Ticking the clock: Modified Kirby-Bauer’s technique for accelerated antibiotic susceptibility reporting 

• Author Details:   
• R Gowtham
• Sowmya G Shivappa ^*
• Rashmi P Mahale
• Morubagal Raghavendra Rao
• Sulochanadevi B C
• Ranjitha Shankare Gowda
• Vidyavathi B Chithragi
• Neetha S Murthy

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Background: Antibiotic resistance poses a global health threat, potentially leading to a post-antibiotic era with severe consequences. Timely and accurate antimicrobial susceptibility testing (AST) is critical for effective treatment, reducing mortality, and combating antimicrobial resistance (AMR). This study evaluates the efficacy of early disc diffusion (EDD) testing by using 6-hour and 10-hour old growth compared to the standard 18-24 hours growth in performing the Kirby-Bauer disc diffusion method.

Materials and Methods: A cross-sectional study was conducted at a tertiary care hospital on five quality control (QC) strains and 100 clinical isolates. Additionally, growth from primary isolation plates of 25 turbid urine and 25 positive flagged blood culture samples were also analyzed.

Results: EDD 6-hour and 10-hour testing of QC strains showed 100% CA with the 24-hour growth to reference method. Clinical isolates demonstrated 97.48% CA for EDD 6-hour testing and 97.1% CA for EDD 10-hour testing, with minimal discrepancies (VME ≤ 0.63%, ME ≤ 0.58%, mE ≤ 1.94%). Early growth (EDD 10-hour) from primary isolation plates of urine and positive flagged blood cultures showed >99% CA, with no major or very major discrepancies.

Conclusion: EDD 10-hour testing demonstrated high accuracy and concordance with the standard 18-24 hour method, offering a cost-effective alternative method for faster AST reporting. Early reporting using EDD can enhance timely antibiotic administration, reduce AMR, and improve patient outcomes without additional costs. This method aligns with FDA-recommended thresholds for AST systems and provide significant advantage in clinical settings.