Effect of Incubation Time on Zone Size of Antimicrobials by Disk Diffusion Method for Pseudomonas Aeruginosa

Abstract

Background: Pseudomonas aeruginosa is a prominent pathogen in healthcare settings, notorious for its rapid development of resistance to multiple antimicrobial agents. Effective susceptibility testing is critical for managing infections caused by this bacterium. This study investigates the impact of varying incubation times on the efficacy of the disk diffusion method. Objective: To evaluate the influence of incubation time on the zone sizes of antimicrobials against Pseudomonas aeruginosa using the disk diffusion method in a tertiary care setting. Methods: Conducted at the Microbiology Department of Combined Military Hospital, Lahore, from October 2022 to March 2023, this descriptive study included 71 clinical isolates of Pseudomonas aeruginosa. Samples were inoculated on Mueller Hinton Agar and incubated at 35°C ±2°C for 6, 10, and 24 hours. Antimicrobial susceptibility was tested using a panel of clinically relevant antibiotics in triplicate, with zone sizes interpreted according to Clinical and Laboratory Standards Institute guidelines. Results: Among the isolates, 59.15% were from males and 40.85% from females. The most affected age group was 15-60 years, comprising 59.52% of cases. Antimicrobial response varied with incubation times: Ceftazidime, Piperacillin-Tazobactam, and Cefepime showed increased zone sizes over time, while Tobramycin’s zones steadily enlarged. Colistin consistently produced the largest zones at all time points. Conclusion: The study highlights the significance of incubation time in disk diffusion testing for Pseudomonas aeruginosa. Adjusting incubation times can expedite results without incurring additional costs, enhancing the efficiency of antimicrobial susceptibility testing in clinical settings.