💡 The human gut microbiome is a known ‘melting pot’ for plasmid conjugation, with ARG transfer in this environment widely documented. There is a need to better understand the factors affecting the incidence of these transfer events, and to investigate methods of potentially counteracting the spread of ARGs. This review describes the use and potential of three approaches to studying conjugation in the human gut: observation of in situ events in hospitalized patients, modelling of the microbiome in vivo predominantly in rodent models, and the use of in vitro models of various complexities.
📍 Key Findings:
In Vivo Models: Mice
Model Choice: Rodents, especially mice, are extensively used for in vivo studies due to historical research and their established status as models for human health and disease physiology.
Microbiota Differences: Comparative meta-analyses highlight differences in the murine and human gut microbiota, but mice with natural microbiota are still valuable for studying plasmid transmission.
Applications: In vivo models demonstrated the impact of synthetic fatty acids on plasmid conjugation, role of conjugation in bacteriocin-producing Enterococci, and antibiotic selection dependence for reducing plasmid prevalence.
Model Limitations: Fundamental differences between murine and human microbiota suggest limitations in translatability; diassociated mice, defined microbiota, and antibiotic-treated mice offer alternative models.
📌 Diassociated Mice:
Model Concept: Diassociated mice (germ-free mice inoculated with known microbes) allow high colonization levels and facilitate studying plasmid transmission.
Applications: Used for proof-of-concept studies for conjugation in the gut; observed conjugation between Gram-positive and -negative species in the absence of antibiotic selection.
📌 Mice with Defined Microbiota:
Model Concept: Inoculating germ-free mice with defined microbiota offers a physiological model with controlled complexity.
Examples: ASF model (free of Enterobacteriaceae) allows colonization by specific strains; Oligo-MM12 designed for colonization resistance against S. enterica; HFA model involves inoculation with human faecal bacteria.
📌 Antibiotic-Treated Mice:
Model Concept: Antibiotic-treated mouse model involves depleting select bacterial species, reducing colonization resistance, and aiding disease models.
Applications: Streptomycin-pretreated models used for studying Salmonella infection, persistence, and antibiotic resistance transmission; streptomycin, gentamicin, and erythromycin treatment explored for inducing dysbiosis and studying pheromone-responsive plasmids.
Other Animal Models:
Rat Models: Diassociated Sprague–Dawley rats demonstrated rare plasmid transfer; HFA rats studied plasmid-mediated transmission.
Fruit Fly (Drosophila melanogaster): Proposed as a model for in vivo plasmid transfer due to its reduced complexity; demonstrated E. coli transconjugant isolation.
Wax Moth Larvae (Galleria mellonella): Used for studying plasmid transfer and bacterial cooperation, demonstrating the importance of antibiotic-treated models.
📍 In Vitro Models:
Advantages: In vitro models offer controllable parameters, easy access, monitoring, and sampling.
Established Models: Multivessel chemostat models (e.g., SHIME®, PolyFermS) simulate gut environments; mucosal SHIME incorporates artificial mucosal components; TIM-2, TIM-1, TSI, and ARCOL offer various compartments for studying plasmid transmission.
Key Variables: Factors like pH, anaerobic conditions, agitation, mucosal components, and bile influence plasmid dynamics in in vitro models.
Common Observations:
Role of Mucosal Structures: In vitro models incorporating mucosal structures or biofilm lifestyles show increased conjugation, highlighting the importance of these elements.
Conjugation Efficiency: Conjugation frequencies can vary based on the model, bacterial strains, and environmental factors such as antibiotics and inflammation.
Conjugation in Presence of Antibiotics: Antibiotic-treated models are crucial for studying the impact of antibiotics on plasmid dynamics, transmission, and bacterial cooperation.
Link to the article: http://tinyurl.com/bde3wz4s
