Septicemic Melioidosis Detection Using Support Vector Machine with Five Immune Cell Types

Melioidosis, caused by Burkholderia pseudomallei (B. pseudomallei), predominantly occurs in the tropical regions. Of various types of melioidosis, septicemic melioidosis is the most lethal one with a mortality rate of 40%. Early detection of the disease is paramount for the better chances of cure. In this study, we developed a novel approach for septicemic melioidosis detection, using a machine learning technique-support vector machine (SVM). Several SVM models were built, and 19 features characterized by the corresponding immune cell types were generated by Cell type Identification Estimating Relative Subsets Of RNA Transcripts (CIBERSORT). Using these features, we trained a binomial SVM model on the training set and evaluated it on the independent testing set. Our findings indicated that this model performed well with means of sensitivity and specificity up to 0.962 and 0.979, respectively. Meanwhile, the receiver operating characteristic (ROC) curve analysis gave area under curves (AUCs) ranging from 0.952 to 1.000. Furthermore, we found that a concise SVM model, built upon a combination of CD8+ T cells, resting CD4+ memory T cells, monocytes, M2 macrophages, and activated mast cells, worked perfectly on the detection of septicemic melioidosis. Our data showed that its mean of sensitivity was up to 0.976 while that of specificity up to 0.993. In addition, the ROC curve analysis gave AUC close to 1.000. Taken together, this SVM model is a robust classification tool and may serve as a complementary diagnostic technique to septicemic melioidosis.

The Cox model of predicting mortality among melioidosis patients in Northern Malaysia: A retrospective study

ABSTRACT

Melioidosis is an infectious disease that is initiated by a bacteria recognized as Burkholderia pseudomallei. Despite the high fatality rate from melioidosis, there is a minimal published study about the disease in Malaysia.This study aimed to identify the prognostic factors of mortality among melioidosis patients in northern Malaysia.All inpatient patients who were admitted to Hospital Sultanah Bahiyah, Kedah and Hospital Tuanku Fauziah, Perlis with culture-confirmed melioidosis during the period 2014 to 2017 were included in the study. The study retrospectively collected 510 melioidosis patients from the Melioidosis Registry. Hazard ratio (HR) used in advanced multiple Cox regression was used to obtain the final model of prognostic factors of melioidosis. The analysis was performed using STATA/SE 14.0 for Windows software.From the results, among the admitted patients, 50.1% died at the hospital. The mean age for those who died was 55 years old, and they were mostly male. The most common underlying disease was diabetes mellitus (69.8%), followed by hypertension (32.7%). The majority of cases (86.8%) were bacteremic. The final Cox model identified 5 prognostic factors of mortality among melioidosis patients. The factors were diabetes mellitus, type of melioidosis, platelet count, white blood cell count, and urea value. The results showed that bacteremic melioidosis increased the risk of dying by 3.47 (HR: 3.47, 95% confidence intervals [CI]: 1.67-7.23, P = .001) compared to non-bacteremic melioidosis. Based on the blood investigations, the adjusted HRs from the final model showed that all 3 blood investigations were included as the prognostic factors for the disease (low platelet: HR = 1.76, 95% CI: 1.22-2.54, P = .003; high white blood cell: HR = 1.49, 95% CI 1.06-2.11, P = .023; high urea: HR = 2.92, 95% CI: 1.76-4.85, P < .001; and low level of urea: HR = 2.69, 95% CI: 1.69-4.29, P < .001). By contrast, melioidosis patients with diabetic had 30.0% lower risk of dying from melioidosis compared to those with non-diabetic (HR = 0.70, 95% CI: 0.52-0.94, P = .016).Identifying the prognostic factors of mortality in patients with melioidosis allows a guideline of early management in these patients, which may improve patient's survival.

Melioidosis DS rapid test: A standardized serological dipstick assay with increased sensitivity and reliability due to multiplex detection

Background

Melioidosis, caused by Burkholderia pseudomallei, is a severe infectious disease with high mortality rates, but is under-recognized worldwide. In endemic areas, there is a great need for simple, low-cost and rapid diagnostic tools. In a previous study we showed, that a protein multiplex array with 20 B. pseudomallei-specific antigens detects antibodies in melioidosis patients with high sensitivity and specificity. In a subsequent study the high potential of anti-B. pseudomallei antibody detection was confirmed using a rapid Hcp1 single protein-based assay. Our protein array also showed that the antibody profile varies between patients, possibly due to a combination of host factors but also antigen variations in the infecting B. pseudomallei strains. The aim of this study was to develop a rapid test, combining Hcp1 and the best performing antigens BPSL2096, BPSL2697 and BPSS0477 from our previous study, to take advantage of simultaneous antibody detection.

Methods and principal findings

The 4-plex dipstick was validated with sera from 75 patients on admission plus control groups, achieving 92% sensitivity and 97–100% specificity. We then re-evaluated melioidosis sera with the 4-plex assay that were previously misclassified by the monoplex Hcp1 rapid test. 12 out of 55 (21.8%) false-negative samples were positive in our new dipstick assay. Among those, 4 sera (7.3%) were Hcp1 positive, whereas 8 (14.5%) sera remained Hcp1 negative but gave a positive reaction with our additional antigens.

Conclusions

Our dipstick rapid test represents an inexpensive, standardized and simple diagnostic tool with an improved serodiagnostic performance due to multiplex detection. Each additional band on the test strip makes a false-positive result more unlikely, contributing to its reliability. Future prospective studies will seek to validate the gain in sensitivity and specificity of our multiplex rapid test approach in different melioidosis patient cohorts.

The Gram-negative environmental pathogen Burkholderia pseudomallei, causes the severe disease melioidosis. It is highly endemic in southeast Asia and northern Australia, but recent studies suggest that it is also present in many other parts of the world where it is severely underreported. The latter results from the extremely variable and non-specific clinical manifestations of the disease, lack of clinical recognition, and the global scarcity of good quality laboratories to allow diagnosis from microbiological culture. This is even more unfortunate, as early diagnosis of the disease is indispensable for an effective therapy, since B. pseudomallei is intrinsically resistant to many antibiotics used for empirical treatment in endemic areas. Therefore, the development of new, standardized and sensitive tools is of high importance for both diagnostics and epidemiology. We focused on the development of a dipstick assay, which is based on the detection of serum antibodies against four B. pseudomallei specific protein antigens. Here we present a cost effective, simple and rapid melioidosis assay with improved sensitivity that does not depend on sophisticated laboratory equipment and therefore addresses most of the before mentioned obstacles and is easy to manufacture in large scales.

