Multi-Year Comparison of VITEK(R) MS performance for identification of rarely encountered pathogenic gram-negative bacilli (GNBs) in a large integrated Canadian healthcare region.

BackgroundThis multi-year study (2014-19) compared identification of rare and unusual GNB by MALDI-TOF MS (VITEK(R) MS, bioMerieux, Laval Que.) to 16S rRNA gene sequencing (16S) according to our laboratories routine workflow; 16S is done if initial MALDI-TOF MS results were discordant, wrong or absent. Materials and MethodsGNB isolates were first analyzed by standard phenotypic methods and MALDI-TOF MS using direct deposit with full formic acid extraction; proteomics was repeated if no result occurred. Medically approved 16S analyses were done using fast protocols. Isolate sequences were analyzed using IDNS3 bacterial database (SmartGene, Lausanne, Switzerland). Results329 GNB isolates were recovered from 304 specimens; >1 isolate was recovered from 19(6%). 250(76%) NFGNBs, 62(19%) fGNBs, and 17(5%) CAMPB were mainly recovered from blood cultures (31.6%) and lower respiratory specimens (43%) (one-half were isolated from cystic fibrosis patients). Accurate genus vs. species identities were obtained for 67.2%/26% NFGNBs, 74.2%/53.2% fGNBs, and 22% CAMPB (with no discrepant species), respectively. Wrong or no results were obtained for 82(32.8%) NFGNB, 17(27.4%) fGNB, and 13(72.2%) CAMPB. Absent or misidentifications occurred for NFGNBs (33%), fGNBs (26%) and CAMPB (89%) due to absence of species in the instruments database. VITEK MS performance remained stable for NFGNBs and fGNBs but improved for CAMPB but with the addition of Campylobacter rectus and Campylobacter curvus to the database. ConclusionsVITEK(R) MS databases need to be continually updated to include an increasing number of rare and unusual GNBs causing invasive human infections. 16S remains important for identification of GNBs where proteomics fails.