Streptococcus pyogenes MTB314 genome sequencing. Streptococcus pyogenes strain:MTB314

Two Streptococcus pyogenes serotype M1 (emm1) strains with mucoid (MTB313) and nonmucoid (MTB314) colony morphologies of were isolated on sheep-blood agar plates at the same time from the cerebrospinal fluid of a single patient suffering from acute streptococcal meningitis. The whole-genome sequencing and comparative genomic analysis of MTB313 and MTB314 revealed that only MTB313 carried the amber codon within rocA (a positive regulator of covR). It is common knowledge that the CovR/CovS two-component regulatory system (also known as CsrR/CsrS) suppresses the expression of multiple virulence genes including hasA (hyaluronic acid [HA] capsule synthesis), whereas the covR/covS mutation enhances the expression of speB (cysteine protease) and does not affect the streptolysisn O (SLO) expression. First, MAT101 was generated from MTB313 by introducing pRocA, which contained the full-length rocA of MTB314 in the cloning plasmid pLZ12-Km2. Simultaneously, MAT100 was also generated by introducing pLZ12-Km2 into MTB313. Then, MTB313 and MAT100 showed the large quantities of cell-associated HA in the cell pellets and the small quantities of SpeB associated with low activities in the culture supernatants. In contrast, MTB314 and MAT101 showed the opposite results. Meanwhile, the SLO production was much the same among these four strains in the culture supernatants. Finally, when the mortality rates by two weeks of these four strains were examined in a CD46-expressing transgenic mouse model of subcutaneous infection into both hind footpads, the higher mortalities were observed in the MTB313- or MAT100-infected mice than in the MTB314- or MAT101-infected mice. These results clearly indicate that the point mutation in the rocA gene of S. pyogenes led to the high-pathogenicity phenotype associated with the suppression of covR expression, which occurred within the patient.