We reported a unique case of posttraumatic giant infratentorial extradural intradiploic epidermoid cyst. A 54-year-old male, with a previous history of an open scalp injury and underlying linear skull fracture in the left occipital region in childhood, presented with a painful subcutaneous swelling, which had been developed gradually in the same region and moderate headache, nausea, vomiting and cerebellar ataxia. The duration of symptoms on admission was 3 months. Imaging studies revealed occipital bone destruction and giant extradural intradiploic lesion. The preoperative diagnosis was giant infratentorial extradural intradiploic epidermoid cyst. Surgery achieved total removal of the lesion, which was histologically confirmed and the postoperative course was uneventful. To our knowledge, this is the first case of giant infratentorial extradural intradiploic epidermoid cyst with a traumatic etiology described in the literature.
Neoplasm; Epidermoid cyst; Cranial fossa; Posterior; Trauma; Etiology
Osteonecrosis (avascular necrosis) is known to be caused by high-dose corticosteroid therapy, alcoholism and rarely by infections. However, a tubercular etiology of this condition is very rare. A review of the literature yielded only a few cases of polyarticular tuberculosis with osteonecrosis in immunosuppressed individuals. No case of monoarticular tubercular osteonecrosis diagnosed by aspiration cytology was found. Since tuberculosis is a curable disease, an early and accurate diagnosis is essential.
A 60-year-old Indian man presented with diffuse swelling and pain in the left shoulder for the previous 6 months. A computed tomography scan of the left shoulder revealed crescentic lucency in the humeral head, suggestive of osteonecrosis. Fine needle aspiration cytology smears from the swelling showed features of an acute suppurative lesion. Stain for acid-fast bacillus was positive and thus, a final clinico-pathological diagnosis of osteonecrosis of humeral head with tubercular etiology was rendered. The patient was initiated on anti-tuberculous therapy with symptomatic improvement in his condition.
Osteonecrosis, a debilitating disease, may rarely occur due to tuberculosis, especially in endemic areas. Fine needle aspiration cytology is an effective and inexpensive modality for an early diagnosis of the tubercular etiology of osteonecrosis.
Intramedullary and subarachnoidal tubercular abscesses are rare forms of spinal tuberculosis as compared with extradural collections secondary to vertebral tuberculosis.
We herein present a 33-year-old, apparently healthy male patient who presented clinically as transverse myelitis, with a lesion at detected at conus cauda, developing fulminant holocord intramedullary tubercular abscess, treated with surgical evacuation and much later with anti-tubercular drugs. Atypical clinical, serological, imaging findings in addition to lack of knowledge of occurrence of fulminant intramedullary tuberculosis led to the delay in starting anti-tubercular treatment.
Early diagnosis requires a high index of suspicion, search for a primary focus of tubercular infection, investigation with magnetic resonance imaging (MRI) of spinal cord, biopsy, and confirmation with microscopy and culture, even in immunocompetent individuals. Early diagnosis, prompt treatment with surgical evacuation of abscess, and anti-tubercular drugs can lead to a good neurological recovery.
Filum terminale; intramedullary; spinal tuberculosis; subarachnoidal; tubercular abscess
Skull base osteomyelitis (SBO) is a rare clinical presentation and usually occurs as a complication of trauma or sinusitis. A 5-year-old child presented to the emergency department with a three-week history of fever associated with drowsiness and left parietal headache, and a week's history of swelling on the left frontoparietal soft tissue. He had suffered a penetrating scalp injury four month ago. On physical examination, there was a tender swelling with purulent stream on the lateral half of his scalp. His vital signs are within normal limits. Plain X-ray of the skull showed a lytic lesion on the left frontoparietal bone. A cranial computed tomography (CT) scan demonstrated a large subgaleal abscess at the left frontoparietal region. SBO possesses a high morbidity and mortality; therefore, prompt diagnosis and appropriate treatment are mandatory to prevent further complications and to reduce morbidity and mortality significantly.
