Penetration of clinical isolates of Pseudomonas aeruginosa through MDCK epithelial cell monolayers

Pseudomonas aeruginosa causes both invasive (bacteremic) and chronic noninv asive infections. A simple in vitro system to screen P. aeruginosa clinical isolates for their capacity to penetrate MDCK cell monolayers has been dev eloped. By means of this system, P. aeruginosa clinical isolates, including 32 blood and 45 respiratory isolates, were examined. When monolayers were infected with 3.5 x 10(7) cfu of bacteria, significantly more blood (93.7%) than respiratory (54.4%) isolates (P<.001) were detected in the basolatera l medium after 3 h, Penetration ability was usually independent of cytotoxi city. Only 8 (4 blood and 4 respiratory) isolates were cytotoxic, possessed exoU, and passed through the monolayer after epithelial cell death, associ ated with a marked drop in transepithelial electrical resistance. Conversel y, noncytotoxic isolates with high penetration ability but without severe e pithelial damage were invasive. This system is well suited for screening cl inical isolates and their mutants for specific genes conferring the invasiv eness phenotype.