الفهرس 
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Abstract
Tigecycline is a semi-synthetic tetracycline (glycylcycline) derived from minocycline . It is active against Gram-positive cocci and Gram-negative rods, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus spp., macrolide- or penicillin-resistant Streptococcus pneumoniae, extended spectrum β -lactamase (ESBL)-producing Enterobacteriaceae and carbapenem-resistant Acinetobacter spp (Petersen et al., 1999). Furthermore, tigecycline is active against tetracycline- and minocycline-resistant microorganisms and does not present cross-resistance with other antibiotics such as β -lactams or fluoroquinolones (Noskin, 2005).
Tigecycline crosses the external membrane of bacteria through porins via passive diffusion and reaches the cytoplasm by an energy-dependent mechanism. It binds to the ribosome thereby inhibiting protein synthesis. The absence of anti-eukaryotic activity means that it has selective antibacterial properties (Projan, 2000).
ESBLs are plasmid-borne enzymes produced by Gram negative rods that confer resistance to all the penicillins, cephalosporins (with the exception of cephamycins) and monobactams. The plasmids encoding these enzymes can also carry genes for resistance to other antibiotics such as cotrimoxazole, aminoglycosides and tetracyclines. ESBL-producing microorganisms are also resistant to fluoroquinolones more frequently than other non-ESBL-producing isolates (Bradford, 2007).
Therefore, sometimes the only possibility of treatment is using carbapenems . However, these should be used in moderation as they have been associated with an increase in infections by carbapenem-resistant Acinetobacter baumannii or P. aeruginosa , with the result that treatment of these infections is remarkably difficult (Lee et al., 2004).
The present study was designed to study the in vitro activity of tigecycline against clinical isolates of ESBL-producing Gram negative bacilli, isolated from patients with UTIs, LRTIs and in pus samples in ICUs and surgery department in ASUHs .
Fifty seven urine samples (MSU or CSU), 54 respiratory samples (sputum or ETA) and 24 pus samples were collected and processed for microbiological examination. The samples were cultured and the isolated pathogens were identified by using conventional microbiological methods and confirmed by BBL Crystal system.
A total of 69 isolates of Enterobacteriaceae spp, Pseudomonas aeruginosa and Acinetobacter baumannii, were isolated from 135 patients, ESBL production form the 69 isolates was determined by disc diffusion method and MIC using Hicomb MIC test .
Our results revealed that 43.5% (30/69) of tested Enterobacteriaceae spp. and P.aeruginosa were positive for ESBL production.
Results of ESBL Tigecycline susceptibility among ESBL positive species by disc diffusion method and E test revealed that K.pneumoniae were sensitive (100%) ; E.coli were sensitive (87.5%) , while were intermediate (12.5%) ; P.mirabilis were sensitive (50%) , while were intermediate (50%) ; Pseudomonas aeruginosa were intermediate, (40%) were resistant (60%) ; and in Acinetobacter baumannii were sensitive (50%) , (50%) were resistant.