Distinct classes and subclasses of antibodies to hemolysin co-regulated protein 1 and O-polysaccharide and correlation with clinical characteristics of melioidosis patients

Melioidosis is a tropical infectious disease caused by Burkholderia pseudomallei that results in high mortality. Hemolysin co-regulated protein 1 (Hcp1) and O-polysaccharide (OPS) are vaccine candidates and potential diagnostic antigens. The correlation of classes/subclasses of antibodies against these antigens with clinical characteristics of melioidosis patients is unknown. Antibodies in plasma samples from melioidosis patients and healthy donors were quantified by ELISA and compared with clinical features. In melioidosis patients, Hcp1 induced high IgG levels. OPS induced high IgG and IgA levels. The area under receiver operating characteristic curve (AUROCC) to discriminate melioidosis cases from healthy donors was highest for anti-Hcp1 IgG (0.92) compared to anti-Hcp1 IgA or IgM. In contrast, AUROCC for anti-OPS for IgG (0.91) and IgA (0.92) were comparable. Anti-Hcp1 IgG1 and anti-OPS IgG2 had the greatest AUROCCs (0.87 and 0.95, respectively) compared to other IgG subclasses for each antigen. Survivors had significantly higher anti-Hcp1 IgG3 levels than non-survivors. Male melioidosis patients with diabetes had higher anti-OPS IgA levels than males without diabetes. Thus, diverse and specific antibody responses are associated with distinct clinical characteristics in melioidosis, confirming the diagnostic utility of these responses and providing new insights into immune mechanisms.

Rapid detection of Burkholderia pseudomallei with a lateral flow recombinase polymerase amplification assay

Melioidosis is a severe infectious disease caused by gram-negative, facultative intracellular pathogen Burkholderia pseudomallei (B. pseudomallei). Although cases are increasing reported from other parts of the world, it is an illness of tropical and subtropical climates primarily found in southeast Asia and northern Australia. Because of a 40% mortality rate, this life-threatening disease poses a public health risk in endemic area. Early detection of B. pseudomallei infection is vital for prognosis of a melioidosis patient. In this study, a novel isothermal recombinase polymerase amplification combined with lateral flow dipstick (LF-RPA) assay was established for rapid detection of B. pseudomallei. A set of primer-probe targeting orf2 gene within the putative type III secretion system (T3SS) cluster genes was generated and parameters for the LF-RPA assay were optimized. Result can be easy visualized in 30 minutes with the limit of detection (LOD) as low as 20 femtogram (fg) (ca. 25.6 copies) of B. pseudomallei genomic DNA without a specific equipment. The assay is highly specific as no cross amplification was observed with Burkholderia mallei, members of the Burkholderia cepacia-complex and 35 non-B. pseudomallei bacteria species. Moreover, isolates from patients in Hainan (N = 19), Guangdong (N = 1), Guangxi (N = 3) province of China as well as in Australia (N = 3) and Thailand (N = 1) were retrospectively confirmed by the newly developed method. LODs for B. pseudomallei-spiked soil and blood samples were 2.1×10³ CFU/g and 4.2×10³ CFU/ml respectively. The sensitivity of the LF-RPA assay was comparable to TaqMan Real-Time PCR (TaqMan PCR). In addition, the LF-RPA assay exhibited a better tolerance to inhibitors in blood than TaqMan PCR. Our results showed that the LF-RPA assay is an alternative to existing PCR-based methods for detection of B. pseudomallei with a potentiality of early accurate diagnosis of melioidosis at point of care or in-field use.

Serological evidence of Burkholderia pseudomallei infection in U.S. Marines who trained in Australia from 2012-2014: a retrospective analysis of archived samples

Infection with the gram-negative bacterium Burkholderia pseudomallei can result in a life-threatening disease known as melioidosis. Historically, melioidosis was a common infection in military forces serving in Southeast Asia, and it has the potential to have a serious impact on force health readiness. With the U.S. Department of Defense's increasing strategic and operational focus across the Pacific Theater, melioidosis is an increasingly important issue from a force health protection perspective. U.S. Marines deploy annually to Darwin, Australia, a "hyperendemic" region for B. pseudomallei, to engage in training exercises. In an effort to assess the risk of B. pseudomallei infection to service personnel in Australia, 341 paired samples, representing pre- and post-deployment samples of Marines who trained in Australia, were analyzed for antibodies against B. pseudomallei antigens. Serological evidence of possible deployment-related infection with B. pseudomallei was found in 13 Marines. Future prospective studies are required to further characterize the risk to service members deployed to melioidosis endemic areas.

Disease progression in mice exposed to low-doses of aerosolized clinical isolates of Burkholderia pseudomallei

Mouse models have been essential to generate supporting data for the research of infectious diseases. Burkholderia pseudomallei, the etiological agent of melioidosis, has been studied using mouse models to investigate pathogenesis and efficacy of novel medical countermeasures to include both vaccines and therapeutics. Previous characterization of mouse models of melioidosis have demonstrated that BALB/c mice present with an acute infection, whereas C57BL/6 mice have shown a tendency to be more resistant to infection and may model chronic disease. In this study, either BALB/c or C57BL/6 mice were exposed to aerosolized human clinical isolates of B. pseudomallei. The bacterial strains included HBPUB10134a (virulent isolate from Thailand), MSHR5855 (virulent isolate from Australia), and 1106a (relatively attenuated isolate from Thailand). The LD₅₀ values were calculated and serial sample collections were performed in order to examine the bacterial burdens in tissues, histopathological features of disease, and the immune response mounted by the mice after exposure to aerosolized B. pseudomallei. These data will be important when utilizing these models for testing novel medical countermeasures. Additionally, by comparing highly virulent strains with attenuated isolates, we hope to better understand the complex disease pathogenesis associated with this bacterium.

Metabolomic Profiling of Plasma from Melioidosis Patients Using UHPLC-QTOF MS Reveals Novel Biomarkers for Diagnosis

To identify potential biomarkers for improving diagnosis of melioidosis, we compared plasma metabolome profiles of melioidosis patients compared to patients with other bacteremia and controls without active infection, using ultra-high-performance liquid chromatography-electrospray ionization-quadruple time-of-flight mass spectrometry. Principal component analysis (PCA) showed that the metabolomic profiles of melioidosis patients are distinguishable from bacteremia patients and controls. Using multivariate and univariate analysis, 12 significant metabolites from four lipid classes, acylcarnitine (n = 6), lysophosphatidylethanolamine (LysoPE) (n = 3), sphingomyelins (SM) (n = 2) and phosphatidylcholine (PC) (n = 1), with significantly higher levels in melioidosis patients than bacteremia patients and controls, were identified. Ten of the 12 metabolites showed area-under-receiver operating characteristic curve (AUC) >0.80 when compared both between melioidosis and bacteremia patients, and between melioidosis patients and controls. SM(d18:2/16:0) possessed the largest AUC when compared, both between melioidosis and bacteremia patients (AUC 0.998, sensitivity 100% and specificity 91.7%), and between melioidosis patients and controls (AUC 1.000, sensitivity 96.7% and specificity 100%). Our results indicate that metabolome profiling might serve as a promising approach for diagnosis of melioidosis using patient plasma, with SM(d18:2/16:0) representing a potential biomarker. Since the 12 metabolites were related to various pathways for energy and lipid metabolism, further studies may reveal their possible role in the pathogenesis and host response in melioidosis.

