Commercial microbroth dilution (MBD) panels are commonly used for determining minimum inhibitory concentrations (MIC). Manual reading of these panels is tedious, time consuming and potentially error-prone. This study compared the accuracy of automated versus manual reading of Sensititre™ SGP1MBD panels (Sensititre) when tested on multi-drug resistant organisms (MDRO). A secondary objective was to compare susceptibility results obtained for a subset of antibiotics between MBD and Vitek® 2 Compact (Vitek).
MIC testing was performed by Vitek and Sensititre on 42 unique clinical MDRO isolates. Following incubation, Sensititre were read manually and using two automated commercial readers namely Sensititre™ Vizion (Vizion) and BIOMIC® digital reader. Categorical interpretation was determined using CLSI guidelines, with categorical agreement defined as concordant, minor errors, major errors or very major errors, using manual reading as the gold standard. In addition, Sensititre results for Meropenem, Imipenem, Piperacillin-tazobactam, Levofloxacin, Amikacin and Aztreonam were compared to Vitek results.
Isolates included Acinetobacter baumanii (n=8) and Enterobactericeae (n=34) strains positive for ESBL (n=12), AmpC (n=13), carbapenemases (n=16) and mcr-1 (n=2). A total of 714 drug-organism combinations were tested. 99.7% and 98.5% categorical agreements were achieved for BIOMIC® and Vizion results respectively when compared to manual reading. All errors observed were minor and there was no significant result discordance for any antibiotic. MICs obtained by all three methods were within one-fold dilution difference. There was 83.3% categorical agreement for Sensititre results when compared to Vitek. Of the 16.7% errors observed, 60% (n=25) were minor and 40% (n=17) were major errors. No very major error was observed. Carbapenems demonstrated the most number of discordant findings, with 46.2% (12/26) minor errors and 50% (8/16) major errors.
Automated reading of Sensititre by both systems is reliable as both showed no significant result discordance when compared with manual reading. Discordant findings between Vitek and Sensititre were most notable in Carbapenems amongst the six tested antibiotics.