A simple scoring system to differentiate between relapse and re-infection in patients with recurrent melioidosis

Epidemiology and genetic diversity of Burkholderia pseudomallei from Riau Province, Indonesia

Melioidosis is a bacterial infection caused by Burkholderia pseudomallei, that is common in tropical and subtropical countries including Southeast Asia and Northern Australia. The magnitude of undiagnosed and untreated melioidosis across the country remains unclear. Given its proximity to regions with high infection rates, Riau Province on Sumatera Island is anticipated to have endemic melioidosis. This study reports retrospectively collected data on 68 culture-confirmed melioidosis cases from two hospitals in Riau Province between January 1, 2009, and December 31, 2021, with full clinical data available on 41 cases. We also describe whole genome sequencing and genotypic analysis of six isolates of B. pseudomallei. The mean age of the melioidosis patients was 49.1 (SD 11.5) years, 85% were male and the most common risk factor was diabetes mellitus (78%). Pulmonary infection was the most common presentation (39%), and overall mortality was 41%. Lung as a focal infection (aOR: 6.43; 95% CI: 1.13-36.59, p = 0.036) and bacteremia (aOR: 15.21; 95% CI: 2.59-89.31, p = 0.003) were significantly associated with death. Multilocus sequence typing analysis conducted on six B.pseudomallei genomes identified three sequence types (STs), namely novel ST1794 (n = 3), ST46 (n = 2), and ST289 (n = 1). A phylogenetic tree of Riau B. pseudomallei whole genome sequences with a global dataset of genomes clearly distinguished the genomes of B. pseudomallei in Indonesia from the ancestral Australian clade and classified them within the Asian clade. This study expands the known presence of B. pseudomallei within Indonesia and confirms that Indonesian B. pseudomallei are genetically linked to those in the rest of Southeast Asia. It is anticipated that melioidosis will be found in other locations across Indonesia as laboratory capacities improve and standardized protocols for detecting and confirming suspected cases of melioidosis are more widely implemented.

Marmosets as models of infectious diseases

Animal models of infectious disease often serve a crucial purpose in obtaining licensure of therapeutics and medical countermeasures, particularly in situations where human trials are not feasible, i.e., for those diseases that occur infrequently in the human population. The common marmoset (Callithrix jacchus), a Neotropical new-world (platyrrhines) non-human primate, has gained increasing attention as an animal model for a number of diseases given its small size, availability and evolutionary proximity to humans. This review aims to (i) discuss the pros and cons of the common marmoset as an animal model by providing a brief snapshot of how marmosets are currently utilized in biomedical research, (ii) summarize and evaluate relevant aspects of the marmoset immune system to the study of infectious diseases, (iii) provide a historical backdrop, outlining the significance of infectious diseases and the importance of developing reliable animal models to test novel therapeutics, and (iv) provide a summary of infectious diseases for which a marmoset model exists, followed by an in-depth discussion of the marmoset models of two studied bacterial infectious diseases (tularemia and melioidosis) and one viral infectious disease (viral hepatitis C).

Characteristics and One Year Outcomes of Melioidosis Patients in Northeastern Thailand: A Prospective, Multicenter Cohort Study

Background

Melioidosis is a neglected tropical infection caused by the environmental saprophyte Burkholderia pseudomallei.

Methods

We conducted a prospective, observational study at nine hospitals in northeastern Thailand, a hyperendemic melioidosis zone, to define current characteristics of melioidosis patients and quantify outcomes over one year.

Findings

2574 individuals hospitalised with culture-confirmed melioidosis were screened and 1352 patients were analysed. The median age was 55 years, 975 (72%) were male, and 951 (70%) had diabetes. 565 (42%) patients presented with lung infection, 1042 (77%) were bacteremic, 442 (33%) received vasopressors/inotropes and 547 (40%) received mechanical ventilation. 1307 (97%) received an intravenous antibiotic against B. pseudomallei. 335/1345 (25%) patients died within one month and 448/1322 (34%) of patients died within one year. Most patients had risk factors for melioidosis, but patients without identified risk factors did not have a reduced risk of death. Of patients discharged alive, most received oral trimethoprim-sulfamethoxazole, which was associated with decreased risk of post-discharge death; 235/970 (24%) were readmitted, and 874/1015 (86%) survived to one year. Recurrent infection was detected in 17/994 patients (2%). Patients with risk factors other than diabetes had increased risk of death and increased risk of hospital readmission.

