Recovery of mycobacteria from patients with cystic fibrosis

Despite decontamination, overgrowth by pseudomonads renders cultural isolat ion of mycobacteria from respiratory specimens of patients with cystic fibr osis (CF) difficult or impossible. We performed a prospective study by comp aring levels of reduction of overgrowth and recovery of mycobacteria using either pretreatment with N-acetyl-L-cysteine (NALC)-NaOH alone or pretreatm ent with NALC-NaOH and then with oxalic acid. From 406 specimens of 148 CF patients, 11 specimens were positive for mycobacteria, 5 of which grew myco bacteria after decontamination by either procedure. Three specimens grew my cobacteria only after decontamination with NALC-NaOH, whereas three specime ns grew mycobacteria only after treatment with NALC-NaOH followed by oxalic acid but were overgrown after decontamination with NALC-NaOH. Thus, inacti vation of mycobacteria by the more aggressive oxalic acid treatment offsets its beneficial effect of reducing the proportion of cultures overgrown wit h microorganisms other than mycobacteria.