Análisis epidemiológico y molecular de la virulencia y la antibiorresistencia en acinetobacter baumannii

Zusammenfassung

Acinetobacter baumannii is a pathogen implicated in infecting critically ill patients. CRAB isolates are increasing in frequency worldwide, forcing clinicians to use colistin. A. baumannii has numerous intrinsic resistance mechanisms, virulence determinants, and can acquire resistance to almost all antibiotics. OXAs among clinically significant ICs are the most common cause of carbapenem resistance. A. baumannii can differentially express virulence determinants and the cause of this is not extensively investigated. In this Doctoral Thesis, the relationship between clonality, virulence, and antimicrobial resistance is investigated in two sets of isolates obtained from hospitals from Spain and Lebanon. Our aim is providing clinicians and infection control specialists with tools that could be used to improve therapy and limit the spread of CRAB isolates; and to better understand the interaction between virulence and antibiotic resistance. Fifty nine clinical A. baumannii isolates were obtained from HU-LP, Spain and 90 from SGH-UMC, Lebanon. Identification was performed using API strips, PCR amplification of blaOXA-51-like, and MALDI-TOF MS. Susceptibility testing was performed according to CLSI guidelines and clonality was determined by tri-locus sequence typing and PFGE. PCR for common carbapenemases was then performed and biofilms, hemolysis, siderophores, motility, proteolytic activity, and doubling times were phenotypically detected. Additionally, sequencing of the pmrCAB operon and the entire genome was performed for two sets of isolates that acquired colistin resistance during therapy. Also, the patterns of biofilm formation were determined for some isolates through growth on steel coupons and CLSM analysis. Our data show high rates of carbapenem resistance in both hospitals, indicating an immediate need for intervention. IC II was predominant in both countries while OXA-24-like was predominant in HU-LP as opposed to the predominance of OXA-23-like in SGH-UMC. PFGE analysis showed that strains pertaining to 7 pulsotypes were responsible for most infections. This shows the ability of a few clones to cause repeated infections and the international spread of ICs and OXAs. Virulence profiles were variable among the different isolates but, among the Spanish set, IC II and OXA-23-like were associated with increased virulence. This association was absent among the Lebanese set suggesting the locality of the association and the need for local analyses before clinically exploiting the relationship between these phenomena. Associations between the different virulence factors was evident and further investigating this relationship could help better understand the pathogenicity of A. baumannii. Genomic analysis of colistin resistant strains showed that the P233S and deletion of Ile in PmrB mutations caused colistin resistance. The former mutation affected virulence while the latter novel mutation had no effect on virulence. Moreover, blaGES-5 was identified for the first time in A. baumannii indicating inter-species exchange of carbapenemases. Investigating the patterns of biofilm formation showed a possible relationship between aminoglycoside sensibility and fast rates of biofilm formation, and between carbapenem resistance and dense biofilm formations. These preliminary findings require further investigations using larger pools of isolates. In conclusion, this study shows high rates of CRAB isolates and predominance of IC II in HU-LP and SGH-UMC. It also shows a predominance of OXA-24-like in HU-LP, as opposed to OXA-23-like in SGH-UMC. An association between virulence and clonality seems to exist but needs to be determined locally before being exploited. Additionally, previously identified and a novel mutation in pmrB conveyed resistance to colistin but only the P233S mutation had an effect on virulence. Finally, a preliminary relationship between dense biofilms and carbapenem resistance has been identified.