Acinetobacter baumannii is a bacterium prioritized by the CDC and WHO because of its increasing antibiotic resistance, leading to treatment failures. The hallmark of this pathogen is the high heterogeneity observed among isolates, due to a very dynamic genome.
Mycobacterium avium subsp. paratuberculosis is responsible for paratuberculosis in animals. This disease, leading to an inflammation of the gastrointestinal tract, has a high impact on animal health and an important economic burden. The environmental life cycle of M. avium subsp. paratuberculosis is poorly understood and several studies suggest that free-living amoebae (FLA) might be a potential environmental host. FLA are protozoa found in water and soil that are described as reservoirs of pathogenic and non-pathogenic bacteria in the environment. Indeed, bacteria able to survive within these amoebae would survive phagocytosis from immune cells. In this study, we assessed the in vitro interactions between several strains of M. avium subsp. paratuberculosis and Acanthamoeba castellanii. The results indicate that the bacteria were able to grow within the amoeba and that they can survive for several days within their host. To explore the presence of M. avium subsp. paratuberculosis in environmental amoebae, we sampled water from farms positive for paratuberculosis. A M. avium subsp. paratuberculosis strain was detected within an environmental amoeba identified as related to the poorly described Rosculus genus. The bacterial strain was genotyped, showing that it was similar to previous infectious strains isolated from cattle. In conclusion, we described that various M. avium subsp. paratuberculosis strains were able to grow within amoebae and that these bacteria could be found on farm within amoebae isolated from the cattle environment. It validates that infected amoebae might be a reservoir and vector for the transmission of M. avium subsp. paratuberculosis.
A major debate in evolutionary biology is whether virulence is maintained as an adaptive trait and/or evolves to non-virulence. In the environment, virulence traits of non-obligatory parasites are subjected to diverse selective pressures and trade-offs. Here, we focus on a population of Vibrio splendidus that displays moderate virulence for oysters. A MARTX (Multifunctional-autoprocessing repeats-in-toxin) and a type-six secretion system (T6SS) were found to be necessary for virulence toward oysters, while a region (wbe) involved in O-antigen synthesis is necessary for resistance to predation against amoebae. Gene inactivation within the wbe region had major consequences on the O-antigen structure, conferring lower immunogenicity, competitive advantage and increased virulence in oyster experimental infections. Therefore, O-antigen structures that favour resistance to environmental predators result in an increased activation of the oyster immune system and a reduced virulence in that host. These trade-offs likely contribute to maintaining O-antigen diversity in the marine environment by favouring genomic plasticity of the wbe region. The results of this study indicate an evolution of V. splendidus towards moderate virulence as a compromise between fitness in the oyster as a host, and resistance to its predators in the environment.
Vibrios are ubiquitous in marine environments and opportunistically colonize a broad range of hosts. Strains of Vibrio tasmaniensis present in oyster farms can thrive in oysters during juvenile mortality events and behave as facultative intracellular pathogen of oyster haemocytes. Herein, we wondered whether V. tasmaniensis LGP32 resistance to phagocytosis is specific to oyster immune cells or contributes to resistance to other phagocytes, like marine amoebae. To address this question, we developed an integrative study, from the first description of amoeba diversity in oyster farms to the characterization of LGP32 interactions with amoebae. An isolate of the Vannella genus, Vannella sp. AP1411, which was collected from oyster farms, is ubiquitous, and belongs to one clade of Vannella that could be found associated with Vibrionaceae. LGP32 was shown to be resistant to grazing by Vannella sp. AP1411 and this phenotype depends on some previously identified virulence factors: secreted metalloprotease Vsm and copper efflux p-ATPase CopA, which act at different steps during amoeba-vibrio interactions, whereas some other virulence factors were not involved. Altogether, our work indicates that some virulence factors can be involved in multi-host interactions of V. tasmaniensis ranging from protozoans to metazoans, potentially favouring their opportunistic behaviour.
We assembled the whole genome sequence (WGS) of a collection of 43 non-redundant modern clinical isolates and four broadly used reference strains of Acinetobacter baumannii. Comparison of these isolates and their WGS confirmed the high heterogeneity in capsule loci, sequence types, the presence of virulence and antibiotic resistance genes. However, a significant portion of clinical isolates strongly differ when compared to several reference strains in the light of colony morphology, cellular density, capsule production, natural transformability and in vivo virulence. These genetic and phenotypic differences between current circulating strains of A. baumannii and established reference strains could hamper the study of A. baumannii as an entity. The broadly used reference strains led to the current state of the art of the A. baumannii field, however, we propose that established reference strains in the A. baumannii field should be carefully used, because of the high genetic and phenotypic heterogeneities. In this study, we generated a collection of high-quality nucleotide sequences of 43 modern and non-redundant clinical isolates with the corresponding multi-level phenotypic characterizations. Beside the contribution of novel fundamental observations generated in this study, the phenotypic and genetic data, along with the bacterial strains themselves, will be further accessible using the first open access online platform called Acinetobase. Therefore, a rational choice of modern strains will be possible to select the ones that suit the needs of specific biological questions.
Vibrios are ubiquitous in marine environments and opportunistically colonize a broad range of hosts.Strains of Vibrio tasmaniensis present in oyster farms can thrive in oysters during juvenile mortality events. Among them, V. tasmaniensis LGP32 behaves as a facultative intracellular pathogen of oyster hemocytes, a property rather unusual in vibrios. Herein, we asked whether LGP32 resistance to phagocytosis could result from coincidental selection of virulence factors during interactions with heterotrophic protists, such as amoeba, in the environment. To answer that question, we developed an integrative study, from the first description of amoeba diversity in oyster-farming areas to the characterization of LGP32 interactions with amoebae of the Vannella genus that were found abundant in the oyster environment.LGP32 was shown to be resistant to grazing by amoebae and this phenotype was dependent on previously identified virulence factors: the secreted metalloprotease Vsm and the copper efflux p-ATPase CopA. Using dedicated in vitro assays, our results showed that these virulence factors act at different steps during amoeba-vibrio interactions than they do in oysters-vibrio interactions. Hence, the virulence factors of LGP32 are key determinants of biotic interactions with multiple hosts ranging from protozoans to metazoans, suggesting that the selective pressure exerted by amoebae in marine coastal environments favor coincidental selection of virulence factors.
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