Identification of Gram-Positive and Gram-Negative Bacteria in Post-Surgical Patients and Their Antibiotic Sensitivity Pattern

Background: Surgical site infections (SSIs) continue to be a major postoperative complication, particularly in resource-limited healthcare settings. These infections significantly prolong hospitalization, increase morbidity, and escalate healthcare costs. Both Gram-positive and Gram-negative bacteria are implicated, and the rise of antimicrobial resistance has further complicated management. Accurate identification of pathogens and their resistance patterns is essential to guide empirical therapy and strengthen infection control practices. Objective: To identify Gram-positive and Gram-negative bacteria isolated from post-surgical patients and to evaluate their antimicrobial susceptibility patterns. Methods: A descriptive cross-sectional study was conducted in the Department of Microbiology, Arif Memorial Teaching Hospital, Lahore, from August 2024 to January 2025. A total of 104 clinical specimens, including pus, wound swabs, and blood samples, were collected using convenient sampling. Standard microbiological procedures such as Gram staining, colony morphology, catalase, coagulase, and biochemical assays were employed for bacterial identification. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method in accordance with CLSI 2018 guidelines. Data were analyzed using SPSS version 25, with frequencies and percentages calculated for isolates and resistance profiles. Results: Out of 104 collected specimens, 63 (60.6%) were culture-positive, while 41 (39.4%) showed no growth. Staphylococcus aureus was the predominant pathogen (23.1%), followed by Escherichia coli (19.2%), Enterobacter species (7.7%), Staphylococcus species (3.8%), Pseudomonas (1.9%), Proteus vulgaris (1.9%), and Klebsiella species (1.9%). Gram-positive isolates showed complete resistance to penicillin and ampicillin (100%) but full sensitivity to vancomycin (100%) and high sensitivity to linezolid (81.8%). Gram-negative isolates exhibited marked resistance to ceftazidime (96.0%), ciprofloxacin (82.4%), and levofloxacin (82.5%), whereas carbapenems such as imipenem (80.0%) and meropenem (74.3%) retained considerable efficacy. Conclusion: The findings highlight the coexistence of Gram-positive and Gram-negative organisms as major contributors to SSIs, with alarmingly high resistance to first-line antibiotics. Vancomycin, linezolid, and carbapenems remain effective therapeutic options. The results emphasize the urgent need for continuous surveillance, rational antimicrobial use, and stronger infection control strategies to reduce SSI-related morbidity.