Genotypic and phenotypic characterization of Pseudomonas aeruginosa isolates from post-cataract endophthalmitis patients.

Endophthalmitis caused by Pseudomonas aeruginosa is associated with rapid disease progression and poor visual outcome due to high virulence of the organism. Our aim was to characterize the virulence determinants of P. aeruginosa causing post-operative endophthalmitis. Repetitive sequence analysis (ERIC PCR) was done to study the clonal relatedness of the 17 P. aeruginosa isolates. Type 3 secretion system (T3SS) genotypes were determined and the isolates were further classified as invasive or cytotoxic based on gentamicin survival, trypan blue dye exclusion and MTT assays. Phenotypically, the strains were characterized based on bacterial motility patterns, biofilm formation, phospholipase production and antibiotic susceptibility patterns. Most of our ocular isolates were invasive in nature and nearly half of them were multi-drug resistant. 47% of the isolates formed a strong biofilm, whereas the rest formed moderate to weak biofilms, which may account for an increased colonization and antibiotic resistance. Although the T3SS genotypes correlated well with the invasive/cytotoxic nature of the strains, none of the genotypes were associated with any particular phenotypic trait. To the best of our knowledge, this is the first report on the phenotypic characteristics of P. aeruginosa strains causing post-operative endophthalmitis. Our findings demonstrate that these strains have higher invasive potential and an ability to form biofilm which possibly contributes to an increased ocular virulence.