Epidemiology of Burkholderia pseudomallei in Thailand

Newly detected paediatric melioidosis cases in a single referral children's hospital in Ho Chi Minh City indicate the probable underrecognition of melioidosis in South Vietnam

BACKGROUND

The epidemiology of melioidosis in Vietnam, a disease caused by the soil bacterium Burkholderia pseudomallei, remains unclear. This study aimed to detect paediatric melioidosis in South Vietnam and describe clinical features and the geographic distribution.

METHODS

We introduced a simple laboratory algorithm for detecting B. pseudomallei from clinical samples at Children's Hospital 2 in Ho Chi Minh City in July 2015. A retrospective observational study of children <16 y of age with culture-confirmed melioidosis between July 2015 and August 2019 was undertaken.

RESULTS

Thirty-five paediatric cases of melioidosis were detected, with cases originating from 13 of 32 provinces and cities in South Vietnam. The number of paediatric melioidosis cases detected from a certain region correlated with the overall number of inpatients originating from the respective geographic area. Suppurative parotitis (n=15 [42.8%]) was the most common clinical presentation, followed by lung infection (n=10 [28.6%]) and septicaemia (n=7 [20%]). Fourteen (40%) children had disseminated disease, including all cases of lung infection, four cases with central nervous system symptoms and four (11.4%) deaths.

CONCLUSIONS

The patients' origin indicates a wide distribution of melioidosis in South Vietnam. It seems probable that cases not only in children, but also in adults, remain grossly undiagnosed. Further awareness raising and laboratory capacity strengthening are needed in this part of the country.

Under-Reporting Cases and Deaths from Melioidosis: A Retrospective Finding in Songkhla and Phatthalung Province of Southern Thailand, 2014-2020

Melioidosis, caused by Burkholderia pseudomallei, is a notifiable disease associated with a high mortality rate in Thailand. The disease is highly endemic in northeast Thailand, while its prevalence in other parts of the country is poorly documented. This study aimed at improving the surveillance system for melioidosis in southern Thailand, where the disease was believed to be underreported. Two adjacent southern provinces, Songkhla and Phatthalung, were selected as the model provinces to study melioidosis. There were 473 individuals diagnosed with culture-confirmed melioidosis by clinical microbiology laboratories at four tertiary care hospitals in both provinces from January 2014 to December 2020. The median age was 54 years (IQR 41.5-64), 284 (60%) of the patients were adults ≥50 years of age, and 337 (71.2%) were male. We retrospectively analyzed 455 patients treated at either Songklanarind Hospital, Hatyai Hospital, Songkhla Provincial Hospital, or Phatthalung Provincial Hospital, of whom 181 (39.8%) patients died. The median duration from admission to death was five days (IQR 2-17). Of the 455 patients, 272 (57.5%) had at least one clinical risk factor, and 188 (39.8%) had diabetes. Two major clinical manifestations, bacteremia and pneumonia, occurred in 274 (58.1%) and 166 (35.2%) patients, respectively. In most cases, 298 (75%) out of 395 local patients were associated with rainfall. Over the seven years of the study, the average annual incidence was 2.87 cases per 100,000 population (95% CI, 2.10 to 3.64). This study has confirmed that these two provinces of southern Thailand are endemic to melioidosis; even though the incidence rate is much lower than that of the Northeast, the mortality rate is comparably high.

Glanders (Burkholderia mallei infection) in an Iranian man: A case report

Background

Glanders is a rare disease that has been eradicated in many countries but may be difficult to diagnose due to its nonspecific symptoms. This disease, which can be highly fatal if left untreated, is caused by a bacterium called Burkholderia mallei. Humans can get the disease through contact with infected animals, such as horses. Over time, various treatment strategies have been proposed for this disease, and attempts haveeven been made to develop a vaccine, but thus far, no effective vaccine has been developed to prevent it.

Case presentation

In this article, we describeacase of Glanders disease in KamkarArabnia Hospital in Qom, Iran. The patient was a 22-year-old man with headache, fever, chills, diarrhea, and vomiting of blood, and was admitted to the infectious ward in isolation.

Conclusion

The lack of definitive diagnostic symptoms and the rarity of this disease make it difficult to diagnose, and one should be careful in dealing with its symptoms. Also, paying attention to the patient's medical history and travel history to endemic areas, can lead to timely diagnosis and treatment.

Distribution of Burkholderia pseudomallei within a 300-cm deep soil profile: implications for environmental sampling

The environmental distribution of Burkholderia pseudomallei, the causative agent of melioidosis, remains poorly understood. B. pseudomallei is known to have the ability to occupy a variety of environmental niches, particularly in soil. This paper provides novel information about a putative association of soil biogeochemical heterogeneity and the vertical distribution of B. pseudomallei. We investigated (1) the distribution of B. pseudomallei along a 300-cm deep soil profile together with the variation of a range of soil physico-chemical properties; (2) whether correlations between the distribution of B. pseudomallei and soil physico-chemical properties exist and (3) when they exist, what such correlations indicate with regards to the environmental conditions conducive to the occurrence of B. pseudomallei in soils. Unexpectedly, the highest concentrations of B. pseudomallei were observed between 100 and 200 cm below the soil surface. Our results indicate that unravelling the environmental conditions favorable to B. pseudomallei entails considering many aspects of the actual complexity of soil. Important recommendations regarding environmental sampling for B. pseudomallei can be drawn from this work, in particular that collecting samples down to the water table is of foremost importance, as groundwater persistence appears to be a controlling factor of the occurrence of B. pseudomallei in soil.

Melioidosis Pneumonia in Saudi Arabia: A Rare Case Report and Review of the Literature

Melioidosis is a serious infection caused by the bacterium Burkholderia pseudomallei (B. pseudomallei) mostly found in endemic areas like Southeast Asia and Northern Australia. However, in non-endemic regions, such as Saudi Arabia, it remains somewhat rare and unknown to healthcare workers and the public. Herein, we present a case of melioidosis in a 59-year-old Bangladeshi man who presented with pneumonia. He recently returned from Bangladesh, was a known case of type 2 diabetes on metformin, and presented to the emergency department (ED) with a history of cough, shortness of breath, and fever for three weeks. He was initially misdiagnosed and treated as pulmonary tuberculosis in another hospital prior to his latest presentation. Melioidosis is a severe infection that can be misdiagnosed due to variable presentation and low awareness among healthcare workers of the disease. Diagnosis requires high clinical suspicion, especially in patients who are coming from endemic areas with appropriate risk factors such as diabetes mellitus. Treatment with appropriate antibiotics for a long duration, and outpatient follow-up is vital to reduce the risk of recurrence.

A multi-country study using MALDI-TOF mass spectrometry for rapid identification of Burkholderia pseudomallei

Background

Burkholderia pseudomallei is the bacterial causative agent of melioidosis, a difficult disease to diagnose clinically with high mortality if not appropriately treated. Definitive diagnosis requires isolation and identification of the organism. With the increased adoption of MALDI-TOF MS for the identification of bacteria, we established a method for rapid identification of B. pseudomallei using the Vitek MS, a system that does not currently have B. pseudomallei in its in-vitro diagnostic database.

Results

A routine direct spotting method was employed to create spectra and SuperSpectra. An initial B. pseudomallei SuperSpectrum was created at Shoklo Malaria Research Unit (SMRU) from 17 reference isolates (46 spectra). When tested, this initial SMRU SuperSpectrum was able to identify 98.2 % (54/55) of Asian isolates, but just 46.7 % (35/75) of Australian isolates. Using spectra (430) from different reference and clinical isolates, two additional SMRU SuperSpectra were created. Using the combination of all SMRU SuperSpectra with seven existing SuperSpectra from Townsville, Australia 119 (100 %) Asian isolates and 31 (100 %) Australian isolates were correctly identified. In addition, no misidentifications were obtained when using these 11 SuperSpectra when tested with 34 isolates of other bacteria including the closely related species Burkholderia thailandensis and Burkholderia cepacia.

