الفهرس | Only 14 pages are availabe for public view |
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., Summary 123 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 Summary 124 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 Summary 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 |