Dissemination of cephalosporin-resistant Serratia marcescens strains producing a plasmidic SHV type beta-lactamase in Greek hospitals.

The resistance to third generation cephalosporins in nine Serratia marcescens strains isolated in Greek hospitals was studied. Eight of the strains transferred resistance to Escherichia coli by means of large plasmids that encoded for an extended-spectrum beta-lactamase. Hybridization, isoelectric focusing and hydrolysis studies showed that the enzyme resembled the SHV-5 beta-lactamase. In the eight isolates that possessed the SHV type enzyme, cephalosporinase expression was inducible, whereas the remaining strain was a cephalosporinase hyperproducing strain. Introduction of a plasmid coding for the regulatory ampD gene in the latter strain eliminated beta-lactamase production and rendered the strain susceptible to cephalosporins.