Detection and Characterization of Nosocomial Carbapenem - Resistant Gram Negative Bacilli from Assuit University Hospitals

Abstract

Background: Carbapenem resistant gram negative bacilli (CRGNB) pose significant risks. They are difficult to detect, they have a role in unnoticed spread within hospitals and they are able to participate in horizontal gene transfer with other pathogens in hospitals. Objectives: This study was conducted to determine the frequency of carbapenem resistance among nosocomial GNB infections, to compare different phenotypic methods to PCR for accurate detection of CRGNB isolates, to define the risk factors for carbapenem resistance in GNB infections and to define possible treatment alternatives for CRGNB. Methodology: Three hundred fifty five specimens were collected from 134 nosocomially infected patients admitted to different hospital wards at Assuit University Hospitals. Phenotypic identification of CRGNB isolates were performed by antimicrobial susceptibility testing. Further confirmation and biotyping were done by API20E and API20NE kits. Phenotypic detection of carbapenemases was done by determination of MIC by Imipenem-E test and Meropenem-E test, CHROM agar KPC TM medium, modified Hodge test (MHT), combined disc method (CD), double disc synergy test (DDST).The isolated CRGNB were further identified genetically using the conventional polymerase reaction (PCR). Results: out of total 745 isolates, GNB represented 47.9%. Ninety seven isolates of GNB (27.17%) were resistant to carbapenems. All CRGNB isolates were tested by PCR for detection of bla genes (bla kpc, bla IMP-1, bla VIM-1 and bla oxa 48). 32.84% isolates were positive to bla KPC gene only, 17.92% were positive to bla IMP-1 gene only, 16.42% were positive to bla VIM-1 gene only, 13.43% were positive to both bla IMP-1 and bla VIM-1 genes, 7.46% were positive to bla OXA-48 gene only, 7.46% were positive to bla KPC and bla IMP-1 / bla VIM-1 and 4.47% strains were positive to bla KPC, bla IMP-1 / bla VIM-1 and bla OXA-48. Comparing the different phenotypic methods used for detection of CRGNB to PCR, E-test had 100% sensitivity and 93.33% specificity, DDST had 100% sensitivity and 96.67% specificity, CD test had 100% sensitivity and 23.33% specificity, CHROM agar KPC medium had 88.06% sensitivity and 73.33% specificity and MHT had 98.5% sensitivity and 60% specificity. In this study, both tigecycline and colistin were the most effective antimicrobial agents against carbapenem resistant GNB strains. Conclusions: resistance to carbapenems raises a significant alarm signal to put the possibility of carbapenem resistant pathogens as an important cause of worsening the patient condition especially in ICUs. DDST can be used as a convenient screening method in microbiology laboratories but genetic confirmation by PCR and analysis of carbapenemases producers is mandatory for positive isolates.