Effects of erythromycin onPseudomonas aeruginosaadherence to collagen and morphologyin vitro

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Abstract
The airways of patients with bronchiectasis and cystic fibrosis are often chronically colonised byPseudomonas aeruginosa(PA), which is virtually impossible to eradicate. Low-dose erythromycin (EM), for unknown mechanisms, is efficacious in bronchiectasis and diffuse panbronchiolitis.In this study, anin vitromodel to investigate PA adherence to human type IV basement collagen was developed by using scanning electron microscopy (SEM). There were significantly less PA bacilli per 20 random SEM fields (4,000×) when PA was cultured in 0.05, 0.5 and 5 µg·mL−1of EM compared with control (absence of EM). Adherence density (20 SEM fields·log−1inocular size) for PA obtained from no EM (56.8±43.16) was significantly higher than that obtained from 0.05, 0.5, and 5 µg·mL−1EM (21.5±17.56, 23.3±16.65, and 21.4±12.65 respectively). By using SEM it was found that PA, when incubated in EM (0.05, 0.5, 5 µg·mL−1) had a significant reduction in its diagonal length, radius, height, volume and surface area.It is possible, therefore, that these misshapedPseudomonas aeruginosabacilli are more susceptible to host defence mechanisms, while at the same time less adherent to the basement membrane of the airwayin vivo. Therefore, this could help explain the clinical efficacy of low-dose erythromycin therapy on patients withPseudomonas aeruginosainfection.