الفهرس 
EnterobacteriaceaeOnly 14 pages are availabe for public view
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Abstract
The increase in antibiotic resistance in the Enterobacteriaceae family has become a major threat to public health. Enterobacteriaceae are important nosocomial pathogens; they can lead to severe morbidity and mortality, particularly in ICU.
CRE are often resistant to all β-lactam drugs and frequently carry mechanisms conferring resistance to other antimicrobial classes, so limiting treatment options.
Different mechanisms are responsible for carbapenem resistance in Enterobacteriaceae, which are hyper production of ESBL or AmpC enzymes combined with either porin loss or alteration, or active transport of carbapenem drugs out of the cell due to augmented efflux pump and production of carbapenem-hydrolyzing carbapenemases
Carbapenemases are divided into different Ambler molecular classes, class A carbapenemase which include KPC enzyme, class B MBLs which include VIM, IMP, and NDM enzymes, and class D carbapenemase which include OXA-48 like enzymes.
Carbapenemase producing Enterobacteriacea can disseminate rapidly from person to person because genes, which encode carbapenemases, are mostly plasmid-mediated thus can spread horizontally between isolates by conjugation.
The most important genes responsible for carbapenemase production are blaKPC, blaVIM, bla IMP, blaNDM and blaOXA-48.
Rapid identification of these bacteria is necessary for preventing their dissemination and decreasing mortality.
Real-time and multiplex PCR can identify these bla genes accurately, but these methods are not suitable for daily testing in clinical laboratories due to their high cost. Thus, simple cost-effective phenotypic techniques are used for screening for presence of these genes.
The CLSI published a recommendation that stated that Enterobacteriaceae with elevated carbapenem MIC or reduced disk diffusion inhibition zones should be tested for carbapenemase production using MHT.
The MHT is an easy and accurate assays for the phenotypic detection of KPC carbapenemases and OXA-48-like enzymes with available reagents in all laboratories but perform poorly for MBLs, NDMs, VIMs, and IMPs.
Several screening methods incorporating the use of metal chelating agents, such as EDTA which are capable of blocking MBL activity, have been developed to detect MBL-producing organisms. EDST is a simple, inexpensive phenotypic method for detection of MBL that could be easily incorporated into the routines of clinical laboratories
The present study aimed to investigate the phenotypic and genotypic characteristics of CRE isolated from patients in ICU of Ain Shams University hospitals.
One hundred fourty four different clinical samples were collected from the internal medicine ICU of Ain Shams university hospital from July 2017 to January 2018.
All samples were collected under complete aseptic conditions. These sampls included 118 urine samples, 4 sputum samples, 2 pus samples, 4 blood samples, 2 wound swabs and 14 endotracheal tubes (ETT) aspirates.
Fifty-four Enterobacteriaceae isolates were identified by conventional methods. They were 28(51.8%) K. pneumoniae followed by 14(25.9%) E.coli, 5(9.6%) Citrobacter and 7(12.9%) Proteus.
Then detection of 30 CRE strains were done by meropenem and imipenem disk diffusion test. The isolated CRE were 22 K. pneumoniae, 3 E.coli, and 5 Citrobacter isolates.
The antimicrobial susceptibility patterns for CRE isolates were determined by disc diffusion test. Then Phynotypic detection of carbapenemase production in CRE isolates by MHT and EDST, and genotypic detection of carbapenemase encoding genes blaKPC, blaVIM, blaIMP, blaNDM and blaOXA-48 by using multiplex PCR.
The prevalence rate of CRE in ICU patients was 30/144 (20.8%) of the general ICU population, and 30/54 (55.6%) of Enterobacteraicae positive ICU population. In addition they are responsible for 25% of catheter related UTIs and 57%of VAP.
Antimicrobial susceptibility pattern of CRE isolates to different antimicrobial classes show that half of the CRE were multi-drug-resistant MDR being resistant to all tested antibiotics. In addition, most of CRE isolates were susceptible to Gentamycin.
About 86% of CRE isolates show positve EDST and 52% show positive MHT.
The blaOXA48 and blaNDM genes were the commonest gene detected but blaVIM and blaIMP genes were not detected by PCR in any of the isolated CRE strains. In addition, 10 isolates of isolated CRE were contained multiple genes.
There is strong correlation with great significance (P value > 0.001) between MHT and PCR according to detection of blaOXA48 gene in CRE with high sensitivity and specificity (83.35% and 91.67% respectively) and PPV and NPV reaching (93.75% and 78.75% respectively).
There was statistical significance (P > 0.05) between MHT and PCR according to the detection of blaKPC gene in CRE isolates with high sensitivity but low specificity (100% and 53.85% respectively) and PPV and NPV reaching (25% and 100% respectively)
There is non-significant relationship (p <0.05) between EDST and PCR as regarding blaNDM gene detection in CRE isolates with sensitivity and specificity reaching (89.9% and 16.7% respectively) and PPV and NPV reaching (61.5% and 50% respectively).