Population structure and biofilm formation of Pseudomonas aeruginosa isolated from patients with severe burn wounds at Tygerberg Hospital.

[摘要] ENGLISH ABSTRACT : Pseudomonas aeruginosa is a common opportunistic pathogen which is responsible for more than11% of nosocomial infections including urinary tract infections (UTI's), bacteraemia, pneumonia andsoft tissue infections. Little is known about P. aeruginosa associated infections in burn wound patientsin South Africa, and in particular at Tygerberg hospital. Burn wound patients are highly vulnerable toinfections due to natural defence destruction. P. aeruginosa has the ability to form a biofilm andcause persistent biofilm associated infections. The biofilm acts as a protective layer defendingorganisms against the environment, host immune system and antibiotic treatment. P. aeruginosainfections have a mortality rate of 40-50% in burn wound patients.This study aimed to determine the population structure of P. aeruginosa isolated from the burns unitand burns ICU in comparison to isolates from other wards at Tygerberg hospital, to investigate theirability to form biofilms and to determine the impact of various antibiotics on biofilm formation. P.aeruginosa isolates from blood cultures, swabs and tissue specimens from adult and paediatricpatients at Tygerberg hospital were collected from February 2015 to March 2016. Forty isolates fromthe burns unit and 40 isolates from outside the burns unit were used for the study. Multiple locusvariable number tandem repeat analysis (MLVA) was used for strain typing. Biofilm formation wasassessed by crystal violet staining. The strength of biofilm formation of the isolates was determinedafter a 12h incubation period and the effects of varying concentrations of four different classes ofantibiotic on biofilm formation was determined over a 24 hour period.Forty two different MLVA types were described, of which ten were assigned to two or more isolates.Thirty two MLVA patterns were unique to a single isolate. MLVA type 1 was the most abundantMLVA type; 60% of the isolates from the burns unit and burns ICU were type 1. The predominance ofa single MLVA type within the burns unit implies nosocomial transmission within the burns unit.Greater diversity was observed outside the burns unit. P. aeruginosa appeared to form multiplebiofilm formation patterns. Three distinct patterns of biofilm formation could be described after 10hours incubation. These patterns did not correlate with MLVA type. The effect of exposure to fourantibiotics (cefepime, ciprofloxacin, imipenem, and gentamicin) on biofilm formation over time wasshown to differ between organisms with early and late onset biofilm formation patterns, but is notpredicted by MLVA type. The mechanisms of action of the antibiotics also did not seem to predict theresponse since two antibiotics with the same mechanism of action (cefepime and imipenem) haddifferent biofilm formation patterns.Increased knowledge of the P. aeruginosa population structure and biofilm forming ability in thispatient group, and enhanced understanding of the effect of antibiotic treatment on biofilm formationmay enable improvements in transmission prevention, the selection and use of antibiotics fortreatment and, ultimately, improve patient outcome.

[发布机构] Stellenbosch University