Antigenic differences between clinical and environmental isolates of Burkholderia pseudomallei

A naturally derived outer-membrane vesicle vaccine protects against lethal pulmonary Burkholderia pseudomallei infection

Burkholderia pseudomallei, and other members of the Burkholderia, are among the most antibiotic-resistant bacterial species encountered in human infection. Mortality rates associated with severe B. pseudomallei infection approach 50% despite therapeutic treatment. A protective vaccine against B. pseudomallei would dramatically reduce morbidity and mortality in endemic areas and provide a safeguard for the U.S. and other countries against biological attack with this organism. In this study, we investigated the immunogenicity and protective efficacy of B. pseudomallei-derived outer membrane vesicles (OMVs). Vesicles are produced by Gram-negative and Gram-positive bacteria and contain many of the bacterial products recognized by the host immune system during infection. We demonstrate that subcutaneous (SC) immunization with OMVs provides significant protection against an otherwise lethal B. pseudomallei aerosol challenge in BALB/c mice. Mice immunized with B. pseudomallei OMVs displayed OMV-specific serum antibody and T-cell memory responses. Furthermore, OMV-mediated immunity appears species-specific as cross-reactive antibody and T cells were not generated in mice immunized with Escherichia coli-derived OMVs. These results provide the first compelling evidence that OMVs represent a non-living vaccine formulation that is able to produce protective humoral and cellular immunity against an aerosolized intracellular bacterium. This vaccine platform constitutes a safe and inexpensive immunization strategy against B. pseudomallei that can be exploited for other intracellular respiratory pathogens, including other Burkholderia and bacteria capable of establishing persistent infection.

Genomic acquisition of a capsular polysaccharide virulence cluster by non-pathogenic Burkholderia isolates

Background

Burkholderia thailandensis is a non-pathogenic environmental saprophyte closely related to Burkholderia pseudomallei, the causative agent of the often fatal animal and human disease melioidosis. To study B. thailandensis genomic variation, we profiled 50 isolates using a pan-genome microarray comprising genomic elements from 28 Burkholderia strains and species.

Results

Of 39 genomic regions variably present across the B. thailandensis strains, 13 regions corresponded to known genomic islands, while 26 regions were novel. Variant B. thailandensis isolates exhibited isolated acquisition of a capsular polysaccharide biosynthesis gene cluster (B. pseudomallei-like capsular polysaccharide) closely resembling a similar cluster in B. pseudomallei that is essential for virulence in mammals; presence of this cluster was confirmed by whole genome sequencing of a representative variant strain (B. thailandensis E555). Both whole-genome microarray and multi-locus sequence typing analysis revealed that the variant strains formed part of a phylogenetic subgroup distinct from the ancestral B. thailandensis population and were associated with atypical isolation sources when compared to the majority of previously described B. thailandensis strains. In functional assays, B. thailandensis E555 exhibited several B. pseudomallei-like phenotypes, including colony wrinkling, resistance to human complement binding, and intracellular macrophage survival. However, in murine infection assays, B. thailandensis E555 did not exhibit enhanced virulence relative to other B. thailandensis strains, suggesting that additional factors are required to successfully colonize and infect mammals.

Conclusions

The discovery of such novel variant strains demonstrates how unbiased genomic surveys of non-pathogenic isolates can reveal insights into the development and emergence of new pathogenic species.

Use of a low-dose steroid as an adjunct in the treatment, in mice, of severe sepsis caused by Burkholderia pseudomallei