Burkholderia pseudomallei: Its Detection in Soil and Seroprevalence in Bangladesh

Background

Melioidosis, caused by Burkholderia pseudomallei, is an endemic disease in Bangladesh. No systematic study has yet been done to detect the environmental source of the organism and its true extent in Bangladesh. The present study attempted to isolate B. pseudomallei in soil samples and to determine its seroprevalence in several districts in Bangladesh.

Methodology and Results

Soil samples were collected from rural areas of four districts of Bangladesh from where culture confirmed melioidosis cases were detected earlier. Multiple soil samples, collected from 5–7 sampling points of 3–5 sites of each district, were cultured in Ashdown selective media. Suspected colonies of B. pseudomallei were identified by biochemical and serological test, and by polymerase chain reaction (PCR) using 16s rRNA specific primers. Blood samples were collected from 940 healthy individuals of four districts to determine anti- B. pseudomallei IgG antibody levels by indirect enzyme linked immunosorbent assay (ELISA) using sonicated crude antigen. Out of 179 soil samples, B. pseudomallei was isolated from two samples of Gazipur district which is located 58 km north of capital Dhaka city. Both the isolates were phenotypically identical, arabinose negative and showed specific 550bp band in PCR. Out of 940 blood samples, anti- B. pseudomallei IgG antibody, higher than the cut-off value (>0.8), was detected in 21.5% individuals. Seropositivity rate was 22.6%-30.8% in three districts from where melioidosis cases were detected earlier, compared to 9.8% in a district where no melioidosis case was either detected or reported (p<0.01). Seropositivity increased with the advancement of age from 5.3% to 30.4% among individuals aged 1–10 years and > 50 years respectively. The seropositivity rates were 26.0% and 20.6% in male and female respectively, while it was 20–27% among different occupational groups. No significant association was observed with gender (χ2 = 3.441, p = 0.064) or any occupational group (χ² = 3.835, p = 0.280).

Conclusion

This is the first study demonstrating the presence of B. pseudomallei in the environmental (soil) samples of Bangladesh. It also suggested that a large proportion of people, residing in these districts, were exposed to the organism.

Melioidosis, caused by B. pseudomallei, can be a fatal disease if not treated with appropriate antibiotics. The organism is mainly present in soil and water in endemic areas, and people become infected through skin inoculation, inhalation or ingestion. The disease has been sporadically detected in Bangladesh over last several decades. However, its actual prevalence in Bangladesh is largely unknown due to the lack of systematic study and awareness of the medical community about the disease and the organism. In order to address the issue, we have undertaken this study to assess the presence of the organism in the soil as well as its magnitude of exposure among the people of selected areas of the country. The study revealed the presence of B. pseudomallei in the soil and its exposure among the people of different areas. The information would increase the awareness of the medical community for prevention and correct diagnosis of the disease.

Diabetes-independent increase of factor VII-activating protease activation in patients with Gram-negative sepsis (melioidosis)

BACKGROUND

The plasma protease factor VII-activating protease (FSAP) can release nucleosomes from late apoptotic cells. Nucleosomes are markers of cell death, and extracellular cell-free DNA has been suggested to play an important role in inflammation and has been demonstrated to correlate with severity and outcome in sepsis patients.

OBJECTIVE

To investigate FSAP activation in patients suffering from Burkholderia pseudomallei infection (melioidosis), an important cause of Gram-negative sepsis in Southeast Asia. As diabetes mellitus (DM) is the most important risk factor for both melioidosis and sepsis, we were also able to examine the role of DM in FSAP activation in this cohort of patients.

METHODS

In a prospective observational study, complexes of FSAP with α2 -antiplasmin (AP) were assayed in 44 patients with melioidosis, 34 of whom were classified as diabetic. Eighty-two healthy subjects served as controls (52 with DM and 30 without).

RESULTS

FSAP-AP complex levels were markedly elevated in patients as compared with controls. The FSAP level increased by 16.82 AU mL(-1) in patients with melioidosis after adjustment for the effect of DM in the regression model. As expected, FSAP activation was correlated with nucleosome release (slope = 0.74). No difference in FSAP activation on admission was seen between survivors and non-survivors, but the extent of FSAP activation correlated with stage of the disease; repeated testing during convalescence showed a return towards normal values (day 0 vs. day 28, 4.16 AU mL(-1) , 95% confidence interval [CI] 1.42-12.22).

CONCLUSION

Patients with Gram-negative sepsis caused by B. pseudomallei have abundant FSAP activation, which significantly correlates with stage of disease. The presence of DM, however, does not influence the extent of FSAP activation.

Use of a safe, reproducible, and rapid aerosol delivery method to study infection by Burkholderia pseudomallei and Burkholderia mallei in mice

Burkholderia pseudomallei, the etiologic agent of melioidosis, is a saprophytic bacterium readily isolated from wet soils of countries bordering the equator. Burkholderia mallei is a host-adapted clone of B. pseudomallei that does not persist outside of its equine reservoir and causes the zoonosis glanders, which is endemic in Asia, Africa, the Middle East and South America. Infection by these organisms typically occurs via percutaneous inoculation or inhalation of aerosols, and the most common manifestation is severe pneumonia leading to fatal bacteremia. Glanders and melioidosis are difficult to diagnose and require prolonged antibiotic therapy with low success rates. There are no vaccines available to protect against either Burkholderia species, and there is concern regarding their use as biological warfare agents given that B. mallei has previously been utilized in this manner. Hence, experiments were performed to establish a mouse model of aerosol infection to study the organisms and develop countermeasures. Using a hand-held aerosolizer, BALB/c mice were inoculated intratracheally with strains B. pseudomallei 1026b and B. mallei ATCC23344 and growth of the agents in the lungs, as well as dissemination to the spleen, were examined. Mice infected with 10², 10³ and 10⁴ organisms were unable to control growth of B. mallei in the lungs and bacteria rapidly disseminated to the spleen. Though similar results were observed in mice inoculated with 10³ and 10⁴B. pseudomallei cells, animals infected with 10² organisms controlled bacterial replication in the lungs, dissemination to the spleen, and the extent of bacteremia. Analysis of sera from mice surviving acute infection revealed that animals produced antibodies against antigens known to be targets of the immune response in humans. Taken together, these data show that small volume aerosol inoculation of mice results in acute disease, dose-dependent chronic infection, and immune responses that correlate with those seen in human infections.

Endogenous protein C has a protective role during Gram-negative pneumosepsis (melioidosis)

BACKGROUND

Activated protein C (APC) exerts anticoagulant effects via inactivation of factors Va and VIIIa and cytoprotective effects via protease activated receptor (PAR)1. Inhibition of endogenous APC in endotoxemia and sepsis results in exacerbation of coagulation and inflammation, with consequent enhanced lethality.

OBJECTIVES

We here sought to dissect the distinct roles of the anticoagulant and cytoprotective functions of endogenous APC in severe Gram-negative pneumonia-derived sepsis (melioidosis).

