Molecular detection of SHV and AmpC (CITM, FOX)-type lactamase in clinical isolates of Escherichia coli

Abstract number: P725

Objective: Co-production of extended spectrum b-lactamase (ESBLs) and AmpC enzymes has been detected as one of the most important mechanism of resistance to b-lactam antibiotics among some pathogens especially E. coli. In recent years, the prevalence of b-lactamase producer organisms is increased and it led to a problem for diagnosis via Disk diffusion method. On the other hand, SHV, CITM and FOX genes have several subfamilies, and designing universal primers could be valuable to detect all of them. Therefore, the aim of this study was to detection of SHV and AmpC (CITM, FOX)-type b-lactamase genes by using specific primers through PCR.

Materials and Methods: More than 500 clinical samples were collected from hospitals of Tehran and 265 E. coli isolates were detected by standard biochemical tests such as IMVIC. Subsequently, these isolates were screened for b-lactamase production by Disk diffusion method and confirmatory test (Combined Disk). Resistant isolates was evaluated for molecular assessing with PCR.

Results: In Disk Agar Diffusion test, 128 (64%) E. coli isolates which resistant to ceftazidime and cefotaxim were selected and followed by Combined Disk (ceftazidime, cefotaxim and clavulanic acid) assay. In Combined Disk, among 128 screened isolates, 115(89.8%) and 13 (10.2%) isolates were as ESBLs and AmpC producers, respectively. PCR was performed on all 128 resistant isolates and results were showed among 115 and 13 isolates, 7 (6.1%) and 13 (100%) to have bla SHV and bla CITM, respectively. Fox Gene was not detected in any samples.

Conclusion: According to the recommendation of the Clinical and Laboratory Standards Institute (CLSI), isolates which showed negative confirmatory test are potentially producer of AmpC. This survey improved CLSI recommendation because among 13 AmpC producer isolates, the result of CITM PCR was 100% positive. SHV gene was detected in just 6.1% of isolates and others b-lactamase genes may be have a role in b-lactam antibiotics along with other isolates.