Mecanismos involucrados en la evolución hacia la extrema droga resistencia del patógeno Serratia marcescens
Serratia marcescens is a Gram-negative, motile, free-living, ubiquitous bacillus belonging to the family Yersiniaceae. In recent decades, S. marcescens has been recognized by the World Health Organisation as a priority antibiotic resistant pathogen. The emergence of S. marcescens in the in-hospital...
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| Formato: | Tesis doctoral acceptedVersion |
| Lenguaje: | Español |
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Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica
2023
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| Acceso en línea: | http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=posgraafa&cl=CL1&d=HWA_7826 https://repositoriouba.sisbi.uba.ar/gsdl/collect/posgraafa/index/assoc/HWA_7826.dir/7826.PDF |
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| Sumario: | Serratia marcescens is a Gram-negative, motile, free-living, ubiquitous bacillus belonging to the family Yersiniaceae. In recent decades, S. marcescens has been recognized by the World Health Organisation as a priority antibiotic resistant pathogen. The emergence of S. marcescens in the in-hospital niche combined with its intrinsic resistance to antibiotics (ATBs) could lead to the emergence of lineages with limited therapeutic options.
Today, given the existence of multiple evidences on the accelerated acquisition of antibiotic resistance in this species, we hypothesize that the in-depth study of its resistome and mobilome will provide valuable information on the molecular basis associated with adaptation to the in-hospital niche. First, S. marcescens strain SCH909, a multidrug-resistant (MDR) isolate that has been used as a biological model in our laboratory, was selected and sequenced, which was the starting point for the genomic analyses of this thesis. Subsequently, the genomes of a collection of clinical strains of S. marcescens (n=152), obtained from different health entities located in four provinces of Argentina (14 hospitals, 1997-2018), were sequenced. As a result of the latter, a local database of genomes from our region was constructed. To understand the components that nourish the resistome, this database was compared with the genomes of other strains from different niches, including an environmental strain called S. marcescens He2Co2 isolated from the pavement of the Autonomous City of Buenos Aires. Finally, we evaluated the ability of S. marcescens to capture, maintain and disseminate plasmids carrying ?-lactamases both intraspecies and interspecies, evidencing the possibility of this species to microevolve towards extreme (XDR) and pandrug resistance (PDR).
Two already sequenced S. marcescens isolates, one from the in-hospital niche (S. marcescens SM39) and one from the environmental niche (S. marcescens Db11), were selected; comparative genomics studies were performed with S. marcescens SCH909. The study of the mobilome of these three strains revealed that their genomes contain a wide variety of mobile genetic elements (MGEs). A total of 13 prophages, 39 insertion sequences (ISs), five distinct integrons, one Group II intron, one genomic island (GI), three plasmids and a total of 30 antibiotic resistance genes (ARGs) were identified in the three selected genomes. At the same time, when analyzing the resistome of the three strains, we found that S. marcescens SCH909 is the major carrier of ARGs (n=18), of which 61.11% (11/18) are inserted in the chromosome. Most of these ARGs were located within a novel resistance GI that we named SmaR, whose structure is similar to the characteristic GIs of A. baumannii.
Likewise, within the resistome of S. marcescens strains circulating in Argentina, we also located other chromosomal resistance GIs that had not been previously described. One was named SmaR-2, which carries the blaCTX-M-2 gene disseminating in several clusters. In turn, within the vertically inherited resistome, we analyzed other components such as intrinsic ARGs, efflux pumps and antibiotic resistance proto-genes, observing their abundance and diversity. We identified all acquired ARGs contributing to the resistome (n=593), most of them spreading across different genetic platforms. Among them, the presence of the mcr9.1 gene, conferring resistance to colistin is highlighted. This ATB, to which S. marcescens is intrinsically resistant, is used as last resort for infections caused by XDR pathogens.
Phylogenetic analysis of the strains revealed lineages exhibiting resistomes with high clinical impact including polyclonal dissemination of the blaCTX-M-2 and blaKPC-2 genes as well as the presence of plasmids carrying the carbapenemases blaNDM-1 and blaIMP-8 genes. We also found a cluster grouping three strains from different hospitals containing a novel allele of the carbapenemase blaSPR-1.
To understand the role of S. marcescens in the dissemination of antibiotic resistance, we studied the activity of plasmids associated with the dissemination of ?-lactam resistance in our strain´s collection. Four Plasmids and two plasmid pseudo molecules were molecularly characterized. The conjugative capacity of these plasmids was evaluated, both interspecies (E. coli J53) and intraspecies (S. marcescens SCH909). In vivo assays resulted in pDCASG1-CTX (carrying the blaCTX-M-2 gene) and pDCASG6-NDM (carrying blaNDM-1 gene) were conjugative. When evaluating plasmid maintenance in the transconjugant strains, the results showed that S. marcescens SCH909 was able to maintain the pDCASG6-NDM plasmid longer than E. coli J53 (97,78% versus 20% at ten days, respectively).
In conclusion, this work revealed the heterogeneity of the antibiotic resistance patterns that compose the resistome of S. marcescens species. Its ability to maintain and disseminate MGEs associated with MDR genetic platforms could serve as a "Trojan horse", silently contributing to the dissemination of clinically relevant acquired ARGs in the in-hospital niche over time. In turn, the carriage of a wide variety of genetic platforms allows for greater adaptability and survival in different habitats including both environmental and clinical niches, making this species a likely nexus between different bacterial groups. |
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