Molecular detection of AmpC-beta lactamase CITM gene in gram-negative bacterial isolates obtained from clinical specimens in a tertiary hospital in Nigeria.

Abstract

In most developing countries, the β-lactam antibiotics are still the most predominantly prescribed antibiotics to treat bacterial infections. Resistance to third-generation cephalosporins is typical of multidrug resistance (MDRs), being mainly due to the production of AmpC-type β-lactamases. The aim of the study was to detect bla_CITM gene in Gram-negative bacterial isolates obtained from clinical specimens in a tertiary hospital.

A total of 220 Gram-negative bacterial isolates obtained from clinical specimens were involved in the study.  The primary screening of the AmpC enzyme-producing strains was conducted by the Kirby-Bauer disk diffusion method. Isolates that yielded a zone diameter ≤18 mm (screen positive) to cefoxitin sensitivity disc were further subjected to confirmatory tests using the AmpC disc test technique. Genomic DNA was extracted using Quick-DNA^TM Fungal/Bacterial Miniprep Kit; Zymo Research). Conventional Polymerase Chain Reaction (PCR) analysis was carried out in order to detect the presence of  bla_CITM.

Out of 220 isolates, 45 (20.5%) were found to be resistant to cefoxitin (Screening test for AmpC β-lactamase) of which 10 (4.5%) were positive for AmpC β-lactamase (confirmatory positive by AmpC Disk Test). However, polymerase chain reaction (PCR) analysis revealed that none of the isolates harboured the bla_CITM gene.  The results from this study implied that not all cefoxitin resistant isolates are AmpC β-lactamase producers. The absence of bla_CITM gene may be as a result of other enzymatic mechanism such as extended spectrum beta lactamases (ESBLs) and metallo beta-lactamase (MBL) or because of the non-enzymatic mechanism such as porin channel mutation.