However, the molecular mechanisms involved with the enhanced expression of PSMα MK5108 price were not clarified [39]. Despite the importance of these virulence factors for S. aureus pathogenicity, it is remarkable that among the agr-dysfunctional variants, 4 were recovered from cases of BSI, 2 from colonization, 1 from pneumonia and 1 from

infected prosthesis, showing that these variants were able to colonize and cause both severe acute (pneumonia and BSI) and chronic (foreign-body infection) staphylococcal diseases in humans. These data demonstrated that regardless the reduced virulence of agr-laboratory knockouts in some animal models [40], the virulence of naturally dysfunctional agr variants was confirmed for hospitalized patients. In contrast to the assumption that

agr-dysfunctional isolates may not be able to initiate infections [41], the isolate 08–008 was able to colonize polyurethane endovenous catheter in a foreign-body mouse model, forming a denser learn more biofilm accumulation when compared with the agr-functional isolate. It is important to state that because the ST1 isolates studied were not isogenic, it is possible that factors other than the inhibition of agr might also have accounted for the increased biofilm accumulation observed. Nevertheless, find more supporting our data, similar increase of the biofilm formed on catheters implanted in mice was previously reported for an agr laboratory knockout [28]. In opposition to the results obtained by Traber et al. [41], all individual

colonies formed by the agr-dysfunctional MRSA remained non-hemolytic before and after passages in mice, strongly suggesting the genetic stability of the phenotype. This stability was confirmed eltoprazine for all agr-dysfunctional isolates from our collection. Corroborating our findings, while we were finishing this manuscript, we noticed the work by Park et al. [42] that found agr dysfunction in S. aureus significantly associated with persistent bacteremia with eradicated foci, even though the predominant MRSA isolates showed SCCmecII, agrII (possible belonging to USA100-New York/Japan clone) while the isolates studied here displayed SCCmecIV, agrIII and clustered in USA400-MW2/WA-1 clone. In fact, the bacterial ability to adhere to and invade epithelial cells, and consequently evade host defense mechanisms, has already been associated with persistence in host cells and development of disseminated infections [43, 44]. In the present study, the differential expression of agrRNAIII in MRSA clinical isolates had a significant impact on adherence and invasion at 3h30min incubation. The same impact was observed for the agr isogenic knockout, as previously showed by others using different cell lines and mostly laboratory mutants [26, 45]. Recently, Pozzi et al. demonstrated that high level of PBP2a expression by the homogeneous methicillin-resistant derivative of the strain 8325–4 induced a proteinaceous biofilm and significant repression of the agr locus [46].