A naturally competent Acinetobacter baumannii clinical isolate as a convenient model for genetic studies

M.S. RAMIREZ, M. DON, D. CENTRON, AND M. TOLMASKY.

Philadelphia, USA

Congreso; 109 Congreso General de la American Society for Microbiology; 2009

American Society for Microbiology

Background: Clinical Acinetobacter baumannii (Ab) strains are often multiresistant, which complicates treatment and performance of genetic experiments. Although bacteria of the genus Acinetobacter have been shown to be naturally competent, studies on strains of the Ab species are scarce.  We have isolated a clinical Ab strain that is susceptible to most antibiotics and studied its natural competence and the stability of several plasmid replicons.   Methods: Susceptibility to antibiotics was determined using the agar dilution method.  Natural competence was tested incubating untreated cells with plasmid DNA or a 10-mer phosphorothioate DNA analog labeled with Oregon Green 48 at its 5f end. Plasmid stability was tested calculating the proportion of cells that lost the plasmid after 40 generations of growth in the absence of selection. Transformation with the labeled oligomer was tested by fluorescence microscopy.  Results: Ab A118 was isolated from the blood culture of a patient.  Ab A118 is susceptible to ceftazidime, minocycline, cefepime, piperacillin, gentamicin, kanamycin, trimethoprime-sulfamethoxazole, ciprofloxacin, zeocin, and amikacin. All five plasmids pJHCMW1, pMET1, pLQ369Z (ColE1 replicon), pCR2.1 (pUC18 replicon), and pLQ426K (pACYC184 derivative, p15A replicon), and the fluorophore-labeled oligomer were readily taken up by Ab A118.  With the exception of pLQ426K, an unstable plasmid that was lost in a significant percentage of Ab A118 and E. coli cells, plasmids were stably maintained after 40 generations. Conclusions: Ab A118 is a naturally competent clinical isolate that takes up plasmids and oligonucleotides, and can support the replication of at least 5 replicons, 3 of which are commonly used in molecular biology studies. These properties plus its susceptibility to a large number of antibiotics make it an ideal tool for genetic studies on Ab.