الفهرس 
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Abstract
Infections by antibiotic-resistant Gram-negative bacteria have recently increased, and these resistant strains express various resistance mechanisms. In ICUs in particular, carbapenems have been used as the last resort to treat such infections. However, increased carbapenem resistance is problematic since it leads to higher morbidity and mortality. The aim of the present study was to determine the prevalence of carbapenem resistance in GNB collected from ICU patients, identify their resistance mechanisms using both phenotypic and genotypic methods and to evaluate the importance of application of antibiotic policy with infection control.
A total of 400 clinical samples were collected from El-Minia University Hospital, Health Insurance Hospital, Obstetrics and Gynecology Hospital, and Nephrology and Urology Hospital ICUs in Minia, Egypt including Surgical and trauma, general, internal medicine, and obstetric ICUs as well as the post-anesthesia care unit and the critical care nephrology unit. Of them, 180 Gram-negative bacterial isolates were recovered and identified using standard microbiological methods. In this study, P. aeruginosa represented the leading organism among isolates in ICUs (32.2%).
Antimicrobial susceptibility testing was performed using different antimicrobial agents. The present work has detected high level of MDR to the tested antibiotics. Enterobacteriaceae showed the highest resistance to amoxicillin-clavulanic acid (85.2%), followed by cefotaxime (77%) and sulfamethoxazole-trimethoprim (72.2%) and the lowest rate of resistance to ertapenem (39.3%) and gentamicin (37.7%), with gentamicin being the most effective antimicrobial agent. Among the carbapenem antibiotics, meropenem and ertapenem were the most effective. P. aeruginosa showed the least resistance (24.1%) to gentamicin, making it the most effective antimicrobial agent. The resistance rate was 27.6% for both ofloxacin and the carbapenems (imipenem, meropenem, and doripenem).
Out of all isolates, 40 selected CR-GNB tested for carbapenemases, MBLs, AmpC, and ESBLs production well as the harboring of carbapenemase-encoding genes. CR-GNB show near to complete resistance among the tested antibiotics, being most susceptible to gentamicin (42.9%). The production of carbapenemases, MBLs, AmpC, and ESBLs were detected phenotypically by MHT, IMP-EDTA CDT, disc approximation test and CDT, respectively. Of 40 CR-GNB, 16 (40%), 12 (30%), 28 (70%), and 20 (50%) isolates were positive for ESBLs, AmpC, carbapenemase, and MBLs production, respectively.
The ESBL and AmpC co-producers were observed in four of the 40 (10%) (2 Enterobacter spp. and 2 P. aeruginosa), while ESBL/MBL/AmpC co-producers were observed in eight of the 40 (20%) isolates (4 P. aeruginosa, 2 Enterobacter spp. and 2 E. coli). No ESBL/MBL or AmpC/MBL co-production was observed in this study.
PCR analysis was performed to detect the presence of some of carbapenemase-encoding genes including blaIMP-2, blaVIM-2, blaNDM-1, blaKPC-2, and blaOXA-48. Out of the 40 CR-GNB, 22 were identified as carbapenemases harboring CR-GNB. Of these 22 CR-GNB, four (18.2%) harbored more than one carbapenemase gene, including 2 Enterobacter spp., which harbored blaOXA48+blaNDM-1genes and 2 P. aeruginosa, which harbored blaVIM-2+blaNDM-1genes. Isolates carrying blaNDM-1alone, blaVIM-2 alone, blaOXA-48+blaNDM-1, and blaVIM-2 +blaNDM-1constituted (16, 72.7%), (2, 9.1%), (2, 9.1%), and (2, 9.1%), respectively, noting that this is the first time to detect NDM-1 gene in K. oxytoca from Egyptian ICUs.
Phenotypic and genotypic results were not statistically significant. considering PCR as the gold standard test, the IMP-EDTA CDT showed higher specificity and accuracy compared with the MHT. However, the MHT was more sensitive. MHT (AUC = 0.631) and CDT (AUC =0.652) had poor diagnostic precision of carbapenemases and MBL production.