• Hozan Salahaddin Mahdi College of Science, University of Salahaddin, Kurdistan Region, Iraq.
  • Sherko A Omer Department of Microbiology, College of Medicine, University of Sulaimani, Kurdistan Region, Iraq.



Pseudomonas aeruginosa, Antimicrobial Combination, Disk Synergy, Biofilm



Pseudomonas aeruginosa is an opportunistic nosocomial pathogen responsible for several infections. For such infections, limited antibiotics are suggested and combination therapy and subsequent synergetic effects may be useful. 


To determine antimicrobial susceptibility and biofilm formation of clinical isolates of P. aeruginosa, and to test synergy between commonly used antimicrobials.

Patients and Methods

Pseudomonas aeruginosa isolates were collected from several hospitals and community health laboratories. The isolate's identities were confirmed, disk diffusion antimicrobial sensitivity test was performed and double-disk synergy test was carried out to detect synergism between seven antimicrobial combinations. The ability to form biofilm was tested using microtiter plate assay.


One hundred clinical isolates of Pseudomonas aeruginosa were tested. Twenty-two isolates were from community laboratories, and 78 were from hospital laboratories. Thirty-four isolates were from urine, 32 from burn wound tissue, 13 from blood and 21 from other specimens. Polymyxin B was the most effective agent (92%) followed by meropenem (65%), while 75% of the isolates were resistant to ticarcillin-clavulanate and 59% to netilmicin. Forty synergism observations were detected between ticarcillin-clavulanate & netilmicin combination and 12 between ticarcillin-clavulanate & meropenem.


Ticarcillin-clavulanate was least effective while polymyxin B was more effective against clinical isolates of P. aeruginosa. Double-disk synergy revealed synergism with ticarcillin-clavulanate & netilmicin combination, disk synergy results can aid in deciding combination therapy. Biofilm formation was common in P. aeruginosa but was not found to affect disk synergy.


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How to Cite

Mahdi H, Omer S. DOUBLE DISK SYNERGY TEST AND BIOFILM FORMATION IN CLINICAL ISOLATES OF PSEUDOMONAS AERUGINOSA. JSMC [Internet]. 2019 Sep. 21 [cited 2024 Jul. 15];9(3):201-8. Available from:

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