Next, we considered the possibility that an in vivo effect might be more clearly dissected if studies were performed in the background of a non-clinical strain. We hypothesized that an in vivo effect of a virulence determinant

might more likely be seen in strains which are less successful clinically; that is, that a commensal strain such as TX1330RF [11] is likely to have decreased fitness or ability to produce disease compared to TX16 [35] and, thus, acquisition plus subsequent loss of a virulence determinant that alters such fitness would be easier to identify [11]. Thus, the mutated plasmid from strain TX16(pHylEfmTX16Δ7,534) was transferred to TX1330RF by conjugation and the in vivo effect of acquiring the intact click here plasmid [11] vs the plasmid carrying the deletion was evaluated. The two strains [TX1330RF(pHylEfmTX16) and TX1330RF(pHylEfmTX16Δ7,534)] appeared to differ only in the size of the hyl Efm plasmid by PFGE and S1 nuclease assays [11] (not shown). Figure 4B shows that deletion of 7,534 bp in the hyl Efm region

of TX1330RF(pHylEfmTX16) caused an in vitro growth defect. The alteration of growth was also seen in a second transconjugant from the same mating experiment between TX16(pHylEfmTX16Δ7,534) Selleck S63845 and TX1330RF (TC-II in Figure 4B). The mutant strain TX1330RF(pHylEfmTX16Δ7,534) was attenuated in the mouse model of peritonitis (even when an increased intraperitoneal inoculum for the mutant were used) (Figure 4C and 4D) (P < 0.05).

Due to the alterations produced in the Chloroambucil growth of TX1330RF(pHylEfmTX16Δ7,534), these results suggest that the attenuation in virulence may have also been due to factors other than those specifically related to virulence. Complementation of the hyl Efm -region mutant with hyl Efm and a combination of hyl Efm and the downstream gene did not Selleck Emricasan restore the virulence of TX1330RF(pHylEfmTX16Δ7,534) In order to further evaluate if the attenuation observed in TX1330RF(pHylEfmTX16Δ7,534) (as described above) was mediated by a direct effect of hyl Efm in the peritonitis model, we explored complementation of this mutant in trans with the full hyl Efm gene and a combination of hyl Efm and the downstream gene using the shuttle vector pAT392 [30]. The cloning strategy placed these genes upstream of the aac(6′)-aph(2″”) gene (which confers resistance to gentamicin) resulting in all open reading frames under the control of the constitutive P2 promoter. Up to 80% loss was observed with all strains in the absence of gentamicin; however, in the presence of the antibiotic during inoculum preparation, the TX1330RF(pHylEfmTX16Δ7,534)-derivatives containing the pAT392 constructs were stable both in vitro and in vivo (5% maximum percentage of plasmid loss).