الفهرس 
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Abstract
SUMMARY
seudomonas aeruginosa is a gram negative opportunistic
bacillus that primarily infects individuals who are
immunocompromised or having breaches in normal barriers
such as in cases of burns, using indwelling medical devices, or
prolonged use of broad-spectrum antibiotics (De Kievit and
Iglewski, 2000). Many factors account for pseudomonal strong
resistance to antibiotics like the low outer membrane
permeability and the presence of several active multidrug efflux
pumps, as well as their existence in biofilm. Biofilm is a
complex structure firmly attached to biotic & abiotic surfaces
consisting of many bacterial microcolonies in an extracellular
polymeric substance with channels for free diffusion of
nutrients, waste products & autoinducers (Sanchez et al.,
2013). Biofilm production has been accused for emergence of
Multi drug resistant (MDR) strains by allowing selection for
highly resistant strains (Sanchez et al., 2013). MDR
pseudomonal strains are responsible for increased morbidity
and mortality among hospitalised patients (Aloush et al., 2006).
The growing fear of heading to a postantibiotic era
permitted thinking of novel strategies to combat infections
focusing on chemicals that decrease bacterial virulence such as
quorum sensing inhibitors (QSIs), subsequently facilitating
clearance of the bacterial load by the host’s self (K Bhardwaj et
al., 2013).
P
Summary
122
Quorum sensing (QS) systems are intra- and inter-species’
signaling systems present in both gram negative & gram positive
bacteria (Sturme et al., 2002) that regulate the expression of
several genes, many of which code for virulence factors (Li and
Tian, 2012). Each bacterial species secretes and has receptors
for one or more chemical signal molecule(s); some diffuse freely
into & out of the cell and some are partly effluxed by efflux
pump; whenever the local concentration reaches a threshold
level (which corresponds to a certain bacterial density- quorum),
a set of genes inductions and repressions are activated via an
activated transcription factor; allowing for community-based
decisions among bacteria (De Kievit and Iglewski, 2000).
Biofilm community forms the ideal environment for QS since it
allows local elevation of signal molecules concentrations (Li and
Tian, 2012) and it is also under QS system control (Davies et al.,
1998). Quorum- controlled pseudomonal genes include those
essential for biofilm formation as well as elastase-enzyme,
rhamnolipids, pyocyanin, proteases, and hemolysin production
(Ishida et al., 2007).
Quorum sensing inhibitors (QSIs) are chemicals that
interfere with QS-controlled gene regulation; these include
naturally existing molecules & new synthetic homologues, as
well as many drugs that were already in clinical use but for
completely different purposes (Yang et al., 2009).
Acetylsalicylic acid (aspirin) has been widely studied for
this purpose and proved to be a potent QSI (Prithiviraj et al.,
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2005); the mechanism of inhibition was found out to be due to
inhibition of prostaglandin synthesis in the primitive cell
through COX-like enzyme inhibitory effects (Alem and
Douglas, 2004).
A selective COX2 inhibitor was expected to have the
same effects on quorum sensing inhibition without having toxic
effects on gastric mucosa; moreover, COX2-inhibitors have
been demonstrated to be accountable for inhibiton of COXdependable
multidrug efflux pumps in prokaryotic cells
possibly leading to premature intracellular increase of
autoinducer and several antibiotics concentrations, thus leads to
premature expression of quorum-controlled genes facilitating
host clearance, as well as decreased antibiotics resistance (Kalle
and Rizvi, 2011), which means that along with the QSI effects,
it is a promising solution for the MDR organisms problem.
The aim of this work was to compare the QS inhibitory
effects of aspirin with etodolac (a selective COX-2 inhibitor) on
Pseudomonas aeruginosa strains isolated from patients with
hospital acquired infections in vitro.
Thirty Pseudomonas aeruginosa isolates from hospital
acquired infections were obtained from Ain Shams University
Hospital. Assessment of bacterial growth, biofilm formation,
pyocyanin production and elastase production by each isolate
was done with addition of aspirin and repeated with etodolac as
well as with a control set with no drug added. Results followed
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by statistical analysis were used to compare the effects of both
drugs to the normal as well as with each other.
Only approximately one quarter of the isolates had
inhibited biofilm formation ability and elastase enzyme activity
with each of the 2 drugs. On the other hand, Pyocyanin
production was more sensitive to the QSIs with as much as
73.3% of isolates being inhibited by Aspirin and 40% of them
were inhibited with Etodolac.
As regards Mean percentage inhibition among sensitive
isolates, Etodolac showed stronger activity of 49.8% for
pyocyanin pigment production as compared to Aspirin which
had only 28.1% inhibition activity. On the other hand, Aspirin
more strongly inhibited biofilm formation by 32.6% in contrast
to 20.4% by Etodolac. Both drugs exhibited comparable
inhibition of 51.6% and 56% for elastase enzyme production by
Aspirin and Etodolac respectively.
There were substantial isolates exhibiting resistance to
the tested QSIs. This was in the form of no effect or
paradoxical stimulatory effects as compared to their untreated
counterparts.
72.4% of isolates were resistant to both drugs inhibition
of biofilm formation as well as to inhibition of elastase enzyme
production by Aspirin. Slightly higher percentage (75.8%) of
isolates were resisting inhibition of elastase activity by
Etodolac. Isolates resistant to inhibition of pyocyanin
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125
production were much less; only 26.7% were resistant to
aspirin and 60% were resistant to Etodolac.
Although both COX inhibitors were shown to have
effective QSI effects on some Pseudomonas aeruginosa
isolates; a significant proportion showed resistance to, or
paradoxical stimulatory effects. When inhibitory, both Aspirin
and Etodolac had comparable inhibitory strengths; however,
they did not necessarily have similar effects on individual
isolates This highlights the necessity of pretreatment laboratory
testing of their efficacy as QSIs, which should be conducted
along with the conventional antimicrobial susceptibility testing.
Further research studies are needed to confirm these
results, get more insight on the cause of different effects and
show whether these results predict a promising future or, in
opposition, carry a warning signal of probable end of some
QSIs even before they are officially used for this therapeutic
purpose