From isoelectric focusing and polymerase chain reaction analysis (PCR), the transconjugates of 12 clinical isolates of Enterobacter cloacae had encoded extended spectrum beta-lactamase (ESBL) SHV-12 and pI 8.8 AmpC beta-lactamases in their plsmids. By comparison these pI 8.8 AmpC beta-lactamases with wild-type AmpC in E. cloacae MHN1 (GenBank accession no. X08082), there were 94-98% identity and amino acid substitutions were identified in all strains. Multiple drug resistance Serratia marcescens also encoded AmpC beta-lactamases in their plasmid, comparison with AmpC in S. marcescens (accession no. AAK15701), showed 82-93% identity in 10 strains. We found out that multiple drug resistant trains of E. cloacae had encoded SHV-12 and AmpC beta-lactamases in their conjugative plasmids. All the ampC genes in plasmid of E. cloacae and S. marcescens showed close similarity to the chromosomal ampC gene. The ESBL producing strains often are cross-resistant to quinolones. In this research 5 E. cloacae and 12 S. marcescens isolates were examined by PCR and direct nucleotide sequencing for genetic alterations in the quinolone-resistance determining regions (QRDRs) gyrA and parC. The minimal inhibitory concentration results suggest that there is not a relationship between the presence of genetic alterations and the resistance to quinolones (nalidixic acid and ciprofloxacin) in this study. We tested for the presence of qnr genes by PCR in 5 E. cloacae and 12 S. marcescens strains, but no qnr genes were found.
