Version 1: Evaluation of optimal agar medium for detecting hypervirulent Klebsiella pneumoniae using string test

1. Abstract The string test is a screening method for detecting hypervirulent Klebsiella pneumoniae (hvKp). Agar media are typically used for string test; however, the effect of media type on the test results remains unclear. We aimed to determine the optimal agar medium and cutoff value for the string test. We tested the string test for 99 Klebsiella strains using different agar media: sheep blood, chocolate, Drigalski's, and MacConkey. Diagnostic accuracy was calculated in concordance with the rmpA, rmpA2, or iuc gene levels. The diagnostic accuracy rates for sheep blood, chocolate, Drigalski's, and MacConkey agar were 0.79, 0.75, 0.73, and 0.64, respectively. When the cutoff was changed from 5 mm to 10 mm, the diagnostic accuracy rate for sheep blood agar decreased from 0.79 to 0.65. Our findings suggest that agar medium type affect the string test results and sheep blood agar with a cutoff of 5 mm is the optimal condition for detecting hvKp.