Quantitative real time RT-PCR for RNAIII demonstrated that IGF-1R inhibitor TPS3105r produced 325-fold more RNAIII than TPS3105. Virulence was also restored and TPS3105r caused greater weight loss, skin lesion area and CFU recovery from lesions compared to the parental strain TPS3105 (p < 0.0001, Figure 5). There was no significant difference between JKD6159 and TPS3105r in all outcome measures in the mouse skin infection model (Figure 5). These experiments show that intact agr
is essential for the virulence of ST93 CA-MRSA. The agrA repaired mutant of TPS3105, TPS3105r expressed significantly greater amounts of PSMα3 (p < 0.0001) and Hla (p = 0.0019), consistent with agr control of these virulence determinants (Figure 6). Thus, despite the genetic divergence of ST93 from other S. aureus, the molecular BKM120 price foundation of virulence for this CA-MRSA clone is similar in this respect to USA300 [9, 26, 27] and other S. aureus strains [28, 29], where the importance of agr
has been very well established. Figure 5 The importance of agr and aryK in the virulence FK228 in vitro of ST93 CA-MRSA. Isogenic repaired agr mutant TPS3105r compared to TPS3105 and JKD6159, and JKD6159 compared with isogenic repaired AraC/XylS family regulator mutant (JKD6159_AraCr) in a BALB/c mouse skin infection assay. At least 10 mice were used for each bacterial strain. (A) Weight loss induced by intradermal infection with S. aureus strains is demonstrated as percentage loss of weight over 5 days. There was no difference between JKD6159 and TPS3105r in all outcome measures.
TPS3105r infected mice had significantly increased weight loss compared to TPS3105 (p < 0.0001). There was a small increase in weight loss in mice infected with JKD6159_AraCr compared to JKD6159 (p = 0.0311). Data shown are mean weight loss and SEM. (B) Skin lesion area (mm2) at 5 days after infection in TPS3105r infected mice was significantly increased compared to TPS3105 (p < 0.0001). Mice infected with JKD6159_AraCr had increased lesion area compared with JKD6159 (p < 0.0001). Data shown are mean area and SEM. Tacrolimus (FK506) (C) Recovery of S. aureus (log CFU) from infected tissues at 5 days after infection from TPS3105r was significantly greater than from TPS 3105 infected mice (p < 0.0001). There was no difference in S. aureus recovered from mice infected with JKD6159 and JKD6159_AraCr. Data shown are mean CFU and SEM. Note, *** p < 0.001, * p < 0.05. Figure 6 In vitro PSMα3 and Hla expression of mutant S. aureus isolates. JKD6159 compared with JKD6159_AraCr. TPS3105 compared with TPS3105r. (A) PSMα3 expression measured by HPLC. JKD6159_AraCr expressed more PSMα3 than JKD6159 (p = 0.0325). TPS3105r expressed more PSMα3 than TPS3105 (p < 0.0001). Data shown are mean concentration (μg/ml), presented as vertical stacked bars and SEM. Deformylated PSMα3 is shown in grey bars.