Gasque, M. | bioRxiv Science

bioRxiv2026

Comparative evaluation of sample preparation and enrichment methods for culture and molecular detection of Burkholderia pseudomallei in naturally contaminated soils from Thailand over one year.

Background Burkholderia pseudomallei is a soil-dwelling bacterium that causes melioidosis. Accurate environmental detection of B. pseudomallei is critical for surveillance strategies and for tracing the source of human infection. However, the detection of B. pseudomallei in soil samples, which are complex matrices with a high microbial background, remains difficult. This study aimed to compare the culture and the molecular detection of B. pseudomallei with or without pre-enrichment in naturally contaminated soils from Thailand. Methodology/principal findings In 2025, a total of 640 soil samples were collected from 10 sites from different environments and sampling periods in Amnat Charoen Province. The soils were evaluated for the presence of B. pseudomallei either without enrichment or following enrichment in Ashdown or ACER broths, using culture and real-time PCR detection methods. qPCR consistently identified a higher number of B. pseudomallei positive samples than culture regardless of the pre-treatment method and sampling period. ACER enrichment nearly doubled the odds of detection compared with no enrichment (OR = 1.90) or with Ashdown enrichment (OR = 2.09), with a model-estimated mean Ct difference of 13.6 between ACER enrichment and no enrichment. Overall, qPCR yielded higher detection rates than culture for B. pseudomallei in soil samples, particularly following enrichment. Conclusions/significance This study highlights the importance of pre-enrichment protocols with detection techniques to successfully identify B. pseudomallei in environmental samples. For both culture and molecular detection methods, B. pseudomallei was better detected when the soil samples were enriched in ACER broth compared to Ashdown broth and without enrichment. These findings highlight the need for combining optimal selective enrichment strategies with detection techniques for environmental surveillance. Although ACER enrichment improved the recovery of viable strains, culture recovered B. pseudomallei from only a fraction of qPCR-positive samples, highlighting the need for more selective media to facilitate isolation of B. pseudomallei.

microbiology↗

bioRxiv2024

Serological screening in animals combined with environmental surveys provides definite proof of the local establishment of Burkholderia pseudomallei in Guadeloupe

BackgroundMelioidosis is an emerging infectious disease caused by the soil-dwelling bacterium Burkholderia pseudomallei that affects both humans and animals. It is endemic in South and Southeast Asia, and northern Australia, causing an estimated 165,000 human cases annually worldwide. Human cases have been reported in the French West Indies (Martinique and Guadeloupe) since the 1990s. Conversely, no human cases have been reported in French Guiana, a French territory in South America. Our study aimed to investigate whether B. pseudomallei is locally established in Guadeloupe and French Guiana. We assessed animal exposure by serology and examined the presence of B. pseudomallei in the environment of seropositive animals. Methodology/Principal findingsBlood samples were collected from domestic animals in two goat farms in Les Saintes, Guadeloupe (n=31), and in 56 farms in French Guiana (n=670) and tested by ELISA. Serological follow up was performed on selected farms. Soil, water and goat rectal swabs were collected and analysed by culture and PCR. In French Guiana, the highest prevalence rates were observed in equids (24%) and cattle (16%), while in Les Saintes, a prevalence of 39% was observed in goats. The longitudinal study in Les Saintes revealed consistent high seropositivity in goats. A B. pseudomallei strain was isolated from the soil from one of the farms and detected in goat rectal swabs from the other farm. Conclusions/SignificanceOur environmental investigation prompted by the serologic data confirms the presence of B. pseudomallei in Les Saintes, consistent with documented human cases of melioidosis on this island. In French Guiana, our serologic results call for environmental surveys and a re-evaluation of human infections with melioidosis-like symptoms. The approach developed in this study may help to identify high-risk areas that warrant further investigation. Author summaryBurkholderia pseudomallei, an environmental bacterium, is the causative agent of melioidosis in humans and animals. If the disease has been historically reported to be endemic in South Asia and northern Australia, recent studies reveal its presence outside of these territories, both in the environment and among patients who have not travelled to endemic areas. Furthermore, the projected increase in extreme climatic events in the near future could increase the prevalence of the disease as well as cause its emergence in new territories. For these reasons, it is important to identify new areas at risk. Our study aimed to investigate the presence of the pathogen in French West Indies. We combined surveys in domestic animals (cattle, goats, horses, sheep, and pigs) and in the environment. The identification of seropositive animals without clinical signs, together with the isolation of B. pseudomallei in the environment of a goat farm in Guadeloupe, underscores the importance of including melioidosis in animal surveillance programs. The use of serologic methods can help identify animal exposure to the pathogen, thereby helping to identify areas where the pathogen may be present in the environment.

microbiology↗

bioRxiv2021

Simultaneous hybrid genome sequencing of Vermamoeba vermiformis and its Dependentiae endosymbiont Vermiphilus pyriformis

A hybrid sequencing approach, using short and long reads sequencing, was employed for characterizing the genomes of the free-living amoeba host Vermamoeba vermiformis, along with its Dependentiae endosymbiont Vermiphilus pyriformis. The amoeba host reconstructed nuclear genome is 39.5 Mb, and its full mitochondrial genome is 61.7 kb. The closed, circular genome of the Dependentiae endosymbiont Vermiphilus pyriformis, naturally infecting V. vermiformis is 1.1 Mb.

genomics↗