Epidemiology and Antimicrobial Resistance Trends of Invasive Bacterial Pathogens in The Gambia: A Retrospective analysis, 2019-2024.

OBJECTIVES: To characterize the epidemiology and antimicrobial resistance (AMR) trends of invasive bacterial pathogens (IBPs) in The Gambia and identify demographic and seasonal predictors of infection. METHODS: A six-year retrospective cross-sectional study of specimens processed at the Clinical Microbiology Laboratory, Medical Research Council Unit, The Gambia (2019-2024). A subset of S. aureus isolates (2005-2024) underwent whole-genome sequencing for phylogenetic and mecA genotype analysis. Bacterial identification and antimicrobial susceptibility testing (AST) were performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Multivariable logistic regression was used to assess predictors of bacterial infection burden and estimate adjusted odds ratios (aOR). RESULTS: Of 7,496 clinical specimens processed, 423 yielded IBPs. Staphylococcus aureus (32.9%), Escherichia coli (17.5%), and Streptococcus pyogenes (9.9%) were the predominant pathogens causing invasive bacterial infection (IBIs) in our study. Infants were disproportionately affected by Streptococcus pneumoniae and E. coli; adults aged ≥60 years had over threefold higher odds of Enterobacterales infection. S. pneumoniae predominated in the dry season (aOR = 2.26, p=0.030), while Klebsiella pneumoniae peaked in the wet season (aOR = 0.41, p=0.014). S. aureus showed 92.0% penicillin resistance, with 10.0% Methicillin-resistant S. aureus prevalence. E. coli exhibited 92.0% ampicillin and 44.2% ciprofloxacin resistance. S. pneumoniae was near-universally cotrimoxazole-resistant (97.0%). Whole-genome sequencing of 40 S. aureus isolates revealed high concordance between cefoxitin phenotype and mecA genotype, with mecA-positive isolates distributed across multiple phylogenetic clades, indicating polyclonal rather than single-strain MRSA emergence. CONCLUSIONS: S. aureus, E. coli, and S. pyogenes dominate IBPs at this institution in The Gambia, with some pathogens having critically high resistance to first-line antibiotics, underscoring the need for revised institution-level empirical treatment guidelines and expanded, coordinated national AMR surveillance.