Melioidosis or infection with Burkholderia pseudomallei presents with protean manifestations. We present a case of melioidosis in a diabetic patient from India. The case is presented to highlight the importance of early microbiologic diagnosis and subsequent institution of appropriate therapy to achieve a better prognosis
A male bachelor around 50 years of age from India presented with low grade fever, bilateral ankle swelling and hypochondrial pain. On examination patient had diabetes and had multiple abscesses in bilateral ankle, knee and splenic region. Microbiologic diagnosis revealed the etiologic agent to be Burkholderia pseudomallei. Patient was managed with iv ceftazidime and surgical excision.
The case report highlights the importance of early identification of etiologic agent. B. pseudomallei identification requires a great deal of clinical suspicion as well as alertness on the part of the medical microbiologist as these isolates are often reported as Pseudomonas spp. Correct identification of the etiologic agent is essential as B pseudomallei requires prolonged antimicrobial therapy for a better clinical outcome.
Burkholderia pseudomallei is the causative agent of melioidosis. It is endemic in South East Asian countries and North Australia. Sporadic cases of melioidosis have been reported from several parts of South India. Melioidosis may manifest as chronic pneumonia mimicking tuberculosis and generally be seen as a single entity. We report the first case of melioidosis and pulmonary tuberculosis co-infection in a diabetic patient. The causative agents were identified using standard methods and the patient recovered after completion of the recommended antibiotic therapy. Melioidosis is an emerging infectious disease in India. Though melioidosis and tuberculosis present with similar clinical picture, co-infections are rare. Hence, increased awareness among clinicians and microbiologists can help in diagnosing the disease even when there is no clinical suspicion.
Burkholderia pseudomallei; melioidosis; tuberculosis
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.
Burkholderia pseudomallei, the etiologic agent of melioidosis, is endemic to tropic regions, mainly in Southeast Asia and northern Australia. Melioidosis occurs only sporadically in travellers returning from disease-endemic areas. Severe clinical disease is seen mostly in patients with alteration of immune status. In particular, pericardial effusion occurs in 1-3% of patients with melioidosis, confined to endemic regions. To our best knowledge, this is the first reported case of melioidosis in a traveller complicated by a hemodynamically significant pericardial effusion without predisposing disease.
A 44-year-old Caucasian man developed pneumonia, with bilateral pleural effusions and complicated by a hemodynamically significant pericardial effusion, soon after his return from Thailand to Switzerland. Cultures from different specimens including blood cultures turned out negative. Diagnosis was only accomplished by isolation of Burkholderia pseudomallei from the pericardial aspirate, thus finally enabling the adequate antibiotic treatment.
Melioidosis is a great mimicker and physicians in non-endemic countries should be aware of its varied manifestations. In particular, melioidosis should be considered in differential diagnosis of pericardial effusion in travellers , even without risk factors predisposing to severe disease.
Melioidosis; Burkholderia pseudomallei; Pericardial effusion; Traveller
A case report of an orbital eosinophilic granuloma presenting as a fistula in a 15-year-old boy is presented. The patient had a history of a painful right upper eyelid swelling which required drainage and was considered as an abscess. An increase in swelling occurred and a small fistula appeared in the area subsequently. Computed tomography scan revealed a large soft tissue lesion in right superolateral orbit having intracranial extradural extension with destruction of bony orbital margin. Fine needle aspiration biopsy of the lesion revealed eosinophilic granuloma. A complete excision of the lesion was performed by a brow incision and histopathological examination of the excised specimen confirmed diagnosis. Although upper eyelid area eosinophilic granuloma is known to occur, its presentation as a fistula is not known.
