85 Investigation into the antibiotic resistome of the Streptococcus genus from adult cystic fibrosis patients

Abstract

Objective: The use of chronic azithromycin treatment has been linked with increased macrolide resistance. Although, Prevotella spp. are one of the most common anaerobes detected in CF pulmonary samples, the effect of chronic azithromycin exposure on this genus is unknown. The aims of this study were to i. investigate if resistance is associated with azithromycin prescription ii. compare azithromycin and clindamycin MICs between Prevotella isolates cultured from CF patients and healthy control subjects. Methods: Isolates were grouped according to source and patient prescription of azithromycin: CF (currently prescribed), n = 27; CF (not currently prescribed), n = 30; healthy controls (none), n = 17. Susceptibility was determined by Etest® and MICs compared between groups using the Mann-Whitney test. Results: CF isolates had significantly higher azithromycin and clindamycin MICs compared to the healthy control isolates (P < 0.001). Current prescription of azithromycin was associated with significantly higher azithromycin MICs (P= 0.016) in the CF isolates. CF isolates (not currently prescribed) had significantly higher azithromycin MICs (P= 0.009) compared to isolates from healthy control subjects. Isolates from the 2 CF groups had equal resistance to clindamycin (P= 0.228). Conclusions: CF patients harbour isolates with increased resistance to azithromycin and clindamycin. Azithromycin resistance is associated with current azithromycin prescription. Work supported by a Department of Employment and Learning, NI (DEL) studentship to L. Sherrard and by HSC Research and Development, Public Health Agency, NI and the Medical Research Council through a US-Ireland Partnership Grant.