الفهرس 
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Abstract
Acinetobacters play a significant role in the colonization and infection of patients admitted to hospitals. They have been implicated in a variety of nosocomial infections including bacteremia, pneumonia, UTI and meningitis. Such infections are often extremely difficult to treat because of widespread resistance of these bacteria to the major groups of antibiotics. Various mechanisms of antibiotic resistance have been recognized in these bacteria and combination therapy is usually required for effective treatment.
This study was conducted in Suez Canal University Hospital to explore different prevalent biotypes , detect their resistance pattern, to examine synergistic effect of different antibiotic combination and to determine mechanism of resistance.
During the period of study extending from June 2011 to February 2012,350 clinical specimens were collected from 350 nosocomially infected patients from different ICU wards of the hospital including general ICU, hepatology ICU, NICU,BICU and CCU. All age groups and both sexes were included in the study. All respiratory, urine, burn wound and blood specimens were cultured onto different media according to type of specimen.
Ten A. baumannii (2.85%) strains were isolated. They were identified depending on morphological appearance by Gram stained smears, cultural characteristics and finally biochemical profile using both the conventional tube method and API 20NE system. Biotyping showed that biotype 0001073 was the commonest among 5 other biotypes.
In this work, Acinetobacters were most commonly isolated from respiratory specimens(48.57%) followed by urine specimens (34.28%) then burn wound swabs (12.85%) and blood specimens(4.28%).Fifty percent of patients were admitted to general medical and surgical ICU while( 22.85% )were admitted to NICU.
By using Kirby Bauer disk diffusion method, Acinetobacter isolates were found to be highly resistant to most tested antibiotics. All tested10 strains were found to be imipenem resistant ,amikacin and tobramycin resistant, ciprofloxacin resistant, penicillin resistant and cephalosporins resistant.
Detection of genes coding for carbapenem resistance by PCR, usually give reliable and satisfactory results, but this method is of limited practical use for daily application in clinical laboratories because of the cost. Thus, a simple and inexpensive testing method for screening of carbapenemase producers is necessary. Therefore this study was undertaken to detect MBLs and AmpC β-lactamases in clinical isolates of Acinetobacter baumannii. The detection of MBL and other carbapenemases is of utmost importance in deciding the most appropriate therapeutic regimen for treatment of carpabenem resistant nonfermenters.
In our study MBL production is not considered an important mechanism of carbapenem resistance among isolated acinetobacter strains while carbapenemases other than MBL are responsible for carbapenem resistance as indicated by positive modified hodge test in 60% of tested strains. AmpC B-lactamases is also a contributory factor for resistance among the isolates in our hospital.
Synergy studies were done using preliminary E-test method and subsequently TKA.Best in vitro synergy was observed with azithromycin and polymyxin while rifampicin and polymyxin showed antagonism. The fairly high concordance (66.6%) between E-test and TKA suggests that E-test method may be used as alternative to TKA studies for in vitro synergy testing of Acinetobacter. E-test is simple to use, time efficient, inexpensive and reproducible and yielded results comparable to TKA. However the optimal in vitro testing method that best correspond with clinical outcomes of infections with A.baumannii remains to be ascertained.