Eosinophilic granuloma; Fistula; Histopathological; Excision
A 45-year-old man visited our clinic with a painless swelling of the left scrotum and an ulcer as chief complaints. A hard and indurated mass was palpable with ulcerating foci that were proximal and distal, measuring 3 × 2 cm and 2 × 1 cm respectively and about 2 cm apart. Laboratory data were normal except for an elevated erythrocyte sedimentation rate (ESR), and white blood cell (WBC) differential showed neutropenia and lymphocytosis. A diagnosis of left testicular tumor was made and the patient had a left orchidectomy with fistulectomy. Histopathology results showed a stratified squamous epithelium with tuberculous granuloma and necrotic caseation. Patient is currently on anti-tubercular medication. The rarity of this condition makes these findings important to report.
left scrotal mass; tuberculosis; caseous necrosis; tuberculous granulomas
Melioidosis, which is caused by a soil saprophyte, Burkholderia pseudomallei, is most prevalent in the south–west coast of India. Although it is frequently seen in immunocompromised patients, melioidosis can occur in apparently normal individuals. Melioidosis can involve almost any organ. A relapse of melioidosis is usually associated with a poor adherence to the eradication therapy, a multifocal involvement and bacteraemia. A relapsing melioidosis is usually known to follow a similar pattern of organ involvement in the first and second episodes of the infection. We are discussing here, a rare case of melioidosis in a 38-year-old construction-worker, with no risk factors, who presented initially with a pericardial effusion. It relapsed 6 months after he completed the prescribed eradication therapy for 3 months, as an anterior chest wall abscess. The author recommends a high index of suspicion for the relapsed melioidosis cases, inspite of the primary episode being non-bacteraemic and compliant with the recommended therapy, in order to avoid further complications.
Melioidosis; Relapse; Pericardial effusion; Chest wall abscess
Melioidosis is a severe bacterial infection caused by Burkholderia pseudomallei. Rapid antimicrobial therapy is necessary to improve patient outcome, which is aided by direct detection of B. pseudomallei in clinical samples. A drawback for all antigen assays is that the number of B. pseudomallei in blood usually falls below the achievable level of detection. We performed a prospective cohort study of 461 patients with 541 blood cultures to evaluate the utility of a pre-incubation step prior to detection of B. pseudomallei using a monoclonal antibody-based immunofluorescent assay (Mab-IFA). The Mab-IFA was positive in 74 of 76 patients with melioidosis (sensitivity = 97.4%), and negative in 385 patients who did not have blood cultures containing B. pseudomallei (specificity = 100%). The Mab-IFA could be a valuable supplementary tool for rapid detection. We recommend the use of the Mab-IFA to test blood cultures that flag positive in regions where melioidosis is endemic.
Primary Non-Hodgkin's Lymphoma of the cranial scalp and skull vault is a rare disease. We are describing a case of the same in a 50-year-old man. He was presented with a diffuse swelling in the left side scalp since 4 months of duration and progressively enlarging in size. On local Examination of the scalp, there was a diffuse swelling in the left parietal and occipital region of scalp. Imaging showed diffuse infiltration of the skull vault with extracranial soft tissue masses. Further investigations with CT scan chest, abdomen, and pelvis did not reveal any other evidence of systemic lymphoma. Biopsy of one of the scalp masses showed a small to intermediate cell B-cell lymphoma. Other nine previously reported cases of primary skull vault lymphoma were reviewed.
Burkholderia pseudomallei, the etiological agent of melioidosis, is a facultative intracellular pathogen. As B. pseudomallei is a gram-negative bacterium, its outer membrane contains lipopolysaccharide (LPS) molecules, which have been shown to have low-level immunological activities in vitro. In this study, the biological activities of B. pseudomallei LPS were compared to those of Burkholderia thailandensis LPS, and it was found that both murine and human macrophages produced levels of tumor necrosis factor alpha, interleukin-6 (IL-6), and IL-10 in response to B. pseudomallei LPS that were lower than those in response to B. thailandensis LPS in vitro. In order to elucidate the molecular mechanisms underlying the low-level immunological activities of B. pseudomallei LPS, its lipid A moiety was characterized using mass spectrometry. The major lipid A species identified in B. pseudomallei consists of a biphosphorylated disaccharide backbone, which is modified with 4-amino-4-deoxy-arabinose (Ara4N) at both phosphates and penta-acylated with fatty acids (FA) C14:0(3-OH), C16:0(3-OH), and either C14:0 or C14:0(2-OH). In contrast, the major lipid A species identified in B. thailandensis was a mixture of tetra- and penta-acylated structures with differing amounts of Ara4N and FA C14:0(3-OH). Lipid A species acylated with FA C14:0(2-OH) were unique to B. pseudomallei and not found in B. thailandensis. Our data thus indicate that B. pseudomallei synthesizes lipid A species with long-chain FA C14:0(2-OH) and Ara4N-modified phosphate groups, allowing it to evade innate immune recognition.
