Molecular Characterization of Extended-Spectrum Beta-Lactamase Genes in Gram-Negative Bacteria from Clinical Isolates in Ibadan, Oyo State

The global proliferation of extended-spectrum beta-lactamase (ESBL)-producing Gram-negative bacteria threatens the clinical utility of beta-lactam antibiotics and demands precise molecular characterization to inform treatment strategies. This analytical study molecularly characterized ESBL-encoding genes in clinical Gram-negative isolates from University College Hospital (UCH) Ibadan, Oyo State, in the South West geopolitical zone of Nigeria. A total of 200 consecutive non-duplicate Gram-negative isolates from clinical samples were phenotypically screened for ESBL production using combined disk synergy tests per CLSI guidelines. Confirmed ESBL producers underwent multiplex polymerase chain reaction (PCR) targeting blaTEM, blaSHV, and blaCTX-M gene families. Sequencing of amplicons was performed to identify specific CTX-M subtypes. Of 200 isolates, 43.5 percent were phenotypic ESBL producers. CTX-M-15 was the dominant gene detected in 78.2 percent of ESBL producers, followed by TEM-type genes in 42.5 percent. Co-harboring of multiple ESBL genes was documented in 34.5 percent of positive isolates. Klebsiella pneumoniae and Escherichia coli were the most prevalent ESBL-producing species. All ESBL-positive isolates demonstrated multi-drug resistance, with retained susceptibility only to meropenem and colistin. These findings demonstrate that CTX-M-15 is the dominant ESBL determinant in the study setting and support carbapenem stewardship as a critical priority at UCH Ibadan. Keywords: ESBL, CTX-M-15, molecular characterization, Ibadan, Gram-negative bacteria.