الفهرس 
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Abstract
The cephalosporin antibiotics have become a major part of the antibiotic formulary for
hospitals all over the world. They are prescribed for a wide variety of infections every day.
Their undoubted popularity relies upon lesser toxicity risks as well as a broad spectrum of
activity. It is the latter feature; however, that encourages the appearance of microorganisms that
are resistant to these agents.
The aim of the present work was to evaluate the frequency of bacterial resistance against
cefepime, a relatively recent antibiotic in Alexandria and Beheira governorates, to determine
the possible mechanisms of resistance of Gram-negative bacteria to it and to test the efficacy of
some antibiotic combination against some selected isolates.
One hundred and thirteen various clinical isolates obtained from different specimens were used
in this study. These isolates were identified, by macroscopical examination of the colony
morphology, the classical microscopical examination and some important biochemical tests, as
38 E.coli (33.6%), 25 Pseudomonas aeruginosa (22.1%), 23 Klebsiella spp. (20.4%), 15
Acinetobacter spp. (13.3%), 6 Serratia spp. (5.3%) and 6 Proteus spp. (5.3%).
The resistance pattern of the collected isolates against cefepime and other twelve selected
antibiotics belonging to several classes and having different modes of action was evaluated
using the standard disc agar diffusion technique.
Out of the 113 collected isolates, 57% were resistant to cefepime and more than 80% of these
isolates were also resistant to other β-lactam antibiotics as (amoxicillin, amoxicillin/ clavulanic
acid, cephalexin, cefuroxime, ceftriaxone and ceftazidime), as well as rifampin and
azithromycin. In general, most of the tested isolates showed multidrug resistance with twelve
different resistance patterns observed.
The MIC of cefepime against the clinical isolates was investigated using the agar dilution
technique. The MICs ranged between 1 and > 1280 μg/ml. All the tested isolates under
investigation were considered sensitive at ≤ 8 μg/ml according to CLSI 2011 guidelines.
The main mechanism of resistance to cefepime which is ESBL production was investigated
among our clinical isolates using three phenotypic methods: Modified Double Disc Synergy
test (MDDST), Disk diffusion method according to CLSI 2011 and the three
dimensional (3D) test.
The three dimensional test has been found to be better than Double disc synergy test in the
detection of ESBLs, since it detected ESBL in 54 (55.1%) isolates whereas 47 (48%) isolates
were detected by MDDST, so 7 (7.14%) isolates were missed by MDDST. It was found that
ESBL producers were mainly of E.Coli, Klebseilla spp., Pseudomonas aeruginosa followed by
Acinetobacter spp., Proteus spp. and Serratia spp.
Our study tended also to detect AmpC β-lactamases produced by Gram-negative bacteria using
three phenotypic laboratory tests: AmpC disc test, cloverleaf test (cefoxitin Hodge test) and the
three-dimensional (3D) test. The overall sensitivity of phenotypic tests for detection of
AmpC β-lactamase was as follow: the 3D test and AmpC disc test were the most sensitive
(48.6% and 29.7% resp.) followed by cloverleaf test (13.5%).