Extended culture adds little to the identification of potential pathogens in adult patients with stable non-cystic fibrosis bronchiectasis

Abstract

Aim To characterize the microbial colonization of a group of stable adults with non-CF bronchiectasis using an extended culture protocol. Methods Sputum was collected over an 18-month period from clinically stable patients. Standard semi-quantitative bacterial culture was extended to 7 days with the addition of fungal and mycobacterial culture as routine. Results 61 specimens of spontaneously expectorated sputum were collected from 28 patients; mean age 62 years (21-87 years); mean (SD) FEV1/FVC ratio 63% (22%); 21/28 never smokers; 19/28 on inhaled or oral corticosteroids. The bacteria identified were P. aeruginosa (21% of specimens), H. influenzae (18%), H. parainfluenzae (5%), Acinetobacter baumanii (2%), Enterobacteriaceae (6%). Commensals only were identified in 43% of specimens. Fungi included Candida species (20%), Aspergillus fumigatus (5%) and Penicillium species (2%). Non-tuberculous mycobacteria (NTMB) were grown in 11% of specimens: M. gordonae (7%), M. intracellulare (2%) and M. lentiflavum (2%). The NTM identified were all considered non-pathogenic. Only the mycobacteria were identified after day 2. Conclusion Microorganisms with potential pathogenicity are frequently identified in adult patients with non-cystic fibrosis bronchiectasis who are not experiencing an acute exacerbation. All these organisms were identified using a standard short culture protocol. The extended regimen, which was costly, did not identify any unusual or unexpected pathogens. It was rare for patients to be colonized with fungi. This study suggests there is limited value in requesting extended culture for bacterial pathogens, including looking for fungi or NMTB in this stable patient group as this adds little to the empiric antibiotic choice for infective exacerbations.