Group A streptococcal Vir types are M-protein gene (emm) sequence type specific

Abstract

The M-protein genes (emm genes) of 103 separate impetiginous Streptococcus pyogenes isolates were sequenced and the sequence types were compared to the types obtained by Vir typing. Vir typing is based on restriction fragment length polymorphism (RFLP) analysis of a 4- to 7-kb pathogenicity island encoding emm and other virulence genes. By using both HaeIII and HinfI to generate RFLP profiles, complete concordance between Vir type and emm sequence type was found. Comparison of the emm sequences with those in GenBank revealed new sequence types sharing less than 90% identity with known types. Diversity in the emm sequence was generated by corrected frameshift mutations, point mutations, and small in-frame mutations.

FIG. 1

Ethidium bromide-stained gel of RFLP profiles of VT 3 (lanes 1 to 3), VT 17 (lanes 4 to 7), VT 29 (lanes 8 and 9), and VT 7 (lanes 10 and 11). (A) Undigested PCR product. (B) PCR product digested with HaeIII. (C) PCR product digested with HinfI. Lane 1, VT 3.1; lane 2, VT 3.2; lane 3, VT 3.3; lane 4, VT 17.1; lane 5, VT 17.2; lane 6, VT 17.3; lane 7, VT 17.4; lane 8, VT 29.1; lane 9, VT 29.2; lane 10, VT 7.1; lane 11, VT 7.2; lane M, bacteriophage λ DNA digested with HindIII.

FIG. 2

Alignment of nucleotide sequences of VT 3.3 (accession no. AF018176) and emm49 (accession no. M31789), VT 10 (accession no. AF018178) and emmL2.1 (accession no. X56398), and VT40 (accession no. AF018177) and emm19.1 (accession no. U39838) in the region of in-frame and frameshift insertions or deletions. Asterisks represent identity of the corresponding nucleotide, and dots represent missing nucleotides. Highlighted regions in VT 3.3 and emm49 represent the position of the frameshift mutation, while the arrows in VT 10, VT 40, emm2.1, and emm19.1 represent tandem repeats. The numbers attached to the sequences correspond to the position in the nucleotide sequence in GenBank.

FIG. 3

(A) Aligned nucleotide sequences of STBL18, emm70 (STBSB75), emm33, and STPK14. The emm33 sequence was published by Whatmore et al. (38), while the emm70 sequence was first described from the Northern Territory but was identified more recently (1, 31). Hyphens indicate identical nucleotide sequence, and dots represent missing nucleotides. (B) Aligned translated protein sequences of STBL18, emm70 (STBL25), emm33, and STPK14. Hyphens indicate identical amino acid sequence, and dots represent missing amino acids.