According to the Centers for Disease Control and Prevention, Acinetobacter baumannii is listed among the most threatening pathogens. A. baumannii is mainly a nosocomial pathogen with a distinctive ability to survive in multiple environments. These characteristics together with this bacterium’s ability to acquire antibiotic resistance determinants make it a notorious pathogen. The presence of human serum albumin (HSA) is associated with modifcation of expression levels in numerous genes. The presence of HSA in the culture medium is also correlated with a reduction in levels of the global suppressor histone-like nucleoid structure protein, H-NS. Comparative transcriptome analysis of the wild type and isogenic Δhns strains cultured in lysogeny broth (LB) in the presence or absence of HSA revealed that the expression of a subset of eleven genes are modifed in the Δhns cultured in LB and the wild-type strain in the presence of HSA, pointing out these genes as candidates to be regulated by the presence of HSA through H-NS. Six and fve of these genes were up- or down-regulated, respectively. Three of these genes have functions in quorum sensing (acdA, kar and fadD), one in quorum quenching (aidA), two in stress response (katE, ywrO), three in metabolism (phaC, yedL1, and yedL2), one in bioflm formation (csuAB), and one in β-oxidation of fatty acids (fadA). The regulation of these genes was assessed by: (i) transcriptional analysis and qPCR at the transcriptional level; and (ii) by determining the phenotypic characteristics of each function. The results of these studies support the hypothesis that HSA-mediated reduction of H-NS levels may be one very important regulatory circuit utilized by A. baumannii to adapt to selected environments, such as those where HSAcontaining human fuids are abundant.Fil: Escalante, Jenny. California State University Fullerton. College of Natural Sciences and Mathematics. Department of Biological Science. Center for Applied Biotechnology Studies; United States.Fil: Nishimura, Brent. California State University Fullerton. College of Natural Sciences and Mathematics. Department of Biological Science. Center for Applied Biotechnology Studies; United States.Fil: Pimentel, Camila. California State University Fullerton. College of Natural Sciences and Mathematics. Department of Biological Science. Center for Applied Biotechnology Studies; United States.Fil: Georgeos, Nardin. California State University Fullerton. College of Natural Sciences and Mathematics. Department of Biological Science. Center for Applied Biotechnology Studies; United States.Fil: Tomalsky, Marcelo E. California State University Fullerton. College of Natural Sciences and Mathematics. Department of Biological Science. Center for Applied Biotechnology Studies; United States.Fil: Ramírez, María Soledad. California State University Fullerton. College of Natural Sciences and Mathematics. Department of Biological Science. Center for Applied Biotechnology Studies; United States.Fil: Tuttobene, Marisel Romina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Área Biología Molecular; Argentina.Fil: Tuttobene, Marisel Romina. Instituto de Biología Molecular y Celular de Rosario (IBR-CONICET-UNR); Argentina.Fil: Subils, Tomás. Instituto de Procesos Biotecnológicos y Químicos de Rosario (IPROBYQ-CONICET-UNR); Argentina.Fil: Sieira, Rodrigo. Fundación Instituto Leloir (IIBBA-CONICET); ArgentinaFil: Bonomo, Robert A. Research Service and GRECC. Louis Stokes Cleveland Department of Veterans Affairs Medical Center; United States.Fil: Bonomo, Robert A. Case Western Reserve University School of Medicine. Pharmacology, Molecular Biology and Microbiology, Biochemistry, Proteomics and Bioinformatics. Departments of Medicine; United States.Fil: Bonomo, Robert A. CWRU-Cleveland VAMC Center for Antimicrobial Resistance and Epidemiology ; United States.