Biology subjects

Laroucau, K.

Publications and source records attributed to Laroucau, K..

5 recordsLinked to original sources

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↗

bioRxiv2026

Drivers of host-infectious agent community associations in seabirds from sub-Antarctic oceanic islands

Understanding the patterns and drivers of infectious disease dynamics at different levels of life organization is a fundamental disease ecology challenge. In this study, we performed a multi-infectious agents (IA) screening of 1,983 individuals belonging to 18 seabird species, sampled between 2017 and 2022 across five sub-Antarctic islands in the Southern Indian and Atlantic Oceans. Our aim was to identify the drivers of IA community in these seabirds by considering intrinsic and extrinsic factors on three dimensions: distance between seabird metapopulations and within-island sites, macro-community (host functional traits based on feeding and breeding features) and intra-host IA community composition. Samples were screened for 24 DNA-based IAs using a high-throughput real-time PCR method, followed by subsequent hierarchical modelling of species communities. Campylobacter lari, Escherichia coli, Pasteurella multocida, Chlamydiaceae and Mycobacterium spp. were found to be present on all islands in some, but not all, species. However, only E. coli was detected in all species. According to our modelling results, the influence of year and within-island site had limited influence on IA presence/absence, accounting respectively for an average of 1.0% and 1.8% of the variation in IA community. Including host species as a response variable produced a better model fit than including host species functional traits, highlighting the difficulty in simplifying systems by focusing on high-level functional categories. Model outputs show how each species influences IA distribution depending on IA traits, but no clear trend has emerged. Interestingly, burrowing species were less frequently infected with directly transmitted IAs, probably due to the low frequency of transmission events associated with their breeding features and limited social contacts. Our findings pave the way for further multi-dimension studies that would combine complementary approaches to disentangle the complex processes at play in the dynamics of hosts and IAs interactions.

ecology↗

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↗

bioRxiv2022

Extensive genomic divergence among 61 strains of Chlamydia psittaci

Chlamydia (C.) psittaci, the causative agent of avian chlamydiosis and human psittacosis, is a genetically heterogeneous species. Its broad host range includes parrots and many other birds, but occasionally also humans (via zoonotic transmission), ruminants, horses, swine and rodents. To assess whether there are genetic markers associated with host tropism we comparatively analyzed whole-genome sequences of 61 C. psittaci strains. Initially, poorly assembled genomes in public databases were subjected to clean-up, reassembly and polishing. Multiple sequence alignment of the genome sequences revealed four major clades within this species. Clade 1 represents the most recent lineage comprising 40/61 strains and contains 9/10 of the psittacine strains, including type strain 6BC, and 10/13 of human isolates. Clades 2-4 carry strains from different non-psittacine hosts. We found that clade membership correlates with classification schemes based on SNP types, ompA genotypes, multilocus sequence types as well as plasticity zone (PZ) structure and host preference. Genome analysis also revealed that i) sequence variation in the major outer membrane porin OmpA can result in 3D structural changes of immunogenic domains, ii) past host change of Clade 3 and 4 strains could be associated with loss of MAC/perforin in the PZ, rather than the large cytotoxin, iii) the distinct phylogeny of atypical strains (Clades 3 and 4) is also reflected in their repertoire of inclusion proteins (Inc family) and polymorphic membrane proteins (Pmps). Altogether, our study identified a number of genomic features that can be correlated with the phylogeny and host preference of C. psittaci strains.

genomics↗

bioRxiv2020

A glycoengineered antigen exploiting a conserved protein O-glycosylation pathway in the Burkholderia genus for diagnosis of glanders infections

We recently described a protein O-glycosylation pathway conserved in all species of the Burkholderia genus that results in synthesis and incorporation of a trisaccharide glycan to membrane-exported proteins. Here, we exploited this system to construct and evaluate a diagnostic tool for glanders. Burkholderia mallei, the causative agent of glanders, is a highly infectious and fatal zoonotic pathogen that mainly infects horses, mules, donkeys and occasionally humans. A highly sensitive and specific diagnostic tool is crucial for the control, elimination and eradication of B. mallei infections. We constructed plasmids carrying synthetic genes encoding a modified, previously unannotated Burkholderia glycoprotein containing three glycosylation sequons fused to the cholera toxin B-subunit. The resulting proteins were glycosylated in the B. cenocepacia K56-2 parental strain, but not in glycosylation-deficient mutants, as determined by SDS-PAGE and fluorescent lectin blots. One of these glycoproteins was used as an antigen in ELISA and western blots to screen a panel of serum samples collected from glanders-infected and healthy horses previously investigated by complement fixation test and indirect ELISA based on a semi-purified fraction of B. mallei. We show that ELISA and western blot assays based on our glycoprotein antigen provide 100 % specificity, with a sensitivity greater than 88%. The glycoprotein antigen was recognized by serum samples collected from patients infected with B. pseudomallei, B. mallei, B. multivorans and B. cenocepacia. Our results indicate that protein O-glycosylation in Burkholderia can be exploited as a biomarker for diagnosis of Burkholderia-associated infections. IMPORTANCEGlanders is a severe zoonotic disease caused by the Gram-negative bacterium Burkholderia mallei, which affects horses, mules and donkeys, as well as humans. B. mallei is also considered a category B biothreat agent. Due to insufficient pathognomonic symptoms in the early stages of glanders, diagnosis can be difficult. Complement fixation is the most accurate and reliable serological test prescribed by the World Organization for Animal Health; however, this test has a considerable number of false-positive results. We have recently described a conserved protein O-glycosylation pathway present in all species of the Burkholderia genus; we also demonstrated that Burkholderia-infected humans develop anti-glycan antibodies. Here, we exploited this system to construct and evaluate a synthetic glycoengineered protein antigen as a diagnostic tool for glanders. Our results show 100 % specificity in the detection of antibodies from infected horses, indicating that protein O-glycosylation in Burkholderia can be exploited as a biomarker for diagnosis of Burkholderia-associated infections.

microbiology↗