Simple Inexpensive Test Rapidly Identifies Resistant Infections

The protocol for a relatively new test for a dangerous form of Gram-negative bacteria antibiotic resistance has been modified increasing its specificity to 100%.

Polymerase chain reaction (PCR), a DNA-based test, is currently the gold standard for detecting carbapenem-resistant Enterobacteriaceae (CRE), but it is expensive and requires equipment that many laboratories do not have, especially in low-income countries that are large reservoirs for CRE.

Microbiologists at the Oregon State Public Health Laboratory (Portland, OR, USA) used a modification of the test, called Carba NP, which was originally developed at the University of Fribourg (Switzerland) and the University Hospital of the South-Paris Medical School (France), to rapidly identify CRE, often referred to in the media as "super bugs" for their ability to resist most major antibiotics.

The scientists evaluated the ability of the Carba NP test to properly identify 59 of the 201 clinical isolates as carbapenemase producers. They used a previously published protocol and correctly identified 92% as being carbapenemase producers, including all strains of New Delhi metallo-beta-lactamase-1 (NDM-1) and Klebsiella pneumoniae carbapenemase (KPC), two important types of CRE. When they adjusted the protocol to increase the inoculum size and tested again they achieved 100% sensitivity. The average time to complete a test was 2.5 hours.

Karim Morey-Castro, PSM, a coauthor of the study, said, “Over the past decade carbapenemase-producing CRE (CP-CRE) have rapidly spread around the globe and are currently considered an urgent public health threat by the [US] Centers for Disease Control and Prevention (CDC). Timely detection of CP-CRE is critical to patient care and infection control. Carba NP is a much less expensive test that most labs should be able to afford.” The study was presented at the 54th Interscience Conference on Antimicrobial Agents and Chemotherapy held September 5–9, 2014, in Washington DC (USA).

Related Links:
Oregon State Public Health Laboratory
University of Fribourg
University Hospital of the South-Paris Medical School