Population dynamics of persistent Staphylococcus aureus isolated from the airways of cystic fibrosis patients during a 6-year prospective study

Abstract

Molecular typing of normal (n = 456) and small-colony-variant (SCV; n = 239) Staphylococcus aureus isolates cultured from the airways of 52 of 72 cystic fibrosis (CF) patients (72.2%) during a 6-year prospective study revealed a median long-term persistence of 37 months (range, 6 to 70). SCV persisted longer in the airways than the normal S. aureus (statistically not significant). Pulsed-field gel electrophoresis identified six prevalent clonal lineages, which were cultured from more than one patient (3 to 12 patients), and 39 individual clones, which were isolated only from single patients. The SCV phenotype was not restricted to a distinct clonal lineage but occurred in many different clones. Most patients (33 of 52, 63.46%) harbored single clones. This study provides a basis for improved understanding of S. aureus colonization and infection dynamics in CF patients.

FIG. 1.

Persistence of normal and SCV S. aureus in a single CF patient. Consecutive isolates were cultured from the sputum of a CF patient from June 1994 until January 2000. Results of PFGE after SmaI digestion of chromosomal DNA from normal and SCV S. aureus isolates are shown. The marker is a molecular weight marker of concatemers of lambda phage DNA.

FIG. 2.

PFGE of persistent clones from nine CF patients. The numbers above the lanes are patient numbers and indicate clones isolated from the airways of individual patients. The marker (M) is a molecular weight marker of concatemers of lambda phage DNA.

FIG. 3.

Dendrograms of the six prevalent clonal lineages and of the isolates belonging to clonal lineage B from nine patients, showing the levels of similarity between SmaI restriction fragment patterns determined by PFGE and subsequent analysis of the Dice coefficient by the software Quantity One. The values show the genetic relatedness of the clones and isolates. (A) Relatedness of the six prevalent clonal lineages, which were isolated from more than one patient (3 to 12 patients). Superscript 1, capital letters indicate clonal lineages. (B) Relatedness of different isolates cultured from nine patients persistently, which belong to clonal lineage B. Superscript 2, each number identifies one patient.