Biogeography and genetic diversity of clinical isolates of Burkholderia pseudomallei in Sri Lanka

A systematic review and meta-analysis of the global prevalence and relationships among Burkholderia pseudomallei sequence types isolated from humans, animals, and the environment

Background and Aim

Burkholderia pseudomallei, a highly pathogenic bacterium responsible for melioidosis, exhibits ecological ubiquity and thrives within soil and water reservoirs, posing significant infection risks to humans and animals through direct contact. The aim of this study was to elucidate the genetic diversity and prevalence patterns of B. pseudomallei sequence types (STs) across a global spectrum and to understand the relationships between strains isolated from different sources.

Materials and Methods

We performed a systematic review and meta-analysis in this study. Extensive research was carried out across three comprehensive databases, including PubMed, Scopus, and ScienceDirect with data collected from 1924 to 2023.

Results

A total of 40 carefully selected articles contributed 2737 B. pseudomallei isolates attributed to 729 distinct STs and were incorporated into the systematic review. Among these, ST46 emerged as the most prominent, featuring in 35% of the articles and demonstrating a dominant prevalence, particularly within Southeast Asia. Moreover, ST51 consistently appeared across human, animal, and environmental studies. Subsequently, we performed a meta-analysis, focusing on nine specific STs: ST46, ST51, ST54, ST70, ST84, ST109, ST289, ST325, and ST376. Surprisingly, no statistically significant differences in their pooled prevalence proportions were observed across these compartments for ST46, ST70, ST289, ST325, and ST376 (all p > 0.69). Conversely, the remaining STs, including ST51, ST54, ST84, and ST109, displayed notable variations in their prevalence among the three domains (all p < 0.04). Notably, the pooled prevalence of ST51 in animals and environmental samples surpassed that found in human isolates (p < 0.01).

Conclusion

To the best of our knowledge, this study is the first systematic review and meta-analysis to investigate the intricate relationships between STs and their sources and contributes significantly to our understanding of B. pseudomallei diversity within the One Health framework.

Melioidosis Queensland: An analysis of clinical outcomes and genomic factors

BACKGROUND

The clinical and genomic epidemiology of melioidosis varies across regions.

AIM

To describe the clinical and genetic diversity of B. pseudomallei across Queensland, Australia.

METHODS

Whole genome sequencing of clinical isolates stored at the melioidosis reference lab from 1996-2020 was performed and analysed in conjunction with available clinical data.

RESULTS

Isolates from 292 patients were analysed. Bacteraemia was present in 71% and pneumonia in 65%. The case-fatality rate was 25%. Novel sequence types (ST) accounted for 51% of all isolates. No association was identified between the variable virulence factors assessed and patient outcome. Over time, the proportion of First Nation's patients declined from 59% to 26%, and the proportion of patients aged >70 years rose from 13% to 38%.

CONCLUSION

This study describes a genomically diverse and comparatively distinct collection of B. pseudomallei clinical isolates from across Queensland, Australia. An increasing incidence of melioidosis in elderly patients may be an important factor in the persistently high case-fatality in this region and warrants further investigation and directed intervention.

Burkholderia pseudomallei in soil and natural water bodies in rural Sri Lanka: A hidden threat to public health

Burkholderia pseudomallei is the causative agent of the potentially fatal infection, melioidosis. This study provides the first evidence for the presence of B. pseudomallei in soil and water in Sri Lanka. Targeted sampling of soil and natural water sources was done between November 2019 and October 2020 over eight field visits encompassing the neighborhood of 28 culture and/or antibody-positive melioidosis patients in northwestern, western and southern Sri Lanka. A total of eight environmental isolates of B. pseudomallei (BPs-env1 to BPs-env8) were cultured from 116 soil and 117 natural water samples collected from 72 locations. The presence of B. pseudomallei in soil and natural water in these areas poses a risk of melioidosis for populations cultivating crops in such soils and using untreated water from these sources for drinking, bathing, and other domestic purposes. Identifying sites positive for B. pseudomallei may help to mitigate risk by raising public awareness of contaminated environmental sources and allowing soil and water remediation.

