Bacterial Profile and Antimicrobial Resistance Patterns among Patients with Surgical Site Infections: A Prospective Study

Abstract

Background: Surgical site infections (SSIs) represent a major subgroup of healthcare-associated infections that escalate postoperative morbidity, extend hospital stays, and increase financial burdens. Understanding local microbiological profiles and antibiotic resistance trends is crucial for informing targeted empirical therapy and antimicrobial stewardship. Objective: To isolate and characterize bacterial pathogens from surgical site wound specimens, evaluate their antimicrobial susceptibility profiles, and determine the prevalence of multidrug-resistant (MDR) strains among hospitalized surgical patients.

Methods: A prospective hospital-based observational study was conducted over a 12-month period at Khaja Bandanawaz University, Gulbarga, Karnataka, India. A total of 100 clinical surgical site specimens (pus aspirates and wound swabs) were collected from eligible post-operative patients showing clinical evidence of SSI. Standard laboratory procedures, including direct microscopy, selective culture, and phenotypic biochemical assays, were utilized for bacterial identification. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disk diffusion technique on Mueller–Hinton agar in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines.

Results: Among 100 analyzed specimens, 92 (92.0%) yielded positive bacterial cultures, giving a total of 102 bacterial isolates (82 monomicrobial and 10 polymicrobial infections). Gram-negative bacteria predominated, comprising 59.8% (n=61) of the total isolates, whereas Gram-positive bacteria accounted for 40.2% (n=41). The leading pathogens were Escherichia coli (22.5%, n=23), Staphylococcus aureus (20.6%, n=21), Klebsiella pneumoniae (14.7%, n=15), Pseudomonas aeruginosa (11.8%, n=12), and Acinetobacter baumannii (9.8%, n=10). Among S. aureus isolates, 33.3% (n=7/21) were methicillin-resistant S. aureus (MRSA); notably, all Gram-positive isolates remained fully susceptible (100%) to vancomycin and linezolid. Gram-negative bacilli demonstrated severe resistance to ampicillin (88.5%), ceftriaxone (68.9%), and ciprofloxacin (63.9%), but maintained substantial susceptibility to amikacin (73.8%), piperacillin-tazobactam (70.5%), and meropenem (80.3%). Multidrug resistance was observed in 37.3% (n=38/102) of all isolates, with Gram-negative organisms demonstrating higher MDR rates (41.0%) than Gram-positive organisms (31.7%).

Conclusion: Gram-negative pathogens dominate the microbiological spectrum of SSIs in our institution, with high levels of resistance to routinely prescribed first- and second-line antibiotics. Continuous microbiological surveillance, institutional antibiograms, and structured antimicrobial stewardship programs are vital to optimize empirical therapy and control the spread of multi-resistant bacterial pathogens.