Coban et al.
37 tested the biofilm-formation ability of
P. aeruginosa isolates from patients with cystic fibrosis and found that biofilm production was detected in 33.3% (20/60) of the samples tested. Oncel et al.
38 found that 60% (6/10) of
P. aeruginosa isolates from chronic rhinosinusitis produced bacterial biofilms. Kádár et al.
39 investigated the biofilm production of 60
P. aeruginosa strains isolated from clinical samples, and found that 23.3% of
P. aeruginosa strains were biofilm positive. To our knowledge, there are no ophthalmic reports demonstrating the biofilm-forming capacity of
P. aeruginosa clinical isolates from large sample size. Pinna et al.
40 showed a strong adherent ability of one corneal
P. aeruginosa isolate to AcrySof IOLs in vitro, however, we were unable to identify a biofilm-positive strain of
P. aeruginosa . Our results indicate ophthalmic isolates of
P. aeruginosa could not produce biofilms in vitro. We analyzed the source of the strains and found that, unlike strains of
S. epidermidis and
S. aureus , which were collected from various locations of the eye, all the isolates of
P. aeruginosa analyzed in this study were collected from the cornea and conjunctiva of patients who suffered from corneal ulcers and conjunctivitis. This may be one of the reasons that the isolates of
P. aeruginosa in our study could not produce biofilms in vitro. So it deserves further study to explore the biofilm-forming capacity of the
P. aeruginosa isolates collected from CL, IOL, glaucoma tubes, scleral buckle, or other ocular biomaterials, and vitreous and aqueous humors, or other different ocular tissues as well. On the other hand, our results are based on the experiments in vitro, so the estimation of the ability of
P. aeruginosa to form biofilms in vivo may be different and requires further study. Previous reports suggested an essential role for the
psl gene cluster in the initial step of
P. aeruginosa biofilm formation,
15 so we focused on the functional assignment of the
pslA gene. In our study, although none of the
P. aeruginosa strains were biofilm-positive, 9 of 27 (31.03%) strains carried the
pslA gene, which means that the expression of the
pslA gene is influenced by other factors, or that the
pslA gene is unnecessary for the formation of biofilms in bacterial strains taken from patients with ocular infections. In addition, there are reports that the
pel gene clusters and
alg gene clusters are also associated with biofilm formation.
41 Biofilm formation may be determined by the interaction of many gene clusters, some of which still have not been identified yet.