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

Development of a Novel Internally Controlled HrpB1 Gene-Based Real-Time qPCR Assay for Detection of Burkholderia pseudomallei

BACKGROUND

Melioidosis, caused by category B bioterrorism agent Burkholderia pseudomallei, is a seasonal disease of tropical and subtropical regions with a high mortality rate. An early and culture-independent detection of B. pseudomallei is required for the appropriate disease management and prevention. The present study is designed to identify novel and unique sequences of B. pseudomallei and development of quantitative polymerase chain reaction (qPCR) assay.

METHODS

A novel B. pseudomallei-specific target sequence was identified by in silico analysis for the qPCR assay development. The specificity of the developed assay was assessed using purified DNA of 65 different bacterial cultures, and the sensitivity was estimated using a cloned target gene. Further, a type III secretion protein HrpB1 (HrpB1) gene-based duplex qPCR assay incorporating suitable extraction and amplification control was developed, and its viability was assessed in different clinical and environmental matrices for the detection of B. pseudomallei.

RESULTS

In this study, an 80-nucleotide-long B. pseudomallei-specific region within the gene HrpB1 was identified by computational analysis. The developed HrpB1-based qPCR assay was highly specific for B. pseudomallei detection when evaluated with 65 different bacterial cultures. The sensitivity of the qPCR assay with the HrpB1-recombinant plasmid was found to be five copies per qPCR reaction. The assay's detection limit was found to be 5 × 102 CFU/mL for human blood and urine, 5 × 101 CFU/mL in river water, and 2 × 103 CFU/gm in paddy field soil.

CONCLUSION

The results of the study showed the applicability of a novel HrpB1-based qPCR assay for sensitive and specific detection of B. pseudomallei in diverse clinical and environmental samples.

Development of neutropenic sepsis during the eradication phase with co-trimoxazole in patients with melioidosis: two case reports

Introduction

Burkholderia pseudomallei is the bacterium that causes melioidosis. It is mostly a tropical disease, and particularly common in Southeast Asia and northern Australia. The intensive intravenous phase and the oral prolonged eradication phase are the two phases of melioidosis treatment. The current recommended treatment for melioidosis eradication is oral co-trimoxazole (TMP/SMX).

Case report

Two patients were diagnosed with B. pseudomallei bacteremia without a focus and were treated with oral TMP/SMX with folic acid during the eradication phase. Both presented with neutropenic sepsis with pneumonia and pyelonephritis at days 48 and 45 following TMP/SMX 320/1600 mg q12h (4 tablets) and in both of them, the folic acid compliance was poor. One patient died and the other survived following intensive treatment for neutropenia. At the presentation following neutropenic sepsis among both patients, the red blood cells and platelets were within normal limits. Both patients were on a high dose of TMP/SMX, as both were within 40-60 kg of body weight the ideal TMP/SMX dose would be 240/1200 mg q12h (3 tablets). Pancytopenia caused by TMP/SMX can frequently develop gradually over time. Alternately, it can develop rapidly and swiftly escalate to fulminant sepsis, disseminated intravascular coagulation, and fast hemolysis. However, the development of isolated neutropenia is rarely described in the literature.

Conclusions

Prolonged use of TMP/SMX is important to eradicate B. pseudomallei and always the possibility of rare adverse effects has to be considered. Always weight-based TMP-SMX dosing has to be encouraged with need to ensure the compliance of folic acid. During the eradication phase, continuous monitoring of blood cell lines with weekly full blood count would be essential to identify neutropenia in advance.