Abstract
The biofilm-forming capabilities and antimicrobial resistance of metallo-β-lactamase-producing Pseudomonas aeruginosa isolates were investigated and a molecular epidemiology study conducted using pulsed-field gel electrophoresis (PFGE). A total of 123 metallo-β-lactamase-producing P. aeruginosa isolates, including 79 isolates from urine, 10 isolates from sputum, 10 isolates from feces, 5 isolates from pus, 2 isolates from blood and 17 isolates from other sites, were collected from patients (one isolate per patient) admitted to three hospitals from 2001 through 2006. Of the 123 isolates, 106 (86.2%) isolates were resistant to imipenem, ciprofloxacin and amikacin, indicating multiple-drug-resistant P. aeruginosa (MDRP). The in vitro microtiter plate assay was used to quantify biofilm formation into three groups: strong (OD570≧1) in 29 (23.6%), medium (OD570≧0.5 to <1) in 47 (38.2%), and weak (OD570≧0 to <0.5) in 47 (38.2%). The biofilm-forming capabilities of metallo-β-lactamase-producing P. aeruginosa isolates (mean±SE 0.71±0.04 [n=123]) were significantly greater than those of non-producing isolates (mean±SE 0.28±0.04 [n=122]). Of the 76 isolates with strong and medium biofilm formation, 71 (93.4%) isolates were MDRP and 57 isolates (75.0%) were urine isolates. PFGE analysis showed that no identical isolates were found among the 123 metallo-β-lactamase-producing P. aeruginosa isolates, but 12 paired isolates were found at a similarity level of 85%. Of the 12 pairs, one pair was found on the same day, and other pairs were found within 4-day to 3-month intervals. The persistent biofilms formed by metallo-β-lactamase-producing P. aeruginosa isolates could cause serious problems in hospital acquired infections. The development of strategies to prevent the spread of this organism in the hospital setting is needed.