Interpretation

In northeastern Thailand patients with melioidosis experience high rates of bacteremia, organ failure and death. Most patients discharged alive survive one year although all-cause readmission is common. Recurrent disease is rare. Strategies that emphasize prevention, rapid diagnosis and intensification of early clinical management are likely to have greatest impact in this and other resource-restricted regions.

Funding

US NIH/NIAID U01AI115520.

DNase I and chitosan enhance efficacy of ceftazidime to eradicate Burkholderia pseudomallei biofilm cells

Biofilm-associated Burkholderia pseudomallei infection contributes to antibiotic resistance and relapse of melioidosis. Burkholderia pseudomallei biofilm matrix contains extracellular DNA (eDNA) that is crucial for biofilm establishment. However, the contribution of eDNA to antibiotic resistance by B. pseudomallei remains unclear. In this study, we first demonstrated in vitro that DNase I with the administration of ceftazidime (CAZ) at 24 h considerably inhibited the 2-day biofilm formation and reduced the number of viable biofilm cells of clinical B. pseudomallei isolates compared to biofilm treated with CAZ alone. A 3-4 log reduction in numbers of viable cells embedded in the 2-day biofilm was observed when CAZ was combined with DNase I. Confocal laser-scanning microscope visualization emphasized the competence of DNase I followed by CAZ supplementation to significantly limit B. pseudomallei biofilm development and to eradicate viable embedded B. pseudomallei biofilm cells. Furthermore, DNase I supplemented with chitosan (CS) linked with CAZ (CS/CAZ) significantly eradicated shedding planktonic and biofilm cells. These findings indicated that DNase I effectively degraded eDNA leading to biofilm inhibition and dispersion, subsequently allowing CAZ and CS/CAZ to eradicate both shedding planktonic and embedded biofilm cells. These findings provide efficient strategies to interrupt biofilm formation and improve antibiotic susceptibility of biofilm-associated infections.

Efficacy of Co-Trimoxazole against Experimental Melioidosis Acquired by Different Routes of Infection

Burkholderia pseudomallei is the causative agent of melioidosis and presents with diverse clinical manifestations. Naturally occurring infection occurs following contamination of cuts or skin abrasions, or ingestion of contaminated water, and occasionally through inhalational of infected soil or water particles. The influence of the route of disease acquisition on the efficacy of medical countermeasures has not been explored in humans or in appropriate animal models. The efficacy of co-trimoxazole against melioidosis acquired by different routes of exposure was assessed in postexposure prophylaxis (PEP) and treatment studies in marmoset models of melioidosis. Following challenge with B. pseudomallei by the inhalational, subcutaneous, or ingestion routes of administration, animals were given co-trimoxazole at 12 hourly intervals for 14 days, starting either 6 h postchallenge or at the onset of fever. Animals were then observed for 28 days. All animals that received antibiotic 6 h postchallenge survived the duration of dosing. All animals that received antibiotics at the onset of fever completed the treatment, but 10%, 57%, and 60% of those with ingestion, subcutaneous, and inhalation challenge relapsed, respectively. Bacteriological and histological differences were observed between placebo-control animals and those that relapsed. Immunological profiles indicate difference between animals given placebo and those that relapsed or survived the duration of the study. A broad T-cell activation was observed in animals that survived. Overall, these data suggest the efficacy of co-trimoxazole, as measured in the incidence of relapse, differs depending on the disease-acquisition route. Therefore, there are implications in treating this disease in regions of endemicity.

