Combining functional and structural genomics to track antibiotic resistance genes in mobile elements in clinical bacterial strains

Abstract

The rise of multi-antibiotics resistant bacteria represents an emergent threat to human health. Here, we investigate antibiotic resistance mechanisms in bacteria of several species isolated from an intensive care unit in Brazil. We used whole-genome analysis to identify antibiotic resistance genes (ARGs) and plasmids in 35 strains of Gram-negative and Gram-positive bacteria, including the first genomic description of Morganella morganii and Ralstonia mannitolilytica clinical isolates from South America. We identify a high abundance of beta-lactamase genes in highly resistant organisms, including seven extended-spectrum {beta}-lactamases shared between organisms from different species. Additionally, we identify several ARGs-carrying plasmids indicating the potential for fast transmission of resistance mechanism between bacterial strains, comprising a novel IncFII plasmid recently introduced in Brazil from Asia. Through comparative genomic analysis, we demonstrate that some pathogens identified here are very distantly related to other bacteria isolated worldwide, demonstrating the potential existence of endemic bacterial pathogens in Brazil. Also, we uncovered at least two couples of (near)-identical plasmids exhibiting multi-drug resistance, suggesting that plasmids were transmitted between bacteria of the same or different species in the hospital studied. Finally, since many highly resistant strains carry several different ARGs, we used functional genomics to investigate which of them were indeed functional. In this sense, for three bacterial strains (Escherichia coli, Klebsiella pneumoniae, and M. morganii), we identify six beta-lactamase genes out of 15 predicted in silico as the main responsible for the resistance mechanisms observed, corroborating the existence of redundant resistance mechanisms in these organisms. ImportanceBig data and large-scale sequencing projects have revolutionized the field, achieving a greater understanding of ARGs identification and spreading at global level. However, given that microbiota and associated ARGs may fluctuate across geographic zones, hospital-associated infections within clinical units still remain underexplored in Brazil - the largest country in South America; 210 million inhabitants - and neighboring countries. This work highlighted the identification of several ARGs shared between species co-occurring simultaneously into a Brazilian hospital, some of them associated with large plasmids, mostly endowed with transposable elements. Also, genomic features of clinically underrepresented pathogens such M. morganii and B. cepacia were revealed. Taken together, our results demonstrate how structural and functional genomics can help to identify emerging mechanisms of shared antibiotic resistance in bacteria from clinical environments. Systematic studies as the one presented here should help to prevent outbreaks of novel multidrug resistance bacteria in healthcare facilities.