Human melioidosis caused by Burkholderia pseudomallei is a severe septic disease that is associated with high mortality, even under appropriate antibiotic treatment. The therapeutic effects of low-dose hydrocortisone plus ceftazidime, and of ceftazidime alone, have recently been investigated in the treatment of acute, severe sepsis caused by B. pseudomallei, both in normal BALB/c mice and in BALB/c mice with streptozotocin-induced diabetes. The mice were infected and then treated intravenously, from day 1 or day 2 post-infection, with saline (as a control, given twice daily for 10 days), low-dose hydrocortisone (given in twice-daily doses of 5 mg/kg, for 5 days) plus ceftazidime (given in twice-daily doses of 1200 mg/kg, for 10 days), or the same doses of ceftazidime alone. Although the infected, untreated mice all died within 14 days, almost all of the treated animals were still alive at the end of the follow-up, 30 days post-infection. The addition of the steroid appeared to have no benefit, with bacterial loads and plasma concentrations of tumour necrosis factor, aspartate aminotransferase, alanine aminotransferase and creatinine decreasing similarly in all the treated groups. The infected diabetic mice given hydrocortisone-ceftazidime from day 1 (but not those given just ceftazidime from day 1) showed an increase in their blood glucose concentrations. When infected mice were treated with the low-dose steroid and lower doses of the antibiotic (in twice-daily doses of 120-600 mg/kg), the steroid not only offered no apparent benefit but seemed to reduce survival. It therefore appears that low-dose hydrocortisone, as an adjunct to antibiotic treatment, does not provide benefit in the treatment of murine melioidosis and may have negative effects on human cases of the disease who have diabetes mellitus.

TBK1 does not play a role in the control of in vitro Burkholderia pseudomallei growth

Burkholderia pseudomallei, the causative agent of melioidosis, is an important intracellular pathogen in tropical regions. TANK-binding kinase (TBK1), part of the pathway that induces transcription of Type I interferon genes, has been demonstrated to play an important role in controlling intracellular bacterial infections. To investigate the role of tbk1 in protecting against B. pseudomallei we developed tbk1-deficient cell lines by using shRNA for transient knockdown of the tbk1 gene in HeLa and RAW 264.7 cells. In tbk1-deficient RAW cells, the replication of invasive and non-invasive Escherichia coli was significantly increased at 48 h after infection compared with wild-type cells. The result was confirmed using Brucella melitensis in tbk1-deficient HeLa cells, which demonstrated a >1.5-2.0 log higher bacterial count at 6-48 h after infection compared to wild-type cells. By contrast, the growth of Burkholderia pseudomallei expressing either typical (A2) or atypical (G207) lipopolysaccharide was not significantly different between the tbk1-deficient and control cells. These results suggest that the tbk1 gene and its activation may be able to control invasive E. coli, non-invasive E. coli and B. melitensis growth but may not be able to control B. pseudomallei infection. The role of the tbk1 gene in proinflammatory cytokine induction and bacterial intracellular infection needs further investigation to identify mechanistic differences among the life cycles of various intracellular bacteria.

Comparative study of interleukin-1beta expression by peripheral blood mononuclear cells and purified monocytes experimentally infected with Burkholderia pseudomallei and Burkholderia thailandensis

Burkholderia pseudomallei is a causative agent of melioidosis. The present study investigated IL-1beta mRNA and protein expression by peripheral blood mononuclear cells and purified monocytes (n = 10) in response to infection with B. pseudomallei and B. thailandensis. Similarly increased IL-1beta mRNA and protein expression was found in both PBMC and purified monocytes stimulated with B. pseudomallei and B. thailandensis. Thus, this study suggests that IL-1beta response does not differ between infections with B. pseudomallei and its non-virulent counterpart and other mechanisms may be involved in their distinct virulence in causing the disease.

Development of Mouse Hybridomas for Production of Monoclonal Antibodies Specific toBurkholderia malleiandBurkholderia pseudomallei

