H-058. The Role of a LysR-Family Regulator in the Formation of Acinetobacter baumannii Biofilms

C. N. McQueary, L. A. Actis;
Miami Univ., Oxford, OH.

Background: Acinetobacter baumannii is a gram-negative opportunistic pathogen that is a causative agent of significant infections in compromised patients. This organism persists for long periods of time in hospital environments most likely due to its ability to form biofilms, cell structures thought to lend to its increased survival. In this work we identified a LysR-like regulator that plays a role in the ability of the type strain 19606 to form biofilms on plastic surfaces. Methods: A lysR mutant, Bio12, was generated by electroporation of transposon-transposase complexes and characterized using biofilm assays, transmission and scanning electron microscopy (TEM and SEM, respectively), and gene expression tests. Results: Screening of a transposome library using biofilm assays resulted in the isolation of a derivative, Bio12, with a drastically reduced capacity to form biofilms on polystyrene when compared with the parental strain 19606. SEM analysis confirmed this observation, revealing a lesser developed biofilm and alterations in the pattern of adhered cells when compared with the biofilms formed by the parental strain. Similarly, TEM showed a drastic alteration in the formation of pili, which were different from those produced by the 19606 strain, and observation that was confirmed by the analysis of pili preparations. RT-PCR and western blotting showed a drastic reduction in the expression of the csuA/B gene, which codes for the putative pilin subunit of the 19606 pili assembled by the CsuA/BABCDE chaperon-usher system. These pili were shown to be essential for the ability of A. baumannii to attach to and form biofilms on abiotic surfaces. Interestingly, the gene coding for this LysR-like regulator is not present in the genome of the strain 17978, which forms biofilms different from those made by the strain 19606. Conclusion: A transcriptional regulator that belongs to the LysR-family controls biofilm formation by the A. baumannii 19606 type strain. This regulator modulates the expression of the polycistronic csuA/BABCDE operon and ultimately influences pili production and biofilm formation on plastic surfaces.