In vitro assessment of antimicrobial resistance dissemination dynamics during multidrug resistant bacteria invasion events using a continuous culture device

Antimicrobial resistant pathogens display significant public health threats by causing difficulties in clinical treatment of bacterial infection. Antimicrobial resistance (AMR) is transmissible between bacteria, significantly increasing the appearance of antimicrobial resistant pathogens, aggravating the AMR problem. In this work, the dissemination dynamics of AMR from invading multidrug resistant (MDR) Escherichia coli to a community of pathogenic Salmonella enterica was investigated using a continuous culture device, and the behaviors of dissemination dynamics under different levels of antibiotic stress were investigated. Three MDR E. coli invasion events were analyzed in this work: MDR E. coli-S. enterica co-colonization, MDR E. coli invasion after antibiotic treatment of S. enterica, and MDR E. coli invasion before antibiotic treatment of S. enterica. It was found that both horizontal gene transfer (HGT) and vertical gene transfer (VGT) play significant roles in AMR dissemination, although different processes contribute differently under different circumstances; that environmental levels of antibiotics promote AMR dissemination by enhancing HGT rather than leading to selective advantage for resistant bacteria; and that early invasion of MDR E. coli completely and quickly sabotages the effectiveness of antibiotic treatment. These findings contribute to understanding the drivers of AMR dissemination under different antibiotic stress, the detrimental impact of environmental tetracycline contamination, and the danger of nosocomial presence and dissemination of MDR non-pathogens. IMPORTANCE Antimicrobial resistance poses a grave threat to public health and reduces the effectiveness of antimicrobial drugs in treating bacterial infections. Antimicrobial resistance is transmissible, either by horizontal gene transfer between bacteria, or by vertical gene transfer following inheritance of genetic traits. The dissemination dynamics and behaviors of this threat, however, hasn’t been rigorously investigated. In this work, with a continuous culture device, we studied antimicrobial resistance dissemination processes by simulating antimicrobial resistant Escherichia coli invasion to a pathogenic Salmonella enterica community. Using this novel tool, we provide evidence on the drivers of antimicrobial resistance dissemination, on the detrimental impact of environmental antibiotic contamination, and on the danger of antimicrobial resistance in hospitals, even if what harbors the antimicrobial resistance is not a pathogen. This work furthers our understanding on antimicrobial resistance and its dissemination between bacteria, and on antibiotic therapy, our most powerful tool against bacterial infection.

The Search for Common Origin: Homology Revisited

Understanding the evolution of biodiversity on Earth is a central aim in biology. Currently, various disciplines of science contribute to unravel evolution at all levels of life, from individual organisms to species and higher ranks, using different approaches and specific terminologies. The search for common origin, traditionally called homology, is a connecting paradigm of all studies related to evolution. However, it is not always sufficiently taken into account that defining homology depends on the hierarchical level studied (organism, population, and species), which can cause confusion. Therefore, we propose a framework to define homologies making use of existing terms, which refer to homology in different fields, but restricting them to an unambiguous meaning and a particular hierarchical level. We propose to use the overarching term “homology” only when “morphological homology,” “vertical gene transfer,” and “phylogenetic homology” are confirmed. Consequently, neither phylogenetic nor morphological homology is equal to homology. This article is intended for readers with different research backgrounds. We challenge their traditional approaches, inviting them to consider the proposed framework and offering them a new perspective for their own research.

Evolution of Leucyl-tRNA Synthetase Through Eukaryotic Speciation

Aminoacyl-tRNA synthetases (aaRSs) are part of the cellular translation machinery and as such, they are essential enzymes for every known cell. Due to their ubiquitous nature, their evolutionary history has been intensely researched to better understand the origins of life on a molecular level. Herein, we examine the evolutionary relatedness of leucyl-tRNA synthetases (LeuRS) from each major eukaryotic branch through the speciation process. This research effort was centered on amino acid sequence data as well as generating homology protein models for each LeuRS enzyme. Comparative analysis of this sequence and structural data for LeuRS amongst eukaryotes has indicated a high level of conservation within the active sites of these enzymes. Phylogenetic analysis confirmed this high degree of conservation as well as established evolutionary relatedness between these LeuRS enzymes. Based on this data, vertical gene transfer propagated LeuRS throughout the eukaryotic domain. Horizontal gene transfer and domain acquisition events were not observed within the eukaryotic organisms studied. Our data also highlighted LeuRS adaptation through the speciation process due to slight variability of scaffolding residues outside of the active site regions. We hypothesize that this variability may be due to mechanistic differences amongst LeuRS enzymes that have assumed non-translational functionality through the evolutionary process. KEYWORDS: tRNA Synthetase; Leucyl-tRNA Synthetase; Eukaryotic Evolution; LeuRS Conservation; Vertical Gene Transfer; Horizontal Gene Transfer; Convergent Evolution; Primordial Enzymes