Predominance of Gram-Negative Bacteria and Their Antibiotic Resistance Profiles in Orthopedic Implant Infections at a Tertiary Hospital in Kenya

Background Implant-related infections are a major complication of orthopedic implant surgeries and represent a significant public health concern, as they contribute to prolonged morbidity, increased antibiotic use, and high treatment costs. This study aimed to identify the bacterial species involved in these infections, analyze their distribution across infection phases and determine their antimicrobial susceptibility profiles among patients receiving surgical care at Kakamega County Teaching and Referral Hospital, Kenya. Methods This was a hospital-based, descriptive cross-sectional study conducted between August 2024 and April 2025. From a target population of approximately 600 patients orthopedic implant patients, 191 were systematically selected after obtaining informed consent. Swab samples were collected and cultured on Sheep Blood Agar (SBA), Chocolate agar and MacConkey agar supplemented with Crystal violet. Purity plating was performed to isolate pure colonies. Bacterial identification and antimicrobial susceptibility testing (AST) were conducted using the VITEK 2 system. The interpretation of AST results was done according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Descriptive statistics were used to determine the frequency of bacterial species and their antibiotic susceptibility patterns. Results The most prevalent Gram-negative bacterial species isolated were Klebsiella pneumoniae (29.2%), Escherichia coli (17.9%), Pseudomonas aeruginosa (16.9%), and Citrobacter freundii (10.3%). Other Gram-negative bacteria, including Proteus mirabilis (4.1%), Providencia stuartii, Raoultella ornithinolytica and Klebsiella oxytoca, were each detected in less than 2.2% of cases. Staphylococcus aureus (14.9%) and Staphylococcus epidermidis (2.1%) were the only Gram-positive species isolated . No bacterial growth was observed in 1.0% of the samples. The distribution of infections by phase was 47.7% in the early phase, 50.7% in the delayed phase, and 1.6% in the late phase. High resistance rates were observed to ampicillin, penicillin, vancomycin, and the cephalosporins cefazolin, cefixime, ceftriaxone, and Ceftazidime. In contrast, amikacin and piperacillin-tazobactam showed the highest sensitivity across multiple isolates. Conclusion These findings demonstrate a marked predominance of Gram-negative bacteria as the primary causative agents of orthopedic implant infections at the study site, suggesting a potential shift from Staphylococcus aureus, which is indicated in most studies as the leading pathogen. The observed resistance pattern highlights the need for routine, individualized antimicrobial susceptibility testing to guide effective, targeted antibiotic therapy in postoperative orthopedic implant infections.