CSOM is considered as a complex infectious and inflammatory diseases that affect middle ear. The complications are due to CSOM including, intracranial like meningitis and brain abscess which are the most common causes of death in patient with CSOM.
Pseudomonas aeruginosa are difficult to treat because the majority of isolates present high level of resistance to many types of antibiotics this is associated to its ability for biofilm production.
Biofilm-associated infections cause considerable problems, thus the major objective of the present study is to evaluate the frequency of phenotypic biofilm production and the role of the selected Quorum Sensing Genes in pseudomonas aeruginosa that is the most common and serious bacterial type isolated from CSOM patients.
Material and Methods: In a cross sectional study, a total of (31) isolated strains of Pseudomonas aeruginosa from (82) patients suffering from CSOM were collected between January to the end of April 2019 admitted at the main hospitals in Al-Najaf province.
Results: Among 31 isolates of Ps. aeruginosa collected from CSOM patients Detection of In-vitro biofilm formation in these isolates were carried out by tissue-culture plate TCP method (the most sensitive method for detection biofilm production) the method detected (45%)as strong, (42%)as moderate, (13%) weak adherent and (0%) non biofilm production. Screening for some selected genes responsible for biofilm formation was done by PCR (LasI, LasR, rhlI, Rh IR) were present in most of the Ps. aeruginosa isolates, 27(87%) of isolates give positive results for LasI; 25(80.64%) of isolates give positive results for LasR gene; 25(80.6%) of isolates show positive result for rhlI and 28(90.3%) %) of isolates show positive result for RhlR gene.
Conclusion: The results revealed that the presence of Quorum sensing genes (lasI, lasR, rhII, RhlR) which are responsible in biofilm formation were present in most of the Ps. aeruginosa isolates.

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