A 21-year-old man presented to the emergency department with pain and swelling to the right side of his neck and chest wall with associated shortness of breath. Two days earlier, while playing football, he had been involved in a minor collision with another player where he was struck on the right side of his head, but had managed to continue playing. On examination, the patient had extensive cervical surgical emphysema. There were no further positive findings on respiratory and general examination. A chest x-ray demonstrated no rib or clavicular fractures and no pneumothorax. Therefore, a CT was undertaken to ascertain the cause of the surgical emphysema. This demonstrated a pneumomediastinum, pneumopericardium and extradural air in the spinal column in addition to the subcutaneous air. The CT identified no bony trauma and no other injuries. The symptoms resolved spontaneously and follow-up radiography, 9 days later, showed no residual air.
The genus Burkholderia includes pathogenic gram-negative bacteria that cause melioidosis, glanders, and pulmonary infections of patients with cancer and cystic fibrosis. Drug resistance has made development of new antimicrobials critical. Many approaches to discovering new antimicrobials, such as structure-based drug design and whole cell phenotypic screens followed by lead refinement, require high-resolution structures of proteins essential to the parasite.
We experimentally identified 406 putative essential genes in B. thailandensis, a low-virulence species phylogenetically similar to B. pseudomallei, the causative agent of melioidosis, using saturation-level transposon mutagenesis and next-generation sequencing (Tn-seq). We selected 315 protein products of these genes based on structure-determination criteria, such as excluding very large and/or integral membrane proteins, and entered them into the Seattle Structural Genomics Center for Infection Disease (SSGCID) structure determination pipeline. To maximize structural coverage of these targets, we applied an “ortholog rescue” strategy for those producing insoluble or difficult to crystallize proteins, resulting in the addition of 387 orthologs (or paralogs) from seven other Burkholderia species into the SSGCID pipeline. This structural genomics approach yielded structures from 31 putative essential targets from B. thailandensis, and 25 orthologs from other Burkholderia species, yielding an overall structural coverage for 49 of the 406 essential gene families, with a total of 88 depositions into the Protein Data Bank. Of these, 25 proteins have properties of a potential antimicrobial drug target i.e., no close human homolog, part of an essential metabolic pathway, and a deep binding pocket. We describe the structures of several potential drug targets in detail.
This collection of structures, solubility and experimental essentiality data provides a resource for development of drugs against infections and diseases caused by Burkholderia. All expression clones and proteins created in this study are freely available by request.
The clinical and radiological features of pulmonary melioidosis can mimic tuberculosis. We prospectively evaluated 118 patients with suspected pulmonary tuberculosis who were acid-fast bacilli (AFB) smear negative at Udon Thani Hospital, northeast Thailand. Culture of residual sputum from AFB testing was positive for Burkholderia pseudomallei in three patients (2.5%; 95% confidence interval [CI] 0.5–7.3%). We propose that in melioidosis-endemic areas, residual sputum from AFB testing should be routinely cultured for B. pseudomallei.
