Chest
Volume 128, Issue 2, August 2005, Pages 912-919
Journal home page for Chest

Laboratory and Animal Investigations
Effects of Azithromycin on Clinical Isolates of Pseudomonas aeruginosa From Cystic Fibrosis Patients

https://doi.org/10.1378/chest.128.2.912Get rights and content

Abstract

There is considerable interest in the use of azithromycin for the treatment of lung disease in patients with cystic fibrosis (CF). Although its mechanism of action as an inhibitor of bacterial protein synthesis has been well-established, it is less clear how azithromycin ameliorates the lung disease associated withPseudomonas aeruginosa, which is considered to be resistant to the drug. We tested the effects of azithromycin on clinical isolates (CIs) from CF patients and compared them with laboratory reference strains to establish how this drug might interfere with the production of bacterial virulence factors that are relevant to the pathogenesis of airway disease in CF patients. Azithromycin inhibitedP aeruginosaPAO1 protein synthesis by 80%, inhibiting bacterial growth and the expression of immunostimulatory exoproducts such as pyocyanin, as well as the gene products necessary for biofilm formation. In contrast, the effects of azithromycin on CIs ofP aeruginosawere much more variable, due in large part to their slow growth and limited exoproduct expression. Culture supernatants for two of three clinical strains induced appreciable CXCL8 expression from cultured epithelial cells. Azithromycin treatment of the organisms inhibited 65 to 70% of this induction; azithromycin had no direct effect on the ability of either normal cells or CF epithelial cells to produce CXCL8. Azithromycin does decrease theP aeruginosasynthesis of immunostimulatory exoproducts and is likely to be most effective against planktonic, actively growing bacteria. This effect is less predictable against CIs than the prototypic strain PAO1

Section snippets

Bacterial Strains and Culture Conditions

All strains were grown in Luria broth (LB) or M9 plus casamino acids.P aeruginosaPAO1 was used as a prototype. This strain has been sequenced and is generally used as the reference strain forP aeruginosagenetics. JP2 (PAO1lasIrhlI), a quorum-sensing mutant, has been previously described.14 A pyoverdin null mutant, PAO1pvdF, was obtained (M. Vasil, University of Colorado; Denver, CO)18 and was grown under selection as previously noted.P aeruginosaCIs 49, 63, and 78 were

Results The Effects of Azithromycin onP aeruginosaGrowth

The effect of clinically achievable amounts of azithromycin (approximately 2.5 to 5 μg/mL)5 on the growth rates of PAO1, a quorum-sensing mutant,lasIrhlI, a pyoverdin mutant,pvdF, and three CIs were compared (Fig 1). Azithromycin at a concentration of 5 μg/mL began to affect PAO1 growth at the end of the log phase and similarly inhibited the growth of the mutants lacking either quorum sensing genes or siderophore expression. The CIs behaved differently. All three were noted to be auxotrophs,

Discussion

There have been numerousin vitroandin vivostudies demonstrating that macrolide antibiotics have clinically useful effects in patients withP aeruginosapulmonary infection. Randomized, placebo-controlled studies 5 have indicated clinical improvement in CF patients receiving azithromycin without major adverse effects detected, as yet. In the studies reported herein, we have demonstrated that the effects of this macrolide antibiotic onP aeruginosaPAO1 protein synthesis may help to explain the

References (26)

  • J Wolter et al.

    Effect of long term treatment with azithromycin on disease parameters in cystic fibrosis: a randomised trial

    Thorax

    (2002)
  • K Tateda et al.

    Direct evidence for antipseudomonal activity of macrolides: exposure-dependent bactericidal activity and inhibition of protein synthesis by erythromycin, clarithromycin, and azithromycin

    Antimicrob Agents Chemother

    (1996)
  • R Mizukane et al.

    Comparativein vitroexoenzyme-suppressing activities of azithromycin and other macrolide antibiotics againstPseudomonas aeruginosa

    Antimicrob Agents Chemother

    (1994)
  • Cited by (70)

    • Erythromycin resistance features and biofilm formation affected by subinhibitory erythromycin in clinical isolates of Staphylococcus epidermidis

      2016, Journal of Microbiology, Immunology and Infection
      Citation Excerpt :

      The quality control was performed with S. aureus ATCC 29213 and values of MICs were in the ranges stipulated by the CLSI.16 Biofilm formation was tested by the growth of isolates in 96-well Corning flat-bottom plates, essentially as described previously. 6,17 An overnight culture of cells grown in TSB (37°C, 180 rpm) was diluted 1:100, and 100 μL aliquots and 100 μL TSB in the presence and absence of 0.5 MIC ERY (final concentration: 0.25 MIC) were added to the 96-well plate with four replicates.

    • Azithromycin and ciprofloxacin: A possible synergistic combination against Pseudomonas aeruginosa biofilm-associated urinary tract infections

      2015, International Journal of Antimicrobial Agents
      Citation Excerpt :

      At these concentrations, the combination showed 100% antibacterial effect since no bacterial growth was observed 4 h after incubation. Although AZM is not an antipseudomonal agent, the synergy achieved in this study at sub-MIC levels of AZM against planktonic P. aeruginosa may be due to its interference with quorum-sensing circuitry or inhibition of the production of virulence factors [3,20]. The current findings corroborate earlier studies depicting modest synergistic and additive activities of macrolides (AZM and clarithromycin) paired with ceftazidime, quinolones and other agents interfering with protein synthesis against P. aeruginosa clinical isolates [21].

    • Role of the Pseudomonas quinolone signal (PQS) in sensitising Pseudomonas aeruginosa to UVA radiation

      2015, Journal of Photochemistry and Photobiology B: Biology
      Citation Excerpt :

      Cells from stationary phase cultures were removed by centrifugation and the supernatants were filtered through 0.22 μm nitrocellulose filters for siderophore quantification. Absorbance was measured at 405 nm for pyoverdine quantification [24]. For pyochelin quantification, fluorescence (360 excitation, 535 emission) was measured with a microplate reader [24].

    View all citing articles on Scopus

    This work was supported by the United States Cystic Fibrosis Foundation. Dr. Wagner was supported by a grant from Pfizer (Groton, CT)

    View full text