Modelling dynamics between free-living amoebae and bacteria

Free-living amoebae (FLA) serve as hosts for a variety of endosymbionts, which are microorganisms that reside and multiply within the FLA. Some of these endosymbionts pose a pathogenic threat to humans, animals, or both. The symbiotic relationship with FLA not only offers these microorganisms protection but also enhances their survival outside their hosts and assists in their dispersal across diverse habitats, thereby escalating disease transmission. This review is intended to offer an exhaustive overview of the existing mathematical models that have been applied to understand the dynamics of FLA, especially concerning their interactions with bacteria. An extensive literature review was conducted across Google Scholar, PubMed, and Scopus databases to identify mathematical models that describe the dynamics of interactions between FLA and bacteria, as published in peer-reviewed scientific journals. The literature search revealed several FLA-bacteria model systems, including Pseudomonas aeruginosa, Pasteurella multocida, and Legionella spp. Although the published mathematical models account for significant system dynamics such as predator-prey relationships and non-linear growth rates, they generally overlook spatial and temporal heterogeneity in environmental conditions, such as temperature, and population diversity. Future mathematical models will need to incorporate these factors to enhance our understanding of FLA-bacteria dynamics and to provide valuable insights for future risk assessment and disease control measures.

Long-Term Persistence of <i>Yersinia pestis</i> in Association with Acanthamoeba castellanii in Experiment

The aim of the study was to test the feasibility of long-term survival and preservation of the properties of Yersinia pestis in association with soil amoeba Acanthamoeba castellanii. Materials and methods. Y. pestis strains and acanthamoeba isolated in the common area of the Gorno-Altai high-mountain plague focus were used for the study. The systematic affiliation of protozoa was determined through analyzing the 18S rRNA gene fragment sequencing data, followed by alignment with amoeba sequences from the NCBI GenBank database. A fluorescent Y. pestis strain was obtained by electroporation using the pTurboGFP-B plasmid. Co-cultivation was carried out in saline buffer in the absence of nutrients for the cells of plague pathogen. The influence of co-culturing with protozoa on Y. pestis properties was determined using microbiological, biological, and molecular-genetic methods. Results and discussion. The cell viability preservation for 22 months of the experiment in Y. pestis strain belonging to the main subspecies of the antique biovar, the 4.ANT phylogenetic line in co-culture with amoeba cells in the absence of additional nutrients has been established. Co-cultivation with amoebae did not lead to a change in the cultural, morphological, genetic and virulent properties of the plague pathogen strain. The data obtained confirm the possibility of using Acanthamoeba castellanii by the plague microbe to persist in soil biocenoses and open up the prospect of studying the mechanisms of plague pathogen surviving during extended inter-epizootic periods.

<i>Yersinia pestis</i> Strains of the 1.ORI Line as Etiological Agent of the Plague Pandemic III

Yersinia pestis strains of the 1.ORI lineage originate from China as a result of evolution of the 1.ANT phylogenetic branch. Strains of the biovar orientalis are divided into three major lines of evolution: 1.ORI1, 1.ORI2, 1.ORI3. Lines 1.ORI1 and 1.ORI2 originated in China and then spread across the east and west coasts of India, respectively. Strains of the biovar orientalis have widely spread throughout the world, mainly as a result of introduction by sea. This way, the 1.ORI1 line was imported onto the territory of North America. 1.ORI2 line has spread to Southeast Asia, Africa, Europe, and South America. In addition, the strains of the biovar orientalis were brought to the territory of Australia, however, the formation of natural foci did not occur. The spread of strains to new territories during the third plague pandemic, as a rule, took place with the participation of one strain, which caused epizootics among synanthropic rodents. After that, outbreaks were recorded among the population of port cities, followed by drifting into the countryside and the formation of natural foci under suitable natural conditions. In the absence of such, the plague pathogen was eliminated from natural biotopes, and the formation of a natural focus did not occur. In recent decades, most cases of human plague in the world have been caused by strains of the biovar orientalis (1.ORI). However, the emergence and spread of the evolutionary line “1” is insufficiently studied. Currently, there is a lack of both historical data and strains that are ancestors of modern strains in many countries to clarify the details of the irradiation of strains of the biovar orientalis. As a result, the concepts of dissemination of many evolution branches of the strains, biovar orientalis are in the form of hypotheses to date. In this work, the collection and analysis of literature data on the history and epidemiology of plague over the third pandemic, a search for a connection between epidemic manifestations and the appurtenance of the strains that caused them to certain phylogenetic lineages was carried out.

