Secondary cell wall polysaccharides (SCWPs) are important structural components of the Bacillus cell wall and contribute to the array of antigens presented by these organisms in both spore and vegetative forms. We previously found that antisera raised to Bacillus anthracis spore preparations cross-reacted with SCWPs isolated from several strains of pathogenic B. cereus, but did not react with other phylogenetically related but nonpathogenic Bacilli, suggesting that the SCWP from B. anthracis and pathogenic B. cereus strains share specific structural features. In this study, SCWPs from three strains of B. cereus causing severe or fatal pneumonia (G9241, 03BB87 and 03BB102) were isolated and subjected to structural analysis and their structures were compared to SCWPs from B. anthracis. Complete structural analysis was performed for the B. cereus G9241 SCWP using NMR spectroscopy, mass spectrometry and derivatization methods. The analyses show that SCWPs from B. cereus G9241 has a glycosyl backbone identical to that of B. anthracis SCWP, consisting of multiple trisaccharide repeats of: →6)-α-d-GlcpNAc-(1 → 4)-β-d-ManpNAc-(1 → 4)-β-d-GlcpNAc-(1→. Both the B. anthracis and pathogenic B. cereus SCWPs are highly substituted at all GlcNAc residues with α- and β-Gal residues, however, only the SCWPs from B. cereus G9241 and 03BB87 carry an additional α-Gal substitution at O-3 of ManNAc residues, a feature lacking in the B. anthracis SCWPs. Both the B. anthracis and B. cereus SCWPs are pyruvylated, with an approximate molecular mass of ≈12,000 Da. The implications of these findings regarding pathogenicity and cell wall structure are discussed.
Bacillus anthracis; Bacillus cereus; cell wall; polysaccharide; structure
Molecular subtyping of Bacillus anthracis played an important role in differentiating and identifying anthrax strains during the 2001 bioterrorism-associated outbreak. Because B. anthracis has a low level of genetic variability, only a few subtyping methods, with varying reliability, exist. We initially used multiple-locus variable-number tandem repeat analysis (MLVA) to subtype 135 B. anthracis isolates associated with the outbreak. All isolates were determined to be of genotype 62, the same as the Ames strain used in laboratories. We sequenced the protective antigen gene (pagA) from 42 representative outbreak isolates and determined they all had a pagA sequence indistinguishable from the Ames strain (PA genotype I). MLVA and pagA sequencing were also used on DNA from clinical specimens, making subtyping B. anthracis possible without an isolate. Use of high-resolution molecular subtyping determined that all outbreak isolates were indistinguishable by the methods used and probably originated from a single source. In addition, subtyping rapidly identified laboratory contaminants and non-outbreak–related isolates.
B. anthracis; subtyping; multiple-locus variable-number tandem repeat analysis (MLVA); pagA
To determine potential links between the clinical isolate to animal products and their geographic origin, we genotyped (MLVA-8, MVLA-15, and canSNP analysis) 80 environmental and 12 clinical isolates and 2 clinical specimens from five cases of anthrax (California in 1976 [n = 1], New York in 2006 [n = 1], Connecticut in 2007 [n = 2], and New Hampshire in 2009[n = 1]) resulting from recreational handling of animal products. For the California case, four clinical isolates were identified as MLVA-8 genotype (GT) 76 and in the canSNP A.Br.Vollum lineage, which is consistent with the Pakistani origin of the yarn. Twenty eight of the California isolates were in the A.Br.Vollum canSNP lineage and one isolate was in the A.Br. 003/004 canSNP sub-group. All 52 isolates and both clinical specimens related to the New York and Connecticut cases were MLVA-8 GT 1. The animal products associated with the NY and CT cases were believed to originate from West Africa, but no isolates from this region are available to be genotyped for comparison. All isolates associated with the New Hampshire case were identical and had a new genotype (GT 149). Isolates from the NY, CT and NH cases diverge from the established canSNP phylogeny near the base of the A.Br.011/009. This report illustrates the power of the current genotyping methods and the dramatically different epidemiological conditions that can lead to infections (i.e., contamination by a single genotype versus widespread contamination of numerous genotypes). These cases illustrate the need to acquire and genotype global isolates so that accurate assignments can be made about isolate origins.
