Figure 1.
PFGE profiles after XhoI digestion of methicillin-resistant S. hominis isolates.
The dendrogram showing the clustering of strains was performed by analysis of PFGE profiles with the Bionumerics software, with 1% tolerance and 0.8% optimization (this study). Clusters were defined at a cut-off value of 90%.
Table 1.
Molecular and phenotypic characterization of methicillin-resistant S. hominis (MRSHo) isolates.
Table 2.
Molecular and phenotypic characterization of the 11 methicillin-susceptible S. hominis (MSSHo) isolates.
Figure 2.
Phylogram (average distance) using the identity percentage for ccrB1 and ccrB4 carried by S. hominis isolates and ccrB prototype sequences available on 17 June 2010 at the ‘ccrB typing tool’ online resource.
The tree was automatically drawn by the Java applet available through the ‘ccrB typing tool’ using the default parameters [14]. MRSHo and MSSHo isolates from this study are underlined. Control isolates were the following by order of appearance from top to bottom: ATCC12228, Methicillin-susceptible S. epidermidis (MSSE) strain; carrying the SCCpbp4; HDE288, methicillin-resistant S. aureus (MRSA), carrying SCCmec VI; C10682, MRSA carrying SCCmec type VIII; H65, S. fleuretti isolate from database carrying ccrAB4 from ccrB typing tool database; GIFU1223, MSSHo strain GIFU1223 (ATCC27844), carrying the SCC1223; SH-8-39, S. hominis isolate carrying ccrAB1 from the database; D64, S. haemolyticus isolate carrying ccrAB1 from the database; PER184, MRSA, carrying SCCmec I; COL, MRSA carrying SCCmec I; PL72, MRSA carrying SCCmec I; SE6-42, S. epidermidis isolate from the database, carrying ccrAB1; SH13-27, S. hominis from the database carrying ccrAB1; MSSA476, methicillin-susceptible S. aureus (MSSA), carrying SCCMSSA476. SA, S. aureus; SE, S. epidermidis; SHo, S. hominis; SHa, S. haemolyticus; SF, S. fleuretti.
Figure 3.
Model for the contribution of S. hominis species for SCCmec evolution, based on our data and data collected from the bibliography (see discussion).
S. epidermidis is the primary reservoir of ccrAB2, mec complex B, and probably was the species where SCCmec IV was assembled. S. hominis might have been the primary reservoir of ccrAB1, ccrAB4, and mec complex A, and probably was the species where new SCCmec type 1A and SCCmec VIII were first assembled. SCCmec type VI probably resulted from the acquisition by S. epidermidis of a SCC non-mec carrying ccrAB4 genes from S. hominis. In S. epidermidis, this SCC non-mec probably received the mec complex B that is very frequent in this species and rare in S. hominis. According to this model S. epidermidis was the most probable donor of SCCmec I, IV, and VI, to S. aureus, whereas S. hominis was the most probable donor of SCCmec type VIII to S. aureus.