Conclusions

This study has established a method for identification of B. pseudomallei using Vitek MS, and highlights the impact of geographical differences between strains for identification using this technique.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02276-1.

One Health Approach of Melioidosis and Gastrointestinal Parasitic Infections from Macaca fascicularis to Human at Kosumpee Forest Park, Maha Sarakham, Thailand

Background and Objectives

Gastrointestinal parasitic and melioidosis infections are major causes of morbidity and mortality from infectious disease in rural areas, especially in northeastern Thailand. Both diseases are zoonotic giving rise to health problems in both long-tailed macaques and in humans. In Thailand, macaques have adapted to live and share space with humans and can spread some zoonoses to humans. Therefore, this research aimed to measure the prevalence of gastrointestinal parasitic infections and melioidosis in long-tailed macaques at Kosumpee Forest Park and measure associated risk factors of their diseases among people in this area.

Methods

This study was conducted at Kosumpee Forest Park, Maha Sarakham, Thailand. Twenty-eight blood samples and 135 fecal samples were collected from free-ranging long-tailed macaques. Blood samples were tested by indirect hemagglutination test and fecal samples were analyzed by formalin–ethyl acetate concentration technique. A cross-sectional study was conducted among 350 respondents who were involved with the Forest Park using a multi-stage stratified random sampling method and performed to measure knowledge, attitude, and practice toward the zoonoses among the respondents.

Results

It was found that seroprevalence of melioidosis was 57.1% from macaque samples. The prevalence of gastrointestinal parasites infection was 35.11% from fecces samples, including Strongyloides spp. (15.27%), Trichuris spp. (22.9%), hookworm (4.58%) and Ascarid spp. (1.53%). KAP study indicated that the level of knowledge related to melioidosis and gastrointestinal parasites of people in the area was very low and moderate, respectively. The attitude of respondents who were aware of the diseases was at a moderate level for melioidosis and a high level for parasitic infection.

Conclusion

The study therefore emphasizes the importance of one health approach for diagnosis, surveillance and management of zoonotic diseases to promote the development of hygiene measures and to educate people in the community around Kosumpee Forest Park.

Functional analysis of BPSS2242 reveals its detoxification role in Burkholderia pseudomallei under salt stress

A bpss2242 gene, encoding a putative short-chain dehydrogenase/oxidoreductase (SDR) in Burkholderia pseudomallei, was identified and its expression was up-regulated by ten-fold when B. pseudomallei was cultured under high salt concentration. Previous study suggested that BPSS2242 plays important roles in adaptation to salt stress and pathogenesis; however, its biological functions are still unknown. Herein, we report the biochemical properties and functional characterization of BPSS2242 from B. pseudomallei. BPSS2242 exhibited NADPH-dependent reductase activity toward diacetyl and methylglyoxal, toxic electrophilic dicarbonyls. The conserved catalytic triad was identified and found to play critical roles in catalysis and cofactor binding. Tyr162 and Lys166 are involved in NADPH binding and mutation of Lys166 causes a conformational change, altering protein structure. Overexpression of BPSS2242 in Escherichia coli increased bacterial survival upon exposure to diacetyl and methylglyoxal. Importantly, the viability of B. pseudomallei encountered dicarbonyl toxicity was enhanced when cultured under high salt concentration as a result of BPSS2242 overexpression. This is the first study demonstrating that BPSS2242 is responsible for detoxification of toxic metabolites, constituting a protective system against reactive carbonyl compounds in B. pseudomallei..

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.

Melioidosis: Case reports of confirmed Burkholderia pseudomallei in Saudi Arabia

Melioidosis is an infectious disease of tropical climates. The disease is caused by the bacterium Burkholderia pseudomallei. Most cases are diagnosed in southeast Asia and northern Australia. Some imported cases diagnosed in returning tourists, soldiers, and immigrants from endemic areas. It caught much attention since the Centers for Disease Control and Prevention (CDC) designated B. pseudomallei as an agent for biological warfare and terrorism. We describe two cases of a 26-year-old Saudi woman who had fulminant sepsis soon after returning from Thailand & a 48-year-old woman with a long history of fever. B. pseudomallei was isolated from both patients blood cultures, and they had different consequences. A confirmed case of melioidosis was not reported before in Saudi Arabia.

Clinical Epidemiology of 7126 Melioidosis Patients in Thailand and the Implications for a National Notifiable Diseases Surveillance System

Background

National notifiable diseases surveillance system (NNDSS) data in developing countries are usually incomplete, yet the total number of fatal cases reported is commonly used in national priority-setting. Melioidosis, an infectious disease caused by Burkholderia pseudomallei, is largely underrecognized by policy-makers due to the underreporting of fatal cases via the NNDSS.

Methods

Collaborating with the Epidemiology Division (ED), Ministry of Public Health (MoPH), we conducted a retrospective study to determine the incidence and mortality of melioidosis cases already identified by clinical microbiology laboratories nationwide. A case of melioidosis was defined as a patient with any clinical specimen culture positive for B. pseudomallei. Routinely available microbiology and hospital databases of secondary care and tertiary care hospitals, the national death registry, and NNDSS data were obtained for analysis.

Results

A total of 7126 culture-confirmed melioidosis patients were identified from 2012 to 2015 in 60 hospitals countrywide. The total number of cases diagnosed in Northeast, Central, South, East, North, and West Thailand were 5475, 536, 374, 364, 358, and 19 cases, respectively. The overall 30-day mortality was 39% (2805/7126). Only 126 (4%) deaths were reported to the NNDSS. Age, presentation with bacteremia and pneumonia, prevalence of diabetes, and 30-day mortality differed by geographical region (all P < .001). The ED at MoPH has agreed to include the findings of our study in the next annual report of the NNDSS.

Conclusions

Melioidosis is an important cause of death in Thailand nationwide, and its clinical epidemiology may be different by region. In developing countries, NNDSS data can be supplemented by integrating information from readily available routine data sets.

Population-Based Estimate of Melioidosis, Kenya

Melioidosis is thought to be endemic, although underdiagnosed, in Africa. We identified 5 autochthonous cases of Burkholderia pseudomallei infection in a case series in Kenya. Incidence of B. pseudomallei bacteremia in Kenya’s Kilifi County is low, at 1.5 cases per million person-years, but this result might be an underestimate.

Identification of Burkholderia pseudomallei by Use of the Vitek Mass Spectrometer

Burkholderia pseudomallei is the causative agent of melioidosis. This condition most often presents as pneumonia and bacteremia, with mortality rates of 9% to 70%. Therefore, early identification of this organism may aid in directing appropriate management. This study aimed to use the Vitek matrix-assisted laser desorption ionization-time of flight mass spectrometer to create a spectrum for the rapid identification of B. pseudomallei Spectra from 85 isolate cultures were acquired using the Vitek mass spectrometer research mode. A SuperSpectrum was created using peak matching and subsequently activated for analysis of organism identification. All 85 isolates were correctly identified as B. pseudomallei A total of 899 spectra were analyzed and demonstrated a specificity of 99.8%. Eighty-one clinical isolates were used, of which 10 were neuromelioidosis, and no discernible spectrum difference was appreciated. Spectrum acquisition from a single spot was only successful in 374/899 (41%) of isolates. This increased to 100% when 3 spots of the same extract were analyzed. The Vitek mass spectrometer can be used for the rapid identification of B. pseudomallei with a high level of specificity.

