In the past few decades Acinetobacter baumannii has emerged as a notorious nosocomial pathogen because of its ability to acquire genetic material and persist in extreme environments. Recently, human serum albumin (HSA) was shown to significantly increase natural transformation frequency in A. baumannii. This observation led us to perform transcriptomic analysis of strain A118 under HSA induction to identify genes that are altered by HSA. Our results revealed the statistically significant differential expression of 296 protein-coding genes, including those associated with motility, biofilm formation, metabolism, efflux pumps, capsule synthesis, and transcriptional regulation. Phenotypic analysis of these traits showed an increase in surface-associated motility, a decrease in biofilm formation, reduced activity of a citric acid cycle associated enzyme, and increased survival associated with zinc availability. Furthermore, the expression of genes known to play a role in pathogenicity and antibiotic resistance were altered. These genes included those associated with RND-type efflux pumps, the type VI secretion system, iron acquisition/metabolism, and ß-lactam resistance. Together, these results illustrate how human products, in particular HSA, may play a significant role in both survival and persistence of A. baumannii.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  A. baumannii A118 was able to acquire genomic DNA (gDNA) of two carbapenem-resistant Klebsiella pneumoniae (CRKp) clinical isolates  The whole genome sequence of two transformants cells was obtained confirming the acquisition of foreign genomic DNA. The K. pneumoniae DNA segments that were acquired, includes mobile elements, resistance determinants, and genes involved in metabolism.  Additional assays showed that A. baumannii A118 was also able to incorporate gDNA of Providencia rettgeri and Staphylococcus aureus, two phylogenetically distant species.  This study showed that A. baumannii can acquire foreign DNA from different species and that transformation may play a fundamental role in the increasing frequency of emergence of MDR strains

In 2014, a novel species of Acinetobacter , strain A47, determined to be hospital-acquired was recovered from a single patient soft tissue sample following a traumatic accident. The complexity of the Acinetobacter genus has been established, and every year novel species are identified. However, specific features and virulence factors that allow members of this genus to be successful pathogens are not well understood. Utilizing both genomic and phenotypic approaches, we identified distinct features and potential virulence factors of the A47 strain to understand its pathobiology. In silico analyses confirmed the uniqueness of this strain and other comparative and sequence analyses were used to study the evolution of relevant features identified in this isolate. The A47 genome was further analyzed for genes associated with virulence and genes involved in type IV pili (T4P) biogenesis, hemolysis, type VI secretion system (T6SS), and novel antibiotic resistance determinants were identified. A47 exhibited natural transformation with both genomic and plasmid DNA. It was able to form biofilms on different surfaces, to cause hemolysis of sheep and rabbit erythrocytes, and to kill competitor bacteria. Additionally, surface structures with non-uniform length were visualized with scanning electron microscopy and proposed as pili-like structures. Furthermore, the A47 genome revealed the presence of two putative BLUF type photoreceptors, and phenotypic assays confirmed the modulation by light of different virulence traits. Taken together, these results provide insight into the pathobiology of A47, which exhibits multiple virulence factors, natural transformation, and the ability to sense and respond to light, which may contribute to the success of an A47 as a hospital dwelling pathogen.

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37Acinetobacter baumannii is a human pathogen that frequently acquires antibiotic 38 resistance genes leading to the emergence of multi-drug-resistant (MDR) strains. 39To investigate the role of transformation in the acquisition of resistance 40 determinants by this species, the susceptible strain A118 was exposed to 41 genomic DNA of carbapenem-resistant Klebsiella pneumoniae (CRKp). Resistant 42 transformants were obtained and an increase in the resistance level to all β-43 lactam antibiotics was observed. Whole genome analysis of transformant clones 44 demonstrated the acquisition of CRKp DNA. The most frequently acquired genes 45 correspond to mobile elements, antibiotic resistance genes, and operons 46 involved in metabolism. Bioinformatic analyses and in silico gene flow prediction 47