METHODS

We infected wild-type (WT) mice with Burkholderia pseudomallei, a common sepsis pathogen in southeast Asia, and treated them with antibodies inhibiting both the anticoagulant and cytoprotective functions of APC (MPC1609) or the anticoagulant functions of APC (MAPC1591) only. Additionally, we administered SEW2871 (stimulating the S1P1-pathway downstream from PAR1) to control and MPC1609-treated mice.

RESULTS

MPC1609, but not MAPC1591, significantly worsened survival, increased coagulation activation, facilitated bacterial growth and dissemination and enhanced the inflammatory response. The effects of MPC1609 could not be reversed by SEW2871, suggesting that S1P1 does not play a major role in this model.

CONCLUSIONS

These results suggest that the mere inhibition of the anticoagulant function of APC does not interfere with its protective role during Gram-negative pneumosepsis, suggesting a more prominent role for cytoprotective effects of APC .

Host responses to melioidosis and tuberculosis are both dominated by interferon-mediated signaling

Melioidosis (Burkholderia pseudomallei infection) is a common cause of community-acquired sepsis in Northeast Thailand and northern Australia. B. pseudomallei is a soil saprophyte endemic to Southeast Asia and northern Australia. The clinical presentation of melioidosis may mimic tuberculosis (both cause chronic suppurative lesions unresponsive to conventional antibiotics and both commonly affect the lungs). The two diseases have overlapping risk profiles (e.g., diabetes, corticosteroid use), and both B. pseudomallei and Mycobacterium tuberculosis are intracellular pathogens. There are however important differences: the majority of melioidosis cases are acute, not chronic, and present with severe sepsis and a mortality rate that approaches 50% despite appropriate antimicrobial therapy. By contrast, tuberculosis is characteristically a chronic illness with mortality <2% with appropriate antimicrobial chemotherapy. We examined the gene expression profiles of total peripheral leukocytes in two cohorts of patients, one with acute melioidosis (30 patients and 30 controls) and another with tuberculosis (20 patients and 24 controls). Interferon-mediated responses dominate the host response to both infections, and both type 1 and type 2 interferon responses are important. An 86-gene signature previously thought to be specific for tuberculosis is also found in melioidosis. We conclude that the host responses to melioidosis and to tuberculosis are similar: both are dominated by interferon-signalling pathways and this similarity means gene expression signatures from whole blood do not distinguish between these two diseases.

Surface plasmon resonance immunosensor for rapid and specific diagnosis of melioidosis antibody

Melioidosis, caused by Burkholderia pseudomallei, is a potentially fatal disease, which requires an accurate and rapid diagnosis. This paper reports on the highly sensitive and specific detection of melioidosis antibodies by surface plasmon resonance immunosensor. The sensing surface was immobilized with B. pseudomallei BipD protein via a 11-mercaptoundecanoic acid self-assembled monolayer. Under optimum conditions individual sera of melioidosis patients, non-melioidosis patients (negative) and blood donors (control) were analyzed at a dilution of 1:6,000 in 10 mM phosphate buffered saline pH 7.50. The cut-off value determined from the mean +/- 2SD of 20 control and 20 negative sera was 3.3 m degrees. At this cut-off both sensitivity and specificity were 100%. The system required only a short analysis (20 minutes) and regeneration time (12 minutes). In addition, one immobilization of the sensing surface could be reused more than 30 times. The advantages of the proposed method are savings in both time and cost of analysis, while at the same time providing excellent sensitivity and specificity.

Mycotic aneurysm caused by burkholderia pseudomallei with negative blood cultures

We describe a case of bacterial aortitis caused by Burkholderia pseudomallei. This patient presented with prolonged fever and hoarseness of voice. Aneurysm removal with Dacron graft replacement was performed, followed by a prolonged course of antibiotics. The patient has progressed satisfactorily without recurrence of symptoms. Previous case reports are summarized.

Lack of correlation of Burkholderia pseudomallei quantities in blood, urine, sputum and pus

We evaluated the correlation of Burkholderia pseudomallei quantities in blood versus urine, sputum or pus. Correlations between bacterial counts in blood and other samples were not found. It is likely that an initial seeding event to extracellular organs is followed by independent growth of B. pseudomallei, and that bacteria in the urine were not passively filtered from the bloodstream.

Comparison of serum F2 isoprostane levels in diabetic patients and diabetic patients infected with Burkholderia pseudomallei

INTRODUCTION

Oxidative stress can occur in sepsis and infection, when overproduction of free radicals is not countered by the host antioxidant system, leading to impairment of host cellular functions. Various disease states are accompanied by the accumulation of 15-F2t-IsoP in biological fluids. These isoprostanes are considered as markers of oxidative stress, and inflammation and inflammatory mediators.

METHODS

We measured total serum 15-F2t-IsoP levels by the immunoassay method in healthy adults, otherwise healthy patients with diabetes mellitus and diabetic patients infected with Burkholderia pseudomallei (B. pseudomallei).

RESULTS

The highest mean value of 4,343.6 pg/ml of 15-F2t-IsoP was found in the diabetic melioidosis patients in comparison with the uninfected diabetic patients and the normal controls. Uninfected diabetic patients had significantly higher levels than the control subjects (p-value is less than 0.001), but lower than the diabetic-melioidosis patients (p-value is less than 0.001). The main finding of the present study was an eight-times higher median circulating total IsoPs levels in diabetic patients infected with B. pseudomallei when compared with the levels in control subjects.

CONCLUSION

The oxidative stress theory proposes that severe sepsis leads to activation of neutrophils and macrophages which subsequently release reactive oxygen-free radicals that may result in lipid peroxidation of endothelial and epithelial cell membrane phospholipids. This chain reaction results in increased levels of isoprostanes, which are thought to contribute to much of the end-stage tissue damage seen in serious infections, such as melioidosis. We believe that this is the first report linking in vivo oxidative stress status and diabetic patients infected with B. pseudomallei.

Activation of coagulation with concurrent impairment of anticoagulant mechanisms correlates with a poor outcome in severe melioidosis

BACKGROUND

Melioidosis, which is caused by infection with the Gram-negative bacterium Burkholderia pseudomallei, is an important cause of sepsis in South-East Asia with a mortality of up to 40%. Knowledge of the involvement of coagulation and fibrinolysis in the pathogenesis of melioidosis is highly limited.

OBJECTIVE

To define the involvement of the coagulation and fibrinolytic systems in patients with severe melioidosis.

METHODS

Parameters of coagulation and fibrinolysis were measured in 34 patients with culture proven septic melioidosis and 32 healthy controls.

