Sub-inhibitory concentrations of polymyxin B modulates pathogenicity factors and transcriptional regulators genes in multi-resistant Acinetobacter baumannii strains/ Concentrações sub-inibitórias de polimixina B modula fatores de patogenicidade e genes reguladores transcricionais em linhagens multirresistentes de Acinetobacter baumannii

Priscila Simão Costa, Izabela Mauricio Rezende, Tassiane Assiria Fontes Martins Luehring, Cristina Dutra Vieira, Betânia Paiva Drumond, Luiz de Macêdo Farias, Vandack Nobre, Ricardo Gonçalves, Simone Gonçalves dos Santos


Acinetobacter baumannii is frequently involved in healthcare-associated infections worldwide.  This occurs mainly due to its ability to invade, colonize and promote tissue destruction, and to the presence of several pathogenicity factors, in addition to high prevalence of antimicrobials resistance. Studies have shown that sub-inhibitory concentrations (sub-MICs) of antimicrobials can alter the transcriptional and phenotypic responses of bacteria. Despite that, little is known about how polymyxin B (PMB) can affect these processes. Thus, this work investigated if the PMB at sub-MICs could modulate the growth curve, the biofilm formation process, the resistance to oxidative stress and the expression levels of genes encoding such processes (abaI, adeR, oxyR and bfmR, bap, recA). Clinical strains of multidrug-resistant (MDR) A. baumannii  and one reference (ATCC 19606) strain were investigated. Our results demonstrated that PMB at sub-MICs decreased the number of planktonic cells in a dose-dependent manner in all tested strains, but the biofilm formation decreased in a dose-dependent-manner only in three strains. The resistance to oxidative stress decreased in all strains only when exposed to ½ MIC PMB. The mRNA levels of all genes increased significantly in the presence of sub-MIC PMB for the reference strain and for the clinical strain S5. In contrast, for the S32 strain a significant decrease of all mRNA levels was found in the presence of PMB. These results provide an interesting information about pathogenicity factors and biofilm formation in clinical strains MDR A. baumannii, which are directly affected by the expression of regulators genes and the presence of PMB. Furthermore, these data warned us about the importance of monitoring patients under antimicrobial therapy and the relevance of rational use of antimicrobials.


Acinetobacter baumannii, pathogenicity, oxidative stress, biofilm, polymyxin B.

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