Phenotypic Characterisation of Resistant Profiles of the Isolates in Orthopaedic Implant Associated Infections: A Cross-sectional Study

Introduction: Orthopaedic Implant Associated Infections (OIAIs) are serious complications associated with prolonged morbidity, implant failure, repeated surgical interventions, and increased healthcare burden. The emergence of antimicrobial-resistant pathogens further complicates treatment outcomes. Aim: To study the phenotypic characterisation of resistant profiles of isolates in OIAIs and to detect the bacteriological profile and antibiogram of these isolates. Materials and Methods: This cross-sectional study was conducted in the Department of Microbiology, Jawaharlal Nehru Medical College (JNMC), KAHER, Belagavi, Karnataka, India over one year (April 2024-March 2025). A total of 66 aspirated pus samples from patients with confirmed OIAIs were included. Samples were processed using standard microbiological techniques. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disc diffusion method according to CLSI M100, 34th edition (2024) guidelines. Phenotypic detection of resistance mechanisms including Methicillin-Resistant Staphylococcus aureus (MRSA), Extended-Spectrum β-Lactamase (ESBL), AmpC, and Metallo-Beta-Lactamase (MBL) production was carried out. Data analysis was performed using Statistical Package for the Social Sciences (SPSS) version 27.0, and p-value<0.05 was considered statistically significant. Results: Out of 66 samples processed, 60/66 (90.9%) showed culture positivity. The highest proportion of patients belonged to the 31-40 years age group {18/66 (27.3%)}, and males accounted for 55/66 (83%) cases. Gram-negative organisms predominated {39/60 (65%)}, while Staphylococcus aureus was the most common individual isolate {21/60 (35%)}. Among S. aureus isolates, MRSA constituted 12/21 (57.1%). ESBL + AmpC co-production was the predominant resistance mechanism among Gram-negative isolates {23/39 (59%)}, followed by ESBL production alone {11/39 (28%)}. All S. aureus isolates remained susceptible to vancomycin and linezolid. Conclusion: OIAIs predominantly affected younger males and were more commonly associated with external implants. Gram-negative organisms showed a high burden of Multidrug Resistance (MDR), including ESBL and AmpC production. Routine antimicrobial susceptibility testing, continuous resistance surveillance, and antibiogram-guided therapy are essential for effective management and antimicrobial stewardship.