The prevalence and distribution of Burkholderia pseudomallei in rice paddy within Hainan, China

Melioidosis is an infectious disease caused by Burkholderia pseudomallei, mainly found in Southeast Asia and northern Australia. In Hainan, sporadic cases were first described in 1990; since then, more cases have been identified. No systematic study has yet been done to detect the environmental source of the organism and its true extent in Hainan. This study is aimed to confirm the prevalence of B. pseudomallei in soil samples in Hainan. 1080 soil samples from 18 different counties were collected from 3 sampling points of 360 sites. They were screened for the presence of B. pseudomallei by Ashdown selective media. Suspected colonies of B. pseudomallei were confirmed by biochemical test and a specific PCR assay. 48 of 360 sites (13.3%) were positive for B. pseudomallei, including all coastal counties in Hainan Island. This study revealed the prevalence and distribution of B. pseudomallei in the soil environment in Hainan Island of southern China and may be helpful to understand the distribution of B. pseudomallei and to access its epidemiological importance.

A case report of Tubo-ovarian abscess caused by Burkholderia pseudomallei

Background

Melioidosis, the disease caused by Burkholderia pseudomallei is endemic in the Northeastern part of Thailand, South-East Asia, and Northern Australia. The pelvic involvement of disease is rare even in an endemic area. Therefore, we describe in this report the clinical presentation, management, and outcome of the patient with primary tubo-ovarian abscess due to melioidosis.

Case presentation

A 31-year-old Thai cassava farmer woman presented with fever and abdominal pain at left lower quadrant for one month. She also had pain, swelling, and redness of the genitalia without any ulcer. She had odorless whitish vaginal discharge. The pelvic examination revealed excitation pain on the left side of her cervix. Transvaginal ultrasonography revealed a large left tubo-ovarian abscess size 9.4 × 4.8 cm located at anterior of the uterus. Urgent exploratory laparotomy revealed left hydrosalpinx with a large amount of pus. The pus culture grew Burkholderia pseudomallei. The computer tomography of the abdomen revealed multiple hepatosplenic abscesses. The patient underwent left salpingo-oophorectomy and pus drainage. The pathological examination of excised left adnexa revealed chronic and acute suppurative inflammation with necrotic tissue. She was given intravenous ceftazidime for one month, and her clinical symptom improved. She was diagnosed with type 2 diabetes mellitus at this visit and treated with insulin injection. She continued to take oral co-trimoxazole for 20 weeks. The final diagnosis was disseminated melioidosis with left tubo-ovarian abscess and hepatosplenic abscesses in a newly diagnosed morbidly obese diabetic patient.

Conclusion

Burkholderia pseudomallei should be considered as the causative organism of gynecologic infection among patient with risk factor resided in an endemic area who do not respond to standard antibiotics. The pus culture from the site of infection is the only diagnostic method of pelvic melioidosis, appropriate antibiotics, and adequate surgical drainage were the components of the successful outcome.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-2986-z) contains supplementary material, which is available to authorized users.

Presence of B. thailandensis and B. thailandensis expressing B. pseudomallei-like capsular polysaccharide in Thailand, and their associations with serological response to B. pseudomallei

BACKGROUND

Burkholderia pseudomallei is an environmental Gram-negative bacillus and the cause of melioidosis. B. thailandensis, some strains of which express a B. pseudomallei-like capsular polysaccharide (BTCV), is also commonly found in the environment in Southeast Asia but is considered non-pathogenic. The aim of the study was to determine the distribution of B. thailandensis and its capsular variant in Thailand and investigate whether its presence is associated with a serological response to B. pseudomallei.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated the presence of B. pseudomallei and B. thailandensis in 61 rice fields in Northeast (n = 21), East (n = 19) and Central (n = 21) Thailand. We found BTCV in rice fields in East and Central but not Northeast Thailand. Fourteen fields were culture positive for B. pseudomallei alone, 8 for B. thailandensis alone, 11 for both B. pseudomallei and B. thailandensis, 6 for both B. thailandensis and BTCV, and 5 for B. pseudomallei, B. thailandensis and BTCV. Serological testing using the indirect hemagglutination assay (IHA) of 96 farmers who worked in the study fields demonstrated that farmers who worked in B. pseudomallei-positive fields had higher IHA titers than those who worked in B. pseudomallei-negative fields (median 1:40 [range: <1:10-1:640] vs. <1:10 [range: <1:10-1:320], p = 0.002). In a multivariable ordered logistic regression model, IHA titers were significantly associated with the presence of B. pseudomallei (aOR = 3.7; 95% CI 1.8-7.8, p = 0.001) but were not associated with presence of B. thailandensis (p = 0.32) or BTCV (p = 0.32). One sequence type (696) was identified for the 27 BTCV isolates tested.

CONCLUSIONS/SIGNIFICANCE

This is the first report of BTCV in Thailand. The presence of B. pseudomallei and B. thailandensis in the same field was not uncommon. Our findings suggest that IHA positivity of healthy rice farmers in Thailand is associated with the presence of B. pseudomallei in rice fields rather than B. thailandensis or BTCV.

Burkholderia pseudomallei in a lowland rice paddy: seasonal changes and influence of soil depth and physico-chemical properties

Melioidosis, a severe infection with the environmental bacterium Burkholderia pseudomallei, is being recognised increasingly frequently. What determines its uneven distribution within endemic areas is poorly understood. We cultured soil from a rice field in Laos for B. pseudomallei at different depths on 4 occasions over a 13-month period. We also measured physical and chemical parameters in order to identify associated characteristics. Overall, 195 of 653 samples (29.7%) yielded B. pseudomallei. A higher prevalence of B. pseudomallei was found at soil depths greater than the 30 cm currently recommended for B. pseudomallei environmental sampling. B. pseudomallei was associated with a high soil water content and low total nitrogen, carbon and organic matter content. Our results suggested that a sampling grid of 25 five metre square quadrats (i.e. 25 × 25 m) should be sufficient to detect B. pseudomallei at a given location if samples are taken at a soil depth of at least 60 cm. However, culture of B. pseudomallei in environmental samples is difficult and liable to variation. Future studies should both rely on molecular approaches and address the micro-heterogeneity of soil when investigating physico-chemical associations with the presence of B. pseudomallei.