RESULTS

Patients demonstrated strong activation of the coagulation system, as reflected by high plasma levels of soluble tissue factor, the prothrombin fragment F(1+2) and thrombin-antithrombin complexes (TATc), and consumption of coagulation factors resulting in a prolonged prothrombin time and activated partial thromboplastin time. Concurrently, anticoagulant pathways were downregulated in patients: protein C, protein S, and antithrombin levels were all decreased when compared to controls. Patients also demonstrated evidence of activation and inhibition of fibrinolysis, as reflected by elevated concentrations of tissue-type plasminogen activator (tPA), plasminogen activator inhibitor type 1, plasmin-alpha2-antiplasmin complexes (PAPc) and D-dimer. High TATc/PAPc ratios in patients pointed to a predominance of the prothrombotic pathway in melioidosis. Furthermore, soluble thrombomodulin levels were increased. The extent of coagulation activation correlated with mortality; patients who went on to die had higher TATc, F(1+2), tPA and PAPc and lower protein C and antithrombin levels on admission than patients who survived.

CONCLUSIONS

The coagulation system is strongly activated during melioidosis. A high degree of activation of the coagulation system is an indicator of poor outcome in patients with melioidosis.

Quantitation of B. Pseudomallei in clinical samples

We undertook a prospective study to quantitate Burkholderia pseudomallei in blood, urine, respiratory secretions, and pus [corrected] obtained from 414 patients with melioidosis. The median was count 1.1, 1.5 x 10(4), 1.1 x 10(5), and 1.1 x 10(7) CFU/mL in these sample types, respectively. This provides important insights into the likely feasibility of future studies such as expression microarray analysis using clinical material.

[Adequate selection of antigens for serologic diagnostics of experimental melioidosis]

Sera of Burkholderia pseudomallei-infected golden hamsters, white mice, guinea pigs and white rats were studied. Immunochemical analysis revealed presence of antibodies against antigens 2, 3, 6, d, and g with significant predominance of antibodies to antigens 6 and d. Antigen d was detected irrespectively to strain used for experimental infection and experimental animal species. Antibodies to antigen 6 were detected only when strains belonging to Asian serovar, but not to Australian serovar, were used. On the basis of antigens 6 and d following methods of serologic diagnostics were developed: reaction of indirect hemagglutination, reaction of latex agglutination, and radioimmunological assay. Their sensitivity and specificity reached 100% during experimental melioidosis in golden hamsters, guinea pigs and white rats.

Attempted passive prophylaxis with a monoclonal anti-Burkholderia pseudomallei exopolysaccharide antibody in a murine model of melioidosis

Melioidosis is a severe gram-negative infection caused by the facultative intracellular bacterium Burkholderia pseudomallei, which is responsible for a broad spectrum of symptoms in both humans and animals. No licensed vaccine currently exists. This study evaluated the protective effect of a monoclonal antibody (Mab Ps6F6) specific to B. pseudomallei exopolysaccharide in an outbred murine model of sub-acute melioidosis. When administered before the infectious challenge, Ps6F6 significantly increased resistance to infection and restrained bacterial burden in the spleen over a 30-days period. Patterns of IFN-gamma production were similar in the treated and non treated groups of mice. However, Ps6F6 lowered IFN-gamma levels over the duration of the assay period, except on day 1, suggesting a transient and rapid production of IFN-gamma under Ps6F6 control. Minor but persisting increases occurred in IL-12 levels while TNF-alpha was detected only in the controls at the later stages of infection. No IL-10 secretion was detected in both groups of mice. These data suggest that passive prophylaxis with Mab Ps6F6 provide a moderate and transient induction of inflammatory responses in infected mice but failed to trigger a sterilizing protective immunity.

Short report: application of a polymerase chain reaction to detect Burkholderia pseudomallei in clinical specimens from patients with suspected melioidosis

The diagnostic potential of a Burkholderia pseudomallei type three secretion system (TTS1) polymerase chain reaction (PCR) was examined on clinical specimens from 27 patients with sepsis in the Northern Territory of Australia, a region endemic for melioidosis. The TTS1 PCR was conducted on DNA extracted from a range of clinical specimens (blood, sputum, urine, joint, pericardial and pleural fluid, and swabs from skin lesions, throat, nose, and rectum). The PCR sensitivity in culture-positive clinical specimens from the nine confirmed patients with melioidosis was 65% and the specificity was 100%, with no PCR-positive results in specimens from 18 patients without melioidosis. The PCR based on the B. pseudomallei TTS1 has the potential to substantially improve the timeliness of diagnosis of melioidosis.

Short report: disease severity and outcome of melioidosis in HIV coinfected individuals

This study examined whether coinfection with HIV and Burkholderia pseudomallei leads to altered disease severity or outcome associated with melioidosis. Coinfection was detected in only 8 of 524 (1.5%) adults with melioidosis in northeast Thailand. Clinical presentation and acute outcome were similar in HIV-positive and HIV-negative patients.

Time-kill curves as a tool for targeting ceftazidime serum concentration during continuous infusion for treatment of septicaemic melioidosis

Melioidosis is a fatal community-acquired infection endemic in tropical areas. Ten isolates of the causative microorganism were subjected to time-kill study using a range of ceftazidime concentrations. This study demonstrated that a ceftazidime concentration of eight times the minimum inhibitory concentration yielded an optimal bactericidal effect and should be the target concentration administered by continuous infusion.

[Some properties of plasmocoagulase of the causative agents of glanders and melioidosis]

Criteria for the evaluation of the plasmocoagulase activity of natural isolates and mutant strains of the causative agents of glanders and melioidosis were worked out, which made it possible to subdivide them by this sign into pathogens with high, moderate and low activity. Plasmocoagulase produced by pathogenic Burkholderia was shown to be a thermolabile enzyme, comparatively stable with respect to the action of such chemico-biological agents as hydrogen peroxide and chloramine.

Relative uptake of technetium 99m stannous colloid by neutrophils and monocytes is altered by gram-negative infection

Gram-negative infection alters phagocytic cell function; hence, it could affect phagocytic uptake of inorganic colloids by these cells. Neutrophil and monocyte uptake of technetium 99m stannous colloid (99mTc SnC) in whole blood was measured in 10 patients with gram-negative infection (Burkholderia pseudomallei) and 7 controls. Mean uptake per individual neutrophil was reduced in infection. Uptake per monocyte was not significantly different. Blood from six normal individuals was incubated with lysed B. pseudomallei and colloid, which showed reduced neutrophil uptake, but increased monocyte uptake. These results indicate that uptake of 99mTc SnC stannous colloid can be used to measure alteration in phagocytic cell function. They suggest that infection with B. pseudomallei is associated with reduced phagocytosis by individual neutrophils, possibly through toxic effects of bacterial products. This could have immunopathogenic consequences for this gram-negative infection and may explain why it responds to granulocyte colony-stimulating factor.

Pulmonary melioidosis presenting with right paratracheal mass

A rare case of pulmonary melioidosis is reported. The patient was a 62-year-old man presenting with subacute fever, dry cough, and significant weight loss. A chest x-ray revealed a right paratracheal mass. The findings from fiberoptic bronchoscopy were a blunt carina and normal tracheobronchial tree. The patient had an underlying disease of poorly controlled diabetes mellitus, heavy smoking, and heavy alcoholic drinking. One of the two cultured blood specimens grew B. pseudomallei. The pathological finding of transbronchial biopsy at the apical segment of the right upper lung showed lymphocytic infiltrates. He was treated with two weeks of intravenous ceftazidime plus cotrimoxazole followed by 5 months of oral doxycycline plus cotrimoxazole. Clinical symptoms significantly improved and the right paratracheal mass disappeared.