We report on the characterization of a group of seven novel Brucella strains isolated in 1964 from three native rodent species in North Queensland, Australia, during a survey of wild animals. The strains were initially reported to be Brucella suis biovar 3 on the basis of microbiological test results. Our results indicated that the rodent strains had microbiological traits distinct from those of B. suis biovar 3 and all other Brucella spp. To reinvestigate these rodent strains, we sequenced the 16S rRNA, recA, and rpoB genes and nine housekeeping genes and also performed multiple-locus variable-number tandem-repeat (VNTR) analysis (MLVA). The rodent strains have a unique 16S rRNA gene sequence compared to the sequences of the classical Brucella spp. Sequence analysis of the recA, rpoB, and nine housekeeping genes reveals that the rodent strains are genetically identical to each other at these loci and divergent from any of the currently described Brucella sequence types. However, all seven of the rodent strains do exhibit distinctive allelic MLVA profiles, although none demonstrated an amplicon for VNTR 07, whereas the other Brucella spp. did. Phylogenetic analysis of the MLVA data reveals that the rodent strains form a distinct clade separate from the classical Brucella spp. Furthermore, whole-genome sequence comparison using the maximal unique exact matches index (MUMi) demonstrated a high degree of relatedness of one of the seven rodent Brucella strains (strain NF 2653) to another Australian rodent Brucella strain (strain 83-13). Our findings strongly suggest that this group of Brucella strains isolated from wild Australian rodents defines a new species in the Brucella genus.
Definitive identification of Brucella species remains a challenge due to the high degree of genetic homology shared within the genus. We report the development of a molecular technique which utilizes real-time PCR followed by high-resolution melt (HRM) curve analysis to reliably type members of this genus. Using a panel of seven primer sets, we tested 153 Brucella spp. isolates with >99% accuracy compared to traditional techniques. This assay provides a useful diagnostic tool that can rapidly type Brucella isolates and has the potential to detect novel species. This approach may also prove helpful for clinical, epidemiological and veterinary investigations.
The immunoreactivities of hydrogen fluoride (HF)-released cell wall polysaccharides (HF-PSs) from selected Bacillus anthracis and Bacillus cereus strains were compared using antisera against live and killed B. anthracis spores. These antisera bound to the HF-PSs from B. anthracis and from three clinical B. cereus isolates (G9241, 03BB87, and 03BB102) obtained from cases of severe or fatal human pneumonia but did not bind to the HF-PSs from the closely related B. cereus ATCC 10987 or from B. cereus type strain ATCC 14579. Antiserum against a keyhole limpet hemocyanin conjugate of the B. anthracis HF-PS (HF-PS-KLH) also bound to HF-PSs and cell walls from B. anthracis and the three clinical B. cereus isolates, and B. anthracis spores. These results indicate that the B. anthracis HF-PS is an antigen in both B. anthracis cell walls and spores, and that it shares cross-reactive, and possibly pathogenicity-related, epitopes with three clinical B. cereus isolates that caused severe disease. The anti-HF-PS-KLH antiserum cross-reacted with the bovine serum albumin (BSA)-conjugates of all B. anthracis and all B. cereus HF-PSs tested, including those from nonclinical B. cereus ATCC 10987 and ATCC 14579 strains. Finally, the serum of vaccinated (anthrax vaccine adsorbed (AVA)) Rhesus macaques that survived inhalation anthrax contained IgG antibodies that bound the B. anthracis HF-PS-KLH conjugate. These data indicate that HF-PSs from the cell walls of the bacilli tested here are (i) antigens that contain (ii) a potentially virulence-associated carbohydrate antigen motif, and (iii) another antigenic determinant that is common to B. cereus strains.