Yersinia pestis: the Natural History of Plague

The Gram-negative bacterium Yersinia pestis is responsible for deadly plague, a zoonotic disease established in stable foci in the Americas, Africa, and Eurasia. Its persistence in the environment relies on the subtle balance between Y. pestis-contaminated soils, burrowing and nonburrowing mammals exhibiting variable degrees of plague susceptibility, and their associated fleas. Transmission from one host to another relies mainly on infected flea bites, inducing typical painful, enlarged lymph nodes referred to as buboes, followed by septicemic dissemination of the pathogen. In contrast, droplet inhalation after close contact with infected mammals induces primary pneumonic plague. Finally, the rarely reported consumption of contaminated raw meat causes pharyngeal and gastrointestinal plague. Point-of-care diagnosis, early antibiotic treatment, and confinement measures contribute to outbreak control despite residual mortality. Mandatory primary prevention relies on the active surveillance of established plague foci and ectoparasite control. Plague is acknowledged to have infected human populations for at least 5,000 years in Eurasia. Y. pestis genomes recovered from affected archaeological sites have suggested clonal evolution from a common ancestor shared with the closely related enteric pathogen Yersinia pseudotuberculosis and have indicated that ymt gene acquisition during the Bronze Age conferred Y. pestis with ectoparasite transmissibility while maintaining its enteric transmissibility. Three historic pandemics, starting in 541 AD and continuing until today, have been described. At present, the third pandemic has become largely quiescent, with hundreds of human cases being reported mainly in a few impoverished African countries, where zoonotic plague is mostly transmitted to people by rodent-associated flea bites.

Yersinia pestis Resists Predation by Acanthamoeba castellanii and Exhibits Prolonged Intracellular Survival

Plague is a flea-borne rodent-associated zoonotic disease caused by Yersinia pestis The disease is characterized by epizootics with high rodent mortalities, punctuated by interepizootic periods when the bacterium persists in an unknown reservoir. This study investigates the interaction between Y. pestis and the ubiquitous soil free-living amoeba (FLA) Acanthamoeba castellanii to assess if the bacterium can survive within soil amoebae and whether intracellular mechanisms are conserved between infection of mammalian macrophages and soil amoebae. The results demonstrate that during coculture with amoebae, representative Y. pestis strains of epidemic biovars Medievalis, Orientalis, and Antiqua are phagocytized and able to survive within amoebae for at least 5 days. Key Y. pestis determinants of the intracellular interaction of Y. pestis and phagocytic macrophages, PhoP and the type three secretion system (T3SS), were then tested for their roles in the Y. pestis-amoeba interaction. Consistent with a requirement for the PhoP transcriptional activator in the intracellular survival of Y. pestis in macrophages, a PhoP mutant is unable to survive when cocultured with amoebae. Additionally, induction of the T3SS blocks phagocytic uptake of Y. pestis by amoebae, similar to that which occurs during macrophage infection. Electron microscopy revealed that in A. castellanii, Y. pestis resides intact within spacious vacuoles which were characterized using lysosomal trackers as being separated from the lysosomal compartment. This evidence for prolonged survival and subversion of intracellular digestion of Y. pestis within FLA suggests that protozoa may serve as a protective soil reservoir for Y. pestisIMPORTANCEYersinia pestis is a reemerging flea-borne zoonotic disease. Sylvatic plague cycles are characterized by an epizootic period during which the disease spreads rapidly, causing high rodent mortality, and an interepizootic period when the bacterium quiescently persists in an unknown reservoir. An understanding of the ecology of Y. pestis in the context of its persistence in the environment and its reactivation to initiate a new epizootic cycle is key to implementing novel surveillance strategies to more effectively predict and prevent new disease outbreaks. Here, we demonstrate prolonged survival and subversion of intracellular digestion of Y. pestis within a soil free-living amoeba. This suggests the potential role for protozoa as a protective soil reservoir for Y. pestis, which may help explain the recrudescence of plague epizootics.