Differences in biofilm formation and antimicrobial resistance of Pseudomonas aeruginosa isolated from airways of mechanically ventilated patients and cystic fibrosis patients

Abstract

Pseudomonas aeruginosa biofilms exhibit increased antimicrobial resistance compared with planktonic isolates and are implicated in the pathogenesis of both acute and chronic lung infections. Whilst antibiotic choices for both infections are based on planktonic antibiotic susceptibility results, differences in biofilm-forming ability between the two diseases have not previously been explored. The aim of this study was to compare differences in biofilm formation and antibiotic resistance of P. aeruginosa isolated from intubated patients and from patients with chronic pulmonary disease associated with cystic fibrosis (CF). The temporal evolution of antibiotic resistance in clonal P. aeruginosa strains isolated from CF patients during periods of chronic infection and acute pulmonary exacerbation was also evaluated. Biofilm formation and biofilm antibiotic susceptibilities were determined using a modified microtitre plate assay and were compared with antibiotic susceptibility results obtained using traditional planktonic culture. Clonality was confirmed using random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) analysis. Pseudomonas aeruginosa isolates collected from intubated patients produced substantially more biofilms compared with CF isolates. There was considerable heterogeneity in biofilm-forming ability amongst the CF isolates and this was unrelated to pulmonary status. Biofilm antibiotic resistance developed rapidly amongst clonal CF isolates over time, whilst traditional antibiotic resistance determined using planktonic cultures remained stable. There was a significant positive correlation between imipenem/cilastatin and ceftazidime resistance and biofilm-forming ability. The variability in biofilm-forming ability in P. aeruginosa and the rapid evolution of biofilm resistance may require consideration when choosing antibiotic therapy for newly intubated patients and CF patients.

Fig. 1

Random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) analysis of Pseudomonas aeruginosa strains from newly colonised mechanically ventilated patients and from cystic fibrosis (CF) patients during periods of clinical stability and acute pulmonary exacerbation. Codes for CF strains indicate patient number and day of isolation.

Fig. 2

Biofilm-forming ability of isolates from six ventilated patients newly colonised with multidrug-resistant Pseudomonas aeruginosa and sequential isolates from three cystic fibrosis (CF) patients. Codes for CF strains indicate patient number and day of isolation. CS, clinical stability; AE, acute pulmonary exacerbation.

Fig. 3

Regression analysis of biofilm formation and antimicrobial resistance [biofilm inhibitory concentration (BIC)] for each of the five antibiotics tested in the study.