Biofilm formation is a developmental process with intercellular signals that regulate growth. Microorganisms growing in a biofilm are associated with chronic and recurrent human infections and are highly resistant to antimicrobial agents e.g., Amoxycillin 93.3%, Aztreonam 86% Amoxyclav 83.3%, Piperacillin 83.3%, Ceftriaxone 80%, Ceftazidime 80% and Amikacin 80%. Objectives: The aim of this work was to determine biofilm production among clinical isolates of Acinetobacter baumanii, (A. baumanii,

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... o determine the antibiotic susceptibility pattern to different antibiotics and to associate between biofilm production and multidrug resistance (MDR). Methods: In a prospective study a total of 30 isolates of A. baumannii were included in this study; these isolates were obtained from clinical specimens like urine, sputum, blood, wound swab and tracheal aspirate of patients admitted to critically care units of Suez Canal University Hospitals. All isolates of A. baumanii were screened for biofilm production by both tube method (TM) and tissue culture plate method (TCP). Biofilm production is demonstrated with TM, in which bacterial film lining a culture tube stained with a cationic dye and visually scaled. In the second TCP method, the optical density of the stained bacterial film is determined spectrophotometrically. Antibiotic susceptibility test for all A. baumannii clinical isolates were done using the Kirby-Bauer disc diffusion method. Results: Thirty strains of A. baumannii were isolated from different clinical specimens; 12 (40 %) from tracheal aspirate, sputum 6 (20%), urine 5(16.7%), blood 5 (16.7%) and Wound swab 2 (6.6%) respectively. Both TCP and TM screened 18 (60%) strains of A. baumannii as biofilm producers. Antibiotic susceptibility tests revealed higher resistance among biofilm producers strains of A. baumanii to most of the generally used antibiotics compared with non-biofilm producers strains. Also we demonstrated a higher difference between frequency of MDR producers strains of A. baumanii [72.2% for penicillins, cephalosporins (including inhibitor combinations), fluoroquinolones and amino glycosides] and (61.2% for Imipenem, Amikacin and Aztreonam); in compare to [41.7% for penicillins, cephalosporins (including inhibitor combinations), fluoroquinolones and amino glycosides] and (33.3% for Imipenem, Amikacin and Aztreonam) among non biofilm producers strains of A. baumanii respectively; and this difference was statistically non significant (P>0.05). The high rate of in vitro antibiotic resistance of the A. baumanii strains indicate the importance of controlled antibiotic usage and appliance of proper hospital infection control measures.