Melioidosis and Burkholderia pseudomallei : progress in epidemiology, diagnosis, treatment and vaccination

PURPOSE OF REVIEW

Melioidosis and its causative bacterium Burkholderia pseudomallei are being found in unexpected locations and bacterial genotyping is providing new insights into global spread and where and how individuals are being infected. This review summarizes recent studies covering the epidemiology, diagnosis, treatment, and prevention of melioidosis.

RECENT FINDINGS

Whole-genome sequencing of B. pseudomallei from patients and environmental sampling is informing the phylogeography of B. pseudomallei at regional, continental, and global levels, while also defining the epidemiology for individual cases. The situation in Africa remains the most unresolved, while the evolving story of B. pseudomallei in the Americas may establish that B. pseudomallei is endemic in parts of southern USA. Guidelines for diagnosis and treatment of melioidosis are well established, and published mortality has decreased from 50% or higher to 10% or lower in some countries but access to laboratory and therapeutic resources are not available or are extremely limited in many melioidosis-endemic regions.

SUMMARY

The enormous clinical diversity of melioidosis and the complexities of laboratory diagnosis and of treatment make it a sentinel disease for highlighting the continuing global disparities in access to and provision of healthcare.

Burden of melioidosis in India and South Asia: Challenges and ways forward

Melioidosis is caused by the environmental bacterium Burkholderia pseudomallei. South Asia is estimated to have 44% of the global disease burden. Among South Asian countries, Bangladesh and Sri Lanka are considered endemic for melioidosis; a few cases have been reported from Nepal, and a few imported cases from Pakistan have also been reported. India has experienced an increase in numbers of melioidosis cases in the recent years. The bacteria is inherently present in the soil and enters the human body via skin abrasions, inhalation, or ingestion. As clinicians are often ignorant about the similar characteristics of this disease and several other common tropical diseases, it causes a major delay in the timely diagnosis and management. The organism is easily mistaken as Pseudomonas spp in microbiology laboratories and may be dismissed as a common laboratory contaminant. The poor diagnostic sensitivity of blood culture also leads to missed diagnosis. Hence, both clinical ignorance and missed laboratory diagnosis have misrepresented melioidosis as a rare entity. The key preventive interventions are avoiding contact with loose and muddy soils of meliodosis-endemic areas, and provision of safe drinking water. The present article describes the various possible attributes for melioidosis underdiagnosis and the challenges of improving the diagnosis in conjunction with viable solutions.

Funding

None.

Melioidosis of the central nervous system; impact of the bimABm allele on patient presentation and outcome

BACKGROUND

The autotransporter protein Burkholderia intracellular motility A (BimA) facilitates the entry of Burkholderia pseudomallei into the central nervous system (CNS) in mouse models of melioidosis. Its role in the pathogenesis of human cases of CNS melioidosis is incompletely defined.

METHODS

Consecutive culture-confirmed cases of melioidosis at two sites in tropical Australia after 1989 were reviewed. Demographic, clinical and radiological data of the patients with CNS melioidosis were recorded. The bimA allele (bimABm or bimABp) of the B. pseudomallei isolated from each patient was determined.

RESULTS

Of the 1587 cases diagnosed at the two sites during the study period, 52 (3.3%) had confirmed CNS melioidosis; 20 (38.5%) had a brain abscess, 18 (34.6%) had encephalomyelitis, 4 (7.7%) had isolated meningitis and 10 (19.2%) had extra-meningeal disease. Among the 52 patients, there were 8 (15.4%) deaths; 17/44 (38.6%) survivors had residual disability. The bimA allele was characterized in 47/52; 17/47 (36.2%) had the bimABm allele and 30 (63.8%) had the bimABp allele. Patients with a bimABm variant were more likely to have a predominantly neurological presentation (odds ratio (OR) (95% confidence interval (CI)): 5.60 (1.52-20.61), p=0.01), to have brainstem involvement (OR (95%CI): 7.33 (1.92-27.95), p=0.004) and to have encephalomyelitis (OR (95%CI): 4.69 (1.30-16.95), p=0.02. Patients with a bimABm variant were more likely to die or have residual disability (odds ratio (95%CI): 4.88 (1.28-18.57), p=0.01).

CONCLUSIONS

The bimA allele of B. pseudomallei has a significant impact on the clinical presentation and outcome of patients with CNS melioidosis.