o determine if extended-spectrum beta-lactamases, plasmid-mediated AmpC beta-lactamases, carbapenemases, chromosomal mutations in ribosomal RNA or other mechanisms of resistance account for antibiotic resistance in commonly encountered Gram negative and Gram positive bacteria at UPMC. Also to determine the molecular epidemiology and in vitro susceptibility of multiply resistant organisms at UPMC and to relate this to antibiotic use in the institution.