PMQR determinants among clinical isolates of ESBL and Amp C producing Serratia marcescens in Mansoura University Hospitals: A 6-year study

Background: Plasmid mediated quinolone resistant determinants (PMQR) are found to be of clinical relevance because it causes decreased quinolones sensitivity. Quinolones are valuable antibiotics against intrinsically resistant Serratia marcescens. Purpose: To determine the occurrence of PMQR  determinants qnr, aac(6′)-Ib-cr and qep and their relation with extended-spectrum β-lactamase (ESBL)  and / or Amp C- producing Serratia marcescens. Material and Method:  One hundred and eleven Serratia marcescens were tested for resistance to five quinolones by disc diffusion method.  Testing for qnr, aac(6′)-Ib-cr and qep was carried by multiplex PCR. Whereas ESBL and Amp C production were evaluated by double disc synergy test and cefoxitin Hodge test respectively. Results: Out of 111 Serratia marcescens , 51 (45.9%) were resistant to one or more of the used quinolones. Among Serratia marcescens isolates, 13 (11.7%) were ESBL producers while 5 (4.5%) were Amp C producers. Multiplex PCR confirmed the presence of PMQR determinant in 14 (12.6%) isolates of Serratia marcescens. Serratia marcescens positive  for qnr determinants were detected as qnrA and qnr B in 3 and 10 isolates respectively whereas one isolate co harbored aac(6')-Ib-cr  and qnrA. Among 13 ESBL producers, 3 and 5 isolates were positive for qnrA and qnr B respectively (8/13, 61.5%). Whereas one isolate co- expressed aac(6')-Ib-cr  and qnrA was associated with Amp C production (1/5, 20%). Conclusion: This study indicated that PMQR play significant role in the occurrence and expansion of fluoroquinolone resistance in Serratia macrscens. Moreover they are closely associated with ESBL and Amp C producers.