Antibiotic therapy and cystic fibrosis: increased resistance of mucoid Pseudomonas aeruginosa to carbenicillin.

The present communication reports the effect of the bacterial mucus on the 
activity of antibodies on strains of P. aeruginosa. Mucoid variants of 
P. aeruginosa obtained from the non-mucoid strains PAO 381 and PAT 
404 by selection for phenotypic resistance to the virulent phage E 
79 were more resistant to carbenicillin than the non-mucoid parent strains. 
Mucoid P. aeruginosa strains isolated from two CF patients were more 
resistant to carbenicillin than non-mucoid strains isolated from the same samples 
of sputum. When the experiments already described were repeated with oxytetracycline, 
in contrast to our experience with carbenicillin, mucoid strains were found 
to be more sensitive than non-mucoid strains. To prove the hypothesis 
that mucoid strains can be selected in vivo by carbenicillin therapy 
it will be necessary to show that the level of carbenicillin 
in CF secretions is less than the minimum inhibitory concentrations of 
mucoid strains but greater than that of non-mucoid strains. We are 
now investigating additional CF isolates in conjunction with the range of 
antibiotics used in chemotherapy of CF patients. 