Burkholderia mallei and B. pseudomallei are designated category B biothreat agents on the "select agents" list established by the NIH and CDC. Development of monoclonal antibodies (MAbs) that could effectively differentiate these two closely related species of bacteria and other non-pathogenic Burkholderia bacteria is urgently needed. Splenocytes from mice immunized with various antigen preparations from either B. mallei (American Type Culture Collection [ATCC] 23344) or B. pseudomallei (ATCC 23343) were used for production of hybridomas. Using a three-step cross-screening protocol, a total of 10 hybridomas were selected that produced MAbs which specifically recognized B. mallei 23344 but did not bind B. pseudomallei, Pseudomonas aeruginasa, or any of the other nine Burkholderia species tested. All 10 MAbs targeted to the lipopolysaccharide (LPS) molecules of B. mallei and reacted strongly with 12 out of 15 different strains of B. mallei tested. A total of 14 hybridomas that produced MAbs reacting with B. pseudomallei 23343, but not with B. mallei, P. aeruginasa, or any other nine non-pathogenic Burkholderia species were also selected. All 14 MAbs appeared to react with a proteinase K-sensitive 200-kDa band by immunoblotting analysis. Surprisingly, these 14 MAbs that were raised against the ATCC 23343 strain failed to react to any of the other 13 different strains of B. pseudomallei examined. In conclusion, our B. mallei-specific MAbs can effectively recognize 80% of the different B. mallei strains tested, and all the B. pseudomallei-specific MAbs appeared to react with a unique antigen present only in the ATCC 23343 strain, but not in any other strains of B. pseudomallei tested.

Melioidosis: epidemiology, pathophysiology, and management

Melioidosis, caused by the gram-negative saprophyte Burkholderia pseudomallei, is a disease of public health importance in southeast Asia and northern Australia that is associated with high case-fatality rates in animals and humans. It has the potential for epidemic spread to areas where it is not endemic, and sporadic case reports elsewhere in the world suggest that as-yet-unrecognized foci of infection may exist. Environmental determinants of this infection, apart from a close association with rainfall, are yet to be elucidated. The sequencing of the genome of a strain of B. pseudomallei has recently been completed and will help in the further identification of virulence factors. The presence of specific risk factors for infection, such as diabetes, suggests that functional neutrophil defects are important in the pathogenesis of melioidosis; other studies have defined virulence factors (including a type III secretion system) that allow evasion of killing mechanisms by phagocytes. There is a possible role for cell-mediated immunity, but repeated environmental exposure does not elicit protective humoral or cellular immunity. A vaccine is under development, but economic constraints may make vaccination an unrealistic option for many regions of endemicity. Disease manifestations are protean, and no inexpensive, practical, and accurate rapid diagnostic tests are commercially available; diagnosis relies on culture of the organism. Despite the introduction of ceftazidime- and carbapenem-based intravenous treatments, melioidosis is still associated with a significant mortality attributable to severe sepsis and its complications. A long course of oral eradication therapy is required to prevent relapse. Studies exploring the role of preventative measures, earlier clinical identification, and better management of severe sepsis are required to reduce the burden of this disease.

Immunostimulatory CpG oligodeoxynucleotide confers protection in a murine model of infection with Burkholderia pseudomallei

Although CpG oligodeoxynucleotides (CpG ODNs) are known to enhance resistance against infection in a number of animal models, little is known about the CpG-induced protection against acute fatal sepsis such as that associated with the highly virulent bacterium Burkholderia pseudomallei. We previously demonstrated in an in vitro study that immunostimulatory CpG ODN 1826 enhances phagocytosis of B. pseudomallei and induces nitric oxide synthase and nitric oxide production by mouse macrophages. In the present study, CpG ODN 1826 given intramuscularly to BALB/c mice 2 to 10 days prior to B. pseudomallei challenge conferred better than 90% protection. CpG ODN 1826 given 2 days before the bacterial challenge rapidly enhanced the innate immunity of these animals, judging from the elevated serum levels of interleukin-12 (IL-12)p70 and gamma interferon (IFN-gamma) over the baseline values. No bacteremia was detected on day 2 in 85 to 90% of the CpG-treated animals, whereas more than 80% of the untreated animals exhibited heavy bacterial loads. Although marked elevation of IFN-gamma was found consistently in the infected animals 2 days after the bacterial challenge, it was ameliorated by the CpG ODN 1826 pretreatment (P = 0.0002). Taken together, the kinetics of bacteremia and cytokine profiles presented are compatible with the possibility that protection by CpG ODN 1826 against acute fatal septicemic melioidosis in this animal model is associated with a reduction of bacterial load and interference with the potential detrimental effect of the robust production of proinflammatory cytokines associated with B. pseudomallei multiplication.