antigens; Bacillus anthracis; Bacillus cereus; polysaccharides; specificity
Systemic anthrax manifests as toxemia, rapidly disseminating septicemia, immune collapse, and death. Virulence factors include the anti-phagocytic γ-linked poly-d-glutamic acid (PGA) capsule and two binary toxins, complexes of protective antigen (PA) with lethal factor (LF) and edema factor. We report the characterization of LF, PA, and PGA levels during the course of inhalation anthrax in five rhesus macaques. We describe bacteremia, blood differentials, and detection of the PA gene (pagA) by PCR analysis of the blood as confirmation of infection. For four of five animals tested, LF exhibited a triphasic kinetic profile. LF levels (mean ± standard error [SE] between animals) were low at 24 h postchallenge (0.03 ± 1.82 ng/ml), increased at 48 h to 39.53 ± 0.12 ng/ml (phase 1), declined at 72 h to 13.31 ± 0.24 ng/ml (phase 2), and increased at 96 h (82.78 ± 2.01 ng/ml) and 120 h (185.12 ± 5.68 ng/ml; phase 3). The fifth animal had an extended phase 2. PGA levels were triphasic; they were nondetectable at 24 h, increased at 48 h (2,037 ± 2 ng/ml), declined at 72 h (14 ± 0.2 ng/ml), and then increased at 96 h (3,401 ± 8 ng/ml) and 120 h (6,004 ± 187 ng/ml). Bacteremia was also triphasic: positive at 48 h, negative at 72 h, and positive at euthanasia. Blood neutrophils increased from preexposure (34.4% ± 0.13%) to 48 h (75.6% ± 0.08%) and declined at 72 h (62.4% ± 0.05%). The 72-h declines may establish a “go/no go” turning point in infection, after which systemic bacteremia ensues and the host's condition deteriorates. This study emphasizes the value of LF detection as a tool for early diagnosis of inhalation anthrax before the onset of fulminant systemic infection.
Brucella species are highly monomorphic, with minimal genetic variation among species, hindering the development of reliable subtyping tools for epidemiologic and phylogenetic analyses. Our objective was to compare two distinct multiple-locus variable-number tandem-repeat analysis (MLVA) subtyping methods on a collection of 101 Brucella melitensis isolates from sporadic human cases of brucellosis in Egypt (n = 83), Qatar (n = 17), and Libya (n = 1). A gel-based MLVA technique, MLVA-15IGM, was compared to an automated capillary electrophoresis-based method, MLVA-15NAU, with each MLVA scheme examining a unique set of variable-number tandem repeats. Both the MLVAIGM and MLVANAU methods were highly discriminatory, resolving 99 and 101 distinct genotypes, respectively, and were able to largely separate genotypes from Egypt and Qatar. The MLVA-15NAU scheme presented higher strain-to-strain diversity in our test population than that observed with the MLVA-15IGM assay. Both schemes were able to genetically correlate some strains originating from the same hospital or region within a country. In addition to comparing the genotyping abilities of these two schemes, we also compared the usability, limitations, and advantages of the two MLVA systems and their applications in the epidemiological genotyping of human B. melitensis strains.
Disease introduction into the New World during colonial expansion is well documented and had a major impact on indigenous populations; however, few diseases have been associated with early human migrations into North America. During the late Pleistocene epoch, Asia and North America were joined by the Beringian Steppe ecosystem which allowed animals and humans to freely cross what would become a water barrier in the Holocene. Anthrax has clearly been shown to be dispersed by human commerce and trade in animal products contaminated with Bacillus anthracis spores. Humans appear to have brought B. anthracis to this area from Asia and then moved it further south as an ice-free corridor opened in central Canada ∼13,000 ybp. In this study, we have defined the evolutionary history of Western North American (WNA) anthrax using 2,850 single nucleotide polymorphisms (SNPs) and 285 geographically diverse B. anthracis isolates. Phylogeography of the major WNA B. anthracis clone reveals ancestral populations in northern Canada with progressively derived populations to the south; the most recent ancestor of this clonal lineage is in Eurasia. Our phylogeographic patterns are consistent with B. anthracis arriving with humans via the Bering Land Bridge. This northern-origin hypothesis is highly consistent with our phylogeographic patterns and rates of SNP accumulation observed in current day B. anthracis isolates. Continent-wide dispersal of WNA B. anthracis likely required movement by later European colonizers, but the continent's first inhabitants may have seeded the initial North American populations.
