Callistemon citrinus bioactive metabolites as new inhibitors of methicillin-resistant Staphylococcus aureus biofilm formation
JOURNAL OF ETHNOPHARMACOLOGY
Authors: Shehabeldine, Amr M.; Ashour, Rehab M.; Okba, Mona M.; Saber, Fatema R.
Abstract
Ethnopharmacological relevance: The development of new inhibitors of bacterial virulence factors from natural origin has recently received significant attention. Callistemon citrinus Skeels is an important plant of great medicinal value. Its antimicrobial activity is well documented. Although several compounds were isolated from this plant, the actual bioactive compounds responsible for its antimicrobial activity are still unrevealed. Aim of the study: To evaluate the effect of C. citrinus crude extract and isolated compounds on methicillin-resistant and sensitive Staphylococcus aureus. Materials and methods: The methylene chloride-methanol extract (MME) of C. citrinus leaves was prepared by Soxhlet apparatus. Biologically guided fractionation of MME was accomplished using several normal and reversed phase silica gel columns. The potency of MME and its isolated compounds against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) was evaluated. In addition, the mechanism of resistance was studied using three virulence factors; antibiofilm activity, inhibition of staphyloxanthin biosynthesis and effect on acid tolerance. Ultrastructural changes in MRSA and MSSA were observed by TEM to understand mode of action of these compounds. Results: Pulverulentone A (C1), 8- desmethyl eucalyptin (C2) and eucalyptin (C3) were isolated from the most bioactive fraction of MME. Confocal scanning laser microscopy images revealed that C. citrinus isolated compounds destroyed the intact architecture of biofilm, thickness and reduced its biomass. Pulverulentone A (C1) showed the most potent anti-biofilm activity up to 71% and 62.3% against MRSA and MSSA, respectively. It also exhibited the highest inhibition of staphyloxanthin biosynthesis of MRSA and MSSA by 55.6% and 54.5%, respectively. The bacterial cell membrane was compromised, losing its integrity and releasing important cellular constituents when exposed to C1-C3 Conclusions: C. citrinus phenolics and acylphloroglucinols may serve as potential source of plant-based antibacterials and thus could be implicated to control MRSA biofilm formation.
Vertical Handover Analysis Using Modified MADM Method in LTE
MOBILE NETWORKS & APPLICATIONS
Authors: Preethi, G. A.; Gauthamarayathirumal, P.; Chandrasekar, C.
Abstract
Ubiquitous Communication is being a trend in this era. It is possible anywhere anytime with the sustenance and by the agreement of different service providers of Mobile technology. A mobile node which is attached to its base station relinquishes its connection while continuous mobility causes a fluctuation of signal strength. To overcome this issue, heterogeneous networks provision is obligatory. Normally Base stations serve several mobile nodes. Whenever a base station cannot handle a mobile terminal, it will assign its node to nearby available base station for service. The process of assignment of mobile nodes to another base station is termed as Heterogeneous handover. This type of Handover is needed for seamless integration of networks. LTE has proved promising outcomes in providing successful handover, Since it uses eNodeB infrastructure. In this work, Received signal strength is taken as main measure and analysed. Received Power acts as the building block for making possible handover across heterogeneous Radio Access Technologies. Proposed method suggests a vertical handover based on various signal measures. Enhanced Weighted Sum Method is incorporated for Handover decision making. Several criteria also utilized.