supports the hypothesis that acquisition of these bacteriophage sequences occurred during or after speciation of B. anthracis relative to B. cereus and B. thuringiensis. This study provides insight into the chromosomal differences between B. anthracis and its closest phylogenetic relatives.

Genetic relationship in the 'Bacillus cereus group' by rep-PCR fingerprinting and sequencing of a Bacillus anthracis-specific rep-PCR fragment

AIMS

To evaluate the genetic relationship in the Bacillus cereus group by rep-PCR fingerprinting.

METHODS AND RESULTS

A collection of 112 strains of the six species of the B. cereus group was analysed by rep-PCR fingerprinting using the BOX-A1R primer. A relative genetic distinctness was found among the species. Cluster analysis of the rep-PCR patterns showed clusters of B. thuringiensis strains quite separate from those of B. cereus strains. The B. anthracis strains represented an independent lineage in a B. cereus cluster. The B. mycoides, B. pseudomycoides and B. weihenstephanensis strains were clustered into three groups at some distance from the other species. Comparison of sequences of AC-390, a typical B. anthracis rep-PCR fragment, from 27 strains of B. anthracis, B. cereus, B. thuringiensis and B. weihenstephanensis, representative of different clusters identified by rep-PCR fingerprinting, confirmed that B. anthracis diverges from its related species.

CONCLUSIONS

The genetic relationship deduced from the rep-PCR patterns indicates a relatively clear separation of the six species, suggesting that they can indeed be considered as separate units.

SIGNIFICANCE AND IMPACT OF THE STUDY

rep-PCR fingerprinting can make a contribution in the clarification of the genetic relationships between the species of the B. cereus group.

Molecular detection of anthrax spores on animal fibres

AIMS

To develop a rapid, specific and sensitive diagnostic test for the detection of the spores of Bacillus anthracis on commercial samples of animal fibres (e.g. wool and cashmere).

METHODS AND RESULTS

Extraction of DNA from spores using a mechanical disruption method based on bead beating was evaluated but subsequently abandoned as it compromised the sensitivity of the overall protocol. A multiplex PCR and two nested amplification reactions designed for B. anthracis were developed during this study.

CONCLUSIONS

A simple selective incubation step in combination with multiplex PCR was found to be more effective than generic DNA extraction coupled to a sensitive nested amplification reaction.

SIGNIFICANCE AND IMPACT OF THE STUDY

The rapid diagnostic test could be applied to the analysis of commercial fibre samples for the detection of anthrax as required by health and safety legislation resulting in considerable savings in time and expense.

Biosensor for the specific detection of a single viable B. anthracis spore

A simple membrane strip-based biosensor for the detection of viable B. anthracis spores was developed and combined with a spore germination procedure as well as a nucleic acid amplification reaction to identify as little as one viable B. anthracis spore in less than 12 h. The biosensor is based on identification of a unique mRNA sequence from the anthrax toxin activator (atxA) gene encoded on the toxin plasmid, pXO1. Preliminary work relied on plasmid vectors in both E. coli and B. thuringiensis expressing the atxA gene. Once the principle was firmly established, the vaccine strain of B. anthracis was used. After inducing germination and outgrowth of spores of B. anthracis (Sterne strain), RNA was extracted from lysed cells, amplified using nucleic acid sequence-based amplification (NASBA), and rapidly identified by the biosensor. While the biosensor assay requires only 15-min assay time, the overall process takes 12 h for the detection of as little as one viable B. anthracis spore, and is shortened significantly, if larger amounts of spores are present. The biosensor is based on an oligonucleotide sandwich-hybridization assay format. It uses a membrane flow-through system with an immobilized oligonucleotide probe that hybridizes with the target sequence. Signal amplification is provided when the target sequence hybridizes to a second oligonucleotide probe that has been coupled to dye-encapsulating liposomes. The dye in the liposomes then provides a signal that can be read visually or quantified with a hand-held reflectometer. The biosensor can detect as little as 1.5 fmol of target mRNA. Specificity analysis revealed no crossreactivity with closely related species such as B. cereus, B. megaterium, B. subtilis, B. thuringiensis etc.

