B-209. DNA Microarray Analysis of Bacterial Pathogens

A. C. Jacobs1, J. Morrison1, S. Welander1, A. Adibi2, C. Lee3, T. T. Luong3, E. Skaar4, G. Pishchany4, P. Fey1, P. Dunman1;
1Univ. of Nebraska Med. Ctr., Omaha, NE, 2Hampton Univ., Hampton, VA, 3Univ. of Arkansas for Med. Sci., Little Rock, AR, 4Vanderbilt Univ., Nashville, TN.

Methicillin resistant Staphylococcus aureus (MRSA), a major nosocomial pathogen, causes serious disease in immuno-compromised patients. Recently, an increase in community-associated MRSA infections in healthy individuals has been found. The main lineage, as defined by pulsed field gel electrophoresis (PFGE), causing disease is USA300. It has been speculated that increased virulence in USA300 is due to differences in DNA composition between USA300 and hospital-associated lineages. Indeed, the presence of the phage encoded Panton-Valentine Leukocidin (PVL) toxin has been linked with USA300 increased virulence in a necrotizing pneumonia model of infection. However, another study found no change in virulence in a skin and soft tissue model. Thus, it remains to be seen whether the acquisition of PVL and/or other exogenous genetic material directly mediates USA300 pathogenesis. We have used S. aureus GeneChips to compare the genetic composition of USA300 to eleven other PFGE-types. Our results suggest that genetic composition of USA300 is very similar to the major hospital-associated lineage (USA100) and less problematic PFGE-types (USA500). We hypothesize that USA300’s hypervirulence can, in part, be attributed to alterations in the expression of virulence factors that are conserved across lineages. To test this hypothesis we used S. aureus GeneChips to compare USA300 virulence factor expression to USA100, and USA500. Results revealed that close to 100 genes, including many putative virulence factors, are differentially expressed within USA300. Northern blotting confirmed this data. A similar approach has been initiated to study the genetic composition and virulence properties of Acinetobacter baumannii. A. baumannii (ACBA) is a multi-drug resistant gram-negative bacteria causing increasing numbers of outbreaks in hospitals in the U.S. A. baumannii infections lead to pneumonia and blood stream infections. Despite its medical importance, little is known about A. baumannii, including the most accurate lineage distinction. Here we demonstrate that DNA microarrays are more accurate than PFGE in defining ACBA relatedness.