Isolation of Staphylococcus aureus from sputum in cystic fibrosis.

The success in the isolation of Staphylococcus aureus of different methods of 
sputum processing was investigated in 60 specimens collected from 14 patients 
with cystic fibrosis during a seven-month period. Fifty specimens (83%) from 
11 patients yielded Staph. aureus by one or more methods. Direct 
plating of purulent portions of sputum on to media designed for 
general use in respiratory infections gave unsatisfactory results (35% yield of 
Staph. aureus). Some increase in isolations was obtained with preliminary liquefaction 
of sputum; but the best results were given by the addition 
of a medium selective for staphylococci (mannitol salt agar, BBL) or 
by initial sonication of sputum (each 83% yield). Seven of the 
11 strains of Staph. aureus were thymidine-dependent and otherwise atypical in 
laboratory characteristics; these were isolated from patients who had received co-trimoxazole. 