Polymorphism in the collagen-like region of the Bacillus anthracis BclA protein leads to variation in exosporium filament length

We recently identified a Bacillus anthracis glycoprotein which is a structural constituent of the exosporium filaments (P. Sylvestre, E. Couture-Tosi, and M. Mock, Mol. Microbiol. 45:169-178, 2002). This Bacillus collagen-like protein (BclA) contains an internal collagen-like region (CLR) of GXX repeats which includes a large proportion of GPT triplets. Here, we report that the polymorphic marker Ceb-Bams13, for which there are nine alleles (P. Le Flèche et al., BMC Microbiol. 1:2, 2001), maps within the open reading frame encoding BclA. The bclA gene in 11 B. anthracis strains representative of seven Ceb-Bams13 alleles was sequenced and compared to the Ames bclA gene sequence. The amino- and carboxy-terminal sequences surrounding the CLR are conserved. The CLR itself is highly polymorphic: it contains between 17 and 91 GXX repeats and one to eight copies of the 21-amino-acid sequence (GPT)(5)GDTGTT, named the BclA repeat. The length of the filament on the spore surface differed between the strains. We exchanged the bclA gene between strains with different CLRs and examined the spore surfaces by electron microscopy analysis. The length of the BclA CLR is responsible for the variation in filament length.

Novel sample preparation method for safe and rapid detection of Bacillus anthracis spores in environmental powders and nasal swabs

Bacillus anthracis spores have been used as a biological weapon in the United States. We wanted to develop a safe, rapid method of sample preparation that provided safe DNA for the detection of spores in environmental and clinical specimens. Our method reproducibly detects B. anthracis in samples containing <10 spores.

Bacillus anthracis diverges from related clades of the Bacillus cereus group in 16S-23S ribosomal DNA intergenic transcribed spacers containing tRNA genes

Mung bean nuclease treatment of 16S-23S ribosomal DNA intergenic transcribed spacers (ITS) amplified from several strains of the six species of the Bacillus cereus group showed that B. anthracis Davis TE702 and B. mycoides G2 have other intermediate fragments in addition to the 220- and 550-bp homoduplex fragments typical of the B. cereus group. Long and intermediate homoduplex ITS fragments from strains Davis TE702 and G2 and from another 19 strains of the six species were sequenced. Two main types of ITS were found, either with two tRNA genes (tRNA(Ile) and tRNA(Ala)) or without any at all. Strain Davis TE702 harbors an additional ITS with a single tRNA gene, a hybrid between the tRNA(Ile) and tRNA(Ala) genes, suggesting that a recombination event rather than a deletion generated the single tDNA-containing ITS. Strain G2 showed an additional ITS of intermediate length with no tDNA and no similarity to other known sequences. Neighbor-joining analysis of tDNA-containing long ITS indicated that B. cereus and B. thuringiensis represent a single clade. Three signature sequences discriminated B. anthracis from B. cereus and B. thuringiensis, indicating that the anthrax agent started evolving separately from the related clades of the B. cereus group. B. mycoides and B. weienstephanensis were very closely related, while B. pseudomycoides appeared the most distant species.

Diversity among French Bacillus anthracis isolates

While outbreaks of animal anthrax zoonoses still regularly occur in France, little is known about the epidemiology links between them. We have used the eight-locus multilocus variable-number tandem repeat analysis typing technique against a collection of 50 Bacillus anthracis isolates from France. There were eight distinct genotypes belonging to two dissimilar genetic clusters. Regional strain patterns were observed, with the B2 genotypes prevalent in southern France and the A1a genotypes found only in northern France.

