Bacteriology of sputum in cystic fibrosis: evaluation of dithiothreitol as a mucolytic agent

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Abstract
Liquefaction and homogenization are recommended to ensure accurate, representative sputum cultures. Dithiothreitol (DTT) was evaluated as a mucolytic agent for culturing sputum samples obtained from 79 cystic fibrosis (CF) patients. Liquefaction with DTT was not superior to direct plating of specimens for routine, qualitative cultures. Unliquefied sputum cultures failed to detect 3 of 47 Pseudomonas aeruginosa isolates; DTT-treated specimens missed 5 of 13 Candida albicans isolates. Neither treated nor untreated sputum cultures were completely successful in detecting Staphylococcus aureus or Enterobacteriaceae. Since Haemophilus influenzae was recovered from only 2 qualitative cultures, the effect of DTT on the recovery of this organism could not be evaluated. Of 29 strains of H. influenzae, 27 were inhibited by concentrations of DTT near the recommended final working concentration of 50 .mu.g/ml, suggesting that liquefaction might impair isolation of this organism. Liquefaction with DDT permitted quantitative cultures of CF sputum. The predominant pathogen in this CF population was P. aeruginosa; 37 of 43 (86%) patients were colonized with this organism. Median densities of rough and mucoid strains were 3.2 .times. 107 and 4.3 .times. 107 colony-forming units/ml, respectively. Previous oral antistaphylococcal therapy may have accounted for the observed low density of S. aureus (mean density, 3.5 .times. 103 colony-forming units/ml). DTT treatment does not improve recovery of organisms from qualitative cultures but does facilitate quantitative studies of S. aureus and P. aeruginosa in CF sputum.