الفهرس 
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Abstract
Pseudomonas aeruginosa, S. maltophilia and Acinetobacter baumannii are nonlactose
fermenters that have emerged as important opportunistic pathogens over the past
decade. They cause opportunistic health care associated infections in patients who are
critically ill or immunocompromised. Their multiple drug resistance is common and
increasing day by day which makes treatment of their infections difficult and tedious.
The aim of this work was to identify these three important nosocomial pathogens,
to determine their antibiotic resistance and detect the role of quorum sensing genes in the
presence of their QS-dependent virulence factors. Our aim was also to assess the clove oil
inhibitory effect on QS-dependent virulence factors in P. aeruginosa.
For antimicrobial susceptibility testing, all isolates were subjected to twenty
different antibiotics using the disc diffusion method. All of them were highly resistant
against all beta lactam antibiotics, ampicillin/sulbactam, amoxicillin/clavulanic acid and
co-trimoxazole. The most effective agents were: polymixin and meropenem for P.
aeruginosa, polymixin, chloramphenicol, cefepime and co-trimoxazole for S. maltophilia,
and polymixin, meropenem, tetracycline and levofloxacin for A. baumannii.
The biofilm formation was detected using the microtitre plate method for all
isolates. The biofilm forming isolates were 38 (76%) for P. aeruginosa, 8 (72%) for S.
maltophilia and 23 (77%) for A. baumannii.
The pyocyanin production by P. aeruginosa was tested using the king A agar (P
agar) and 19 (38%) of our 50 P. aeruginosa isolates were producers.
The twitching motility in P. aeruginosa and S. maltophilia was investigated using
LB agar plates. Forty four (88%) P. aeruginosa isolates and 8 (72%) S. maltophilia isolates
were positive.
Regarding the quorum sensing, the four QS genes (lasI, lasR, rhlI, rhlR) in P.
aeruginosa, the rpf gene in S. maltophilia and the abaI gene in A. baumannii were
molecularly detected using the conventional PCR technique. In P. aeruginosa: 24 (48%)
isolates were positive for lasI, 20 (40%) for lasR, and for rhlI and 18 (36%) for rhlR. In S.
maltophilia: 10 (90.9%) isolates were positive for the rpf gene. And in A. baumannii: 25
(83.3%) isolates were positive for the abaI gene.
Sequencing of lasR, lasI, rhlR and rhlI genes was performed for the P. aeruginosa
isolate (p10) which was genotypically positive and phenotypically negative, and various
point mutations were detected in all the four QS genes.