PCR-based detection of Bacillus anthracis in formalin-fixed tissue from a patient receiving ciprofloxacin

We demonstrate that Bacillus anthracis may be detected from a formalin-fixed, paraffin-embedded biopsy specimen, even after the patient has received antibiotic treatment. Although traditional PCR methods may not be sufficiently sensitive for anthrax detection in such patients, cycle numbers can be increased or PCR can be repeated by using an aliquot from a previous PCR as the template.

Characterization of a repetitive element polymorphism-polymerase chain reaction chromosomal marker that discriminates Bacillus anthracis from related species

AIMS

To identify a chromosomal marker with signature nucleotides specific for Bacillus anthracis.

METHODS AND RESULTS

Repetitive element polymorphism-polymerase chain reaction with BOX-A1R primer was used to discriminate 52 strains of all six species of the 'B. cereus group'. A B. anthracis signature fragment, named AC-390, was cloned and sequenced. The deduced amino acid sequence was homologous to that of YwfK of B. subtilis. Using two internal primers, the AC-390 fragment was sequenced from two other B. anthracis strains as well as from strains of B. cereus and B.thuringiensis which have an AC-390 fragment homologous to that of B. anthracis as shown by Southern hybridization experiments.

CONCLUSIONS

Two new signature sequences specific for B. anthracis were identified on a chromosomal fragment homologous to YwfK, a transcriptional regulator of B. subtilis.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results show a new chromosomal DNA trait useful for distinguishing B. anthracis from the related species of the B. cereus group, regardless of the presence of the virulence plasmids pXO1 and pXO2.

Rapid genotyping of Bacillus anthracis strains by real-time polymerase chain reaction

Rapid and accurate identification of Bacillus anthracis is critical for patient care as well as outbreak control. We have developed 3 separate PCR based assays using fluorescence resonance energy transfer (FRET) to detect the presence of pXO1, pXO2 plasmids and a chromosomal marker. A set of amplification primers and probes were used in each assay. The probes were ad jacently placed inside the primer sites and were 1-bp apart. The upstream probe was labeled with fluorescein at the 3' end, and the downstream probe had Cy5 attached at the 5' end. The probes are included in the PCR reactions and hybridize with the PCR products as they are formed. Binding of probes to PCR products results in transfer of energy from fluorescein to Cy5, resulting in emission from Cy5. Increase in fluorescence, indicating amplification, was monitored in real time on a LightCycler((TM)) LC24. Initial denaturation of target sequences was accomplished at 95 degrees C for 1 min, followed by 28 cycles of denaturation at 95 degrees C for 0 sec, annealing at 58 degrees C for 15 sec, and elongation at 72 degrees C for 5 sec. These assays are specific and can be performed on as little as 25 ng of total DNA or crude cell lysate a from fresh colony. It is thus possible to deter mine the genotype of B. anthracis strains in less than 1 hour.

Bacillus anthracis and antibacterial agents

Anthrax is one of the oldest threats to humankind, and remains endemic in animals in many parts of the world. Human cases are infrequent, and some result from biological warfare. This review summarizes the current knowledge on the antibacterial activity of available antibiotics. For potential use in the most severe cases of anthrax, antibacterials need to exhibit potent in vitro activity, intracellular bioactivity, and suitable locations in lymph nodes. In animal models, it has been shown that doxycycline and fluoroquinolones are the most active compounds. There is a lack of data for animal models for macrolides and ketolides, some of them exhibiting good in vitro activity. However, systemic anthrax (inhalation or gastrointestinal) is mainly due to anthrax toxin, and therapy directed against intoxication is needed as basic treatment.

Occurrence of anthrax in Kars district, Turkey

The aims of the study were to determine the prevalence of anthrax by bacteriologic methods in cattle and sheep between January 2000 and September 2001 and to determine the distribution of this zoonotic disease in humans in Kars district, Turkey. Bacillus anthracis was isolated and identified in 34 out of 38 (91%) cattle and 11 out of 17 (64%) sheep samples obtained from organs suspected of anthrax. The records of the Governmental Health Branch showed that 89 cases of cutaneous anthrax were diagnosed in humans during the study periods in the same district.

