Ability of the VITEK 2 Advanced Expert System To Identify β-Lactam Phenotypes in Isolates of Enterobacteriaceae and Pseudomonas aeruginosa

Abstract

The Advanced Expert System (AES) was used in conjunction with the VITEK 2 automated antimicrobial susceptibility test system to ascertain the β-lactam phenotypes of 196 isolates of the familyEnterobacteriaceae and the species Pseudomonas aeruginosa. These isolates represented a panel of strains that had been collected from laboratories worldwide and whose β-lactam phenotypes had been characterized by biochemical and molecular techniques. The antimicrobial susceptibility of each isolate was determined with the VITEK 2 instrument, and the results were analyzed with the AES to ascertain the β-lactam phenotype. The results were then compared to the β-lactam resistance mechanism determined by biochemical and molecular techniques. Overall, the AES was able to ascertain a β-lactam phenotype for 183 of the 196 (93.4%) isolates tested. For 111 of these 183 (60.7%) isolates, the correct β-lactam phenotype was identified definitively in a single choice by the AES, while for an additional 46 isolates (25.1%), the AES identified the correct β-lactam phenotype provisionally within two or more choices. For the remaining 26 isolates (14.2%), the β-lactam phenotype identified by the AES was incorrect. However, for a number of these isolates, the error was due to remediable problems. These results suggest that the AES is capable of accurate identification of the β-lactam phenotypes of gram-negative isolates and that certain modifications can improve its performance even further.

Colonisation with extended spectrum beta-lactamase-producing and carbapenem-resistant Enterobacterales in children admitted to a paediatric referral hospital in South Africa

“…Enterobacterales were categorised as ESBL-PE according to the Vitek 21 Advanced Expert System (AES) interpretation of the AST GN-N255 card. This categorisation is based solely on the pattern of susceptibility and resistance to different cephalosporins as the card lacks wells containing cephalosporins combined with a beta-lactamase inhibitor [48].…”

Comparison of different methods of determining β-lactam susceptibility in clinical strains of Pseudomonas aeruginosa

“…Several automated systems are available for the identification and susceptibility testing of the most clinically important bacteria (Stager & Davis, 1992). These systems are able to decrease the in-laboratory turnaround time required for standardized methods and to provide physicians with susceptibility profiles to help them select the most appropriate antimicrobial therapy (Felmingham & Brown, 2001;Sanders et al, 2000). The reporting errors by any test systems can have serious implications for the clinical outcome for patients (Micek et al, 2005).…”

Clinical Microbiology Informatics

“…The software then compares the input to the knowledge database by using the inference engine, and the system then outputs the appropriate susceptible, intermediate, or resistant (SIR) interpretation. Expert systems can also be used to infer the mechanism of antimicrobial resistance by comparing a clinical isolate's MIC values to a curated database of strains which have had their MIC values and mechanism(s) of resistance characterized (45). In addition to having the antimicrobial breakpoints in its database, the expert system also has rules which check to see if some drug results need to be reported as resistant even though the organism might test as sensitive.…”