Prevalence and Identification of Burkholderia pseudomallei and Near-Neighbor Species in the Malabar Coastal Region of India

Accurate identification of pathogens with biowarfare importance requires detection tools that specifically differentiate them from near-neighbor species. Burkholderia pseudomallei, the causative agent of a fatal disease melioidosis, is one such biothreat agent whose differentiation from its near-neighbor species is always a challenge. This is because of its phenotypic similarity with other Burkholderia species which have a wide spread geographical distribution with shared environmental niches. Melioidosis is a major public health concern in endemic regions including Southeast Asia and northern Australia. In India, the disease is still considered to be emerging. Prevalence surveys of this saprophytic bacterium in environment are under-reported in the country. A major challenge in this case is the specific identification and differentiation of B. pseudomallei from the growing list of species of Burkholderia genus. The objectives of this study included examining the prevalence of B. pseudomallei and near-neighbor species in coastal region of South India and development of a novel detection tool for specific identification and differentiation of Burkholderia species. Briefly, we analyzed soil and water samples collected from Malabar coastal region of Kerala, South India for prevalence of B. pseudomallei. The presumptive Burkholderia isolates were identified using recA PCR assay. The recA PCR assay identified 22 of the total 40 presumptive isolates as Burkholderia strains (22.72% and 77.27% B. pseudomallei and non-pseudomallei Burkholderia respectively). In order to identify each isolate screened, we performed recA and 16S rDNA sequencing. This two genes sequencing revealed that the presumptive isolates included B. pseudomallei, non-pseudomallei Burkholderia as well as non-Burkholderia strains. Furthermore, a gene termed D-beta hydroxybutyrate dehydrogenase (bdha) was studied both in silico and in vitro for accurate detection of Burkholderia genus. The optimized bdha based PCR assay when evaluated on the Burkholderia isolates of this study, it was found to be highly specific (100%) in its detection feature and a clear detection sensitivity of 10 pg/μl of purified gDNA was recorded. Nucleotide sequence variations of bdha among interspecies, as per in silico analysis, ranged from 8 to 29% within the target stretch of 730 bp highlighting the potential utility of bdha sequencing method in specific detection of Burkholderia species. Further, sequencing of the 730 bp bdha PCR amplicon of each Burkholderia strain isolated could differentiate the species and the data was comparable with recA sequence data of the strains. All sequencing results obtained were submitted to NCBI database. Bayesian phylogenetic analysis of bdha in comparison with recA and 16S rDNA showed that the bdha gene provided comparable identification of Burkholderia species.

Musculoskeletal melioidosis: An under-diagnosed entity in developing countries

BACKGROUND

Melioidosis is a saprophytic infectious disease caused by Gram-negative soil-dwelling bacillus Burkholderia pseudomallei.

MATERIALS & METHODS

We report three cases of musculoskeletal melioidosis that are presented to our department from 2011 to 2013.

RESULTS

One of the patients died due to post-septicemic ARDS. The other two patients have recovered fully and are followed up for minimum of 6 months. There were no recurrences.

CONCLUSIONS

Though musculoskeletal infection due to melioidosis is not common in India, new cases are being reported from Karnataka, Goa and Southern Maharashtra. The need for diagnosing this entity is due to the fact that the septicemic form has a mortality rate that exceeds 90%, and though culture sensitivity report shows susceptibility to various antibiotics, the infection responds to only specific set of antibiotics i.e. intravenous ceftazidime and combination of trimethoprim and sulfamethoxazole.

Direct detection of Burkholderia pseudomallei and biological factors in soil

BACKGROUND

Burkholderia pseudomallei, a Gram-negative saprophytic bacillus, is a severe infectious agent that causes melioidosis and soil is the most important reservoir.

METHODS

One hundred and forty soil samples were tested for pH, moisture content and total C and N measurements and used for DNA extraction and culture for B. pseudomallei. The quantitative real-time PCR (qPCR) targeting wcbG, a putative capsular polysaccharide biosynthesis protein gene of B. pseudomallei, was developed to detect the bacterium, and random amplified polymorphic DNA (RAPD) was used to detect the microbial diversity in soil.

RESULTS

The acidic pH was correlated with the presence of the bacterium. Forty-four soil sites (44/140, 31.4%) were positive for B. pseudomallei by qPCR, of which 21 were positive by culture. The limit of detection is 32 fg of DNA (about 4 genomes). The RAPD method could classify the soil samples into low diversity (LD) and high diversity (HD) sites. The trend of LD was found with B. pseudomallei positive soil sites.

CONCLUSIONS

The acidity of the soil or metabolites from organisms in the sites may contribute to the presence of the bacterium. Further investigation of microbes by a more robust method should elucidate biological factors that promote the presence of B. pseudomallei and may be used for controlling the bacterium in the environment.

Effects of Colonization of the Roots of Domestic Rice (Oryza sativa L. cv. Amaroo) by Burkholderia pseudomallei

Burkholderia pseudomallei is a saprophytic bacterium that causes melioidosis and is often isolated from rice fields in Southeast Asia, where the infection incidence is high among rice field workers. The aim of this study was to investigate the relationship between this bacterium and rice through growth experiments where the effect of colonization of domestic rice (Oryza sativa L. cv Amaroo) roots by B. pseudomallei could be observed. When B. pseudomallei was exposed to surface-sterilized seeds, the growth of both the root and the aerosphere was retarded compared to that in controls. The organism was found to localize in the root hairs and endodermis of the plant. A biofilm formed around the root and root structures that were colonized. Growth experiments with a wild rice species (Oryza meridionalis) produced similar retardation of growth, while another domestic cultivar (O. sativa L. cv Koshihikari) did not show retarded growth. Here we report B. pseudomallei infection and inhibition of O. sativa L. cv Amaroo, which might provide insights into plant interactions with this important human pathogen.

Transcription level analysis of intracellular Burkholderia pseudomallei illustrates the role of BPSL1502 during bacterial interaction with human lung epithelial cells

Melioidosis caused by Burkholderia pseudomallei is a globally important disease of increasing concern according to high case-fatality rate and epidemic spreading. The ability of B. pseudomallei to attach and invade host cells and subsequently survive intracellularly has stimulated many questions concerning the comprehension of bacterial pathogenesis progression. Transcription levels of intracellular B. pseudomallei genes in human lung epithelial cells were therefore analyzed using bioinformatic tools, RT-PCR and real time RT-PCR. Here, it is reported that the identification of bpsl1502, encoding B. pseudomallei SurE (stationary phase survival protein E) located in a global transcriptional regulation operon was accomplished. The up-regulation of B. pseudomallei SurE was demonstrated during intracellular survival of A549 cells at 12, 18, and 24 h post-infection. To investigate the role of this protein, a B. pseudomallei SurE defective mutant was constructed. The invasion and initial survival of the SurE mutants within the A549 cells were impaired. There was no difference, however, between the growth of B. pseudomallei SurE mutant as compared to the wild type in Luria-Bertani culture. These data suggest that SurE may assist B. pseudomallei host cells invade and facilitate early intracellular infection but is not crucial during the stationary growth phase. The identification of B. pseudomallei SurE provides more information of bacterial strategy during an early step of the pathogenesis process of melioidosis.

Retrospective Study on Fatal Melioidosis in Captive Zoo Animals in Thailand

Melioidosis is caused by Burkholderia pseudomallei and is an important zoonotic infectious disease causing high mortality from fulminant septicaemia in humans and a wide variety of animal species. The incidence of fatal melioidosis in zoo animals has been significant in many Thai zoos. A total number of 32 cases were evaluated throughout the Thai zoo animal populations. The highest prevalence of disease has been reported from the north-eastern region followed by the zoos in the southern part of the country, approximately 47% and 38%, respectively, while the other zoos reported sporadic infections. Herbivores and non-human primates were the most commonly affected animals with incidences of 59% and 28%, respectively. This appears to be a seasonal correlation with the highest incidence of melioidosis in zoo animals reported in the rainy season (44%) or subdivided monthly in June (19%) followed by September and November (16% and 12%, respectively). The route of infection and the incubation period still remain unclear. This retrospective study examined the clinical presentation in various zoo species, pathological findings and epidemiological data as well as conducting an in depth literature review.

Seroepidemiology of melioidosis in children from a remote region of Papua New Guinea

BACKGROUND

The Balimo region in Papua New Guinea has previously been identified as melioidosis-endemic with a predilection for children. Where health resources are scarce, seroepidemiology can be used to assess exposure to Burkholderia pseudomallei and therefore risk of acquiring melioidosis.

METHODS

Logistic regression was used to determine associations between indirect haemagglutination assay (IHA) seroreactivity with environmental and demographic/cultural factors to aid in determining risk factors associated with exposure to B. pseudomallei in children.

