The in vitro Effect of Macrolides on the Interaction of Human Polymorphonuclear Leukocytes with Pseudomonas aeruginosa in Biofilm

Abstract

The in vitro effect of macrolides at concentrations below the minimum inhibitory concentration (sub-MIC) on the interaction between Pseudomonas aeruginosa biofilm and human polymorphonuclear leukocytes (PMNs) was investigated by using a chemiluminescence assay. The PMN response to either mucoid or nonmucoid P. aeruginosa biofilm was strongly reduced compared with the response to planktonic bacteria (p < 0.01, p < 0.001, respectively). When biofilms were treated with erythromycin, clarithromycin, roxithromycin and azithromycin prior to incubation with PMNs, the chemiluminescence response was markedly enhanced as compared to untreated controls, and a dose-dependent effect was noted over the range of sub-MIC concentrations studied. In general, macrolides appeared to be slightly more active against mucoid biofilm. Azithromycin was shown to be the most active macrolide against P. aeruginosa biofilms. However, the treatment with sub-MICs of rokitamycin did not have any effect. On the other hand, treatment of planktonic bacteria with macrolides before being exposed to the PMNs did not affect the chemiluminescence response as compared to untreated controls. These findings suggest that macrolides inhibiting the biofilm formation of P. aeruginosa may facilitate the phagocytosis of bacteria by PMNs.

Characterization of Cell-to-Cell Signaling-Deficient Pseudomonas aeruginosa Strains Colonizing Intubated Patients

“…Strains were grown overnight without agitation in LB medium, resuspended in M63 medium supplemented with 0.05% Casamino Acids and 0.2% glucose to an OD 600 of 1, and incubated in microtiter plates at 37°C for 1 h. Quantification of the adhering bacteria to microtiter dishes was determined by crystal violet staining (36). Biofilm formation occurred in static conditions during 3 days as previously described (15,58). Briefly, P. aeruginosa strains were grown in LB medium with agitation at 37°C for 6 h. Sterile polyvinyl chloride (PVC) pieces of 1 cm 2 were incubated for 1 h without agitation to allow bacteria to adhere, transferred to AP medium supplemented with 0.3 M NaCl (59), and incubated for 3 days without agitation at 37°C.…”

Absolute Bioavailability and Intracellular Pharmacokinetics of Azithromycin in Patients with Cystic Fibrosis

“…In particular, the macrolides disrupt the cell-to-cell signaling processes (quorum sensing) responsible for the formation of Pseudomonas biofilms (10,24). In addition, the macrolides exhibit anti-inflammatory activity through inhibition of NF-B and the down regulation of proinflammatory cytokines, a reduction in neutrophil accumulation and migration, and neutrophil oxidant production (11,13,22,23,27). A recent randomized, double-blind clinical trial conducted in CF patients chronically infected with P. aeruginosa demonstrated a significant improvement in lung function and a reduced risk of pulmonary exacerbations in patients receiving azithromycin (AZM) at 500 mg three times weekly over the 6-month study period (19).…”

Immunomodulatory Effects of Macrolide Antibiotics – Part 1: Biological Mechanisms

“…Results of Japanese in vitro studies indicate that azithromycin and clarithromycin change the structure of bacterial biofilms via the inhibition of polysaccharide synthesis [12,14]. An insufficient biofilm allows for enhanced phagocytosis and clearance of bacteria by alveolar macrophages [11,15]. …”