Performance of the Reveal Rapid Antibiotic Susceptibility Testing System on Gram-Negative Blood Cultures at a Large Urban Hospital

Abstract

Timely and effective antibiotic treatment is vital for sepsis, with increasing incidence of antimicrobial-resistant bacteremia driving interest in rapid phenotypic susceptibility testing. To enable the widespread adoption needed to make an impact, antibiotic susceptibility testing (AST) systems need to be accurate, enable rapid intervention, have a broad antimicrobial menu and be easy to use and affordable. We evaluated the Specific Reveal (Specific Diagnostics, San Jose, CA) rapid AST system on positive blood cultures with Gram-negative organisms in a relatively resistant population in a large urban hospital to assess its potential for routine clinical use. One hundred four randomly selected positive blood cultures (Virtuo; bioMérieux) were Gram stained, diluted 1:1,000 in Pluronic water, inoculated into 96-well antibiotic plates, sealed with the Reveal sensor panel, and placed in the Reveal instrument for incubation and reading. The MIC and susceptible/intermediate/resistant category was determined and compared to results from Vitek 2 (bioMérieux) for the 17 antimicrobials available and to Sensititre (Thermo Fisher) for 24 antimicrobials. Performance was also assessed with contrived blood cultures with 33 highly resistant strains. Reveal was in 98.0% essential agreement (EA) and 96.3% categorical agreement (CA) with Sensititre, with just 1.3% very major error (VME) and 97.0%/96.2%/1.3% EA/CA/VME versus Vitek 2. Reveal results for contrived highly resistant strains were equivalent, with EA/CA/VME of 97.7%/95.2%/1.0% with CDC/FDA Antibiotic Resistance Isolate Bank references. Average time to result (TTR) for Reveal was 4.6 h. Sample preparation was relatively low skill and averaged 3 min. We conclude that the Reveal system enables accurate and rapid susceptibility testing of Gram-negative blood cultures.

Keywords: blood cultures; phenotypic antimicrobial susceptibility testing; rapid diagnostics; volatile organic compounds.

FIG 1

Determination of MIC on the Reveal AST. A sheet of small-molecule sensor arrays is sealed onto a 96-well dried antibiotic plate that is inoculated with the bacterial sample (E. coli AR1095). Above each well is a hexagonal array of 7 sensors that show a colorimetric change in response to the volatile emissions produced by microbial growth. The signals from the positive-control well (black trace) and meropenem wells at concentrations of 2 μg/mL and below indicate growth, while the signals from the negative-control well (yellow trace) and wells with meropenem concentrations above 2 μg/mL are flat, indicating no growth. The divergence of sensor response in growth wells from the negative control allows the determination of MIC, which is 4 μg/mL in this case, matching the CDC broth microdilution result.

FIG 2

Reveal AST workflow. The workflow for the Reveal AST is a simple ≈3-min process involving inoculation of a single dilution of the positive blood culture into the AST panel, followed by sealing the sensor sheet.

FIG 3

Average time to result for each antimicrobial on Reveal across all species. The results indicated that TTR varied by drug, with meropenem requiring 6 h on average, while ampicillin results were issued in an average of 3.5 h.