الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Carbapenems play a critically important role in the antibiotic armamentarium of the many hundreds of different β-lactams, carbapenems possess the broadest spectrum of activity and greatest potency against Grampositive and Gramnegative bacteria.
<As a result, they are often used as “last-line agents” or “antibiotics of last resort” when patients with infections become gravely ill or are suspected of harboring resistant bacteria.
Unfortunately, the recent emergence of MDR pathogens seriously threatens this class of lifesaving drugs.
<The aim of this study wastodeterminethe resistance pattern of CR-AB isolates collected from patients in Alexandria Main University Hospital. Furthermore, phenotypic and molecular characterization of the tested isolates to detectthe different enzymes responsible for carbapenem resistance was performed.
<In the present study, seventy fourA. baumannii isolates, from different clinical specimens, were collected from the medical microbiology lab at Alexandria Main University Hospital.
< The isolates were identified as A. baumanniiby MALDI-TOF MS, Vitek system, PCR amplification of blaOXA-51 encoding gene and conventional methods as colony morphology and aerobic growth on MacConkey’s agar at 44°C. The clinical isolates were tested for their susceptibility to 19 different antimicrobial agents, belonging to the β-lactams and other classes of antimicrobial agents, using the disc diffusion technique.
All isolates were resistant to imipenem and meropenem.
< The MIC of imipenem, meropenem and ertapenem were determined against the tested isolates using the agar dilution method and the values lied in ranges of 16-128 μg/mL, 16->256 μg/mL and32-512 μg/mL, respectively.
Since the most prevalent mechanism of carbapenem resistance in A. baumanniiis the enzymatic degradation by carbapenem hydrolyzing β-lactamases, the carbapenem resistant strains were screened for carbapenemase sproduction by a number of phenotypic methods (MHT, CIM, CDT, CarbAcineto NP Test and boronic acid disc test) as well as by PCR.
Taking PCR as the gold standard methodfor detection of different carbapenemases, the sensitivities of theMHT, CIM, CDT, CarbAcineto NP Test and boronic acid disctest were 78.4%, 82.4%, 95.94%, 79.7% and 78.3%, respectively. Regarding PCR amplification of genesresponsible for the resistance to carbapenems, as well as the presence of some insertion sequences, only blaVIM and blaNDM -1 genes encoding for class B carbapenemases were detected in seventy four (100%) and nine (12.1%) tested isolates, respectively.
Regarding the genes encoding class D carbapenemases, three out of the four tested genes were detected.
These three genes were blaOXA-51, blaOXA-23 and blaOXA-58. BothblaOXA-51 and blaOXA-23 were detected in all tested isolates, while blaOXA-58was detected in only one isolate (A81).
On the other hand, blaKPCencoding for class A carbapenemase was not detected in any of the seventy four tested isolates.
The prevalenceof ISAba1,ISAba2 and ISAba3 were100%, 2.7% and 4.1%, respectively. Plasmids from the nine isolates (AS5910, A11, A21, A40, A70, A77, A81, A85 and A86)that were shown by PCR to carry blaNDMwere isolated and their profiles were Summary, Conclusions and Recommendation 66analyzed.
The plasmids’ sizes rangedfrom 1.5to >10Kbps. blaNDMgene was detected in all nine plasmid preparations. The nine plasmid extracts were transformed into carbapenem sensitive A. baumanniiusingelectroporation technique.
All obtained transformants showed resistance to imipenem having256 fold increase in MIC value.blaNDM was detected by PCR in all transformants except that corresponding to isolate A11 probably due to acquisition of other resistance genes.from the data obtained throughout this study, the following conclusions could be drawn:
<The widespread of CR-AB has become a serious challenge in the different Egyptian healthcare settings and community.
<Among the studies cohort of CR-AB clinical isolates, blaOXA-51,blaOXA-23 and blaVIMwere the most prevalent, followed byblaNDM-1andblaOXA-58.
<The genotypic detection of carbapenemases among CR-ABclinical isolates using PCR was more conclusive, compared to the phenotypic tests.Resistance to imipenem can be mediated by plasmid exchange among A. baumanniiclinical isolates, exacerbating the resistance problem and diminishing options left to treat such infections. from the previous findings, the following recommendations are suggested:
Using PCR or a combination of phenotypic methods for the detection of carbapenemases in clinical laboratories.
Further studies are recommended to understand the association between carbapenem resistance and resistance to other antimicrobial agents.
Molecular typing is recommended to describe the population structure of CR-AB isolates in Egypt and to link the resistance profile to the genetic type of the isolates.
<Future genomic studies need to be carried out to further elucidate the fine mechanism of carbapenem resistance among Egyptian A. baumanniiisolates.
Applying strict antimicrobial stewardship guidelines to limit the evolution of carbapenem resistant variants among A. baumanniiisolate