Multiple locus VNTR typing of Staphylococcus aureus in cystic fibrosis patients Sobral, D., Vu Thien H., Hormigos K., Fauroux B., Corvol H., Vergnaud G., Pourcel C.
Background : Infection by Staphylococcus aureus in patients with cystic fibrosis (CF) is frequent and may be due to colonisation by a few pathogenic lineages. Systematic genotyping of isolates is necessary to identify such lineages and follow their evolution in patients.
Aims : We performed a survey of S. aureus infection in a French paediatric CF centre (Paris) during a 30 months period.
Patients and Methods : 108 patients, aged 2 to 21 years, regularly followed up at the centre, provided sputum for culture. A total of 278 isolates were recovered from 79 children. An efficient Multiple-locus variable-number tandem repeat analysis (MLVA / VNTR) scheme was developed using 14 informative and easily typable markers.
Results : Ninety lineages composed of indistinguishable or closely related isolates were identified. In seventeen patients, strains from two to four different lineages could be recovered over time. In only two occasions, S. aureus isolates with the same genotype were shared by 2 different patients and they belonged to the two largest clusters. Spa (Staphylococcus protein A) typing and MLST (Multi locus sequence typing) were performed on representative samples, showing an excellent concordance with MLVA. In the two larger clusters, MLST CC5 (28%), and MLST CC45 (14%), 40% of the strains were methicillin resistant, of which a significant proportion was negative for the mec A gene. Most of these strains were BOR-SA (borderline S. aureus), with overproduction of ß-lactamase, and MOD-SA (modified penicillin-binding capacity) from only one patient.
Conclusion : Using MLVA it is possible to genotype fastly and at a low cost, a large number of S. aureus isolates. It would be interesting to study the source (s) of pulmonary infection in young CF patients, by comparing their first oro-pharyngal or nasal isolates, with those chronically found in purulent sputum. This may contribute to perform an early diagnosis of S. aureus infection in CF patients.
Acknowledgments : We thank the association “Vaincre la Mucoviscidose” for its financial support