Bacterial content and ionic composition of sputum in cystic fibrosis [letter].

Burns and May proposed the following pattern for the bacteriology of cystic 
fibrosis: (1) Staphylococcus aureus is the initial bacterial pathogen, and damage 
caused by it renders the lungs susceptible to infection by other 
species. (2) Control of S. aureus by antibiotics allows the influx 
of Haemophilus influenzae. (3) Pseudomonas aeruginosa is introduced and continued chemotherapy 
encourages its establishment. (4) P. aeruginosa supplants S. aureus and H. 
influenzae, becoming the sole pathogen. I have examined these ideas by 
quantitative culture of sputum from 20 patients seen at the Cystic 
Fibrosis Treatment and Research Center, University of Oregon Health Sciences Center 
from 1965 to 1977. The results accord with the original hypothesis 
of Burns and May. In 13 of 20 patients the sputum 
bacterial flora changed as the hypothesis of Burns and May predicted. 
This preliminary data suggests that one of the primary sputum abnormalities 
in cystic fibrosis may be increased Ca++ which makes the sputum 
susceptible to colonisation by S. aureus. After infection the Ca++ concentration 
is reduced and the lung becomes susceptible to colonisation by other 
microorganisms including H. influenzae, P. aeruginosa, and Escherichia coli. 