Variable numbers of tandem repeat loci in genetically homogeneous Haemophilus influenzae strains alter during persistent colonisation of cystic fibrosis patients

Serial sputum isolates of Haemophilus influenzae (n = 69) were obtained fro m eight patients suffering from cystic fibrosis. For two of these patients all strains were analysed for polymorphism in the major outer membrane prot ein profile. For all patients the strains were genetically characterised by random amplification of polymorphic DNA analysis. Ail strains were include d in a survey for polymorphism in regions containing moieties of repetitive DNA as well. A single locus containing trinucleotide repeat units, three l oci harbouring tetranucleotides, one region comprising pentanucleotide unit s and two hexanucleotide repeat unit-containing loci were analysed for repe at number variability. Most of the regions were previously shown to be dire ctly adjacent to or even within virulence genes. All regions behaved as gen uine variable number of tandem repeat loci in the sense that genetic polymo rphism based on the presence of varying numbers of repeal units could be de monstrated among different strains. Interestingly, several of the repeats s howed variation in the absence of the variability as assessed by major oute r membrane protein or random amplification of polymorphic DNA analysis. The se observations indicate that the repeat loci may vary independently from m ajor chromosomal polymorphism, Consequently, H. influenzae appears to modif y its virulence gene regions of the chromosome during persistent colonisati on of the lung in cystic fibrosis patients. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights r eserved.