Most studies examining the presence of SCCmec
among CoNS isolates have included in their respective analyses few S. hominis
clinical isolates recovered from catheters, the catheter insertion site, pus, wound secretions, cerebral spinal fluid, or blood 
. S. hominis
comprises part of the normal flora colonizing the skin and mucous membranes of humans and may be found as a culture contaminant. However, detection of S. hominis
is indicative of an infection and a probable causative agent of bacteremia. In this study, we analyzed 21 S. hominis
clinical isolates recovered from blood and were causative agents of Laboratory-Confirmed Bloodstream Infection (LCBI) according to CDC criteria. To our knowledge, this is the first report characterizing S. hominis
isolates identified as causative agents of bacteremia recovered from the blood at the microbiological and molecular level.
A significant observation associated with the S. hominis
isolates studied was the ability of almost half of these strains (47.6%) to produce biofilm (since S. hominis
is not known as a major biofilm producer) 
. This characteristic represents a significant virulence factor since biofilms facilitate bacterial adherence to biomedical surfaces (such as catheters), thereby facilitating their entrance into the bloodstream 
. However, the polysaccharide or protein composition of S. hominis
biofilms (or genes involved on its production) remains unknown to date.
Among the mecA
-positive isolates (81%), nearly half were carriers of a putative new SCCmec
. In addition, most expressed the mec
gene class A, ccr
type 1, and others ccr
type 5. This combination of mec-ccr
complexes has been reported in this bacterial species before 
The mec-ccr complexes identified in this study were similar to those reported by Bouchami et al. that demonstrated that S. hominis could serve as a mec-ccr reservoir and also serve as a likely donor of ccrAB1 and mec complex A to other bacterial species. Unlike that study, we found a higher proportion of non-typeable isolates (82%) and isolates harboring ccrC (29%).
The data regarding SCCmec diversity in CoNS presented in this study may be biased due to the typing methodology used that was developed for S. aureus, therefore caution should be taken in the interpretation of these data. Therefore, a variety of non-typeable elements in CoNS may be simply an indication that S. hominis elements are different enough from those of S. aureus that the present typing methods can not be applied to this CoNS.
Data presented in this report also demonstrated that most isolates with new or untypeable SCCmec were resistant to at least three antibiotic classes, and some isolates presented with two or three recombinase complexes types, suggesting the presence of multiple SCCmec elements in tandem. However, to verify this, the S. hominis SCCmec cassette should be sequenced completely and compared to the S. aureus cassette. This analysis is currently underway in our laboratory.
We found that the 82% of mecA
-positive isolates were untypeable and neither of the two methods used amplified any of the know recombinases suggesting that these strains are therefore likely candidates for carrying novel SCCmec
types. This observation was previously described for S. hominis
and may be explained by: a) that this cassette is a carrier of a new recombinase not related to ccr
AB or ccr
C genes, b) they represent new ccr
complex isotypes that cannot be amplified by currently utilized ccr
primers, or c) ccr
genes were not present 
In this study, we identified a high rate of methicillin resistance (81%) in addition to resistance to other antibiotics among the clinical isolates studied; an observation previously reported for S. hominis
and other CoNS species 
. All methicillin resistant isolates were also positive for SCCmec
in addition to displaying resistance to most β-lactams antibiotics tested.
Among the S. hominis isolates collected in the present study none were clonal, therefore we concluded that infections caused by these isolates were not caused by dissemination of the same isolate throughout the hospital. Taking into account the fact that S. hominis is a component of the normal skin and mucous membrane flora, it is likely that these infections were endogenous.
In conclusion, our results showed that S. hominis is a biofilm producer and in combination with its high resistance rate to antibiotics, renders this species a serious threat for infections in immunocompromised patients. Finally, S. hominis isolates may possess different SCCmec types compared to those present in S. aureus.