Thymidine-requiring Staphylococcus aureus [letter].

We confirm that thymidine-requiring (thy-) Staphylococcus aureus strains are common in patients 
with cystic fibrosis. In 7 months, we isolated Staph. aureus from 
11 of 14 patients with C.F. Despite long-term co-trimoxazole Staph. aureus 
tends to persist in the sputum even though isolates do not 
require thymidine at first and are trimethoprim-sensitive in vitro. Staph. aureus 
is less commonly isolated, and of less significance, in most other 
chest conditions for which co-trimoxazole is given. These factors may explain 
why thy- staphylococci are recognised more frequently in C.F. than in 
other diseases. 