ACINETOBACTER BAUMANNII AND OTHER GENOMIC SPECIES: ARE THERE VIRULENCE DIFFERENCES?

Elizabeth Harummyy Takagi (FCF-USP); Marina Baquerizo Martinez (FCF-USP)

Bacterial species of Acinetobacter calcoaceticus-A. baumannii complex are nosocomial pathogens of increasing importance, but the mechanisms involved in their virulence are largely unknown. This study investigated the potential of different species of this complex to produce biofilm on abiotic surface and adhere to eukaryotic cells: Hep-2, NCI-H292 and MRC-5. A modified PCR-based method was created and used to distinguish between Acinetobacter baumannii and Acinetobacter genomic sp. 13TU and 3TU. This genomic identification method exploits differences in gyrB gene and 16S-23S rRNA gene spacer region sequences. Thirty non-clonal isolates from intensive unit care patients, 18 were identified as A. baumannii, eight as  A. 13TU and four A. as 3TU. During this study, 3 clinical strains of A. 3TU, 3 of A. 13TU and 3 of A. baumannii, were examined for biofilm formation and adherence assays. Biofilm formation was evaluated by quantitative method through microtitre plate assay by means the crystal-violet staining method.  Adherence of clinical isolates to eukaryotic cells was examined by light microscopy. The strains under this study displayed high variability in biofilm formation among isolates from the same species. None isolate adhere to Hep-2 cells. On NCI-H292 cells it was possible to observe differences, such as A. baumannii presents dispersed adherence, while A. 13TU shows some cluster cells adherence and A.3TU did not adhere. However, dispersed adherence was observed by A. baumannii, A. 3TU and A. 13TU with variability in number of bacterial cells adhered on MRC-5 cells. This study describes a PCR-based method that allows the identification of major clinical species from Acinetobacter calcoaceticus-Acinetobacter baumannii complex. Differences on assays perfomed on NCI-H292 cells could be a possible explanation for a minor isolation frequency of A. 3TU and A. 13TU.