Multiplex identification of gram-negative bacteria from positive blood culture broths : evaluation of an automated microarray-based molecular assay

Abstract

Bloodstream infection is life threatening and lead to high mortality. Conventional culture is time consuming which is unfavorable to patient outcome. Rapid identification of causative agent is needed to aid the selection of appropriate antimicrobial agent and improve clinical outcome. The recent study is the first multicenter study to evaluate the performance of the Verigene blood culture BC-GN assay against conventional culture methods on bacteria identification in Hong Kong. A total of 139 non-duplicated positive blood culture (BC) samples with Gram negative bacteria were collected from 3 hospitals (UCH, PMH and PYNEH) and the sensitivity of Verigene BC-GN assay and reduction in time to result compared to reference methods (biochemical tests and MADLI-TOF MS) will be calculated. There were 131 pure cultures and 8 mixed cultures. The overall sensitivity for pure culture and mixed culture were 92.4% (121/131) and 25% (2/8) respectively and the specificity of the assay is 99.3%. A total of 147 strains were isolated from 139 BC samples. The overall isolate sensitivity of Verigene result with conventional culture was 91.8% (135/147) and up to 97.1% (135/139) when only in panel organisms were counted. It accurately detected 98% E.coli, 90.9% K. pneumoniae, and 100% of P. aeruginosa, Proteus spp., Enterobacter spp. and Acinetobacter species. There was 1 case misidentified E. colias Enterobacter species, 2 cases considered as falsely positive, 2 K. pneumonia and 1 E. coli were not detected whileanother2 K. pneumoniae were later confirmed as K. variicola. There were 5.8% (8/139) BC recovered with bacteria not featured in the panel including 4 Aeronomas species, 1 Salmonella species, 2 K. variicola and 1 P. pseudoalcaligenes. During the whole study, tno-call rate of BC-GN assay was 0%. The Verigene provides a high level of agreement in bacteria identification. The time from positive Gram result to final report issued is greatly reduced from 36.84 hours to 2 hours when identification shifted from biochemical test to Verigene BC-GN assay. The reduction in turnaround time is significant to clinical management and patient outcome. It also reduces the length of hospital stay and trims down the medical cost.