Deviations from Standard Disk Diffusion Protocols for Antimicrobial Susceptibility Testing in Medical Laboratories in Gharyan

Abstract

Antimicrobial susceptibility testing (AST) is essential for guiding appropriate antibiotic therapy. The disk diffusion method is widely used in Libya due to its low cost, yet deviations from standardized protocols can compromise result accuracy, affecting clinical decisions and patient outcomes. This study evaluated the performance of the disk diffusion AST method in medical laboratories in Gharyan, Libya, using EUCAST guidelines (version 12.0) as a benchmark. Seventy-five AST plates representing 122 clinical specimens were randomly collected from three pathology centers between September and November 2025. Plates were analyzed for the type of culture media, number of specimens per plate, number of antibiotic disks, and readability of results. All plates were 90 mm in diameter. Nutrient agar was used for 118 specimens, and blood agar for two; none used Mueller-Hinton agar as recommended. Only 17% of plates tested a single specimen per plate; the majority tested one specimen on half or a quarter of a plate. The number of antibiotic disks per specimen often exceeded EUCAST limits (up to 20 disks per plate), and only 8% of plates yielded readable results. Widespread deviations from EUCAST protocols—including inappropriate media, specimen overloading, and excessive disks—compromise AST reliability. These errors may lead to incorrect antibiotic prescriptions, delayed recovery, and increased antimicrobial resistance. Strict adherence to standardized guidelines is urgently required to ensure accurate, clinically meaningful AST results.  Moreover, raising awareness of the importance of following standard guidelines is crucial for correcting the course.