C-reactive protein in the diagnosis of melioidosis

Previous work suggested that C-reactive protein (CRP) may be a useful test in the diagnosis of melioidosis, the infection caused by Burkholderia pseudomallei. We reviewed patients with culture-confirmed melioidosis to define the role of this inflammatory marker in the diagnosis of melioidosis. In 175 patients, we found that the admission CRP level may be normal or only mildly elevated, including patients with severe sepsis, fatal cases, and in relapsed melioidosis. In a multivariate analysis, sepsis and bacteremia were more strongly associated with mortality than CRP. Admission levels of CRP are not a sensitive marker for the presence of melioidosis and a normal level cannot be used to exclude acute, chronic, or relapsed melioidosis in febrile patients in or from endemic regions.

A comparison of antibiotic regimens in the treatment of acute melioidosis in a mouse model

Melioidosis is caused by the Gram-negative bacillus Burkholderia pseudomallei. Most clinical reports of disease are from south-east Asia and northern Australia. The organism is intrinsically resistant to most commonly available antibiotics. Standard therapy includes ceftazidime either alone or in combination with co-trimoxazole. The clinical advantage in adding co-trimoxazole has never been determined; nor has the activity of newer, fourth-generation cephalosporins, such as cefepime, been studied in the treatment of this condition. BALB/c mice have been shown to represent an animal model of melioidosis. This animal model was used in this study to compare the efficacy of ceftazidime and cefepime alone or with co-trimoxazole, in the therapy of melioidosis. Antibiotic levels in the mice were determined by HPLC, and dosing was modified to keep plasma antibiotic levels at or above the MIC for the organism-antibiotic combination for a significant part of a 12 h period. Bacterial load, as determined by splenic counts, showed that ceftazidime in combination with co-trimoxazole was the most effective therapeutic option. The animal model described in this study can be used as a preliminary evaluation of therapeutic options for melioidosis.

Seroprevalence of melioidosis in dairy cattle in Chiang Mai Province, northern Thailand

The seroprevalence of melioidosis in dairy cattle in Chiang Mai Province was investigated using of the indirect hemagglutination antibody (IHA) method. Two hundred and fifty-three samples were tested for serum antibodies to Burkholderia pseudomallei. The samples were from a total population of 8,688 dairy cattle in the province; random sampling, stratified by the location of cattle, was used. The seroprevalence was determined as 2% at 1:40 cut-off value, which was estimated to equate to 0.3% to 3.7% (95% CI). This report of relatively low disease prevalence in the animal population corresponds to other prevalence studies of the agent in the environment and the human population in the region. The prevalence is markedly different to that reported from northeastern Thailand, where the disease is highly endemic.

Demonstration of a cell-mediated immune response in melioidosis

Melioidosis is a bacterial infection caused by Burkholderia pseudomallei. The aim of this study was to determine whether a cell-mediated adaptive immune response against B. pseudomallei developed in patients who had recovered from melioidosis. Lymphocyte proliferation assays were done on peripheral blood mononuclear cells from patients (n=13) and control subjects (n=10) to determine the lymphocyte response to B. pseudomallei antigens. Production of interferon-gamma and interleukin-10 was also determined. Activation of T cell subsets was assessed by fluorescence-activated cell sorter analysis, using antibodies to CD4, CD8, and CD69 antigens. Lymphocyte proliferation and interferon-gamma production in response to B. pseudomallei antigens were significantly higher (P<.001 for both) in patients than in control subjects. There was also an increase in the percentage of activated CD4+ (P<.004) and activated CD8+ T cells (P<.035) in cell cultures from patients. The development of such a cell-mediated immune response in patients may be essential for their survival.

Model of differential susceptibility to mucosal Burkholderia pseudomallei infection

Burkholderia pseudomallei is the causative agent of melioidosis, an infectious disease with protean clinical manifestations. The major route of infection is thought to be through subcutaneous inoculation of contaminated soil and water, although ingestion and inhalation of contaminated aerosols are also possible. This study examines infection through the intranasal route in a murine model to mimic infection through inhalation. Two strains of mice, C57BL/6 and BALB/c, exhibit differential susceptibilities to the infection, with the C57BL/6 mice being considerably more resistant. To examine host factors that could contribute to this difference, bacterial loads and cytokine profiles in the two strains of mice were compared. We found that infected BALB/c mice exhibited higher bacterial loads in the lung and spleen and that they produced significantly higher levels of gamma interferon (IFN-gamma) in the serum than C57BL/6 mice. Although tumor necrosis factor alpha and interleukin-1 could be detected in the nasal washes and sera of both strains of mice, the production in serum was transient and much lower than that of IFN-gamma. C57BL/6 mice also exhibited memory responses to bacteria upon reinfection, with the production of serum immunoglobulin G (IgG) and mucosal IgA antibodies. Thus, it is possible that the production of systemic and mucosal antibodies is important for protection against disease in C57BL/6 mice.

groEL encodes a highly antigenic protein in Burkholderia pseudomallei

No recombinant protein is available for serodiagnosis of melioidosis. In this study, we report the cloning of the groEL gene, which encodes an immunogenic protein of Burkholderia pseudomallei. Bidirectional DNA sequencing of groEL revealed that the gene contained a single open reading frame encoding 546 amino acid residues with a predicted molecular mass of 57.1 kDa. Basic Local Alignment Search Tool analysis showed that the putative protein encoded by groEL is homologous to the chaperonins encoded by the groEL genes of other bacteria. It has 98% amino acid identity with the GroEL of Burkholderia cepacia, 98% amino acid identity with the GroEL of Burkholderia vietnamiensis, and 82% amino acid identity with the GroEL of Bordetella pertussis. Furthermore, it was observed that patients with melioidosis develop a strong antibody response against GroEL, suggesting that the recombinant protein and its monoclonal antibody may be useful for serodiagnosis in patients with melioidosis and that the protein may represent a good cell surface target for host humoral immunity. Further studies in these directions would be warranted.

Retrospective study on the diagnostic value of IgG ELISA, dot immunoassay and indirect hemagglutination in septicemic melioidosis

Three serological methods for diagnosis of melioidosis were compared with the culture method currently used as the "gold standard". The diagnostic values of the serological methods were evaluated retrospectively in 306 patients residing in an endemic area. The enzyme-linked immunosorbent assay (ELISA), using affinity purified antigen for detecting specific IgG antibody, showed a slightly higher specificity (86.0%) than the dot immunoassay (DOT) (84.0%) and both were superior to indirect hemagglutination (IHA) (72.0%). The sensitivity of DOT (96.4%) and ELISA (85.7%) were considerably higher than that of IHA (50.0%). The primary benefit of the high negative predictive value of both ELISA (96.4%) and DOT (99.0%) in an area of high prevalence is the ability to rule out most of the non-melioidosis patients.

