B-179. Phenotypic Microarrays and In Vivo Transcriptome Analysis Reveal Molecular and Regulatory Events Underlying Niche-Adaptation of M1T1 S. pyogenes

R. K. Aziz1,2, W. L. Taylor1, R. Kansal1, M. Kubal3, S. L. Rowe1, Y. Su1, G. S. Chhatwal4, M. J. Walker5, M. Kotb1;
1Univ. of Tennessee Hlth. Sci. Ctr., Memphis, TN, 2Faculty of Pharmacy, Cairo Univ., Cairo, EGYPT, 3Univ. of Chicago, Chicago, IL, 4Helmholtz Ctr. for Infection Res., Braunschweig, GERMANY, 5Sch. of Biological Sci., Univ. of Wollongong, Wollongong, AUSTRALIA.

Background and Methods: We reported that M1T1 S. pyogenes switch to a hypervirulent phenotype due to selection of mutants in the covRS locus, which encodes the two-component regulatory system, CovRS. To further characterize differences between the wild type (wt) and mutant genotype, and understand the dynamics of bacterial adaptation to various host niches, we used a murine chamber model to sample bacteria 24h post-infection, prior to selection or expansion of mutants. Subsequently, we conducted comprehensive comparative in vitro and in vivo analyses of the wt and mutant strains using phenotypic microarrays, oligonucleotide microarrays, and custom-made virulence microarrays. Results: Phenotypic microarray analysis using Biolog technology showed minor differences between the wt and a covS mutant, mostly related to differential sensitivity to antimicrobial agents and to N-acetyl-neuraminic acid utilization as a carbon source. By contrast, full transcriptome and virulence transcriptome profiling showed that even bacteria with intact covRS genes attempt to adapt to the hostile host environment by upregulating many virulence genes, including genes encoding M protein, the secreted inhibitor of complement SIC, and streptolysin O, while at the same time downregulating the cysteine protease SpeB operon, the maltose-maltodextrin operon, and the arginine deiminase pathway. However, the observed partial downregulation of SpeB does not seem sufficient for survival, which may explain why SpeB+ wt bacteria disappear from the bacterial population while covRS mutants with a SpeBlo/Sdahi phenotype prevail over host defenses, surviving for 14 days in mice chambers. Transcriptome profiles of the hypervirulent SpeBlo/Sdahi mutant strain were significantly different from that of the wt strain, reflecting the engagement of different virulence modules. Conclusion: This study underlines the complexity of regulation of bacterial virulence factors and offers a unique snapshot of the wt bacteria in vivo, prior to selection of the hypervirulent mutant phenotype.