Bacillus anthracis as an agent of bioterrorism: a review emphasizing surgical treatment

OBJECTIVE

To familiarize surgeons with the specific complications of cutaneous, gastrointestinal, inhalation, and systemic infection with Bacillus Anthracis, which may require surgical treatment.

SUMMARY BACKGROUND DATA

The recent cases of intentional exposure to Bacillus Anthracis in the United States make familiarity with the basic microbiology, clinical manifestations, diagnosis, treatment, and control of this disease essential if mortality and morbidity is to be minimized, particularly following mass exposure. Although the treatment of Bacillus Anthracis infection is primarily medical, there are specific surgical complications with which the surgeon should be familiar.

METHODS

A review of the literature was undertaken, utilizing electronic databases on infection with Bacillus Anthracis, as well as consultation with experts in this field. Emphasis was placed on the diagnosis and treatment of complications of infection that might require surgical intervention.

RESULTS

Cutaneous anthrax infection results in eschar formation and massive soft tissue edema. When involving the extremities, increased compartment pressure requiring fasciotomy may result. Primary infection of the gastrointestinal tract may result in oropharyngeal edema and respiratory compromise requiring a surgical airway. Direct involvement of the lower gastrointestinal tract can result in intestinal ulceration, necrosis, bleeding, and perforation, which would require surgical exploration and resection of affected segments. Systemic sepsis, most often associated with inhalation anthrax, can cause massive ascites, electrolyte derangements, and profound shock requiring aggressive fluid resuscitation and careful hemodynamic monitoring and respiratory support. Systemic anthrax infection can also lead to gastrointestinal involvement by hematogenous dissemination, resulting in complications and requiring surgical management similar to direct gastrointestinal infection.

CONCLUSIONS

Cutaneous, gastrointestinal, inhalation and systemic infection with Bacillus Anthracis can result in complications which would require familiarity with the pathogenesis and manifestations of this disease in order to recognize and treat promptly and successfully by surgical intervention.

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

We determined the patterns of antimicrobial susceptibility of 65 isolates of Bacillus anthracis (50 historical and 15 recent U.S. clinical isolates) to nine antimicrobial agents using the National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution reference method. The results for the 50 historical B. anthracis isolates obtained by the broth microdilution method were compared to those generated by the Etest agar gradient diffusion method. One isolate of B. anthracis was beta-lactamase positive and resistant to penicillin (MIC, 128 microg/ml); a second isolate, which was beta-lactamase negative, was borderline penicillin resistant, with the penicillin MICs for the isolate varying from 0.12 to 0.25 microg/ml; and the remainder of the isolates were beta-lactamase negative and penicillin susceptible (MICs, <or=0.12 microg/ml). Approximately 78% of the isolates showed reduced susceptibility to ceftriaxone (MICs, >or=16 microg/ml). All B. anthracis isolates were susceptible to chloramphenicol (MICs, <or=8 microg/ml), ciprofloxacin (MICs, <or= 1 microg/ml), clindamycin (MICs, <or=0.5 microg/ml), rifampin (MICs, <or=0.5 microg/ml), tetracycline (MICs, <or=0.06 microg/ml), and vancomycin (MICs, <or=2 microg/ml) by use of NCCLS breakpoints for staphylococci. All 15 recent B. anthracis isolates from the United States were susceptible to penicillin, doxycycline, and ciprofloxacin. By use of the susceptibility breakpoint for staphylococci of <or=0.5 microg/ml, 97% of the B. anthracis isolates tested would have been categorized as intermediate to erythromycin. No statistically significant difference was found between the results of broth microdilution testing and the results of the Etest method for any of the antimicrobial agents tested; however, the results for penicillin obtained by the Etest were 1 to 9 dilutions lower than those obtained by the broth microdilution method. The differences in the penicillin MICs by the Etest method and the difficulties of reading the Etest results through the glass of a biological safety cabinet may limit the utility of this alternate susceptibility testing method for B. anthracis isolates.