Assay detects genetic markers for antibiotic-resistant bacteria

The US Food and Drug Administration (FDA) has cleared for marketing the Xpert Carba-R Assay, manufactured by California company Cepheid.

The assay tests patient specimens to detect specific genetic markers associated with bacteria that are resistant to carbapenem antibiotics, which are widely used in hospitals to treat severe infections. The resistant bacteria are commonly referred to as carbapenem-resistant enterobacteriaceae (CRE) and have been reported in almost all states within the US.

According to the US Centers for Disease Control and Prevention, CRE infections most commonly occur in people with exposure to healthcare settings, like hospitals and long-term care facilities. Patients whose care requires devices like ventilators, urinary catheters or intravenous catheters, and patients who are taking long courses of certain antibiotics, are among those at risk for CRE infections. Some CRE bacteria have become resistant to almost all available antibiotics and present a significant public health threat.

Current methods to identify colonisation with CRE or other resistant organisms rely on growing bacteria from faecal material in cultures, which are then subjected to antimicrobial susceptibility testing to determine in vitro susceptibility to antimicrobial agents. Bacterial culture methods and susceptibility testing may take up to four days, and additional testing is often also required to confirm that carbapenemase, the enzyme produced by CRE that inactivates carbapenem antibiotics, is present.

The Xpert Carba-R Assay tests specimens directly taken from patients, which are usually obtained by rectal swabs, for the presence of five different genetic markers that are associated with carbapenemase. It is intended as an aid in infection control and can be used in conjunction with other clinical and laboratory findings.

“By using a specimen taken directly from a patient to test for the presence of genetic markers, hospitals can more quickly identify these dangerous bacteria resistant to certain antibiotics,” said Dr Alberto Gutierrez, director of the FDA’s Office of In Vitro Diagnostics and Radiological Health within the FDA’s Center for Devices and Radiological Health.

The FDA’s decision to provide clearance was based on data from two clinical studies. A prospective study used rectal swabs from 755 patients in hospitals or long-term care facilities to compare results from the Xpert Carba-R Assay with results from reference cultures and automated real-time polymerase chain reaction (PCR) sequencing. A second study designed to test the clinical performance of the assay used 432 rectal swabs that were artificially prepared with specific concentrations of bacteria containing the genes detected by the test. The results of these studies demonstrated similar performance between the assay and the culture method.