Contribution of gene loss to the pathogenic evolution of Burkholderia pseudomallei and Burkholderia mallei

Burkholderia pseudomallei is the causative agent of melioidosis. Burkholderia thailandensis is a closely related species that can readily utilize l-arabinose as a sole carbon source, whereas B. pseudomallei cannot. We used Tn5-OT182 mutagenesis to isolate an arabinose-negative mutant of B. thailandensis. Sequence analysis of regions flanking the transposon insertion revealed the presence of an arabinose assimilation operon consisting of nine genes. Analysis of the B. pseudomallei chromosome showed a deletion of the operon from this organism. This deletion was detected in all B. pseudomallei and Burkholderia mallei strains investigated. We cloned the B. thailandensis E264 arabinose assimilation operon and introduced the entire operon into the chromosome of B. pseudomallei 406e via homologous recombination. The resultant strain, B. pseudomallei SZ5028, was able to utilize l-arabinose as a sole carbon source. Strain SZ5028 had a significantly higher 50% lethal dose for Syrian hamsters compared to the parent strain 406e. Microarray analysis revealed that a number of genes in a type III secretion system were down-regulated in strain SZ5028 when cells were grown in l-arabinose, suggesting a regulatory role for l-arabinose or a metabolite of l-arabinose. These results suggest that the ability to metabolize l-arabinose reduces the virulence of B. pseudomallei and that the genes encoding arabinose assimilation may be considered antivirulence genes. The increase in virulence associated with the loss of these genes may have provided a selective advantage for B. pseudomallei as these organisms adapted to survival in animal hosts.

Virulent Burkholderia pseudomallei is more efficient than avirulent Burkholderia thailandensis in invasion of and adherence to cultured human epithelial cells

Burkholderia pseudomallei, a causative agent of melioidosis, is a facultative intracellular gram-negative bacillus that is closely related to its avirulent counterpart, Burkholderia thailandensis. However, pathogenic mechanisms and virulence factors of B. pseudomallei remain elusive. In the present study, we compared the invasiveness, adherence, and replication of B. pseudomallei and B. thailandensis in human respiratory epithelial cells A549. Invasion was determined after 4 h of coculturing using antibiotic protection assay. Adherence was demonstrated by coculturing the cells with fluorescein-labeled bacteria for 1 h and the number of positive cells was analyzed by flow cytometry. The results obtained with this in vitro study demonstrated that compared with its avirulent counterpart, B. pseudomallei is significantly more efficient (P<0.01) in invasion, adherence and inducing cellular damage, as represented by plaque formation.

Antigenic relatedness between Burkholderia pseudomallei and Burkholderia mallei

Burkholderia pseudomallei and Burkholderia mallei are causative agents of distinct diseases, namely, melioidosis and glanders, respectively. The two species are very closely related, based on DNA-DNA homology, base sequence of the 16S rRNA, and phenotypic characteristics. Based on the use of polyclonal antisera, B. pseudomallei and B. mallei are also found to be antigenically closely related to one another. We previously reported the production of monoclonal antibodies (MAbs) against B. pseudomallei antigens; one group was specific for the 200-kDa exopolysaccharide present on the surface of all B. pseudomallei isolates, and the other was specific for the lipopolysaccharide (LPS) structure present on more than 95% of the B. pseudomallei tested. In the present study, we showed that the MAbs against 200-kDa antigen of B. pseudomallei cross-reacted with a component present also in some B. mallei isolates (3/6), but the positive immunoblot reaction was noted below the 200-kDa position. On the other hand, none of the six B. mallei isolates reacted with the MAb specific for B. pseudomallei LPS. It was of interest to observe that only the 3 exopolysaccharide-positive B. mallei isolates reacted with a commercial MAb against B. mallei LPS. The data presented suggest that B. mallei can be classified antigenically into two types based on their reactivities with different MAbs, i.e., the presence or absence of exopolysaccharide and the types of lipopolysaccharide. The heterogeneity of the LPS from these two closely related organisms is most likely related to the differences in its O-polysaccharide side chain.

