Antibiogram and Molecular Detection of β-Lactamase Genes (blaTEM and blaSHV) in Clinical Isolates from Nigeria

Antimicrobial resistance (AMR) among Gram-negative bacteria represents a major public health challenge in Nigeria and across Sub-Saharan Africa, particularly resistance to β-lactam antibiotics mediated by plasmid-encoded β-lactamase genes. This study assessed phenotypic antibiotic resistance patterns and the presence of blaTEM and blaSHV genes among 40 archived Gram-negative clinical bacterial isolates obtained from urine and wound samples in Nigeria. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disk diffusion method following Clinical and Laboratory Standards Institute guidelines. Molecular detection of resistance genes was carried out using polymerase chain reaction (PCR). Very high resistance rates were observed against ceftazidime (97.7%), cefuroxime (≈99%), amoxicillin–clavulanic acid (≈92–100%), and ciprofloxacin (92%). Relatively higher susceptibility was recorded for nitrofurantoin, gentamicin, and ofloxacin. Molecular analysis showed that 75% (15/20) of isolates screened carried the blaTEM gene, while all isolates screened for blaSHV (24/24; 100%) were positive. The study demonstrates extensive phenotypic resistance and a high prevalence of β-lactamase–encoding genes among Gram-negative clinical isolates in Nigeria, underscoring the urgent need for integrated phenotypic and molecular AMR surveillance and strengthened antimicrobial stewardship.