Hijacking of the Host's Immune Surveillance Radars by Burkholderia pseudomallei

Burkholderia pseudomallei (B. pseudomallei) causes melioidosis, a potentially fatal disease for which no licensed vaccine is available thus far. The host-pathogen interactions in B. pseudomallei infection largely remain the tip of the iceberg. The pathological manifestations are protean ranging from acute to chronic involving one or more visceral organs leading to septic shock, especially in individuals with underlying conditions similar to COVID-19. Pathogenesis is attributed to the intracellular ability of the bacterium to ‘step into’ the host cell’s cytoplasm from the endocytotic vacuole, where it appears to polymerize actin filaments to spread across cells in the closer vicinity. B. pseudomallei effectively evades the host’s surveillance armory to remain latent for prolonged duration also causing relapses despite antimicrobial therapy. Therefore, eradication of intracellular B. pseudomallei is highly dependent on robust cellular immune responses. However, it remains ambiguous why certain individuals in endemic areas experience asymptomatic seroconversion, whereas others succumb to sepsis-associated sequelae. Here, we propose key insights on how the host’s surveillance radars get commandeered by B. pseudomallei.

A Comparison Between 12 Versus 20 Weeks of Trimethoprim-Sulfamethoxazole as Oral Eradication Treatment for Melioidosis (12vs20): An Open-label, Pragmatic, Multicenter, Non-inferiority, Randomized Controlled Trial

Background

Treatment of melioidosis comprises intravenous drugs for at least 10 days, followed by oral trimethoprim-sulfamethoxazole (TMP-SMX) for 12 to 20 weeks. Oral TMP-SMX is recommended for 12 weeks in Australia and 20 weeks in Thailand.

Methods

For this open-label, pragmatic, multicenter, noninferiority, randomized controlled trial, we enrolled patients with culture-confirmed melioidosis who had received oral eradication treatment for 12 weeks and had no clinical evidence of active melioidosis. We randomly assigned patients to stop treatment (12-week regimen) or continue treatment for another 8 weeks (20-week regimen). The primary end point was culture-confirmed recurrent melioidosis within 1 year after enrollment. The noninferiority margin was a hazard ratio (HR) of 2.0. The secondary composite end point, combining overall recurrent melioidosis and mortality, was assessed post hoc.

Results

We enrolled 658 patients: 322 to the 12-week regimen and 336 to the 20-week regimen. There were 5 patients (2%) in the 12-week regimen and 2 patients (1%) in the 20-week regimen who developed culture-confirmed recurrent melioidosis (HR, 2.66; 95% confidence interval [CI], .52–13.69). The criterion for noninferiority of the primary event was not met (1-sided P = .37). However, all-cause mortality was significantly lower in the 12-week regimen group than in the 20-week regimen group (1 [.3%] vs 11 [3%], respectively; HR, 0.10; 95% CI, .01–.74). The criterion for noninferiority of the secondary composite end point, combining overall recurrent melioidosis and mortality, was met (1-sided P = .022).

Conclusions

Based on the lower total mortality and noninferiority of the secondary composite end point observed, we recommend the 12-week regimen of TMP-SMX for oral eradication treatment of melioidosis.

Clinical Trials Registration

NCT01420341.

Human Melioidosis

The causative agent of melioidosis, Burkholderia pseudomallei, a tier 1 select agent, is endemic in Southeast Asia and northern Australia, with increased incidence associated with high levels of rainfall. Increasing reports of this condition have occurred worldwide, with estimates of up to 165,000 cases and 89,000 deaths per year. The ecological niche of the organism has yet to be clearly defined, although the organism is associated with soil and water. The culture of appropriate clinical material remains the mainstay of laboratory diagnosis. Identification is best done by phenotypic methods, although mass spectrometric methods have been described. Serology has a limited diagnostic role. Direct molecular and antigen detection methods have limited availability and sensitivity. Clinical presentations of melioidosis range from acute bacteremic pneumonia to disseminated visceral abscesses and localized infections. Transmission is by direct inoculation, inhalation, or ingestion. Risk factors for melioidosis include male sex, diabetes mellitus, alcohol abuse, and immunosuppression. The organism is well adapted to intracellular survival, with numerous virulence mechanisms. Immunity likely requires innate and adaptive responses. The principles of management of this condition are drainage and debridement of infected material and appropriate antimicrobial therapy. Global mortality rates vary between 9% and 70%. Research into vaccine development is ongoing.

