Entering a New Era of Blood Culture Testing Technology

In a symposium on the laboratory diagnosis of bloodstream infections at ID Week 2018, in San Francisco, California, presenters discussed optimizing use and interpretation of blood cultures, direct detection of bloodstream infections, and the clinical utility of sepsis biomarkers.

In an exclusive interview, Contagion^® sat down with one of the presenters, Melvin Weinstein MD, professor of medicine, pathology, and laboratory medicine, chief of the Division of Infectious Diseases, Allergy, and Immunology, and co-director of the Microbiology Laboratory at Rutgers Robert Wood Johnson Medical School, to discuss the current challenges in the laboratory diagnosis of bloodstream infections and emerging technologies that will advance the field.

Contagion^®: Can you discuss the current technologies that are being used to diagnose bloodstream infections? What gaps exist in the current options?

Melvin Weinstein, MD: The current technologies for diagnosing bloodstream infections are those that people have been used to for a number of years, namely conventional blood cultures. When a blood culture becomes positive there has been a traditional way of processing those blood.

The current action is in rapid diagnostics so when a blood culture becomes positive we now have the ability, at least in some cases, to make the etiologic diagnosis and get some susceptibility information within 1 to 2 hours as opposed to 1 to 2 days, which had been the previous standard. There are also, now, at least 1 US Food and Drug Administration (FDA) cleared direct-from-blood system that can detect Candida species in 3 to 5 hours and also several bacteria within 4 to 8 hours.

Can you speak to some of the newer technologies that are emerging?

The newer technologies are mostly molecular-based; they are either single-plex or multiplex Polymerase chain reaction (PCR) assays or if they’re not PCR, they are other DNA amplification techniques. There are assays that target specific organisms like Staphylococcaceae; the GeneXpert Staph SR assay, can differentiate methicillin-susceptible from methicillin-resistant Staphylococcus aureus from non-Staph aureus isolates and do that in approximately an hour, directly out of a positive blood culture model.

There are also new assays from BioFire, which is called the BCID (blood culture identification) assay, which has 27 different targets—multiple gram-positive targets, gram-negative targets, and also several Candida targets—and can detect the Klebsiella pneumoniae carbapenemase (KPC) and those results are also direct from a positive blood culture and you will get your results within about 1 hour.

There’s a similar technology, similar in concept at least, from Luminex, it’s called the Verigene; that has 30 targets—again gram-positive targets, gram-negative targets—and that technology can provide results for 6 different resistance genes for gram-negatives of the CTX-M-ESBL (CefiTaXime Extended Spectrum Beta-Lactamase), the KPC, and other carbapenemases, and also, for gram-positives, it detects the mecA gene, and also the VanA and VanB genes that confer resistance to vancomycin in enterococci.

Not yet FDA approved, but approval [is] expected, for a new, similar-in-concept system from GenMark which will have somewhere in the range of 65 to 70 different targets—so many more bacterial strains, 5 or more fungal strains—including cryptococcosis and fusarium. That system will be very interesting when it becomes available.

There is yet one additional system that is not molecular that is growth based, it’s called the Accelerate Pheno, which detects 8 gram-positive organisms, 8 gram-negative organisms, 5 Candida species, and provides a phenotypic susceptibility result, so essentially a full-range of susceptibility results and it does the identification in approximately 1 hour and a half and provides the susceptibility results in about 7 hours.