RESULTS

Of the 968 participants, 92.9% (899/968) were children, representing the majority of the community school population in the immediate Balimo region. Of these, 24.6% (221/899) were seropositive. Bathing in the lagoon (OR=2.679), drinking from the well or lagoon (OR=1.474), and being a member of the Siboko (OR=1.914) or Wagumisi (OR=1.942) clans were significantly associated with seropositivity. In the multivariate analysis, drinking from a well or lagoon (OR=1.713), and the Siboko (OR=2.341) and Wabadala (OR=2.022) clans were associated with seropositivity.

CONCLUSIONS

This study in children supports observations that interactions with groundwater in this region are risk factors in acquiring melioidosis. Public health measures intended to limit this exposure may help reduce the risk of acquiring melioidosis in this remote community. Associations with clan structure may provide more cultural specific insights, however this requires further elucidation.

Source-identifying biomarker ions between environmental and clinical Burkholderia pseudomallei using whole-cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)

Burkholderia pseudomallei is the causative agent of melioidosis, which is an endemic disease in Northeast Thailand and Northern Australia. Environmental reservoirs, including wet soils and muddy water, serve as the major sources for contributing bacterial infection to both humans and animals. The whole-cell matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (whole-cell MALDI-TOF MS) has recently been applied as a rapid, accurate, and high-throughput tool for clinical diagnosis and microbiological research. In this present study, we employed a whole-cell MALDI-TOF MS approach for assessing its potency in clustering a total of 11 different B. pseudomallei isolates (consisting of 5 environmental and 6 clinical isolates) with respect to their origins and to further investigate the source-identifying biomarker ions belonging to each bacterial group. The cluster analysis demonstrated that six out of eleven isolates were grouped correctly to their sources. Our results revealed a total of ten source-identifying biomarker ions, which exhibited statistically significant differences in peak intensity between average environmental and clinical mass spectra using ClinProTools software. Six out of ten mass ions were assigned as environmental-identifying biomarker ions (EIBIs), including, m/z 4,056, 4,214, 5,814, 7,545, 7,895, and 8,112, whereas the remaining four mass ions were defined as clinical-identifying biomarker ions (CIBIs) consisting of m/z 3,658, 6,322, 7,035, and 7,984. Hence, our findings represented, for the first time, the source-specific biomarkers of environmental and clinical B. pseudomallei.

Fatal melioidosis in goats in Bangkok, Thailand

Bangkok, Thailand, is a city considered to be at low risk for melioidosis. We describe 10 goats that died of melioidosis in Bangkok. Half of them were born and reared in the city. Multilocus sequence typing ruled out an outbreak. This finding challenges the assumption that melioidosis is rarely acquired in central Thailand.

The concentrations of ambient Burkholderia pseudomallei during typhoon season in endemic area of melioidosis in Taiwan

Background

Melioidosis is a severe bacterial infection caused by Burkholderia pseudomallei with a high case-fatality rate. Epidemiological and animal studies show the possibility of inhalation transmission. However, no B. pseudomallei concentrations in ambient air have been researched. Here, we developed a method to quantify ambient B. pseudomallei and then measured concentrations of ambient B. pseudomallei during the typhoon season and the non-typhoon season to determine the factors influencing ambient B. pseudomallei levels.

Methods

We quantified ambient B. pseudomallei by using a filter/real-time qPCR method in the Zoynan Region in Kaohsiung, southern Taiwan. Twenty-four hour samples were collected at a sampling rate of 20 L/min every day from June 11 to December 21, 2012 including during the typhoon season (June to September) and reference season (October to December).

Results

We successfully developed a filtration/real-time qPCR method to quantify ambient B. pseudomallei. To our knowledge, this is the first report describing concentrations of ambient B. pseudomallei. Ambient B. pseudomallei were only detected during the typhoon season when compared to the reference season. For the typhoons affecting the Zoynan Region, the positive rates of ambient B. pseudomallei were very high at 80% to 100%. During June to December, rainfall was positively correlated with ambient B. pseudomallei with a statistical significance. Sediment at a nearby pond significantly influenced the concentration of ambient B. pseudomallei. During the typhoon month, the typhoon was positively correlated with ambient B. pseudomallei whereas wind speed was reversely correlated with ambient B. pseudomallei.

Conclusions

Our data suggest the possibility of transmission of B. pseudomallei via inhalation during the typhoon season.

Melioidosis is a severe bacterial infection caused by Burkholderia pseudomallei with a high case-fatality rate. Epidemiological and animal studies show the possibility of inhalation transmission. However, no B. pseudomallei concentrations in ambient air have been researched. Here, we successfully developed a method to quantify ambient B. pseudomallei by using a filter/real-time qPCR method. Twenty-four hour samples were collected every day from June 11 to December 21, 2012 including during the typhoon season (June to September) and reference season (October to December) in the Zoynan Region in Kaohsiung, southern Taiwan. To our knowledge, this is the first report describing concentrations of B. pseudomallei in ambient air. For the typhoons affecting the Zoynan Region, the positive rates of ambient B. pseudomallei were very high. Our data imply the possibility of air transmission of Melioidosis during the typhoon season. In addition, ambient B. pseudomallei aerosolized from sediment of a nearby lake should be a concern as an important source of transmission. Our results could provide deeper insight into Melioidosis transmissibility and infection control.

Physicochemical factors affecting the growth of Burkholderia pseudomallei in soil microcosm

Burkholderia pseudomallei causes melioidosis, the third most common cause of death from infectious diseases in northeast Thailand. Four physicochemical factors were set so that their values covered the range of the northeast, which is an endemic area. The soil pH was set at pH 4-10, soil salinity was 0.0-5.0% NaCl, total iron was 50-150 mg/kg soil, and carbon to nitrogen ratio (C/N) was 10:1 to 40:1. The experiments were carried out at 37°C, and soil moisture was maintained for 7 days. The number of viable bacterial cells was counted daily. Soil pH, salinity, Fe, and C/N ratio affected the bacterial growth. The bacterial colony was significantly (P < 0.05) reduced at soil pH > 8, soil salinity > 1% NaCl, and C/N ratio > 40:1. However, the growth of B. pseudomallei was enhanced by increasing the concentrations of iron significantly (P < 0.05). We propose using these findings to control B. pseudomallei in situ.

Two fatal cases of melioidosis on the Thai-Myanmar border

Melioidosis is endemic in areas of Southeast Asia, however, there are no published reports from the Thai-Myanmar border. We report the first two documented cases of fatal melioidosis in this region. This is of great public health importance and highlights the need to both increase clinical awareness of melioidosis on the Thai-Myanmar border, and to assess the true burden of disease in the area through improved case detection and Burkholderia pseudomallei prevalence studies.

The role of short-chain dehydrogenase/oxidoreductase, induced by salt stress, on host interaction of B. pseudomallei

Background

Burkholderia pseudomallei is the causative agent of melioidosis, a frequently occurring disease in northeastern Thailand, where soil and water high in salt content are common. Using microarray analysis, we previously showed that B. pseudomallei up-regulated a short-chain dehydrogenase/oxidoreductase (SDO) under salt stress. However, the importance of SDO in B. pseudomallei infection is unknown. This study aimed to explore the function of B. pseudomallei SDO, and to investigate its role in interactions between B. pseudomallei and host cells.