The Impact of Age and Sex on Mouse Models of Melioidosis

Mouse models have been used to generate critical data for many infectious diseases. In the case of Burkholderia pseudomallei, mouse models have been invaluable for bacterial pathogenesis studies as well as for testing novel medical countermeasures including both vaccines and therapeutics. Mouse models of melioidosis have also provided a possible way forward to better understand the chronicity associated with this infection, as it appears that BALB/c mice develop an acute infection with B. pseudomallei, whereas the C57BL/6 model is potentially more suggestive of a chronic infection. Several unanswered questions, however, persist around this model. In particular, little attention has been paid to the effect of age or sex on the disease outcome in these animal models. In this report, we determined the LD₅₀ of the B. pseudomallei K96243 strain in both female and male BALB/c and C57BL/6 mice in three distinct age groups. Our data demonstrated a modest increase in susceptibility associated with sex in this model, and we documented important histopathological differences associated with the reproductive systems of each sex. There was a statistically significant inverse correlation between age and susceptibility. The older mice, in most cases, were more susceptible to the infection. Additionally, our retrospective analyses suggested that the impact of animal supplier on disease outcome in mice may be minimal. These observations were consistent regardless of whether the mice were injected with bacteria intraperitoneally or if they were exposed to aerosolized bacteria. All of these factors should be considered when designing experiments using mouse models of melioidosis.

What Can Go Wrong When Applying Immune Modulation Therapies to Target Persistent Bacterial Infections

Antibiotics can treat the acute phase of a disease, but often do not completely clear the etiologic agent, allowing the pathogen to establish persistent infection that can revive the disease in a frustrating recurrence of infection. The mechanisms that control chronic bacterial infections are complex and involve pathogen adaptations that favor survival from both host immune responses and antibiotic bactericidal activity. Often, the causative agents of persistent infections are not drug-resistant species. Instead, bacterial persister cells temporarily enter a physiological state that is refractory to different classes of antibiotics. Supplemental therapies that potentiate antibiotic bactericidal efficiency and/or immune clearance of persistent pathogenic species may greatly improve the outcome of infectious disease. Here, we discuss the various outcomes in experimental studies in which a mega-dose of the energy-boosting vitamin B3 (nicotinamide) was applied in murine models of chronic infection to stimulate immune clearance of chronic infection or as an immune prophylactic treatment against the highly infectious pathogen, Burkholderia pseudomallei. It is our intent to raise awareness of the risks associated with immune modulation therapies. There is great variance in host immune responses to pathogenic bacteria. Each immune modulation approach needs to be tailored to a well-characterized host-pathogen interaction.

Melioidosis: Reinfection going incognito as relapse

Melioidosis has recently gained importance as an emerging disease in India. Recurrent melioidosis has been reported from different parts of the world and can be due to relapse or reinfection. Distinction between relapse and reinfection is important for epidemiology, investigation and management. Here, we present the data regarding rate of recurrence and utility of multilocus sequence typing (MLST) in differentiating relapse form reinfection amongst melioidosis patients from a tertiary care hospital in South India. Amongst the 31 patients who survived and underwent follow-up, 4 (13%) presented with recurrence. Three cases (75%) were identified as reinfection and one (25%) as relapse based on MLST. Re-exposure to environmental Burkholderia pseudomallei amongst patients with melioidosis in endemic areas is likely. In such a scenario, more often than not, recurrence of melioidosis can be attributed to reinfection.