Ribotyping of Burkholderia pseudomallei from clinical and soil isolates in Thailand

Burkholderia pseudomallei is a soil saprophyte that causes melioidosis in humans and animals. Restriction fragment length polymorphism of the ribosomal DNA regions (ribotyping) were analyzed in 577 isolates comprising 371 clinical and 206 soil isolates collected throughout Thailand in 1997. A total of 77 distinct ribotype patterns consisting of 2-9 bands with sizes ranging from 2.8 to >23 kb were found. Twelve major ribotypes were identified of which types 3, 8 and 23 were commonly found (278/577, 48.2%) in both clinical (217/371, 58.5%) and environmental isolates (61/206, 29.6%). Three unique environmental types were found whereas a unique clinical type was not observed. Even though ribotypes show high heterogeneity in the rDNA region, the unique environmental patterns were clearly different from the clinical patterns as clearly seen by UPGMA dendrogram. Moreover, the three major types (types 3, 8 and 23) were discovered in nearly half of B. pseudomallei isolates. Subtyping of these major ribotypes in correlation with clinical profiles may help researchers to identify the virulence factor of the organism.

Genotype analysis of Burkholderia pseudomallei using randomly amplified polymorphic DNA (RAPD): indicative of genetic differences amongst environmental and clinical isolates

Burkholderia pseudomallei is the causative agent of melioidosis, an infectious disease common in the tropics. Melioidosis is most prevalent in the northeastern part of Thailand. The diseases has diverse clinical manifestations ranging from mild localized to fatal septicemic forms. The bacterial genetic factors contributing to the severity of melioidosis have not been completely identified. We have developed a genotyping method based upon randomly amplified polymorphic DNA (RAPD) analysis. Eighteen deca-oligo nucleotide primers with 70% GC content, eight previously published 60%GC RAPD primers, and four random deca oligomers were tested on nine strains of B. pseudomallei isolated from five patients with localized and four with septicemic melioidosis. The RAPD patterns were analyzed by polyacrylamide gel electrophoresis using a laser based automated fragment analyzer, GS2000. Based upon the pattern complexity, seven pairs consisting of eight primers were chosen for further analysis. Six hundred and thirty-two samples, including duplicates/triplicates, of B. pseudomallei isolated from melioidosis patients and the environment were analyzed. Two controls were included in each run of the test samples. All the samples were tested and patterns analyzed by blinded technical staff. Apparently, the method is reproducible. This is indicated by the RAPD patterns of the two controls of between run assay. Interestingly, some RAPD patterns were more prevalent in the clinical isolates than the environmental specimens and vice versa. For example, Q162KKU4-0 and Q162KKU1-0 were found 3. 5 and 3.3 times more often in the clinical specimens (P<0.025). Likewise, Q162KKU1-1 and Q162KKU4-1 were found 18 and 37 times more often in the environment (P<0.0000001). In addition, there was a bias in the distribution of arabinose positive strains and particular RAPD patterns; RAPD patterns of B. pseudomallei that were found frequently in septicemic patients were less likely to be arabinose positive. The data suggest the existence of bacterial genetic differences between the clinical and environmental isolates of B. pseudomallei. Further analysis of the RAPD patterns searching for common polymorphic DNA fragments and systemic comparative genomic analysis of B. pseudomallei in accordance with the clinical data should reveal genetic factors involved in severity and bacterial pathogenesis of B. pseudomallei in melioidosis.

Melioidosis research in China

Research on melioidosis and its pathogen has been ongoing in China for more than two decades. It has been demonstrated that the natural foci are located predominantly in Hainan, Guangdong and Guangxi province, where there is a good correlation between soil isolation and the serum prevalence of antibodies to Burkholderia pseudomallei. The cases of melioidosis reported up to now are concentrated in the Hainan and Zhanjiang peninsula. Investigations on serotype, virulence, ecology, antibiotic susceptibility, whole cell analysis by gas chromatography, and genetics have led to a new understanding of the pathology of the disease. Immunological cross reactions between Burkholderia mallei and B. pseudomallei and the difference between melioidosis and glanders in horses is discussed.

