*Corresponding Author Address: Mahmoud A. Elfaky, Department of Natural Products and Alternative Medicine, Faculty of Pharmacy, King Abdulaziz University, P.O. Box: 80200, Zip Code: 21589, Jeddah, Kingdom of Saudi Arabia; E-mail: melfaky@kau.edu.sa World Journal of Pharmaceutical Sciences ISSN (Print): 2321-3310; ISSN (Online): 2321-3086 Published by Atom and Cell Publishers © All Rights Reserved Available online at: http://www.wjpsonline.org/ Original Article Antimicrobial resistance pattern of biofilm forming Pseudomonas aeruginosa isolated from patients with nasogastric and endotracheal tubes Mahmoud Abdelkhalek Elfaky 1* , Mahmoud Abdul Megead Yassien 1 , Ahmed Sherif Attia 2 , Moselhy Salah Mansy 3 , Mohamed Seif Eldin Ashour 4 1 Department of Natural Products and Alternative Medicine, Faculty of Pharmacy, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia 2 Department of Microbiology and Immunology, Faculty of Pharmacy, Cairo University, Cairo, Egypt 3 Department of Microbiology and Immunology, Faculty of Pharmacy, Al-Azhar University, Cairo, Egypt 4 Department of Microbiology and Immunology, Faculty of Pharmacy, Al-Azhar University, Cairo, Egypt Received: 29-01-2015 / Revised: 11-02-2015 / Accepted: 25-02-2015 ABSTRACT Biofilms are communities of microorganisms attached to a surface. It has become clear that biofilm-grown cells express properties distinct from planktonic cells, one of which is an increased resistance to antimicrobial agents. A total of 79 non replicate gram negative bioadherent isolates from 113 patients in intensive care units with nasogastric and endotracheal tubes were collected, identified, then tested for their abilities to form biofilm using tube method, tissue culture plate method and genetically. Antimicrobial susceptibility testing and time-kill assay were done to figure out the role of biofilm formation in antimicrobial resistance. Gram negative isolates were Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Enterobacter cloacae and Citrobacter koseri. The microorganisms were classified into three groups (strongly adherent, moderately adherent and non adherent) according to the biofilm formation that was obtained by optical density (O.D.) values. The antibacterial susceptibility testing revealed that more than 70% of the bioadherent isolates were multi-drug resistant (MDR) with resistance to more than 4 antimicrobials. So it has been observed that the resistance of bacteria in biofilms to antibiotics is increased compared with what is normally seen with planktonic cells. Key words: resistance pattern, antimicrobial, biofilm, nasogastric tube, endotracheal tube INTRODUCTION Biofilm is an accumulation of microorganisms and their extracellular products forming a structured community on a surface, or defined as surface attached microbial populations of either single or multiple species [1] . The first observations of biofilm were obtained through scanning electron microscopy which showed primary attachment of monolayer bacterial consortia, embedded in an amorphous mucous structure on the surfaces of medical devices. This phenotype was initially referred to as slime formation. In retrospect, in most cases, the „slime‟ was very likely polysaccharide intercellular adhesin (PIA), and so PIA and „slime‟ are considered to be the same. Today, this special mode of thick extracellular matrix (maturation phase) is generally termed biofilm formation [2] . Antimicrobial agents effective against planktonic bacteria frequently fail to eradicate bacterial biofilms. The problem is that choosing of antibiotics is based on bacterial cultures derived from planktonic bacteria which differ in behavior and in phenotypic form from bacteria in biofilm. The failure of antimicrobial agents to treat biofilms has been associated with a variety of mechanisms:1-agents often fail to penetrate the full depth of the biofilm (extrinsic resistance), 2- organisms in the biofilm grow more slowly; therefore, they are more resistant to antimicrobial agents that require active growth, 3- antimicrobial binding proteins are poorly expressed in these bacteria, 4-bacteria within a biofilm activate many genes that alter the cell envelope, the molecular targets, and the susceptibility to antimicrobial agents (intrinsic resistance), 5- bacteria in a biofilm can survive in the presence of antimicrobial agents at a concentration 1,000–1,500 times higher than the concentration needed to kill planktonic cells of the same species [3] .