Burkholderia pseudomallei-specific recombinant protein and its potential in the diagnosis of melioidosis

Melioidosis is an important public health problem in Southeast Asia and Northern Australia. This disease is caused by the gram-negative bacilli, Burkholderia pseudomallei. Wide spectra of clinical manifestations are observed in melioidosis ranging from asymptomatic to septicemic infection. Although serodiagnostic methods of melioidosis have been improved significantly in recent years, a highly specific diagnostic test that can differentiate asymptomatic seropositive individuals and melioidosis patients remains to be the subject of current investigations. In this study, a B. pseudomallei-specific gene, pBps-1, expressing a novel 18.7 kDa recombinant protein was selected from genomic libraries of two B. pseudomallei virulent isolates by using pooled sera from septicemic melioidosis patients. Nucleotide sequence analysis demonstrated that this gene is unique and does not show substantial similarity with any known genes in the Genbank database. The Bps-1 recombinant protein was evaluated for its potential in serodiagnosis of melioidosis by Western blot analysis. A high degree of specificity was demonstrated using sera from healthy individuals in the endemic (98.5%) and non-endemic areas (100%), with moderate sensitivity (69.7%) in melioidosis patients. The study demonstrated that this approach can be used to obtain highly specific recombinant antigens such as that described in the present report. A combination of such antigens should provide materials for successful serodiagnosis of melioidosis in the endemic areas.

Comparison of the polymerase chain reaction and serologic tests for diagnosis of septicemic melioidosis

For diagnosis of melioidosis, we compared polymerase chain reaction (PCR)-based DNA detection and three serologic methods with the culture method currently used as gold standard. The diagnostic values of the serologic methods were evaluated in 130 patients. All these patients resided in an endemic area. An enzyme-linked immunosorbent assay (ELISA) gave slightly higher specificity (86.2%) than a dot immunoassay (DOT) (85.3%), but was superior to an indirect hemagglutination assay (IHA) (79.8%). The sensitivities of the DOT (85.7%) and ELISA (71.4%) were considerably higher than that of IHA (61.9%). However, the PCR was the most sensitive (95.2%) and specific (91.7%). Nevertheless, DOT and ELISA are more practical for local hospitals. With the high negative predictive value of both the ELISA (94.0%) and DOT (96.9%) in a high prevalence area, clearly these methods can rule out most of the non-melioidosis patients.

Use of multiplex PCR patterns as genetic markers for Burkholderia pseudomallei

A simple PCR-based typing method was developed to differentiate between strains of Burkholderia pseudomallei. Two pairs of primers, based on sequences from two specific DNA probes, were used to amplify the bacterial DNA by multiplex PCR. We evaluated the PCR method for epidemiological typing of B. pseudomallei and compared this with restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) methods. In RFLP, the DNA of B. pseudomallei was digested with HindIII and the pKKU-S23L was used as a probe while 5' GTTTCGCTCC 3' primer was used in RAPD. DNA was obtained from 37 B. pseudomallei environmental and clinical isolates from humans or animals. These isolates were also classified by their ability to assimilate L-arabinose. A total of 21 type patterns were identified by multiplex PCR. Among human and animal isolates, multiplex PCR revealed ten types, all of which were arabinose negative (Ara-), whereas six of the 11 types of environmental isolates were Ara-. There are two environmental patterns that also were found in clinical isolates. The RFLP technique showed 12 different types in the 37 isolates, and three of these contained both Ara+ and Ara- isolates. The RAPD technique revealed 33 different types in the 37 isolates. Multiplex PCR, therefore, is the genetic marker that best correlates with the ability of the organism to assimilate L-arabinose. Moreover, two types (M4, M15) correlated with disseminated septicemic melioidosis in the northeast Thailand. If a greater number of isolates are tested, the multiplex PCR technique may prove to be useful for rapid epidemiological typing of B. pseudomallei.

Diagnostic and prognostic value of an immunofluorescent assay for melioidosis

Melioidosis caused by Burkholderia pseudomallei is endemic in southeast Asia. The clinical manifestations range from wound infections to acute septicemia. In some cases, recurrence can also occur following complete recovery. Case fatality rates are high and a major factor is the delay in the culture and identification of the bacterium. An immunofluorescent assay (IFAT) using whole-cell antigen for the detection of total antibodies to B. pseudomallei was tested with 650 sera. Using a cut-off value of 1:80, 66 sera from culture-confirmed cases were positive with titers > or = 320. In another 523 sera from patients in which no other etiology could be found, 149 (23.4%) were positive. To monitor disease activity, persistence of antibody levels was investigated on 61 serial sera samples collected from 14 other confirmed cases on follow-up visits while on oral maintenance therapy. The IFAT demonstrated a reduction in titers in cases of localized infections, suggesting that either the infection was being resolved or arrested while septicemic patients maintained high IFAT titers on follow-up, suggesting the possibility of continuous sequestration of antigen from an intracellular source.

Pseudomonas (Burkholderia) pseudomallei in Thailand, 1964-1967: geographic distribution of the organism, attempts to identify cases of active infection, and presence of antibody in representative sera

The purpose of this study, initiated in 1964 and concluded in 1967, was to define the distribution of Pseudomonas (now Burkholderia) pseudomallei in Thailand, to evaluate its importance as an etiologic agent, and to survey the presence of antibody in people that might indicate prior infection and/or contact with the microorganism.

Short report: evaluation of a monoclonal antibody-based latex agglutination test for rapid diagnosis of septicemic melioidosis

A monoclonal antibody (MAb)-based latex agglutination (MAb-LA) test was developed to rapidly identify Burkholderia pseudomallei in hemoculture of patients with septicemic melioidosis. The method was evaluated in a clinical situation on 396 hemocultures positive for bacterial growth, of which 75 cultures were positive for B. pseudomallei by conventional biochemical tests. The sensitivity and specificity of the MAb-LA test were 95% and 100%, respectively. The positive and negative predictive values were 100% and 99%. The method is highly reliable and suitable for rapid diagnosis of septicemic melioidosis, reducing the time normally required from a minimum of 3-4 days by conventional methods to less than 30 hr. Most of these 30 hr are involved in growing up enough bacteria to perform the MAb-LA test, which itself takes only 1 min.

Detection of Burkholderia pseudomallei in blood samples using polymerase chain reaction

A highly sensitive, specific, rapid and simple method to detect Burkholderia pseudomallei in blood samples was developed. Two 22-base oligonucleotide primers, based on sequences from a specific DNA probe, were used for amplification of bacterial DNA by the polymerase chain reaction (PCR). Amplification with these primers yielded a 178-base pair product in 100 clinical isolates of B. pseudomallei. As little as 0.5 fg of B. pseudomallei DNA was detectable by this method. Experiments involving inoculation of the organism into uninfected blood samples showed that the method could be used to detect as few as 1 bacterial cell ml-1 of whole blood. Non-specific amplification of other bacterial DNAs from 18 samples of bacteria was not observed. Blood samples from seven patients proven to have melioidosis by haemoculture were positive using these primers. The total time required for sample processing, amplification and visualization was approximately 3.5 h. The high sensitivity, rapidity and simplicity of this method should make it valuable for diagnosis, monitoring of drug treatment and for epidemiological studies of the melioidosis.