Characterization of Burkholderia pseudomallei isolated in Thailand and Malaysia

A total of 35 Burkholderia pseudomallei isolates from Thailand (16 clinical and eight soil isolates) and Malaysia (seven animal, two isolate each from clinical and soil) were investigated by their antimicrobial resistance, plasmid profiles and were typed by randomly amplified polymorphic DNA analysis. All isolates were found to be resistant to six or more of the 12 antimicrobial agents tested. Only two small plasmids of 1.8 and 2.4 megadalton were detected in two clinical isolates from Thailand. RAPD analysis with primer GEN2-60-09 resulted in the identification of 35 RAPD-types among the 35 isolates. The constructed dendrogram differentiated the 35 isolates into two main clusters and a single isolate. The wide genetic biodiversity among the 35 isolates indicate that RAPD-PCR can be a useful method to differentiate unrelated B. pseudomallei in epidemiological investigation.

Burkholderia uboniae sp. nov., L-arabinose-assimilating but different from Burkholderia thailandensis and Burkholderia vietnamiensis

A polar multitrichous gram-negative motile rod, EY 3383, originally identified as Burkholderia thailandensis, revealed a DNA-DNA reassociation rate of 36.7%, under stringent conditions, with the type strain of B. thailandensis, despite the 16S rDNA homology value between two type strains being as high as 97.9%. The strain was clearly differentiated from the type strain of B. thailandensis by physiological, bio-chemical, and nutritional characteristics, without significant difference in cellular fatty acid and lipid composition. Based on the results of 16S rDNA sequence analysis, DNA-DNA hybridization and phenotypic characterization, Burkholderia uboniae sp. nov. is herein proposed. The type strain is NCTC 13147=EY 3383, isolated on 8 December 1989 from surface soil along the roadside in Ubon Ratchathani, Thailand. Major respiratory quinone is ubiquinone-8(Q8). G+C content of DNA is 69.71%.

Burkholderia pseudomallei induces cell fusion and actin-associated membrane protrusion: a possible mechanism for cell-to-cell spreading

Burkholderia pseudomallei, a facultative intracellular bacterium, is the causative agent of a broad spectrum of diseases collectively known as melioidosis. Its ability to survive inside phagocytic and nonphagocytic cells and to induce multinucleated giant cell (MNGC) formation has been demonstrated. This study was designed to assess a possible mechanism(s) leading to this cellular change, using virulent and nonvirulent strains of B. pseudomallei to infect both phagocytic and nonphagocytic cell lines. We demonstrated that when the cells were labeled with two different cell markers (CMFDA or CMTMR), mixed, and then infected with B. pseudomallei, direct cell-to-cell fusion could be observed, leading to MNGC formation. Staining of the infected cells with rhodamine-conjugated phalloidin indicated that immediately after the infection, actin rearrangement into a comet tail appearance occurred, similar to that described earlier for other bacteria. The latter rearrangement led to the formation of bacterium-containing, actin-associated membrane protrusions which could lead to a direct cell-to-cell spreading of B. pseudomallei in the infected hosts. Results from 4', 6'-diamidine-2-phenylindole dihydrochloride (DAPI) nuclear staining, poly-ADP ribose polymerase cleavage, staining of infected cells for phosphatidylserine exposure with annexin V, and electrophoresis of the DNA extracted from these infected cells showed that B. pseudomallei could kill the host cells by inducing apoptosis in both phagocytic and nonphagocytic cells.

Recovery of Burkholderia pseudomallei and B. cepacia from drinking water

Samples of drinking water were examined in order to evaluate the occurrence of two gram-negative bacteria: Burkholderia pseudomallei and B. cepacia. A total of 85 samples were collected from public and private buildings in the province of Bologna (Italy). Other bacteriological indicators (heterotrophic plate count at 22 and 36 degrees C) were also examined, together with physical and chemical parameters (temperature, pH, residual chlorine, total hardness and chemical oxygen demand (COD)). High levels of B. pseudomallei were recovered (mean value = 578 cfu/100 ml) in about 7% of samples, while B. cepacia was recovered in 3.5% (mean value = < 1) of the samples. The two microorganisms were found to correlate positively with heterotrophic plate counts at 22 and 36 degrees C, but not with the physical and chemical parameters taken into consideration.