Burkholderia pseudomallei is a mostly saprophytic bacterium, but can infect humans where it causes the difficult-to-manage disease melioidosis. Even with proper diagnosis and prompt therapeutic interventions mortality rates still range from >20% in Northern Australia to over 40% in Thailand. Surprisingly little is yet known about how B. pseudomallei infects, invades and survives within its hosts, and virtually nothing is known about the contribution of critical nutrients such as iron to the bacterium's pathogenesis. It was previously assumed that B. pseudomallei used iron-acquisition systems commonly found in other bacteria, for example siderophores. However, our previous discovery of a clinical isolate carrying a large chromosomal deletion missing the entire malleobactin gene cluster encoding the bacterium's major high-affinity siderophore while still being fully virulent in a murine melioidosis model suggested that other iron-acquisition systems might make contributions to virulence. Here, we deleted the major siderophore malleobactin (mba) and pyochelin (pch) gene clusters in strain 1710b and revealed a residual siderophore activity which was unrelated to other known Burkholderia siderophores such as cepabactin and cepaciachelin, and not due to increased secretion of chelators such as citrate. Deletion of the two hemin uptake loci, hmu and hem, showed that Hmu is required for utilization of hemin and hemoglobin and that Hem cannot complement a Hmu deficiency. Prolonged incubation of a hmu hem mutant in hemoglobin-containing minimal medium yielded variants able to utilize hemoglobin and hemin suggesting alternate pathways for utilization of these two host iron sources. Lactoferrin utilization was dependent on malleobactin, but not pyochelin synthesis and/or uptake. A mba pch hmu hem quadruple mutant could use ferritin as an iron source and upon intranasal infection was lethal in an acute murine melioidosis model. These data suggest that B. pseudomallei may employ a novel ferritin-iron acquisition pathway as a means to sustain in vivo growth.
Burkholderia pseudomallei is the etiologic agent of melioidosis, a multifaceted deadly and difficult to treat disease of equatorial regions of the world. Disease manifestations range from acute infections to long term chronic infections. The factors by which this bacterium causes disease are not yet well understood. Studies thus far focused on elucidation of the roles of traditional virulence factors such as secreted proteins and exopolysaccharides, but virtually nothing is known about the roles of nutrient acquisition systems in B. pseudomallei's survival in its mammalian hosts. One nutrient that is essential for bacterial metabolism and pathogenicity is iron. As free iron is not readily available in nature, bacteria developed numerous mechanisms for iron acquisition from abiotic and biotic sources. These mechanisms include siderophores and hemin/hemoglobin utilization systems, and it is therefore not too surprising that mutants defective in these systems are often impaired in virulence. In this study we show that defined B. pseudomallei mutants defective in siderophore and hemin/hemoglobin utilization systems remain fully lethal in a murine melioidosis model and present evidence for in vitro ferritin-iron acquisition which may be one or perhaps the main means by which this pathogen sustains in vivo growth.
The Gram-negative bacterium Burkholderia pseudomallei is the etiological agent of melioidosis and is remarkably resistant to most classes of antibacterials. Even after months of treatment with antibacterials that are relatively effective in vitro, there is a high rate of treatment failure, indicating that this pathogen alters its patterns of antibacterial susceptibility in response to cues encountered in the host. The pathology of melioidosis indicates that B. pseudomallei encounters host microenvironments that limit aerobic respiration, including the lack of oxygen found in abscesses and in the presence of nitric oxide produced by macrophages. We investigated whether B. pseudomallei could survive in a nonreplicating, oxygen-deprived state and determined if this physiological state was tolerant of conventional antibacterials. B. pseudomallei survived initial anaerobiosis, especially under moderately acidic conditions similar to those found in abscesses. Microarray expression profiling indicated a major shift in the physiological state of hypoxic B. pseudomallei, including induction of a variety of typical anaerobic-environment-responsive genes and genes that appear specific to anaerobic B. pseudomallei. Interestingly, anaerobic B. pseudomallei was unaffected by antibacterials typically used in therapy. However, it was exquisitely sensitive to drugs used against anaerobic pathogens. After several weeks of anaerobic culture, a significant loss of viability was observed. However, a stable subpopulation that maintained complete viability for at least 1 year was established. Thus, during the course of human infection, if a minor subpopulation of bacteria inhabited an oxygen-restricted environment, it might be indifferent to traditional therapy but susceptible to antibiotics frequently used to treat anaerobic infections.
