Implementation of semi-automated antimicrobial susceptibility interpretation hardware for nontuberculous mycobacteria may overestimate susceptibility

Nontuberculous mycobacteria (NTM) cause severe opportunistic infections and have a rising incidence in most settings. Rising diagnostic need must be met by national reference laboratories, which rely on Clinical & Laboratory Standards Institute (CLSI) guideline approved manual readout of microtiter plates for antimicrobial susceptibility testing (AST) to determine antibiotic minimum inhibitory concentrations (MICs). Interpretation of these plates leads to different outcomes between laboratories. The SensiTitre™ Vizion™ Digital MIC Viewing System (Vizion) offers a more streamlined approach using semi-automated reading. Here, we conducted a blinded trial comparing the outcome of AST between manual readout and Vizion readout for 132 NTM isolates, amounting to 727 individual tests for antibiotic susceptibility ranging across 13 individual antibiotics with established CLSI breakpoints. From this, we calculated specificity, sensitivity, positive predictive value (PPV), negative predictive value (NPV) and the F1-value, as well as assessing major error (ME) and very major error (VME) rates. We find that Vizion-assisted AST produces significantly lower MICs (paired Wilcox signed rank test; p 50 values, leading to small discrepancies crossing the breakpoint, contributing to VMEs and MEs. Using the Vizion in standard clinical diagnostics for NTM might lead to an overestimation of antibiotic susceptibility.