Acinetobacter baumannii A118, a clinical isolate suitable as model for genetic studies.

RAMÍREZ M.S., DON M., MERKIER A.K., CENTRÓN D., TOLMASKY M.E.

Cordoba

Congreso; 79- VI Congreso Argentino de Microbiología General, SAMIGE,; 2009

SAMIGE

Acinetobacter baumannii (Ab) is an emerging opportunistic human pathogen responsible for a growing number of community and nosocomial infections, that can be life threatening or leave permanent sequel in the patients. Clinical 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.   Susceptibility to antibiotics was determined using the agar dilution method.  Natural competence was tested incubating untreated cells with plasmid DNA (pJHCMW1, pMET1, pAADA1KN, pAADB,  pVK102) or a 10-mer phosphorothioate (PS) 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.  Ab A118 was isolated from the blood culture of a patient and is susceptible to ceftazidime, minocycline, cefepime, piperacillin, gentamicin, kanamycin, trimethoprime-sulfamethoxazole, ciprofloxacin, and amikacin. All five plasmids transformed used in the study A118 at high frequency  (more than 50 colonies per reaction). A118 was also able to take up a fluorophore-labeled PS analog. With the exception of pAADA1KN, an unstable plasmid that was lost in a significant percentage of Ab A118, plasmids were stably maintained after 40 generations. Molecular genetic studies of Ab clinical strains have often been limited because they are usually resistant to most antibiotics. The ability of Ab A118 to be transformed and stably support the replication of several plasmids together with its susceptibility profile make this strain a useful model for genetic analyses and studies on virulence and antibiotic resistance.