Microbiology Research Journal International

Background: Antimicrobial resistance (AMR) is a growing global public health threat that undermines the effective treatment of infectious diseases. The increasing prevalence of resistant bacterial strains has reduced the efficacy of commonly used antibiotics, resulting in treatment failures, prolonged hospitalisation, increased healthcare costs, and higher morbidity and mortality. Continuous monitoring of local antimicrobial susceptibility profiles is therefore essential to guide evidence-based empirical therapy, strengthen antimicrobial stewardship, and improve patient outcomes.

Objective: The present study determines the in vitro antimicrobial susceptibility patterns of bacterial isolates recovered from clinical specimens in a Nigerian tertiary hospital and to evaluate the relative effectiveness of quinolones, cephalosporins, and carbapenems.

Methods: A laboratory-based cross-sectional study was conducted between January 2024 and December 2024 using 100 non-duplicate bacterial isolates recovered from routine clinical specimens processed at a tertiary healthcare facility in Southern Nigeria. The specimens were obtained from patients presenting with various clinical infections and included samples such as urine, high vaginal swabs, wound swabs, sputum, and blood, depending on clinical indication. Only the first isolate per patient was included to avoid duplication and ensure representativeness of the data. All samples were processed in the medical microbiology laboratory under standard operating procedures. Primary isolation was carried out on appropriate culture media, including blood agar, MacConkey agar, and chocolate agar where indicated, followed by incubation under suitable atmospheric and temperature conditions. Bacterial identification was performed using conventional microbiological methods. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disc diffusion technique on Mueller–Hinton agar. Standardised inocula equivalent to 0.5 McFarland turbidity standard were prepared and evenly inoculated onto the agar surface before placement of antibiotic discs.

Results: Among the 100 bacterial isolates analysed, Staphylococcus species were the most frequently recovered bacteria, accounting for 41% of isolates. This was followed by Klebsiella species (15%), Escherichia coli (14%), Streptococcus species (13%), and Pseudomonas species (12%), while Proteus species were the least common, representing 5% of the isolates. Antimicrobial susceptibility testing showed that ertapenem demonstrated the highest activity, with 99% susceptibility among the isolates. Ciprofloxacin showed 75% susceptibility, indicating moderate effectiveness. In contrast, markedly lower susceptibility rates were observed for cephalosporins, including cephalexin (36%), cefuroxime (21%), and cefepime (10%).

Conclusion: The findings of this study indicate that carbapenems, particularly ertapenem, continue to demonstrate substantial in vitro activity against a broad range of bacterial clinical isolates within this healthcare setting. Additionally, continuous surveillance of local and regional antimicrobial resistance trends is essential to guide clinicians in making evidence-based treatment decisions, update hospital formularies, and inform national antibiotic policies. Implementing rational antibiotic prescribing practices, combined with infection prevention and control measures, is vital to curb the spread of multidrug-resistant bacteria and improve patient outcomes. Collectively, these strategies will support sustainable management of bacterial infections and help mitigate the public health impact of antimicrobial resistance in Nigeria and similar resource-limited settings.