Burkholderia pseudomallei activates complement and is ingested but not killed by polymorphonuclear leukocytes

The mechanism by which Burkholderia pseudomallei is resistant to lysis by human serum is unknown but may include interference with complement activation, effective opsonization, or complement-mediated lysis. We investigated the interaction of B. pseudomallei with complement in the presence and absence of specific antibody to determine potential mechanisms of serum resistance. We demonstrated rapid activation and consumption of complement by B. pseudomallei which, in the absence of specific antibody, occurred predominantly via the alternative pathway. Complement activation was associated with deposition of the opsonically active C3b and iC3b fragments on the bacterial surface. C5b-9, detected on the bacterial surface after opsonic periods of 1 to 60 min, was susceptible to elution by 1 M NaCl, indicating that resistance to complement-mediated lysis may result from deposition of the membrane attack complex in a nonmicrobicidal location. To define the role of opsonins, we investigated the ability of polymorphonuclear leukocytes (PMNL) to phagocytose B. pseudomallei. Phagocytosis of bacteria by PMNL, and the observed oxidative response, was significantly increased by opsonization of organisms with complement and/or specific antibody. Despite opsonophagocytosis by PMNL and the production of an oxidative response, no significant bacterial killing was observed.

Experimental melioidosis in hens

Experimental intramuscular infection of hens with Pseudomonas pseudomallei, strain 2796 (1 x 10(9) CFU from a 24-h culture) was reproduced. Clinical, paraclinical and pathomorphological findings were followed from 1 to 30 days after challenge. Haemagglutinin titre, bacterial dissemination in the viscera, number of leucocytes, alveolar (aMa) and peritoneal (pMa) macrophages and their phagocytic activity in vitro were studied. During the course of infection a leucocytosis as well as an increased haemagglutinin titre (1:256) were established. The number of bacteria per gram tissue in the spleen and liver was highest at 1 day post-infection (p.i.). Melioidose bacteria from egg yolk were isolated at 15 and 30 days p.i. Leucocyte and pMa phagocytic activity was maximal at 3 days p.i. unlike the activity of aMa which increased gradually until the end of the study. Inflammatory-necrotic changes were found in the viscera and brain at 3 and 15 days p.i. The investigation of experimental melioidosis infection in hens showed that they are susceptible to P. pseudomallei and this disease takes a generalized subacute course.

Serodiagnosis of melioidosis in Malaysia

Current diagnosis of melioidosis is based on bacterial culture and/or serology which is becoming increasingly useful. An IgM-ELISA using heat-killed whole cells of Pseudomonas pseudomallei was developed and compared with an indirect haemagglutination technique (IHAT) and an indirect immunofluorescent technique(IFAT). The IgM-ELISA using a P:N ratio of > or = 2 had a sensitivity of 91% and a specificity of 96%. All 3 assays were further used in a seroepidemiological survey amongst different groups of patients and healthy individuals. It was found that the IFAT performed better than the IHAT, detecting antibodies to P. pseudomallei in 6% of diabetics, 5% of pyrexics, 8% of pregnant women and 3% of farmers. For the same groups the IgM-ELISA detected antibodies in 1% of pyrexics, 8% of pregnant women and a further 14% of farmers. The IgM-ELISA was found to be sensitive and useful for the serological diagnosis of acute melioidosis.

Elevated serum procalcitonin levels in patients with melioidosis

The prognostic value of serum procalcitonin levels in 43 patients with acute melioidosis, an infection with a wide range of clinical manifestations, was assessed. In eight patients with mild localized infections, the median procalcitonin levels were 0.13 ng/mL (range, 0.02-0.46 ng/mL), which were similar to those in 19 healthy controls (median, 0.07 ng/mL; range, 0.03-0.15 ng/mL). In the patients with severe infections, the initial procalcitonin levels were significantly higher in the patients who died (median, 350 ng/mL; range, 63-3,538 ng/mL) than in the survivors (median, 19 ng/mL; range, 0.55-387 ng/mL) (P < .0001); 16 of 19 patients with procalcitonin levels of > 100 ng/mL died, compared with 2 of 16 patients with levels of < 100 ng/mL (relative risk, 6.7; 95% confidence interval, 1.8-25; P = .0001). In those patients who survived, the subsequent procalcitonin levels reflected closely the clinical course of their infection. The serum concentration of procalcitonin correlates well with the severity of Pseudomonas pseudomallei infection and is comparable with other acute-phase markers. However, this prognostic indicator and marker of continuing disease activity is not specific to melioidosis and could be applied to other severe infections.

The 1990-1991 outbreak of melioidosis in the Northern Territory of Australia: clinical aspects

From November 1990 to June 1991, 33 cases of acute melioidosis were diagnosed in tropical Northern Territory, Australia during an exceptionally wet monsoon. Eighteen (55%) were alcoholic, 16 (48%) diabetic and only 4 (12%, all survivors) had no risk factors. Twenty-seven (82%) were considered recent infection, with an incubation period of 3-21 days (mean 14) documented in eight cases with presumed cutaneous inoculation. Fourteen patients presented with pneumonia (4 septicemic) and of 11 others with septicemia 4 had genitourinary foci. Three of 4 with splenic abscesses required splenectomy. Three had only skin/soft tissue infection. One patient with brainstem encephalitis needed prolonged ventilation. Overall mortality was 36% (12 cases, including three relapses), despite therapy with ceftazidime and intensive care facilities. Pseudomonas pseudomallei is the commonest diagnosed cause of fatal bacteremic pneumonia at Royal Darwin Hospital and emphasis is placed on early appropriate antibiotic therapy and compliance with maintenance therapy for at least three months.

Melioidosis and safety in the clinical laboratory

Human infection with Pseudomonas pseudomallei, the causative agent of melioidosis, typically produces subclinical disease and an asymptomatic carrier state; occasionally clinical illness, frequently with a fatal outcome, may occur. Consequently, to help protect staff from laboratory-acquired melioidosis, microbiological and biomedical laboratories must have adequate facilities for safe work procedures and laboratory staff must engage in safe work practices. Recommendations from a melioidosis-endemic, diagnostic laboratory for the prevention of laboratory-acquired infection with this bacterium are essentially Category 3 (Advisory Committee on Dangerous Pathogens), Risk Group 3 (Australian Standards) or Biosafety Level 2 (National Institutes of Health) precautions. These include safeguards for centrifugation, prohibiting the 'sniff' test and the use of a biological safety cabinet for sputum processing, for subculture of stock strains, for preparation of antigen and for research studies but not for routine diagnostic techniques with P. pseudomallei.