Distribution of the type III effector proteins-encoding genes among nosocomial Pseudomonas aeruginosa isolates from Bulgaria

The aim of this study was to determine the prevalence of type III effector proteins (ExoS, ExoU, ExoT and ExoY)-encoding genes among clonally unrelated nosocomial Pseudomonas aeruginosa strains and to analyze their distribution in respect to the infection site and antimicrobial resistance. Polymerase chain reaction-based detection of the genes was performed on 176 non-duplicate P. aeruginosa isolates from three University hospitals in Sofia, previously genotyped by random amplified polymorphic DNA technique. The prevalence of the studied genes was as follows: exoS-61.9%, exoU-32.4%, exoT-100%, and exoY-85.8%. The part of P. aeruginosa strains harboring either the exoS (54.0%) or the exoU (23.8%) gene was higher (P<0.001) than that of isolates containing both genes (8.5%). The gene dissemination varied according to the infection localization. The exoU gene manifested a higher spread (P<0.001) among multidrug-resistant (MDR) than in non-MDR strains (42.6 vs 18.7%). In conclusion, the P. aeruginosa type III secretion system is present in nearly all studied isolates but the individual isolates from distinct infection sites differ in their effector genotypes. The ubiquity of type III effector proteins-encoding genes among clinical isolates is consistent with an important role for this system in P. aeruginosa pathogenesis.