FDA Clears Rapid Phenotypic Antimicrobial Susceptibility System for Positive Blood Cultures

Bloodstream infections require prompt treatment, but antimicrobial susceptibility results often lag behind a positive blood culture. Conventional testing can take another 24 to 48 hours after a culture flags positive, leaving patients on empiric broad-spectrum therapy while results are pending. A newly cleared diagnostic system now provides phenotypic susceptibility results directly from positive blood cultures in approximately 100 to 140 minutes.

PhAST Corp. received U.S. Food and Drug Administration (FDA) 510(k) clearance for the PhAST instrument and PhAST Blood Culture Gram-negative Panel. The assay is indicated for monomicrobial positive blood cultures containing Acinetobacter spp., Enterobacterales, or Pseudomonas aeruginosa. It provides susceptible, intermediate, or resistant interpretations for 15 antimicrobials and requires organism identification by a separate FDA-cleared method.

Image: Each PhAST instrument supports random-access processing of up to four samples simultaneously, delivering a throughput of up to 12 samples per eight-hour shift. (Photo courtesy of PhAST)

The panel tests blood cultures flagged as positive by a continuous monitoring system without requiring subculture. It uses single-cell time-lapse video microscopy and computer vision to observe how individual bacteria respond to antimicrobials. Sample preparation requires less than one minute of hands-on time, and each instrument can process four samples concurrently, with random access and throughput of up to 12 samples per eight-hour shift.

A clinical study supporting clearance was conducted at four sites, including three U.S. clinical laboratories. Overall categorical agreement was 97.3%, with a major error rate of 0.9% and a very major error rate of 0.2%. Mean time from sample loading to results was 99 ± 6 minutes for Enterobacterales and Acinetobacter spp. and 141 ± 6 minutes for P. aeruginosa.

The panel is categorized as Moderate Complexity under CLIA. PhAST is also developing the platform for use with additional sample types and diagnostic applications, although these remain separate from the cleared blood culture panel.

“The shift that gets the positive blood culture should be the shift that acts on it. This means less time on the wrong drug - for the patient, and for everyone downstream of the resistance we drive with broad-spectrum antibiotics,” said John (JT) Sauls, PhD, CEO of PhAST.

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