Effect of freezing sputum on Pseudomonas aeruginosa population heterogeneity

Pseudomonas aeruginosa develops profound population heterogeneity in CF airways. How changes in these populations relate to clinical status is unknown. In order to facilitate this understanding, frequent sampling of this community is required. To determine if the collection and storage of sputum at home may pose a viable option, we collected sputum from ten patients. Sputum samples were partitioned in two, with half immediately processed on MacConkey agar and half assessed after freezing for one week in a home-freezer. From each sample, 88 isolates were assessed for antibiotic susceptibility and virulence factor production. Freezing resulted in a 10³CFU/ml drop in P. aeruginosa. However, across 1760 isolates, no consistent difference in either antibiotic susceptibility nor virulence factors was observed suggesting freezing induced indiscriminate killing. Home collection and freezing of sputum will enable frequent and convenient assessment of P. aeruginosa population dynamics in CF.