الفهرس 
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Abstract
Pseudomonas aeruginosa and Staphylococcus aureus continue to be predominant
causes of infection with high resistance to antibiotics resulting in treatment failure.
Prevalence of highly resistant strains is potentiated by excessive use of broad-spectrum
antibiotics. Gatifloxacin (GAT) is a broad-spectrum 8-methoxy fluoroquinolones with
broad antimicrobial spectrum, which covers Gram-positive, Gram-negative bacteria as well
as atypical organisms (Mycoplasma spp, Chlamydia spp. and mycobacteria) and anaerobes.
Gatifloxacin contains a methoxy substituent at position 8 of the quinolone ring that has
been associated in some bacteria with increased bacteriostatic and bactericidal activity as
well as decreased selection of resistant mutants.
The aim of the present work was to study the antimicrobial activity of gatifloxacin,
provide information regarding the prevalence of gatifloxacin resistance among P.
aeruginosa and S. aureus isolates collected from community and hospitalized patients in
Alexandria, Egypt. We also felt it was important to investigate the mechanism of resistance
in the resistant strains. Testing the PAE and combinations with other compounds was an
attempt to reduce the resistance and dosing regimens of gatifloxacin.
One hundred and eight clinical isolates (54 P. aeruginosa and 54 S. aureus isolates)
were isolated from different clinical specimens, only one isolate per patient was included.
They were collected from four major hospitals in Alexandria in addition to private labs
between January and June 2014. These isolates were identified, by macroscopical
examination of the colony morphology, the classical microscopical and some important
biochemical tests.
Among the 54 P. aeruginosa isolates tested the highest rate of resistance (100 %)
observed was to ampicillin/sulbactam, while more than 50% of the isolates were resistant
to ceftriaxone, cefoperazone, ofloxacin. Whereas the most effective ones against P.
aeruginosa where the imipinem and tazobactam/piperacillin. Nevertheless, 13% of the P.
aeruginosa isolates were resistant to all tested antibiotics and thus categorized as PDR
isolates. Multi drug resistance MDR is a predominant phenomena among staphylococcal
isolates tested where only 2 isolates did not show MDR. S. aureus isolates showed the
highest rate of resistance (100%) to the penicillinase-stable penicillins cloxacillin and
flucloxacillin. Resistance among the tested S. aureus strains was more prevalent where >
50% of the tested S. aureus isolates were resistant to 16 out of the 20 tested antibiotics.
Again 13% of the S. aureus isolates were resistant to all antibiotics except vancomycin,
imipenem and trimethoprim/sulfamethoxazole, but no PDR strains were observed.