Results

Bioinformatics analysis of B. pseudomallei SDO structure, based on homology modeling, revealed a NAD⁺ cofactor domain and a catalytic triad containing Ser149, Tyr162, and Lys166. This is similar to Bacillus megaterium glucose 1-dehydrogenase. To investigate the role of this protein, we constructed a B. pseudomallei SDO defective mutant, measured glucose dehydrogenase (GDH) activity, and tested the interactions with host cells. The B. pseudomallei K96243 wild type exhibited potent GDH activity under condition containing 300 mM NaCl, while the mutant showed activity levels 15 times lower. Both invasion into the A549 cell line and early intracellular survival within the J774A.1 macrophage cell were impaired in the mutant. Complementation of SDO was able to restore the mutant ability to produce GDH activity, invade epithelial cells, and survive in macrophages.

Conclusions

Our data suggest that induced SDO activity during salt stress may facilitate B. pseudomallei invasion and affect initiation of successful intracellular infection. Identifying the role of B. pseudomallei SDO provides a better understanding of the association between bacterial adaptation and pathogenesis in melioidosis.

Systematic review and consensus guidelines for environmental sampling of Burkholderia pseudomallei

Background

Burkholderia pseudomallei, a Tier 1 Select Agent and the cause of melioidosis, is a Gram-negative bacillus present in the environment in many tropical countries. Defining the global pattern of B. pseudomallei distribution underpins efforts to prevent infection, and is dependent upon robust environmental sampling methodology. Our objective was to review the literature on the detection of environmental B. pseudomallei, update the risk map for melioidosis, and propose international consensus guidelines for soil sampling.

Methods/Principal Findings

An international working party (Detection of Environmental Burkholderia pseudomallei Working Party (DEBWorP)) was formed during the VIth World Melioidosis Congress in 2010. PubMed (January 1912 to December 2011) was searched using the following MeSH terms: pseudomallei or melioidosis. Bibliographies were hand-searched for secondary references. The reported geographical distribution of B. pseudomallei in the environment was mapped and categorized as definite, probable, or possible. The methodology used for detecting environmental B. pseudomallei was extracted and collated. We found that global coverage was patchy, with a lack of studies in many areas where melioidosis is suspected to occur. The sampling strategies and bacterial identification methods used were highly variable, and not all were robust. We developed consensus guidelines with the goals of reducing the probability of false-negative results, and the provision of affordable and ‘low-tech’ methodology that is applicable in both developed and developing countries.

Conclusions/Significance

The proposed consensus guidelines provide the basis for the development of an accurate and comprehensive global map of environmental B. pseudomallei.

Melioidosis is a serious infectious disease caused by the Tier 1 selected agent and Gram-negative environmental saprophyte, Burkholderia pseudomallei. The organism is commonly found in soil and water in melioidosis endemic areas. Infection in humans occurs following bacterial inoculation, inhalation or ingestion. There is a striking lack of accurate information on the global risk of melioidosis, something that could be determined from the global distribution of environmental B. pseudomallei. Soil sampling to detect the presence of B. pseudomallei has been ad hoc, poorly standardized, and the available information poorly collated. Negative studies are almost never reported, and there is no published review on this topic. We responded to this problem during the VI^th World Melioidosis Congress held in Townsville, Australia in December 2010 by forming the ‘Detection of Environmental Burkholderia pseudomallei Working Party (DEBWorP)’. We have since worked together to undertake a systematic review, map the available information, and reach a consensus on low cost methods for the detection of environmental B. pseudomallei. Our goal is to promote the use of these consensus methods and encourage people worldwide to participate in an effort to produce a comprehensive global map of environmental B. pseudomallei.

Burkholderia pseudomallei detection in surface water in southern Laos using Moore's swabs

The causal agent of melioidosis, Burkholderia pseudomallei, has been cultured from paddy fields in the Lao PDR. We carried out a pilot study to examine the relationship between bacterial soil contamination and that of nearby surface waters in Saravane Province. Soil sampling was conducted at a depth of 30 cm (100 holes in a 45 × 45 m grid) at two sites, East and West Saravane. Moore's swabs were used for water sampling of paddy fields, lakes, rivers, boreholes, and storage tanks within 2 km of the two soil sampling sites. B. pseudomallei from soil and water were cultured on Ashdown's agar. Thirty-six percent and 6% of water samples collected around East and West Saravane, respectively, were culture positive for B. pseudomallei. Low pH and high turbidity were independently associated with culture of B. pseudomallei. Most positive water samples were from the Sedone River, downstream of the East Saravane site. Moore's swabs are simple and inexpensive tools for detecting B. pseudomallei in surface waters.

Melioidosis in animals, Thailand, 2006-2010

We retrospectively estimated the incidence of culture-proven melioidosis in animals in Thailand during 2006–2010. The highest incidence was in goats (1.63/100,000/year), followed by incidence in pigs and cattle. The estimated incidence of melioidosis in humans in a given region paralleled that of melioidosis in goats.

Melioidosis acquired by traveler to Nigeria

We describe melioidosis associated with travel to Nigeria in a woman with diabetes, a major predisposing factor for this infection. With the prevalence of diabetes projected to increase dramatically in many developing countries, the global reach of melioidosis may expand.

Improved culture-based detection and quantification of Burkholderia pseudomallei from soil

Environmental surveillance of the Gram-negative soil bacterium Burkholderia pseudomallei, the aetiological agent of melioidosis, is important in order to define human populations and livestock at risk of acquiring the infection. This study aimed to develop a more sensitive method for the detection of B. pseudomallei from soil samples in endemic areas compared with the currently used culture method based on soil dispersion in water. We report the development of a new protocol that involves soil dispersion in a polyethylene glycol (PEG) and sodium deoxycholate (DOC) solution to increase the yield of viable B. pseudomallei from soil samples. Comparative testing of soil samples from Northeast Thailand covering a wide range of B. pseudomallei concentrations demonstrated a significantly higher recovery (P<0.0001) of B. pseudomallei colony-forming units by the new method compared with the conventional method. The data indicate that using the detergents PEG and DOC not only results in a higher recovery of viable B. pseudomallei but also results in a shift in the bacterial species recovered from soil samples. Future studies on the geographical distribution and population structure of B. pseudomallei in soil are likely to benefit from the new protocol described here.

Randomized soil survey of the distribution of Burkholderia pseudomallei in rice fields in Laos

Melioidosis is a major cause of morbidity and mortality in Southeast Asia, where the causative organism (Burkholderia pseudomallei) is present in the soil. In the Lao People's Democratic Republic (Laos), B. pseudomallei is a significant cause of sepsis around the capital, Vientiane, and has been isolated in soil near the city, adjacent to the Mekong River. We explored whether B. pseudomallei occurs in Lao soil distant from the Mekong River, drawing three axes across northwest, northeast, and southern Laos to create nine sampling areas in six provinces. Within each sampling area, a random rice field site containing a grid of 100 sampling points each 5 m apart was selected. Soil was obtained from a depth of 30 cm and cultured for B. pseudomallei. Four of nine sites (44%) were positive for B. pseudomallei, including all three sites in Saravane Province, southern Laos. The highest isolation frequency was in east Saravane, where 94% of soil samples were B. pseudomallei positive with a geometric mean concentration of 464 CFU/g soil (95% confidence interval, 372 to 579 CFU/g soil; range, 25 to 10,850 CFU/g soil). At one site in northwest Laos (Luangnamtha), only one sample (1%) was positive for B. pseudomallei, at a concentration of 80 CFU/g soil. Therefore, B. pseudomallei occurs in Lao soils beyond the immediate vicinity of the Mekong River, alerting physicians to the likelihood of melioidosis in these areas. Further studies are needed to investigate potential climatic, soil, and biological determinants of this heterogeneity.

