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Melioidosis, caused by the Gram-negative bacterium Burkholderia pseudomallei, is a potentially life-threatening infection that can affect humans and a wide variety of animals in the tropics. In December 2017, a swine melioidosis case was discovered during a meat inspection at a privately-owned slaughterhouse in Nakhon Si Thammarat Province in southern Thailand. The infection, which continued for several months, caused a dispute about where the disease began. An environmental investigation into two farms—both involved in raising the first infected pig—ensued. Through genetic analysis, the investigation revealed that a contaminated water supply at one farm was the probable source of infection. The three local sequence types identified in the investigation were types 51, 298 and 392.

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Burkholderia pseudomallei is a Gram-negative bacterium and the causative agent of melioidosis in humans and animals in the tropics. The clinical manifestations of melioidosis are diverse, ranging from localized infections to whole-body sepsis. The effective serological method is crucial for the point-of-care diagnosis of melioidosis. The aim of this study was to develop indirect immunofluorescence assay (IFA)-based methods for detecting immunoglobulin G (IgG) antibodies in melioidosis patients. These methods use whole-cell antigens made from recombinant E. coli strains that express major B. pseudomallei antigens, including TssM, OmpH, AhpC, BimA, and Hcp1. A total of 271 serum samples from culture-confirmed melioidosis patients (n = 81), patients with other known infections (n = 70), and healthy donors (n = 120) were tested. Our study showed that the recombinant TssM strain had the highest performance, with 92.6% sensitivity, 100% specificity, 100% positive predictive value, 96.9% negative predictive value, 97.8% efficiency, 97.0% accuracy, and no cross-reactivity. The method agreement analysis based on k efficiency calculations showed that all five IFA methods perfectly agreed with the standard culturing method, while the traditional indirect hemagglutination (IHA) method moderately agreed with the culture. In summary, our investigations showed that the TssM-IFA method could be used for melioidosis diagnosis.

Melioidosis is an infection that occurs in humans and a wide range of animals by Burkholderia pseudomallei as a causative pathogen, which inhabits environments of tropical and subtropical climate zones, particularly in Thailand. The standard laboratory diagnosis is by culture and biochemical characteristic differentiation. This study aimed to determine the diversity of colony morphology, biochemical characteristics, and drug susceptibility patterns of a B. pseudomallei collection isolated from humans, animals, soil, and water in Thailand. According to the previous characterization of colony morphotypes from Type I to VII, Type I is predominant with B. pseudomallei from humans and animals with a similar water source. Meanwhile, Type III is predominant from soil sources. The results confirmed the hypothesis that infection might be from water instead of soil exposure. The typical biochemical phenotypes were consistent among different isolate sources, including cytochrome oxidase (positive), triple iron sugar (K/N or A/N), sulfide (negative), indole (negative), non-motile, glucose oxidizing, and DNase (positive). The biochemical characteristic results supported the data for the selection of the prepopulated biochemical tests in clinical and research laboratories. The antimicrobial susceptibility patterns by standard disk diffusion showed mode values of inhibition zones for selected drugs that had lower trends in B. pseudomallei isolated from the soil than other sources. The results were consistent with MIC50 and MIC90 values of ceftazidime, which was highest in B. pseudomallei from the soil than other sources. HIGHLIGHTS The previous study reported the characterization of Burkholderia pseudomallei colony morphotypes from Type I to VII. However, there were no reports of the diversity of colony morphology and antibiotic susceptibility pattern from diverse sources Type I is predominant with B. pseudomallei from humans and animals with a similar water source, which confirmed the hypothesis that infection might be from water instead of soil exposure The mode of antimicrobial inhibition zones for selected drugs had lower trends in the isolates from the soil than other sources. The results indicated the soil isolates showed a trend in increasing ceftazidime resistance compared with other sources GRAPHICAL ABSTRACT