ADULT CYSTIC-FIBROSIS - ASSOCIATION OF ACUTE PULMONARY EXACERBATIONS AND INCREASING SEVERITY OF LUNG-DISEASE WITH AUXOTROPHIC MUTANTS OF PSEUDOMONAS-AERUGINOSA

Background-Pseudomonas aeruginosa has been located in the endobronchio lar spaces of patients with cystic fibrosis where nutrients may be lim ited. In these sites it is thought that adaptation of the pathogen mig ht occur and growth factors, present in relative excess, may thus prom ote survival of the organism. Auxotrophy of pulmonary isolates of P ae ruginosa has previously been shown to be a feature of cystic fibrosis and chronic lung sepsis; auxotrophic isolates have additional nutritio nal requirements to the prototrophic ''wild types'' of the species. A study was therefore carried out to determine whether the proportion of auxotrophs differs between stable and acutely ill patients, or correl ates with the extent of underlying disease. Methods-Sputum samples wer e cultured for P aeruginosa and tested for auxotrophy by spreading ser ial dilutions of homogenised sputum on to a minimal medium which suppo rts only prototrophs, and a complete medium which supports both nutrit ional types. The proportion of auxotrophs to prototrophs was determine d and growth factors of confirmed auxotrophs were identified. Results- Thirty two (86%) of 37 adults with cystic fibrosis infected with P aer uginosa harboured auxotrophs; methionine dependent mutants were isolat ed from seven of 16 patients tested (44%). More than 50% of the total number of colonies were auxotrophic in 19 of 26 samples (73%) from pat ients with acute exacerbations and in only six of 15 samples (40%) fro m clinically stable patients. In four patients from whom samples in bo th the acute and stable states were available, the proportion of auxot rophs fell in the sample taken when stable. Auxotrophs predominated in all samples from 11 of those patients with very severe underlying lun g disease, in contrast to 13 of 30 samples from patients with less sev ere disease. There was no association between the percentage of auxotr ophs and the presence of other respiratory pathogens. Conclusions-The majority of adults with cystic fibrosis infected with P aeruginosa har bour auxotrophs in the sputum. A significant proportion of acutely ill patients and those with severe underlying disease have a preponderanc e of auxotrophs in the sputum compared with stable patients and those with less severe disease.