aureus strains to a specific environment may emerge and spread among selleck chem inhibitor this sensitive patient population. Study design In 2006 in Marseille, France, during an epidemiological survey of S. aureus in CF patients, we have detected an atypical GS-MRSA strain with a specific antibiotic susceptibility profile and a unique growth phenotype. The strain was susceptible to gentamicin and resistant to tobramycin, kanamycin, erythromycin, lincomycin, and ofloxacin. The isolate had a hetero-Glycopeptide-Intermediate phenotype of resistance (GISA) and grew with atypical intense orange pigmentation on Cepacia agar (Figure (Figure1a).1a). Because of the clinical importance of the spread of such strain among CF patients we sequenced the genome of one representative isolate (CF-Marseille) and compared this to the published genome sequences, to detect new genetic features responsible for pathogenicity, epidemicity or antibiotic resistance.

For this purpose we used high throughput sequencing system (454 Life Science Corp., Roche) [28] coupled with microarrays and molecular genotyping methods to decipher specificities of this isolate in the CF population. We also conducted a retrospective epidemiological analysis on all S. aureus isolated from 2002 to 2007 in CF patients from our institution to understand dynamics of change and spread of the different strain phenotypes. Finally, specific sequences found in the newly sequenced genome were used to design primers to trace the strain in an epidemic setting [29].

Figure 1 Growth of GS-MRSA strain CF-Marseille on Cepacia agar showing intense orange pigmentation (a) and Transmission Electron Microscopy showing the cell wall thickness and abnormalities of septation (b). Strain CF-Marseille phage induced by antibiotics as … Results Phenotype of strain CF-Marseille The cell wall of CF-Marseille was significantly thicker (33.5 +/- 5.8 nm, n = 100 measurements) than MSSA strain CIP 76.25 (24.7 +/- 4.0 nm, n = 100 measurements) (p < 10-3) (Figure (Figure1b).1b). Presence of phages was not visualized by electron microscopy without induction whereas phages were seen when antibiotics were added to the medium (Figure (Figure1c).1c). Antibiotics able to induce phages were fusidic acid, tobramycin, ciprofloxacin, cotrimoxazole, erythromycin, rifampin and imipenem whereas oxacillin, ceftazidime, vancomycin, fosfomycin, thiamphenicol, and colistin were not.

Apart from its specific antibiotic susceptibility profile, CF-Marseille has a vancomycin MIC of 2�C2.5 ��g/ml (Etest strips with cell suspensions Carfilzomib calibrated at 2 McFarland units) but satellite colonies grew within the ellipse of growth inhibition (Figure (Figure1d).1d). Profile analysis population with teicoplanin confirmed that some colonies were able to grow at 4 ��g/ml (Additional file 1), thus displaying a hetero-GISA phenotype [30].