Infections due to Mycobacterium tuberculosis, Burkholderia pseudomallei and non-typhoidal Salmonella cause significant morbidity and mortality throughout the world. These intracellular pathogens share some common predisposing factors and clinical features. Co-infection with two of these organisms has been reported previously but, to our knowledge, this is the first time that infection with all three has been reported in one person.
In September 2010, a 58-year-old diabetic Malaysian male presented with fever and a fluctuant mass on the right side of his neck. B. pseudomallei was isolated from an aspirate of this lesion and there was radiological evidence of disseminated infection in the liver and spleen. The recurrence of clinical symptoms over ensuing months prompted further aspiration and biopsy of a cervical abscess and underlying lymph nodes. Salmonella enterica serovar Stanley and then M. tuberculosis were identified from these specimens by culture and molecular methods. The patient responded to targeted medical management of each of these infections.
In endemic settings, a high index of suspicion and adequate tissue sampling are imperative in identifying these pathogenic organisms. Diabetes was identified as a predisposing factor in this case while our understanding of other potential risk factors is evolving.
Melioidosis; Tuberculosis; Salmonella stanley; Diabetes
Melioidosis is an emerging infectious disease of humans and animals in the tropics caused by the soil bacterium Burkholderia pseudomallei. Despite high fatality rates, the ecology of B. pseudomallei remains unclear. We used a combination of field and laboratory studies to investigate B. pseudomallei colonization of native and exotic grasses in northern Australia. Multivariable and spatial analyses were performed to determine significant predictors for B. pseudomallei occurrence in plants and soil collected longitudinally from field sites. In plant inoculation experiments, the impact of B. pseudomallei upon these grasses was studied and the bacterial load semi-quantified. Fluorescence-in-situ-hybridization and confocal laser-scanning microscopy were performed to localize the bacteria in plants. B. pseudomallei was found to inhabit not only the rhizosphere and roots but also aerial parts of specific grasses. This raises questions about the potential spread of B. pseudomallei by grazing animals whose droppings were found to be positive for these bacteria.
In particular, B. pseudomallei readily colonized exotic grasses introduced to Australia for pasture. The ongoing spread of these introduced grasses creates new habitats suitable for B. pseudomallei survival and may be an important factor in the evolving epidemiology of melioidosis seen both in northern Australia and elsewhere globally.
Burkholderia pseudomallei, the cause of the severe disease melioidosis in humans and animals, is a gram-negative saprophyte living in soil and water of areas of endemicity such as tropical northern Australia and Southeast Asia. Infection occurs mainly by contact with wet contaminated soil. The environmental distribution of B. pseudomallei in northern Australia is still unclear. We developed and evaluated a direct soil B. pseudomallei DNA detection method based on the recently published real-time PCR targeting the B. pseudomallei type III secretion system. The method was evaluated by inoculating different soil types with B. pseudomallei dilution series and by comparing B. pseudomallei detection rate with culture-based detection rate for 104 randomly collected soil samples from the Darwin rural area in northern Australia. We found that direct soil B. pseudomallei DNA detection not only was substantially faster than culture but also proved to be more sensitive with no evident false-positive results. This assay provides a new tool to detect B. pseudomallei in soil samples in a fast and highly sensitive and specific manner and is applicable for large-scale B. pseudomallei environmental screening studies or in outbreak situations. Furthermore, analysis of the 104 collected soil samples revealed a significant association between B. pseudomallei-positive sites and the presence of animals at these locations and also with moist, reddish brown-to-reddish gray soils.