Bacillus cereus is most commonly associated with foodborne illness (diarrheal and emetic) but is also an opportunistic pathogen that can cause severe and fatal infections. Several multilocus sequence typing (MLST) schemes have recently been developed to genotype B. cereus and analysis has suggested a clonal or weakly clonal population structure for B. cereus and its close relatives B. anthracis and B. thuringiensis. In this study we used MLST to determine if B. cereus isolates associated with illnesses of varying severity (e.g., severe, systemic vs. gastrointestinal (GI) illness) were clonal or formed clonal complexes.
A retrospective analysis of 55 clinical B. cereus isolates submitted to the Centers for Disease Control and Prevention between 1954 and 2004 was conducted. Clinical isolates from severe infections (n = 27), gastrointestinal (GI) illness (n = 18), and associated isolates from food (n = 10) were selected for analysis using MLST. The 55 isolates were diverse and comprised 38 sequence types (ST) in two distinct clades. Of the 27 isolates associated with serious illness, 13 clustered in clade 1 while 14 were in clade 2. Isolates associated with GI illness were also found throughout clades 1 and 2, while no isolates in this study belonged to clade 3. All the isolates from this study belonging to the clade 1/cereus III lineage were associated with severe disease while isolates belonging to clade1/cereus II contained isolates primarily associated with severe disease and emetic illness. Only three STs were observed more than once for epidemiologically distinct isolates.
STs of clinical B. cereus isolates were phylogenetically diverse and distributed among two of three previously described clades. Greater numbers of strains will need to be analyzed to confirm if specific lineages or clonal complexes are more likely to contain clinical isolates or be associated with specific illness, similar to B. anthracis and emetic B. cereus isolates.
Bacillus anthracis; SNP; MLVA; VNTR; Ames strain; letter
Bacillus anthracis, the etiologic agent of anthrax, has been widely described as a genetically monomorphic species. We used both multiple-locus variable-number tandem-repeat analysis (MLVA) and pagA gene sequencing to determine the genetic diversity of a historical collection of B. anthracis isolates collected from the 1950s to the 1980s from various geographic locations and sources. We sequenced the pagA gene of 124 diverse B. anthracis isolates and found all previously identified B. anthracis pagA types except type 4. Sixty-three of the 124 B. anthracis strains were identified as pagA type 6, while 44 were pagA type 5, 12 were pagA type 1, and individual isolates were identified for types 2 and 3, respectively. Two new pagA genotypes were discovered in three environmental isolates within the historical collection. Two isolates had the same new genotype, and an additional isolate produced a second new genotype. MLVA detected 22 previously described genotypes in the historical collection. In addition, 33 new MLVA genotypes were found. For 11 isolates, an MLVA genotype could not be assigned because one or more alleles did not amplify. While only two additional B. anthracis pagA types were identified, in two instances, the use of pagA sequencing discriminated isolates with the same MLVA genotype. MLVA revealed that 39 of the 124 isolates were previously undocumented genotypes and that 1 isolate was found to be in the C cluster when it was subtyped by MLVA.