A MarR family transcriptional regulator and subinhibitory antibiotics regulate type VI secretion gene clusters in Burkholderia pseudomallei

Burkholderia pseudomallei, the aetiological agent of melioidosis, is an inhabitant of soil and water in many tropical and subtropical regions worldwide. It possesses six distinct type VI secretion systems (T6SS-1 to T6SS-6), but little is known about most of them, as they are poorly expressed in laboratory culture media. A genetic screen was devised to locate a putative repressor of the T6SS-2 gene cluster and a MarR family transcriptional regulator, termed TctR, was identified. The inactivation of tctR resulted in a 50-fold increase in the expression of an hcp2-lacZ transcriptional fusion, indicating that TctR is a negative regulator of the T6SS-2 gene cluster. Surprisingly, the tctR mutation resulted in a significant decrease in the expression of an hcp6-lacZ transcriptional fusion. B. pseudomallei K96243 and a tctR mutant were grown to logarithmic phase in rich culture medium and RNA was isolated and sequenced in order to identify other genes regulated by TctR. The results identified seven gene clusters that were repressed by TctR, including T6SS-2, and three gene clusters that were significantly activated. A small molecule library consisting of 1120 structurally defined compounds was screened to identify a putative ligand (or ligands) that might bind TctR and derepress transcription of the T6SS-2 gene cluster. Seven compounds, six fluoroquinolones and one quinolone, activated the expression of hcp2-lacZ. Subinhibitory ciprofloxacin also increased the expression of the T6SS-3, T6SS-4 and T6SS-6 gene clusters. This study highlights the complex layers of regulatory control that B. pseudomallei utilizes to ensure that T6SS expression only occurs under very defined environmental conditions.

Melioidosis

Burkholderia pseudomallei is a Gram-negative environmental bacterium and the aetiological agent of melioidosis, a life-threatening infection that is estimated to account for ∼89,000 deaths per year worldwide. Diabetes mellitus is a major risk factor for melioidosis, and the global diabetes pandemic could increase the number of fatalities caused by melioidosis. Melioidosis is endemic across tropical areas, especially in southeast Asia and northern Australia. Disease manifestations can range from acute septicaemia to chronic infection, as the facultative intracellular lifestyle and virulence factors of B. pseudomallei promote survival and persistence of the pathogen within a broad range of cells, and the bacteria can manipulate the host's immune responses and signalling pathways to escape surveillance. The majority of patients present with sepsis, but specific clinical presentations and their severity vary depending on the route of bacterial entry (skin penetration, inhalation or ingestion), host immune function and bacterial strain and load. Diagnosis is based on clinical and epidemiological features as well as bacterial culture. Treatment requires long-term intravenous and oral antibiotic courses. Delays in treatment due to difficulties in clinical recognition and laboratory diagnosis often lead to poor outcomes and mortality can exceed 40% in some regions. Research into B. pseudomallei is increasing, owing to the biothreat potential of this pathogen and increasing awareness of the disease and its burden; however, better diagnostic tests are needed to improve early confirmation of diagnosis, which would enable better therapeutic efficacy and survival.

Role of Burkholderia pseudomallei biofilm formation and lipopolysaccharide in relapse of melioidosis

We examined whether quantitative biofilm formation and/or lipopolysaccharide type of Burkholderia pseudomallei was associated with relapsing melioidosis. We devised a 1:4 nested case-control study in which both cases and controls were drawn from a cohort of patients with primary melioidosis. Paired isolates from 80 patients with relapse and single isolates from 184 patients without relapse were tested. Relapse was associated with biofilm formation of the primary infecting isolate (conditional OR 2.03; 95% CI 1.27-3.25; p 0.003), but not with lipopolysaccharide type (p 0.74). This finding highlights the importance of biofilm formation in relapsing melioidosis.

Recurrent melioidosis in the Darwin Prospective Melioidosis Study: improving therapies mean that relapse cases are now rare

The Darwin Prospective Melioidosis Study has documented 785 melioidosis cases over 23 years. Recurrent melioidosis occurred in 39/679 (5.7%) patients surviving initial infection; 29 patients suffered relapse of the original infection, and 10 presented with a new Burkholderia pseudomallei infection. With improved therapy, relapse has become rare in recent years.

