الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Clinical isolates of carbapenem resistant Enterobacteriaceae (CRE) by carbapenemase production have now spread worldwide. Carbapenemase producers notoriously exhibit multidrug resistance phenotypes, making treatment of infections extremely difficult as they are able to hydrolyze a broad spectrum of β-lactams including the penicillins, cephalosporins, carbapenems and monobactam. They have the potential to spread rapidly in hospital environment and cause nosocomial infections with high mortality rates.
Rapid identification of carbapenemase producing organisms is extremely important for timely detection, treatment and implementation of infection control measures to prevent their spread. Many phenotypic and molecular commercially available and in-house laboratory tests have been described for detection of carbapenemase.
The Carba NP test is a phenotypic test for carbapenemase detection. It is based on hydrolysis of the β-lactam ring of imipenem by carbapenemases, leading to acid production that can be detected by the change of phenol red from red to yellow or orange.
The Carba NP strip test is a recent modification of the Carba NP test by using filter paper as an inoculation medium for reading the color change and for decreasing the time of identifying the carbapenemase producing Enterobacteriaceae and Pseudomonas spp.
In this study we aimed to evaluate the diagnostic performance of two rapid tests; Carba NP test and Carba NP strip test for the detection of carbapenemase production in fifty different gram-negative isolates versus MIC broth microdilution standard method. Real time PCR was done for confirmation of carbapenemase enzymes production and detection of common carbapenemase genes; blaKPC, blaVIM, blaOXA-48, blaGES, blaIMP.
During this study, fifty gram-negative isolates, collected from different clinical samples submitted for routine culture and sensitivity in Central Microbiology Laboratory Ain Shams University Hospitals, were included.
Thirty four 34/50 (68%) isolates were positive for carbapenemase production by Carba NP tube test and thirty seven (37/50) (74%) were positive by Carba NP strip test. Forty isolates were resistant to imipenem by MIC broth microdilution method (40/50) and ten isolates were sensitive (10/50). Forty isolates were positive for carbapenemase production by PCR (40/50) and ten isolates were negative (10/50).
Carba NP tube test showed an overall sensitivity, specificity, PPV and NPV compared to MIC broth microdilution for imipenem of 85%,100%,100% and 66.7 % respectively.
For the Carba NP strip test the overall sensitivity, specificity, PPV and NPV were 92.5%, 100%, 100% and 76.9% respectively compared to MIC broth microdilution for imipenem.
Major significance of this study was the difference in diagnostic timing between strip and tube method which was less than five minutes for 100% of isolates for strip test and 81 % of isolates were more than five minutes reaching up to two hours for tube method.
In conclusion, The Carba NP test performed by use of the modified strip method in this study is a simple and inexpensive method with high sensitivity and specificity for detecting carbapenemase production in gram negative isolates. It is also a rapid test providing results within five minutes or less instead of two hours for the tube method allowing the rapid initiation of proper treatment. However, we found that the tube method had the upper hand when it came to the Pseudomonas spp. isolates with statistically significant higher diagnostic performance than that of the strip method which needs further evaluation on larger test group.
Although PCR is a rapid and highly sensitive method in detection of Carbapenemase production, it is v expensive and needs trained personnel as well as machinery which may not be available for all microbiology labs especially in low and middle income countries.