FDA Approves Test to Detect Antibiotic Sensitivity in Blood Infections

The US Food and Drug Administration (FDA) has approved a test that can identify organisms that cause blood infections and can also identify which antibiotics should work against them.

It is called the PhenoTest BC Kit.

According to the FDA, the test reduces the amount of time it takes to provide information on antibiotic treatment. That could help the ongoing quest to fight antibiotic resistance by prescribing fewer of these drugs.

"By identifying organisms and knowing earlier which antibiotics the organism is likely to respond to, health care professionals can treat patients with bloodstream infections more appropriately," said Alberto Gutierrez, PhD, director of the Office of In Vitro Diagnostics and Radiological Health at the FDA’s Center for Devices and Radiological Health.

Bacterial or yeast blood infections can occur in patients of all ages, but are particularly severe in infants, the elderly, and those with weakened immune systems. If not treated rapidly, such bloodstream infections can lead to severe complications, such as septic shock and death. Unlike traditional identification and antibiotic susceptibility tests that may take 24 to 48 hours after detection in a positive blood culture to provide test results, the PhenoTest BC Kit can identify bacteria or yeast from a positive blood culture in approximately 1.5 hours. For certain organisms, the test also provides important information to guide treatment recommendations in approximately 6.5 hours after the organisms are detected from blood cultures.

The test can identify 14 different species of bacteria and two species of yeast that cause bloodstream infections, while also providing antibiotic sensitivity information on 18 selected antibiotics for a subset of the identified organisms as appropriate. The test will also identify the presence of two indicators of antibiotic resistance, which can occur when potentially harmful bacteria change in a way that reduces or eliminates the effectiveness of antibiotics.

The PhenoTest BC Kit works by measuring the similarity of the infection-causing organism’s genetic material to DNA known to be unique to specific bacteria or yeast. Once the organism is identified, it is mixed with antibiotics and the growth of the bacteria is measured by time-lapse images. If the organism does not grow when the antibiotic is present, this means that an antibiotic can possibly be used for treatment.

The FDA reviewed the data for the PhenoTest BC Kit through the de novo premarket review pathway, a regulatory pathway for devices of a new type with low-to-moderate-risk that are not substantially equivalent to an already legally marketed device and for which special controls can be developed, in addition to general controls, to provide a reasonable assurance of safety and effectiveness of the devices. The FDA’s decision to allow marketing was based largely on its review of the sponsor’s primary clinical study of 1,850 positive blood cultures. In this study, the PhenoTest BC Kit provided correct identification of the bacteria or yeast in the positive blood culture more than 95% of the time. Results for testing whether the bacteria were sensitive to antibiotics were also accurate when compared to traditional tests.

Risks associated with use of the PhenoTest BC Kit include false positive findings, which can occur when an individual not infected with organisms that cause bloodstream infections receives a test result that incorrectly indicates that he or she is infected. The FDA said results obtained from the test should always be interpreted alongside additional laboratory test results.

The PhenoTest BC Kit and the Pheno System are manufactured by Accelerate Diagnostics Inc. in Tucson, Arizona.