Global transcriptional profiling of Burkholderia pseudomallei under salt stress reveals differential effects on the Bsa type III secretion system

Background

Burkholderia pseudomallei is the causative agent of melioidosis where the highest reported incidence world wide is in the Northeast of Thailand, where saline soil and water are prevalent. Moreover, recent reports indicate a potential pathogenic role for B. pseudomallei in cystic fibrosis lung disease, where an increased sodium chloride (NaCl) concentration in airway surface liquid has been proposed. These observations raise the possibility that high salinity may represent a favorable niche for B. pseudomallei. We therefore investigated the global transcriptional response of B. pseudomallei to increased salinity using microarray analysis.

Results

Transcriptome analysis of B. pseudomallei under salt stress revealed several genes significantly up-regulated in the presence of 320 mM NaCl including genes associated with the bsa-derived Type III secretion system (T3SS). Microarray data were verified by reverse transcriptase-polymerase chain reactions (RT-PCR). Western blot analysis confirmed the increased expression and secretion of the invasion-associated type III secreted proteins BipD and BopE in B. pseudomallei cultures at 170 and 320 mM NaCl relative to salt-free medium. Furthermore, salt-treated B. pseudomallei exhibited greater invasion efficiency into the lung epithelial cell line A549 in a manner partly dependent on a functional Bsa system.

Conclusions

B. pseudomallei responds to salt stress by modulating the transcription of a relatively small set of genes, among which is the bsa locus associated with invasion and virulence. Expression and secretion of Bsa-secreted proteins was elevated in the presence of exogenous salt and the invasion efficiency was enhanced. Our data indicate that salinity has the potential to influence the virulence of B. pseudomallei.

Burkholderia pseudomallei is spatially distributed in soil in northeast Thailand

Background

Melioidosis is a frequently fatal infectious disease caused by the soil dwelling Gram-negative bacterium Burkholderia pseudomallei. Environmental sampling is important to identify geographical distribution of the organism and related risk of infection to humans and livestock. The aim of this study was to evaluate spatial distribution of B. pseudomallei in soil and consider the implications of this for soil sampling strategies.

Methods and Findings

A fixed-interval sampling strategy was used as the basis for detection and quantitation by culture of B. pseudomallei in soil in two environmental sites (disused land covered with low-lying scrub and rice field) in northeast Thailand. Semivariogram and indicator semivariogram were used to evaluate the distribution of B. pseudomallei and its relationship with range between sampling points. B. pseudomallei was present on culture of 80/100 sampling points taken from the disused land and 28/100 sampling points from the rice field. The median B. pseudomallei cfu/gram from positive sampling points was 378 and 700 for the disused land and the rice field, respectively (p = 0.17). Spatial autocorrelation of B. pseudomallei was present, in that samples taken from areas adjacent to sampling points that were culture positive (negative) for B. pseudomallei were also likely to be culture positive (negative), and samples taken from areas adjacent to sampling points with a high (low) B. pseudomallei count were also likely to yield a high (low) count. Ranges of spatial autocorrelation in quantitative B. pseudomallei count were 11.4 meters in the disused land and 7.6 meters in the rice field.

Conclusions

We discuss the implications of the uneven distribution of B. pseudomallei in soil for future environmental studies, and describe a range of established geostatistical sampling approaches that would be suitable for the study of B. pseudomallei that take account of our findings.

Melioidosis is a severe infection caused by the environmental bacterium Burkholderia pseudomallei. Soil sampling is important to identify geographic regions where humans and animals are at risk of exposure. The purpose of this study was to examine a factor that has a major bearing on the accuracy of soil sampling: the spatial distribution of B. pseudomallei in soil of a specified sampling site. Soil sampling was performed using a fixed-interval grid of 100 sampling points in each of two sites (disused land and rice field) in northeast Thailand, and the presence and amount of B. pseudomallei determined using culture. Mapping of the presence and B. pseudomallei count demonstrated that samples taken from areas adjacent to sampling points that were culture positive (negative) for B. pseudomallei were also likely to be culture positive (negative), and samples taken from areas adjacent to sampling points with a high (low) B. pseudomallei count were also likely to yield a high (low) count (spatial autocorrelation). These data were used as the basis for highlighting several pitfalls in current approaches to soil sampling, together with a discussion of the suitability of a range of sampling strategies in different geographical locations and for different study objectives.

Distribution of melioidosis cases and viable Burkholderia pseudomallei in soil: evidence for emerging melioidosis in Taiwan

A survey for the prevalence if Burkholderia pseudomallei in soil in Taiwan found that its incidence is comparable to that in other regions of the world where melioidosis is endemic. The presence of identical genetic patterns among the clinical and environmental isolates evaluated suggested a link between the pathogens present in contaminated soil and the emergence of indigenous melioidosis.

Spatial analysis of melioidosis distribution in a suburban area

Burkholderia pseudomallei, the causative agent of melioidosis is associated with soil. This study used a geographic information system (GIS) to determine the spatial distribution of clinical cases of melioidosis in the endemic suburban region of Townsville in Australia. A total of 65 cases over the period 1996-2008 were plotted using residential address. Two distinct groupings were found. One was around the base of a hill in the city centre and the other followed the old course of a major waterway in the region. Both groups (accounting for 43 of the 65 cases examined) are in areas expected to have particularly wet topsoils following intense rainfall, due to soil type or landscape position.

Genomic transcriptional profiling identifies a candidate blood biomarker signature for the diagnosis of septicemic melioidosis

A diagnostic signature for sepsis caused by Burkholderia pseudomallei infection was identified from transcriptional profiling of the blood of septicemia patients.

Background

Melioidosis is a severe infectious disease caused by Burkholderia pseudomallei, a Gram-negative bacillus classified by the National Institute of Allergy and Infectious Diseases (NIAID) as a category B priority agent. Septicemia is the most common presentation of the disease with a 40% mortality rate even with appropriate treatments. Better diagnostic tests are therefore needed to improve therapeutic efficacy and survival rates.

Results

We have used microarray technology to generate genome-wide transcriptional profiles (>48,000 transcripts) from the whole blood of patients with septicemic melioidosis (n = 32), patients with sepsis caused by other pathogens (n = 31), and uninfected controls (n = 29). Unsupervised analyses demonstrated the existence of a whole blood transcriptional signature distinguishing patients with sepsis from control subjects. The majority of changes observed were common to both septicemic melioidosis and sepsis caused by other infections, including genes related to inflammation, interferon-related genes, neutrophils, cytotoxic cells, and T-cells. Finally, class prediction analysis identified a 37 transcript candidate diagnostic signature that distinguished melioidosis from sepsis caused by other organisms with 100% accuracy in a training set. This finding was confirmed in 2 independent validation sets, which gave high prediction accuracies of 78% and 80%, respectively. This signature was significantly enriched in genes coding for products involved in the MHC class II antigen processing and presentation pathway.

Conclusions

Blood transcriptional patterns distinguish patients with septicemic melioidosis from patients with sepsis caused by other pathogens. Once confirmed in a large scale trial this diagnostic signature might constitute the basis of a differential diagnostic assay.

