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Published on: January 17, 2014
Molecular characteristics of pharyngeal and invasive emm3 Streptococcus pyogenes strains from Norway, 1988-2003
R Meisal1, E A Høiby, D A Caugant
1Division of Infectious Disease Control, Department of Bacteriology and Immunology, Norwegian Institute of Public Health, Oslo, Norway.
Abstract:
A major virulence factor of group A streptococci (GAS) is the M protein. Strains with the M3 type are more often associated with necrotizing fasciitis (NF) and streptococcal toxic shock syndrome, and have a higher case fatality rate than strains of other M types. To better understand the epidemiology of M3 GAS strains in Norway, we analyzed 59 invasive and 69 pharyngeal isolates with respect to prophage content, allelic variation in emm3, mtsR encoding the metal transporter of Streptococcus repressor (mtsR), and sclB coding for streptococcal collagen-like protein B. The Norwegian emm3 strains were very homogeneous, mainly harboring the emm allele 3.1 and prophage profile PhiG3.01. Other prophage profiles were transient. The mutation in mtsR known to truncate the protein and result in decreased capacity to cause NF was not found in our isolates. The sclB gene usually harbored five or eight contiguous repeats of a CAAAA pentanucleotide sequence and a highly modular and variable collagen structural motif (CSM) region with 9 and 12 amino acid M3-specific conserved motif repeats distributed across the entire CSM region. Strains with 5 CAAAA repeats emerged in 1993 and these strains were associated with the increase in invasive M3 cases in the period 1993-2003.
Insights
Group A Streptococcus (GAS) M3 strains in Norway are genetically similar, primarily carrying specific emm and prophage types. A shift in M3 strains with 5 CAAAA repeats correlated with increased invasive cases.
Area of Science:
- Microbiology
- Epidemiology
- Genetics
Background:
- Group A Streptococcus (GAS) is a significant pathogen, with M protein being a key virulence factor.
- M3 GAS strains are disproportionately linked to severe invasive diseases like necrotizing fasciitis (NF) and streptococcal toxic shock syndrome (STSS), exhibiting higher mortality rates.
Purpose of the Study:
- To investigate the epidemiology of M3 GAS strains in Norway.
- To analyze genetic variations in emm3, mtsR, and sclB genes, as well as prophage content, in Norwegian M3 GAS isolates.
Main Methods:
- Analysis of 59 invasive and 69 pharyngeal M3 GAS isolates from Norway.
- Characterization of prophage content, allelic variations in emm3 and mtsR, and sclB gene structure (CAAAA repeats and collagen structural motif regions).
Main Results:
- Norwegian emm3 strains demonstrated high homogeneity, predominantly featuring the emm allele 3.1 and PhiG3.01 prophage profile.
- The specific mtsR mutation associated with reduced NF capacity was absent in the studied isolates.
- The sclB gene typically contained five or eight CAAAA repeats and variable collagen structural motif regions. Strains with 5 CAAAA repeats emerged around 1993, coinciding with an increase in invasive M3 cases from 1993 to 2003.
Conclusions:
- Norwegian M3 GAS strains are genetically conserved, with specific emm and prophage profiles.
- The emergence of M3 strains with 5 CAAAA repeats in the sclB gene is linked to a rise in invasive M3 GAS infections in Norway.
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