Bacillus cereus is ubiquitous in nature, and while most isolates appear to be harmless, some are associated with food-borne illnesses, periodontal diseases, and other more serious infections. In one such infection, B. cereus G9241 was identified as the causative agent of a severe pneumonia in a Louisiana welder in 1994. This isolate was found to harbor most of the B. anthracis virulence plasmid pXO1 (13). Here we report the characterization of two clinical and one environmental B. cereus isolate collected during an investigation of two fatal pneumonia cases in Texas metal workers. Molecular subtyping revealed that the two cases were not caused by the same strain. However, one of the three isolates was indistinguishable from B. cereus G9241. PCR analysis demonstrated that both clinical isolates contained B. anthracis pXO1 toxin genes. One clinical isolate and the environmental isolate collected from that victim's worksite contained the cap A, B, and C genes required for capsule biosynthesis in B. anthracis. Both clinical isolates expressed a capsule; however, neither was composed of poly-d-glutamic acid. Although most B. cereus isolates are not opportunistic pathogens and only a limited number cause food-borne illnesses, these results demonstrate that some B. cereus strains can cause severe and even fatal infections in patients who appear to be otherwise healthy.
We identified three encapsulated Bacillus cereus strains, isolated from patients with severe pneumonia, in a collection of B. cereus isolates associated with human illness. We found that the extent of capsule expression was influenced by culturing conditions. Our findings highlight consequent clinical and laboratory diagnostic challenges posed by such isolates.
Bacillus anthracis and Bacillus cereus can usually be distinguished by standard microbiological methods (e.g., motility, hemolysis, penicillin susceptibility and susceptibility to gamma phage) and PCR. However, we have identified 23 Bacillus spp. isolates that gave discrepant results when assayed by standard microbiological methods and PCR. We used multiple-locus variable-number tandem repeat analysis (MLVA), multiple-locus sequence typing (MLST), and phenotypic analysis to characterize these isolates, determine if they cluster phylogenetically and establish whether standard microbiological identification or PCR were associated with false positive/negative results.
Six isolates were LRN real-time PCR-positive but resistant to gamma phage; MLVA data supported the identification of these isolates as gamma phage-resistant B. anthracis. Seventeen isolates were LRN real-time PCR-negative but susceptible to gamma phage lysis; these isolates appear to be a group of unusual gamma phage-susceptible B. cereus isolates that are closely related to each other and to B. anthracis. All six B. anthracis MLVA chromosomal loci were amplified from one unusual gamma phage-susceptible, motile, B. cereus isolate (although the amplicons were atypical sizes), and when analyzed phylogenetically, clustered with B. anthracis by MLST.
MLVA and MLST aided in the identification of these isolates when standard microbiological methods and PCR could not definitely identify or rule out B. anthracis. This study emphasized the need to perform multiple tests when attempting to identify B. anthracis since relying on a single assay remains problematic due to the diverse nature of bacteria.
The plasmid profiles of 619 cultures of Bacillus anthracis which had been isolated and stored between 1954 and 1989 were analyzed using the Laboratory Response Network real-time PCR assay targeting a chromosomal marker and both virulence plasmids (pXO1 and pXO2). The cultures were stored at ambient temperature on tryptic soy agar slants overlaid with mineral oil. When data were stratified by decade, there was a decreasing linear trend in the proportion of strains containing both plasmids with increased storage time (P < 0.001). There was no significant difference in the proportion of strains containing only pXO1 or strains containing only pXO2 (P = 0.25), but there was a statistical interdependence between the two plasmids (P = 0.004). Loss of viability of B. anthracis cultures stored on agar slants is also discussed.
We used multiple-locus variable-number tandem repeat analysis (MLVA) and pagA sequencing to genotype a Bacillus anthracis isolate from a fatal case of human anthrax in Hong Kong. The isolate has a unique MLVA genotype, is related to the Sterne and Ames strains, and is consistent with genotypes identified in China.