Polar lipids of Burkholderia pseudomallei induce different host immune responses

Melioidosis is a disease in tropical and subtropical regions of the world that is caused by Burkholderia pseudomallei. In endemic regions the disease occurs primarily in humans and goats. In the present study, we used the goat as a model to dissect the polar lipids of B. pseudomallei to identify lipid molecules that could be used for adjuvants/vaccines or as diagnostic tools. We showed that the lipidome of B. pseudomallei and its fractions contain several polar lipids with the capacity to elicit different immune responses in goats, namely rhamnolipids and ornithine lipids which induced IFN-γ, whereas phospholipids and an undefined polar lipid induced strong IL-10 secretion in CD4⁺ T cells. Autologous T cells co-cultured with caprine dendritic cells (cDCs) and polar lipids of B. pseudomallei proliferated and up-regulated the expression of CD25 (IL-2 receptor) molecules. Furthermore, we demonstrated that polar lipids were able to up-regulate CD1w2 antigen expression in cDCs derived from peripheral blood monocytes. Interestingly, the same polar lipids had only little effect on the expression of MHC class II DR antigens in the same caprine dendritic cells. Finally, antibody blocking of the CD1w2 molecules on cDCs resulted in decreased expression for IFN-γ by CD4⁺ T cells. Altogether, these results showed that polar lipids of B. pseudomallei are recognized by the caprine immune system and that their recognition is primarily mediated by the CD1 antigen cluster.

Within-host evolution of Burkholderia pseudomallei over a twelve-year chronic carriage infection

Burkholderia pseudomallei causes the potentially fatal disease melioidosis. It is generally accepted that B. pseudomallei is a noncommensal bacterium and that any culture-positive clinical specimen denotes disease requiring treatment. Over a 23-year study of melioidosis cases in Darwin, Australia, just one patient from 707 survivors has developed persistent asymptomatic B. pseudomallei carriage. To better understand the mechanisms behind this unique scenario, we performed whole-genome analysis of two strains isolated 139 months apart. During this period, B. pseudomallei underwent several adaptive changes. Of 23 point mutations, 78% were nonsynonymous and 43% were predicted to be deleterious to gene function, demonstrating a strong propensity for positive selection. Notably, a nonsense mutation inactivated the universal stress response sigma factor RpoS, with pleiotropic implications. The genome underwent substantial reduction, with four deletions in chromosome 2 resulting in the loss of 221 genes. The deleted loci included genes involved in secondary metabolism, environmental survival, and pathogenesis. Of 14 indels, 11 occurred in coding regions and 9 resulted in frameshift mutations that dramatically affected predicted gene products. Disproportionately, four indels affected lipopolysaccharide biosynthesis and modification. Finally, we identified a frameshift mutation in both P314 isolates within wcbR, an important component of the capsular polysaccharide I locus, suggesting virulence attenuation early in infection. Our study illustrates a unique clinical case that contrasts a high-consequence infectious agent with a long-term commensal infection and provides further insights into bacterial evolution within the human host.

Some bacterial pathogens establish long-term infections that are difficult or impossible to eradicate with current treatments. Rapid advances in genome sequencing technologies provide a powerful tool for understanding bacterial persistence within the human host. Burkholderia pseudomallei is considered a highly pathogenic bacterium because infection is commonly fatal. Here, we document within-host evolution of B. pseudomallei in a unique case of human infection with ongoing chronic carriage. Genomic comparison of isolates obtained 139 months (11.5 years) apart showed a strong signal of adaptation within the human host, including inactivation of virulence and immunogenic factors, and deletion of pathways involved in environmental survival. Two global regulatory genes were mutated in the 139-month isolate, indicating extensive regulatory changes favoring bacterial persistence. Our study provides insights into B. pseudomallei pathogenesis and, more broadly, identifies parallel evolutionary mechanisms that underlie chronic persistence of all bacterial pathogens.

