Clinical Bacterial Profile and Antimicrobial Susceptibility Trends in a Tertiary Care Hospital: A Retrospective Laboratory-Based Study

Abstract

Background: Antimicrobial resistance has become an increasingly important challenge for healthcare systems because resistance among clinically significant bacterial pathogens can compromise empirical treatment, prolong hospitalization, and increase the complexity of infection-control and antimicrobial-stewardship practices. Hospital-specific microbiological surveillance is therefore essential for understanding the organisms responsible for infections and for identifying antimicrobial agents that continue to demonstrate useful activity. The present study was undertaken to describe the bacterial spectrum recovered from routine clinical specimens and evaluate their antimicrobial susceptibility patterns in a tertiary care hospital. Methods: A retrospective, observational, laboratory-based study was performed in the Department of Microbiology, at a tertiary care hospital in Sokoto, Nigeria. Laboratory records generated between January 2025 to July 2026 were reviewed. A total of 400 clinically significant, non-duplicate bacterial isolates recovered from urine, pus/wound, blood, respiratory specimens, and other body fluids were included. Bacterial identification was performed using standard microbiological procedures. Antimicrobial susceptibility testing was performed by the Kirby-Bauer disk diffusion method using Mueller-Hinton agar and interpreted according to the Clinical and Laboratory Standards Institute M100, 35th edition. Multidrug resistance (MDR) was defined as acquired non-susceptibility to at least one antimicrobial agent in three or more antimicrobial categories. Results: Of the 400 bacterial isolates, 300 (75.0%) were Gram-negative and 100 (25.0%) were Gram-positive. Urine was the most frequent specimen source, accounting for 150 (37.5%) isolates, followed by pus/wound specimens (25.0%), blood (17.5%), respiratory specimens (15.0%), and other body fluids (5.0%). Escherichia coli was the predominant organism (30.0%), followed by Klebsiella pneumoniae (17.5%), Staphylococcus aureus (15.0%), Pseudomonas aeruginosa (12.5%), and Acinetobacter spp. (8.8%). Among Gram-negative organisms, meropenem and amikacin demonstrated comparatively higher activity against E. coli and K. pneumoniae, whereas susceptibility to ceftriaxone and ciprofloxacin was considerably lower. Acinetobacter spp. showed the least favorable susceptibility profile among the major Gram-negative pathogens. Meropenem non-susceptibility was observed in 8.3% of E. coli, 14.3% of K. pneumoniae, 32.0% of P. aeruginosa, and 60.0% of Acinetobacter spp. Among S. aureus, 30.0% were classified as MRSA. Vancomycin resistance was detected in 8.0% of Enterococcus spp. MDR status could be evaluated in 385 isolates, of which 160 (41.6%) were MDR. Conclusion: The study demonstrates a substantial burden of antimicrobial resistance among bacterial pathogens isolated in the tertiary-care setting. Gram-negative organisms predominated, with E. coli being the leading isolate. Reduced susceptibility to cephalosporins and fluoroquinolones and substantial resistance among Acinetobacter spp. are particularly important findings. Regular institutional surveillance, periodic antibiogram development, infection-prevention measures, and culture-directed antimicrobial therapy should be strengthened to address the local resistance burden.