Burkholderia pseudomallei and B. mallei, the causative agents of melioidosis and glanders, respectively, are designated category B biothreat agents. Current methods for identifying these organisms rely on their phenotypic characteristics and an extensive set of biochemical reactions. We evaluated the use of 16S rRNA gene sequencing to rapidly identify these two species and differentiate them from each other as well as from closely related species and genera such as Pandoraea spp., Ralstonia spp., Burkholderia gladioli, Burkholderia cepacia, Burkholderia thailandensis, and Pseudomonas aeruginosa. We sequenced the 1.5-kb 16S rRNA gene of 56 B. pseudomallei and 23 B. mallei isolates selected to represent a wide range of temporal, geographic, and origin diversity. Among all 79 isolates, a total of 11 16S types were found based on eight positions of difference. Nine 16S types were identified in B. pseudomallei isolates based on six positions of difference, with differences ranging from 0.5 to 1.5 bp. Twenty-two of 23 B. mallei isolates showed 16S rRNA gene sequence identity and were designated 16S type 10, whereas the remaining isolate was designated type 11. This report provides a basis for rapidly identifying and differentiating B. pseudomallei and B. mallei by molecular methods.
On November 20, 2001, inhalational anthrax was confirmed in an elderly woman from rural Connecticut. To determine her exposure source, we conducted an extensive epidemiologic, environmental, and laboratory investigation. Molecular subtyping showed that her isolate was indistinguishable from isolates associated with intentionally contaminated letters. No samples from her home or community yielded Bacillus anthracis, and she received no first-class letters from facilities known to have processed intentionally contaminated letters. Environmental sampling in the regional Connecticut postal facility yielded B. anthracis spores from 4 (31%) of 13 sorting machines. One extensively contaminated machine primarily processes bulk mail. A second machine that does final sorting of bulk mail for her zip code yielded B. anthracis on the column of bins for her carrier route. The evidence suggests she was exposed through a cross-contaminated bulk mail letter. Such cross-contamination of letters and postal facilities has implications for managing the response to future B. anthracis–contaminated mailings.
Bacillus anthracis; inhalational anthrax; bioterrorism; postal facilities; research
A two-component direct fluorescent-antibody (DFA) assay, using fluorescein-labeled monoclonal antibodies specific to the Bacillus anthracis cell wall (CW-DFA) and capsule (CAP-DFA) antigens, was evaluated and validated for rapid identification of B. anthracis. We analyzed 230 B. anthracis isolates; 228 and 229 were positive by CW-DFA and CAP-DFA assays, respectively. We also tested 56 non–B. anthracis strains; 10 B. cereus and 2 B. thuringiensis were positive by the CW-DFA assay, and 1 B. megaterium strain was positive by CAP-DFA. Analysis of the combined DFA results identified 227 of 230 B. anthracis isolates; all 56 strains of the other Bacillus spp. were negative. Both DFA assays tested positive on 14 of 26 clinical specimens from the 2001 anthrax outbreak investigation. The two-component DFA assay is a sensitive, specific, and rapid confirmatory test for B. anthracis in cultures and may be useful directly on clinical specimens.
Bacillus anthracis; DFA
Protective antigen (PA) is an important component of the edema and lethal toxins produced by Bacillus anthracis. PA is essential for binding the toxins to the target cell receptor and for facilitating translocation of the enzymatic toxin components, edema factor and lethal factor, across the target cell membrane. The structural gene for PA, pagA (previously known as pag), is located on the 182-kb virulence plasmid pXO1 at a locus distinct from the edema factor and lethal factor genes. Here we show that a 300-bp gene located downstream of pagA is cotranscribed with pagA and represses expression of the operon. We have designated this gene pagR (for protective antigen repressor). Two pagA mRNA transcripts were detected in cells producing PA: a short, 2.7-kb transcript corresponding to the pagA gene, and a longer, 4.2-kb transcript representing a bicistronic message derived from pagA and pagR. The 3′ end of the short transcript mapped adjacent to an inverted repeat sequence, suggesting that the sequence can act as a transcription terminator. Attenuation of termination at this site results in transcription of pagR. A pagR mutant exhibited increased steady-state levels of pagA mRNA, indicating that pagR negatively controls expression of the operon. Autogenous control of the operon may involve atxA, a trans-acting positive regulator of pagA. The steady-state level of atxA mRNA was also increased in the pagR mutant. The mutant phenotype was complemented by addition of pagR in trans on a multicopy plasmid.