Improve antibiotic susceptibility test and its quality control by linear-gradient plate

Abstract

Antibiotic susceptibility test (AST) is a precise clinical experiment of choosing sensitive antibiotics, the success of which mainly depends on the reliability of the quality control, and the perspectiveness and accuracy of Minimum inhibitory concentration (MIC). In this paper, the linear-gradient plate method was verified by quality control test and AST. The result of MIC measured by linear-gradient plate method and by the broth and agar dilution is the same, but the former is more accurate due to the linear-gradient antibiotics concentration, which enables researchers to calculate the antibiotic precise concentration and to guarantee the reliability of quality control test. Meanwhile, according to the ranges of sensitive (S), intermediate (I) and resistant (R) defined by Clinical Laboratory Standards Institute (CLSI) or European Committee on Antimicrobial Susceptibility Testing (EUCAST) standards, three linear gradients (0-S, S-R, R-8R) were set in gradient plate for AST. The sensitive range of antibiotic concentration for bacteria was estimated firstly, and then MIC was calculated precisely, which can effectively isolate the resistant strains, foresee the early antibiotic resistance after using the antibiotics and guide the selection and application of clinical antibiotics. The major problem of linear-gradient method lies in the cumbersome and instability resulting from the hand-made process. However, if ready-to-use gradient plates could be produced mechanically, they will facilitate the clinical AST and improve resistance screening technology.