Evaluation of the Diagnostic Accuracy of the T2Resistance Panel (Research Use Only) in Patients With Possible Bacterial Bloodstream Infections

Abstract

Background: Early identification and antimicrobial susceptibility testing (AST) of bloodstream pathogens are important for promptly determining the appropriate therapy. Currently, positive blood culture results (identification and AST) are reported in 2 to 4 days. The T2Resistance (T2R) Panel (T2 Biosystems, Inc) uses DNA amplification with magnetic resonance from 3 mL of whole blood for direct detection of 13 antibiotic resistance genes: bla _KPC, bla _NDM, bla _VIM, bla _IMP, bla _OXA-48, bla _CTX-M-14/15, AmpC bla _CMY/DHA, vanA/B, and mecA/C. We compared the accuracy of T2R testing to AST for positive blood cultures.

Methods: This investigator-sponsored, single-center study prospectively enrolled 802 patients with a standard of care blood culture. Five hundred forty-seven patients had adequate blood for culture and T2R testing. Blood cultures with positive isolates were identified, and AST was performed. Blood samples with positive blood cultures were tested with the T2R Panel.

Results: Blood cultures were positive for 58/547 (10.6%) patients. Contaminants (18/547 [3.3%]) were excluded. T2R testing results (n=31) showed 2 bla _CTX-M-14/15 genes with 100% sensitivity; the remaining gram-negative resistance genes were not detected, so sensitivity could not accurately be determined. Specificity was 100% for the 16 gram-negative bacilli. Three enterococci and 2 Staphylococcus aureus showed 100% sensitivity/specificity. However, 10 coagulase-negative staphylococci showed 17% sensitivity/100% specificity. Antibiotic resistance genes identified were 2 bla _CTX-M-14/15, 2 mecA/C, and 1 vanA/B. T2R testing results were obtained in an average of 7 hours.

Conclusion: T2R testing is highly specific (100%) for the 13 antibiotic resistance genes on the panel. Sensitivity was 100% for the genes detected but was low (17%) for coagulase-negative staphylococci. T2R testing has the potential to diagnose certain antibiotic resistance genes from bacterial bloodstream infections in hours vs the days required for a positive blood culture with AST. Additional studies that include larger numbers of samples with antimicrobial resistance genes are needed.

Keywords: Drug resistance–microbial; genes–MDR; rapid diagnostic tests.

Figure.

T2Resistance Panel results compared to simultaneously drawn blood culture results from patients with a possible bloodstream infection. ^aNone detected=no target genes were detected with T2R testing. ^bBlood culture had 3 bacterial species: Enterococcus faecium (vancomycin resistant); Escherichia coli (ampicillin-sulbactam, amoxicillin-clavulanate, cefazolin, cefepime, and ceftriaxone resistant); and methicillin-resistant Staphylococcus epidermidis (MRSE). T2R Panel results were positive for vanA/B and positive for bla_CTX-M-14/15. ^cBlood culture had 3 bacterial species: methicillin-resistant Staphylococcus epidermidis, Staphylococcus haemolyticus (oxacillin susceptible), and Staphylococcus capitis (oxacillin resistant). In the T2R Panel results, a mecA/C gene was not detected. ^dPatients having a negative simultaneous blood culture but a different positive blood culture collected within 48 hours of the original simultaneous blood culture/T2R sample had their original negative simultaneous blood culture tested with the T2R Panel. BC, blood culture; E cloacae, Enterobacter cloacae; E coli, Escherichia coli; E faecalis, Enterococcus faecalis; E faecium, Enterococcus faecium; h, hour; K pneumoniae, Klebsiella pneumoniae; MRSA, methicillin-resistant Staphylococcus aureus; MRSE, methicillin-resistant Staphylococcus epidermidis; MSSA, methicillin-susceptible Staphylococcus aureus; MSSE, methicillin-susceptible Staphylococcus epidermidis; neg, negative; P aeruginosa, Pseudomonas aeruginosa; P mirabilis, Proteus mirabilis; P shigelloides, Plesiomonas shigelloides; R ornithinolytica, Raoultella ornithinolytica; S aureus, Staphylococcus aureus; S capitis, Staphylococcus capitis; S cohnii, Staphylococcus cohnii; S haemolyticus; Staphylococcus haemolyticus; T2R, T2Resistance Panel.