Publicação
Relationships between mobile genetic elements, antimicrobial resistance, and virulence in clinically relevant Acinetobacter baumannii isolates
| Resumo: | Acinetobacter baumannii is considered one of the most dangerous pathogens causing nosocomial infections. This Gram-negative bacterium colonizes and infects immunocompromised patients and it is very difficult to eradicate. Its remarkable adaptability is facilitated by virulence factors, such as capsule, lipopolysaccharides, secreted proteins, iron acquisition factors, pili, outer membrane vesicles (OMVs), and the SOS response. In addition, its emergence as a multidrug-resistant (MDR) microorganism led the World Health Organization to include this species, Carbapenem-Resistant A. baumannii (CRAb) in particular, in the top priority list of pathogens for the development of new drugs. CRAb emerged through the acquisition of antibiotic-resistance determinants mediated by plasmids, prophages and OMVs. In this study, the main goal was to investigate the role of mobile genetic elements (MGEs) in the evolution of A. baumannii clinical isolates regarding antibiotic resistance and virulence. Initially, a new Prophage Analysis Tool (ProphAnTool) was developed for the comprehensive analysis of prophages among all complete A. baumannii genomes deposited in the National Center for Biotechnology Information (NCBI) database. Using this tool, it was possible to show that intact prophages are present in A. baumannii with a very high prevalence. Next, the SOS response was studied with focus on the ddrR gene, which was deleted from an A. baumannii strain for genome-wide transcriptome analysis to assess its role in virulence and fitness, as well as prophage induction. DdrR was shown to influence several virulence and fitness-related genes, and a model for its involvement in the regulation of phage induction was proposed. Three new A. baumannii isolates from a hospital outbreak, including two CRAb, were sequenced and analyzed, showing the presence of a new plasmid in the CRAb isolates that encodes multiple antibiotic resistance genes, including carbapenemases. OMVs were isolated and characterized by mass spectrometry. This revealed several virulence factors, in particular active carbapenemases in OMVs from the CRAb isolates. Accordingly, these OMVs were shown to protect other susceptible bacteria against carbapenems. MGEs were analyzed revealing the presence of inducible prophages and various other plasmids in the CRAb isolates. This study showed that mobile elements, such as plasmids, prophages, and OMVs, are all together involved in the genetic evolution of A. baumannii, which has ultimately led to the emergence of highly antibiotic-resistant and virulent variants, like CRAb. Besides, as A. baumannii has a unique SOS response, a potential role of DdrR in the regulation of prophage induction was unveiled, opening the field for further studies on these two important elements. |
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| Autores principais: | Monteiro, Rodrigo Pimenta Oliveira |
| Assunto: | A. baumannii Antibiotic-resistance Mobile genetic elements Prophages Virulence Elementos genéticos móveis Resistência a antibióticos Virulência |
| Ano: | 2024 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso embargado |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Acinetobacter baumannii is considered one of the most dangerous pathogens causing nosocomial infections. This Gram-negative bacterium colonizes and infects immunocompromised patients and it is very difficult to eradicate. Its remarkable adaptability is facilitated by virulence factors, such as capsule, lipopolysaccharides, secreted proteins, iron acquisition factors, pili, outer membrane vesicles (OMVs), and the SOS response. In addition, its emergence as a multidrug-resistant (MDR) microorganism led the World Health Organization to include this species, Carbapenem-Resistant A. baumannii (CRAb) in particular, in the top priority list of pathogens for the development of new drugs. CRAb emerged through the acquisition of antibiotic-resistance determinants mediated by plasmids, prophages and OMVs. In this study, the main goal was to investigate the role of mobile genetic elements (MGEs) in the evolution of A. baumannii clinical isolates regarding antibiotic resistance and virulence. Initially, a new Prophage Analysis Tool (ProphAnTool) was developed for the comprehensive analysis of prophages among all complete A. baumannii genomes deposited in the National Center for Biotechnology Information (NCBI) database. Using this tool, it was possible to show that intact prophages are present in A. baumannii with a very high prevalence. Next, the SOS response was studied with focus on the ddrR gene, which was deleted from an A. baumannii strain for genome-wide transcriptome analysis to assess its role in virulence and fitness, as well as prophage induction. DdrR was shown to influence several virulence and fitness-related genes, and a model for its involvement in the regulation of phage induction was proposed. Three new A. baumannii isolates from a hospital outbreak, including two CRAb, were sequenced and analyzed, showing the presence of a new plasmid in the CRAb isolates that encodes multiple antibiotic resistance genes, including carbapenemases. OMVs were isolated and characterized by mass spectrometry. This revealed several virulence factors, in particular active carbapenemases in OMVs from the CRAb isolates. Accordingly, these OMVs were shown to protect other susceptible bacteria against carbapenems. MGEs were analyzed revealing the presence of inducible prophages and various other plasmids in the CRAb isolates. This study showed that mobile elements, such as plasmids, prophages, and OMVs, are all together involved in the genetic evolution of A. baumannii, which has ultimately led to the emergence of highly antibiotic-resistant and virulent variants, like CRAb. Besides, as A. baumannii has a unique SOS response, a potential role of DdrR in the regulation of prophage induction was unveiled, opening the field for further studies on these two important elements. |
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