Soil physicochemical properties related to the presence of Burkholderia pseudomallei

The incidence of Burkholderia pseudomallei in the soil from north-east Thailand is estimated to be 20-fold higher than that from central Thailand, and is associated with a 10-fold higher incidence of melioidosis in the region than in central Thailand. This study investigated the presence of B. pseudomallei in relation to the physicochemical properties of soil from Khon Kaen province, north-east Thailand. Thirteen districts (54.2%) were positive for B. pseudomallei. From a selected district, B. pseudomallei was cultured from 19 of 50 sites (38%). The soil in this area was predominantly sandy. From the positive sites, the organism was found mainly at a depth of 30 cm (43/68, 63% of isolates) and was significantly associated with certain soil physicochemical parameters, including a pH of 5.0-6.0, a moisture content >10%, and higher chemical oxygen demand and total nitrogen than negative sites (P<0.05). Burkholderia pseudomallei is unevenly distributed in this area, with the pH of the soil being the major determinant of the presence of the organism. The sandy soil type of north-east Thailand can support the survival of B. pseudomallei and allow it to move freely with water flow, and thus readily come in contact with people during the rainy season.

Genetic diversity and microevolution of Burkholderia pseudomallei in the environment

Background

The soil dwelling Gram-negative pathogen Burkholderia pseudomallei is the cause of melioidosis. The diversity and population structure of this organism in the environment is poorly defined.

Methods and Findings

We undertook a study of B. pseudomallei in soil sampled from 100 equally spaced points within 237.5 m² of disused land in northeast Thailand. B. pseudomallei was present on direct culture of 77/100 sampling points. Genotyping of 200 primary plate colonies from three independent sampling points was performed using a combination of pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Twelve PFGE types and nine sequence types (STs) were identified, the majority of which were present at only a single sampling point. Two sampling points contained four STs and the third point contained three STs. Although the distance between the three sampling points was low (7.6, 7.9, and 13.3 meters, respectively), only two STs were present in more than one sampling point. Each of the three samples was characterized by the localized expansion of a single B. pseudomallei clone (corresponding to STs 185, 163, and 93). Comparison of PFGE and MLST results demonstrated that two STs contained strains with variable PFGE banding pattern types, indicating geographic structuring even within a single MLST-defined clone.

Conclusions

We discuss the implications of this extreme structuring of genotype and genotypic frequency in terms of micro-evolutionary dynamics and ecology, and how our results may inform future sampling strategies.

The soil dwelling Gram-negative bacterium Burkholderia pseudomallei is the cause of melioidosis, a serious human infection that occurs in Southeast Asia and northern Australia. The purpose of this study was to evaluate the population genetic structure of B. pseudomallei in the environment. To achieve this, we undertook soil sampling and culture for the presence of B. pseudomallei in 100 equally spaced points within an area of disused land in northeast Thailand, and undertook detailed genotyping of primary plate colonies isolated from three independent sampling points. Our results demonstrated that multiple B. pseudomallei genotypes were present within a single soil sample, and that different genotypes were present at independent but nearby sampling points. The B. pseudomallei genetic population was unevenly distributed within a given sample, with a predominant genotype co-existing with several genotypes present as a minority population. We discuss the implications of this structuring of genotypic frequency in terms of micro-evolutionary dynamics and ecology, and how our results may inform future sampling strategies.

Fine-scale genetic diversity among Burkholderia pseudomallei soil isolates in northeast Thailand

Burkholderia pseudomallei soil isolates from northeast Thailand were genotyped using multiple-locus variable-number tandem repeat (VNTR) analysis (MLVA) and multilocus sequence typing (MLST). MLVA identified 19 genotypes within three clades, while MLST revealed two genotypes. These close genetic relationships imply a recent colonization followed by localized expansion, similar to what occurs in an outbreak situation.

The epidemiology of melioidosis in the Balimo region of Papua New Guinea

The distribution of Burkholderia pseudomallei was determined in soil collected from a rural district in Papua New Guinea (PNG) where melioidosis had recently been described, predominately affecting children. In 274 samples, 2.6% tested culture-positive for B. pseudomallei. Pulsed-field gel electrophoresis using SpeI digests and rapid polymorphic DNA PCR with five primers demonstrated a single clone amongst clinical isolates and isolates cultured from the environment that was commonly used by children from whom the clinical isolates were derived. We concluded that individuals in this region most probably acquired the organism through close contact with the environment at these sites. Burkholderia thailandensis, a closely related Burkholderia sp. was isolated from 5.5% of samples tested, an observation similar to that of melioidosis-endemic areas in Thailand. This is the first report of an environmental reservoir for melioidosis in PNG and confirms the Balimo district in PNG as melioidosis endemic.

Prevalence of melioidosis in the Er-Ren River Basin, Taiwan: implications for transmission

An increase in melioidosis cases compared to other areas in Taiwan was observed in the Er-Ren River Basin, southwestern Taiwan, from November 2001 to August 2006. The objective of this study was to determine the association between the level of exposure to Burkholderia pseudomallei and the incidence rate of melioidosis and to survey the transmission modes of B. pseudomallei in the Er-Ren River Basin. The serosurveillance of melioidosis gave seropositivity rates of 36.6%, 21.6%, and 10.9%, respectively, for residents in regions A, B, and C within the Er-Ren Basin area. Culture and PCR-based detection of B. pseudomallei from soil demonstrated that the geographical distribution of this bacterium was confined to a particular site in region B. The distribution of seropositive titers was significantly associated with the incidence rate of melioidosis (120, 68, or 36 incidence cases per 100,000 population in region A, B, or C in 2005), whereas it did not correlate with the geographical distribution of B. pseudomallei within the soil. A survey of transmission modes showed that residents with seropositivity were linked to factors such as having confronted flooding and having walked barefoot on soil, which are potential risk factors associated with exposure to B. pseudomallei. Our findings indicated that the Er-Ren River Basin in Taiwan has the potential to become a high-prevalence area for melioidosis. This is the first report that documents a high prevalence of melioidosis in an area north of latitude 20 degrees N.

Melioidosis complicated by pericarditis

Melioidosis is a bacterial infection caused by the Gram-negative bacillus Burkholderia pseudomallei. We report an unusual case of melioidosis that presented as a pyrexia of unknown origin complicated by pericardial effusion. Our patient received a 6-week course of intravenous antibiotics, followed by 8 months of oral antibiotics, and made a complete recovery. This report illustrates the diagnostic and therapeutic challenge that clinicians may encounter when faced with this potentially fatal infection.

Multilocus sequence typing of historical Burkholderia pseudomallei isolates collected in Southeast Asia from 1964 to 1967 provides insight into the epidemiology of melioidosis

A collection of 207 historically relevant Burkholderia pseudomallei isolates was analyzed by multilocus sequence typing (MLST). The strain collection contains environmental isolates obtained from a geographical distribution survey of B. pseudomallei isolates in Thailand (1964 to 1967), as well as stock cultures and colony variants from the U.S. Army Medical Research Unit (Malaysia), the Walter Reed Army Institute for Research, and the Pasteur Institute (Vietnam). The 207 isolates of the collection were resolved into 80 sequence types (STs); 56 of these were novel. eBURST diagrams predict that the historical-collection STs segregate into three complexes when analyzed separately. When added to the 760 isolates and 365 STs of the B. pseudomallei MLST database, the historical-collection STs cluster significantly within the main complex of the eBURST diagram in an ancestral pattern and alter the B. pseudomallei "population snapshot." Differences in colony morphology among reference isolates were found not to affect the STs assigned, which were consistent with the original isolates. Australian ST84 is likely characteristic of B. pseudomallei isolates of Southeast Asia rather than Australia, since multiple environmental isolates from Thailand and Malaysia share this ST with the single Australian clinical isolate in the MLST database. Phylogenetic evidence is also provided suggesting that Australian isolates may not be distinct from those of Thailand, since ST60 is common to environmental isolates from both countries. MLST and eBURST are useful tools for the study of population biology and epidemiology, since they provide methods to elucidate new genetic relationships among bacterial isolates.