Shedding of lipopolysaccharide and 200-kDa surface antigen during the in vitro growth of virulent Ara- and avirulent Ara+ Burkholderia pseudomallei

Non-virulent Ara+ B. pseudomallei environmental isolates differ from virulent Ara- clinical isolates by their ability to assimilate L-arabinose and the absence of a 200 kDa antigen on their surface. The latter, present only on the Ara- isolates from either clinical or environmental origin, was recently demonstrated by its immunoreactivity with monoclonal antibody (MAb) 5F8. We recently demonstrated that lipopolysaccharide (LPS) from both biotypes were indistinguishable from one another with regard to SDS-PAGE profiles and immunoreactivities with immune sera. In this study, the shedding of LPS and 200-kDa antigen into the culture medium during the in vitro growth of Ara- was compared with that of its Ara+ counterpart, using MAb-based sandwich ELISAs. The results showed that the LPS shedding profiles from the two biotypes were similar to one another. This was in contrast to the situation with the 5F8-reactive antigen. The culture fluid of all Ara- isolates and none of the Ara+ isolates were found to react strongly with the MAb 5F8 during the early log phase of growth. However, during the late stationary phase, a trace amount of the 5F8-reactive material could also be detected in the culture fluid of the Ara+ isolates.

Production and characterization of monoclonal antibodies reactive with the mycelial and yeast phases of Penicillium marneffei

A definitive tissue diagnosis of Penicillium marneffei is hampered by a microscopic similarity to the yeast form of Histoplasma capsulatum and Cryptococcus neoformans. In order to obtain a better discrimination for accurate diagnosis, monoclonal antibodies (MAbs) were produced from hybridomas raised from Balb/c mice immunized with mycelial culture filtrate. By indirect immunofluorescent or immunoblot analysis, one immunoglobulin (Ig) G1 (3C2) MAb and three IgM (8B11, 3B9 and 8C3) MAbs were found to react strongly with P. marneffei antigens. In the immunoblots, the MAbs 8B11 and 3B9 reacted most strongly with a high molecular weight component (> 200 kDa) produced during either the mycelial or yeast phase of fungal growth. The immunoreactive epitopes for these two IgM MAbs were most likely associated with carbohydrate moieties, judging from their susceptibility to periodate oxidation and concanavalin A binding. This is in contrast to the immunoreactive epitopes for the MAbs 8C3 and 3C2, which were resistant to destruction by periodate treatment and did not bind to the lectin. Judging from immunofluorescent intensity, the three IgM MAbs could react strongly with the yeast cells present in the tissue biopsies of patients with P. marneffei infection.

Differences in genomic macrorestriction patterns of arabinose-positive (Burkholderia thailandensis) and arabinose-negative Burkholderia pseudomallei

We reported previously two biochemically and antigenically distinct biotypes of Burkholderia pseudomallei. These two distinct biotypes could be distinguished by their ability to assimilate L-arabinose. Some B. pseudomallei isolated from soil samples could utilize this substrate (Ara+), whereas the other soil isolates and all clinical isolates could not (Ara-). Only the Ara isolates were virulent in animals and reacted with monoclonal antibody directed at the surface envelope, most likely the exopolysaccharide component. In the present study, pulsed-field gel electrophoresis was employed for karyotyping of these previously identified B. pseudomallei strains. We demonstrate here that the DNA macrorestriction pattern allows the differentiation between B. pseudomallei, which can assimilate L-arabinose, and the proposed B. thailandensis, which cannot do so. Bacterial strains from 80 melioidosis patients and 33 soil samples were examined by genomic DNA digestion with NcoI. Two major reproducible restriction patterns were observed. All clinical (Ara-) isolates and 9 Ara- soil isolates exhibited macrorestriction pattern I (MPI), while 24 soil isolates (Ara+) from central and northeastern Thailand displayed macrorestriction pattern II (MPII). The study here demonstrated pulsed-field gel electrophoresis to be a useful tool in epidemiological investigation possibly distinguishing virulent B. pseudomallei from avirulent B. thailandensis or even identifying closely related species of Burkholderia.