Limited experience and a lack of validated diagnostic reagents make Burkholderia pseudomallei, the cause of melioidosis, difficult to recognize in the diagnostic microbiology laboratory. We compared three methods of confirming the identity of presumptive B. pseudomallei strains using a collection of Burkholderia species drawn from diverse geographic, clinical, and environmental sources. The 95 isolates studied included 71 B. pseudomallei and 3 B. thailandensis isolates. The API 20NE method identified only 37% of the B. pseudomallei isolates. The agglutinating antibody test identified 82% at first the attempt and 90% including results of a repeat test with previously negative isolates. Gas-liquid chromatography analysis of bacterial fatty acid methyl esters (GLC-FAME) identified 98% of the B. pseudomallei isolates. The agglutination test produced four false positive results, one B. cepacia, one B. multivorans, and two B. thailandensis. API produced three false positive results, one positive B. cepacia and two positive B. thailandensis. GLC-FAME analysis was positive for one B. cepacia isolate. On the basis of these results, the most robust B. pseudomallei discovery pathway combines the previously recommended isolate screening tests (Gram stain, oxidase test, gentamicin and polymyxin susceptibility) with monoclonal antibody agglutination on primary culture, followed by a repeat after 24 h incubation on agglutination-negative isolates and GLC-FAME analysis. Incorporation of PCR-based identification within this schema may improve percentages of recognition further but requires more detailed evaluation.
Immunochromatographic test (ICT) kits for the rapid detection of immunoglobulin G (IgG) and IgM antibodies to Burkholderia pseudomallei were compared to the indirect hemagglutination (IHA) assay. In 138 culture-confirmed melioidosis cases, sensitivities were 80, 77, and 88% for IHA, ICT IgG, and ICT IgM, respectively. In a prospective study of 160 consecutive sera samples sent for melioidosis serology, respective specificities were 91, 90, and 69, positive predictive values were 41, 32, and 18, and negative predictive values were 99, 98, and 100%. ICT IgM kits are unreliable for diagnosis of melioidosis, but ICT IgG kits may be useful for diagnosing travelers presenting with possible melioidosis who return from regions where melioidosis is endemic.
Burkholderia pseudomallei causes the potentially fatal disease melioidosis. It is generally accepted that B. pseudomallei is a noncommensal bacterium and that any culture-positive clinical specimen denotes disease requiring treatment. Over a 23-year study of melioidosis cases in Darwin, Australia, just one patient from 707 survivors has developed persistent asymptomatic B. pseudomallei carriage. To better understand the mechanisms behind this unique scenario, we performed whole-genome analysis of two strains isolated 139 months apart. During this period, B. pseudomallei underwent several adaptive changes. Of 23 point mutations, 78% were nonsynonymous and 43% were predicted to be deleterious to gene function, demonstrating a strong propensity for positive selection. Notably, a nonsense mutation inactivated the universal stress response sigma factor RpoS, with pleiotropic implications. The genome underwent substantial reduction, with four deletions in chromosome 2 resulting in the loss of 221 genes. The deleted loci included genes involved in secondary metabolism, environmental survival, and pathogenesis. Of 14 indels, 11 occurred in coding regions and 9 resulted in frameshift mutations that dramatically affected predicted gene products. Disproportionately, four indels affected lipopolysaccharide biosynthesis and modification. Finally, we identified a frameshift mutation in both P314 isolates within wcbR, an important component of the capsular polysaccharide I locus, suggesting virulence attenuation early in infection. Our study illustrates a unique clinical case that contrasts a high-consequence infectious agent with a long-term commensal infection and provides further insights into bacterial evolution within the human host.
Some bacterial pathogens establish long-term infections that are difficult or impossible to eradicate with current treatments. Rapid advances in genome sequencing technologies provide a powerful tool for understanding bacterial persistence within the human host. Burkholderia pseudomallei is considered a highly pathogenic bacterium because infection is commonly fatal. Here, we document within-host evolution of B. pseudomallei in a unique case of human infection with ongoing chronic carriage. Genomic comparison of isolates obtained 139 months (11.5 years) apart showed a strong signal of adaptation within the human host, including inactivation of virulence and immunogenic factors, and deletion of pathways involved in environmental survival. Two global regulatory genes were mutated in the 139-month isolate, indicating extensive regulatory changes favoring bacterial persistence. Our study provides insights into B. pseudomallei pathogenesis and, more broadly, identifies parallel evolutionary mechanisms that underlie chronic persistence of all bacterial pathogens.