Melioidosis with a Pericardial Effusion, which Relapsed as a Chest Wall Abscess: A Rare Presentation

Melioidosis, which is caused by a soil saprophyte, Burkholderia pseudomallei, is most prevalent in the south-west coast of India. Although it is frequently seen in immunocompromised patients, melioidosis can occur in apparently normal individuals. Melioidosis can involve almost any organ. A relapse of melioidosis is usually associated with a poor adherence to the eradication therapy, a multifocal involvement and bacteraemia. A relapsing melioidosis is usually known to follow a similar pattern of organ involvement in the first and second episodes of the infection. We are discussing here, a rare case of melioidosis in a 38-year-old construction-worker, with no risk factors, who presented initially with a pericardial effusion. It relapsed 6 months after he completed the prescribed eradication therapy for 3 months, as an anterior chest wall abscess. The author recommends a high index of suspicion for the relapsed melioidosis cases, inspite of the primary episode being non-bacteraemic and compliant with the recommended therapy, in order to avoid further complications.

Development of ceftazidime resistance in an acute Burkholderia pseudomallei infection

Burkholderia pseudomallei, a bacterium that causes the disease melioidosis, is intrinsically resistant to many antibiotics. First-line antibiotic therapy for treating melioidosis is usually the synthetic β-lactam, ceftazidime (CAZ), as almost all B. pseudomallei strains are susceptible to this drug. However, acquired CAZ resistance can develop in vivo during treatment with CAZ, which can lead to mortality if therapy is not switched to a different drug in a timely manner. Serial B. pseudomallei isolates obtained from an acute Thai melioidosis patient infected by a CAZ susceptible strain, who ultimately succumbed to infection despite being on CAZ therapy for the duration of their infection, were analyzed. Isolates that developed CAZ resistance due to a proline to serine change at position 167 in the β-lactamase PenA were identified. Importantly, these CAZ resistant isolates remained sensitive to the alternative melioidosis treatments; namely, amoxicillin-clavulanate, imipenem, and meropenem. Lastly, real-time polymerase chain reaction-based assays capable of rapidly identifying CAZ resistance in B. pseudomallei isolates at the position 167 mutation site were developed. The ability to rapidly identify the emergence of CAZ resistant B. pseudomallei populations in melioidosis patients will allow timely alterations in treatment strategies, thereby improving patient outcomes for this serious disease.

Proteomic analysis of colony morphology variants of Burkholderia pseudomallei defines a role for the arginine deiminase system in bacterial survival

Colony morphology variation of Burkholderia pseudomallei is a notable feature of a proportion of primary clinical cultures from patients with melioidosis. Here, we examined the hypothesis that colony morphology switching results in phenotypic changes associated with enhanced survival under adverse conditions. We generated isogenic colony morphology types II and III from B. pseudomallei strain 153 type I, and compared their protein expression profiles using 2D gel electrophoresis. Numerous proteins were differentially expressed, the most prominent of which were flagellin, arginine deiminase (AD) and carbamate kinase (CK), which were over-expressed in isogenic types II and III compared with parental type I. AD and CK (encoded by arcA and arcC) are components of the arginine deiminase system (ADS) which facilitates acid tolerance. Reverse transcriptase PCR of arcA and arcC mRNA expression confirmed the proteomic results. Transcripts of parental type I strain 153 arcA and arcC were increased in the presence of arginine, in a low oxygen concentration and in acid. Comparison of wild type with arcA and arcC defective mutants demonstrated that the B. pseudomallei ADS was associated with survival in acid, but did not appear to play a role in intracellular survival or replication within the mouse macrophage cell line J774A.1. These data provide novel insights into proteomic alterations that occur during the complex process of morphotype switching, and lend support to the idea that this is associated with a fitness advantage in vivo.

