Image: Scanning electron micrograph of multidrug resistant Acinetobacter baumannii, a non-fermentative aerobic Gram-negative rod (Photo courtesy of Bioquell).
A rapid diagnostic test for multiresistance to broad-spectrum antibiotics has been developed for multidrug-resistant strains of Acinetobacter baumannii
, an important hospital pathogen.
Bacterial resistance to antibiotics has increased considerably over recent years and the situation is particularly dramatic in regard to Gram-negative bacilli such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa,
and A. baumannii,
found in septicemic and abdominal infections and infections of the urinary tract and the lungs.
Microbiologists at the University of Fribourg (Switzerland) and their colleagues at Faculté de Médecine Paris-Sud, Le Kremlin-Bicêtre, France) collected a total of 220 strains to evaluate the performance of the CarbAcineto NP test. The strains included a collection of 151 carbapenemase-producing and 69 non-carbapenemase-producing Acinetobacter
The test is based on the acidification properties generated by the enzymatic hydrolysis of a carbapenem, imipenem, when it is cleaved by a carbapenemase. The medium acidifies and the acidity indicator, which indicates pH, then turns from red to yellow. The detection of this carbapenemase activity can be realized by testing already isolated bacteria or any site infections. The result is obtained in less than two hours, while other techniques currently available require a minimum of 24 hours, most frequently 72 hours.
The specificity and of the CarbAcineto NP test were found to be 100% and the sensitivity was 94.7%. The CarbAcineto NP test efficiently detected OXA-type carbapenemase producers, leading to a significant improvement of the sensitivity to 94.7% for the CarbAcineto NP test versus 11.9% for the original Carba NP test. The use of the CarbAcineto NP test will be particularly important for intensive care unit (ICU) patients, for whom multidrug-resistant isolates belonging to the A. baumannii-A. calcoaceticus
complex are a common source of severe infections. It specifically makes sense to test for carbapenemase production considering that the acquisition of a carbapenemase in A. baumannii
is a marker of multidrug resistance.
The authors concluded that the CarbAcineto NP test is simple, cost-effective and, by detecting multidrug-resistant strains, it can prevent them spreading via outbreaks of hospital infections caused by multidrug-resistant bacteria, particularly among the most seriously ill patients and those undergoing resuscitation. This new test also provides a guide in the choice between the very few remaining treatment options for infected patients. Inserm Transfert (Paris, France) have filed an international patent for the CarbAcineto NP test. The study was published in the May 2014 issue of the Journal of Clinical Microbiology.
University of Fribourg
Faculté de Médecine Paris-Sud