Hypermutable Haemophilus influenzae with mutations in mutS are found in cystic fibrosis sputum

Abstract

Hypermutable bacterial pathogens exist at surprisingly high prevalence and benefit bacterial populations by promoting adaptation to selective environments, including resistance to antibiotics. Five hundredHaemophilus influenzaeisolates were screened for an increased frequency of mutation to resistance to rifampicin, nalidixic acid and spectinomycin: of the 14 hypermutable isolates identified, 12 were isolated from cystic fibrosis (CF) sputum. Analysis by enterobacterial repetitive intergenic consensus (ERIC)-PCR and ribotyping identified eight distinct genetic fingerprints. The hypermutable phenotype of seven of the eight unique isolates was associated with polymorphisms in conserved sites ofmutS. Four of the mutantmutSalleles were cloned and failed to complement the mutator phenotype of amutS : : TSTE mutant ofH. influenzaestrain Rd KW20. Antibiotic susceptibility testing of the hypermutators identified oneβ-lactamase-negative ampicillin-resistant (BLNAR) isolate with two isolates producingβ-lactamase. Six isolates from the same patient with CF, with the same genetic fingerprint, were clonal by multilocus sequence typing (MLST). In this clone, there was an evolution to higher MIC values for the antibiotics administered to the patient during the period in which the strains were isolated. HypermutableH. influenzaewith mutations inmutSare prevalent, particularly in the CF lung environment, and may be selected for and maintained by antibiotic pressure.