Alanine racemase mutants of Burkholderia pseudomallei and Burkholderia mallei and use of alanine racemase as a non-antibiotic-based selectable marker

Burkholderia pseudomallei and Burkholderia mallei are category B select agents and must be studied under BSL3 containment in the United States. They are typically resistant to multiple antibiotics, and the antibiotics used to treat B. pseudomallei or B. mallei infections may not be used as selective agents with the corresponding Burkholderia species. Here, we investigated alanine racemase deficient mutants of B. pseudomallei and B. mallei for development of non-antibiotic-based genetic selection methods and for attenuation of virulence. The genome of B. pseudomallei K96243 has two annotated alanine racemase genes (bpsl2179 and bpss0711), and B. mallei ATCC 23344 has one (bma1575). Each of these genes encodes a functional enzyme that can complement the alanine racemase deficiency of Escherichia coli strain ALA1. Herein, we show that B. pseudomallei with in-frame deletions in both bpsl2179 and bpss0711, or B. mallei with an in-frame deletion in bma1575, requires exogenous D-alanine for growth. Introduction of bpsl2179 on a multicopy plasmid into alanine racemase deficient variants of either Burkholderia species eliminated the requirement for D-alanine. During log phase growth without D-alanine, the viable counts of alanine racemase deficient mutants of B. pseudomallei and B. mallei decreased within 2 hours by about 1000-fold and 10-fold, respectively, and no viable bacteria were present at 24 hours. We constructed several genetic tools with bpsl2179 as a selectable genetic marker, and we used them without any antibiotic selection to construct an in-frame ΔflgK mutant in the alanine racemase deficient variant of B. pseudomallei K96243. In murine peritoneal macrophages, wild type B. mallei ATCC 23344 was killed much more rapidly than wild type B. pseudomallei K96243. In addition, the alanine racemase deficient mutant of B. pseudomallei K96243 exhibited attenuation versus its isogenic parental strain with respect to growth and survival in murine peritoneal macrophages.

Melioidosis: a clinical overview

INTRODUCTION

Melioidosis, an infection caused by the environmental Gram-negative bacillus Burkholderia pseudomallei, has emerged as an important cause of morbidity and mortality in Southeast Asia and northern Australia.

SOURCES OF DATA

a review of the literature using PubMed.

AREAS OF AGREEMENT

Approaches to diagnosis and antimicrobial therapy.

AREAS OF CONTROVERSY

Whether seroconversion signals the presence of a quiescent bacterial focus and an increase in long-term risk of melioidosis.

AREAS TIMELY FOR DEVELOPING RESEARCH

Melioidosis is potentially preventable, but there is a striking lack of evidence on which to base an effective prevention programme. An accurate map defining the global distribution of B. pseudomallei is needed, together with studies on the relative importance of different routes of infection. There is a marked difference in mortality from melioidosis in high-income versus lower income countries, and affordable strategies that reduce death from severe sepsis (from any cause) in resource-restricted settings are needed.

The Treatment of Melioidosis

Melioidosis is a complex bacterial infection, treatment of which combines the urgency of treating rapidly fatal Gram negative septicaemia with the need for eradication of long-term persistent disease in pulmonary, soft tissue, skeletal and other organ systems. Incremental improvements in treatment have been made as a result of multicentre collaboration across the main endemic region of Southeast Asia and northern Australia. There is an emerging consensus on the three main patterns of antimicrobial chemotherapy; initial (Phase 1) treatment, subsequent eradication (Phase 2) therapy and most recently post-exposure (Phase 0) prophylaxis. The combination of agents used, duration of therapy and need for adjunct modalities depends on the type, severity and antimicrobial susceptibility of infection. New antibiotic and adjunct therapies are at an investigational stage but on currently available data are unlikely to make a significant impact on this potentially fatal infection.

Patterns of organ involvement in recurrent melioidosis

Recurrent melioidosis can be caused by two different mechanisms: relapse or re-infection. We examined the pattern of organ involvement in the first and second episodes in individual patients. Evaluation of 140 patients with recurrence showed that similar patterns of disease occurred during the first and second episode, independent of whether this was caused by relapse or re-infection.