Genetic Diversity among Type emm28 Group A Streptococcus Strains Causing Invasive Infections and Pharyngitis

Abstract

Genome sequencing of group A Streptococcus (GAS) has revealed that prophages account for the vast majority of gene content differences between strains. Serotype M28 strains are a leading cause of pharyngitis and invasive infections, but little is known about genetic diversity present in natural populations of these organisms. To study this issue, population-based samples of 568 strains from Ontario, Canada; Finland; and Houston, Texas, were analyzed. Special attention was given to analysis of variation in prophage-encoded virulence gene content by a PCR-based method. Thirty and 29 distinct prophage-encoded virulence gene profiles were identified among pharyngitis and invasive infection isolates. Thirteen profiles, representing the majority of the strains, were shared between these two classes of isolates. Significant differences were observed in the frequency of occurrence of certain prophage toxin gene profiles and infection type. M28 strains are highly diverse in prophage-encoded virulence gene content and integration site, supporting the key concept that prophages are critical contributors to GAS genetic diversity and population biology. Nucleotide sequence variation in the emm gene (encodes M protein) was also examined. Only three allelic variants were identified in the hypervariable portion of the emm28 gene. All but one strain had the same inferred amino acid sequence in the first 100 amino acids of the mature M28 protein. In contrast, size differences in the emm28 gene and inferred protein due to variable numbers of C-terminal repeats were common. The presence of macrolide resistance genes (mefA, ermB, and ermTR) was analyzed by PCR, and less than 2% of the strains were positive.Research on group A Streptococcus (GAS) host-pathogen interactions has been aided greatly by the recent publication of genome sequences from serotype M1, M3, M6, and M18 strains (1,5,16,38,48,51). The availability of multiple genome sequences has also increased our understanding of GAS molecular population genetics, species diversity, and strain variation within and between M-protein serotypes. The majority of differences in gene content between strains are located in 35-to 45-kb insertions corresponding to prophages, prophage-like elements, and other exogenous sequences (1-6, 16, 38, 48, 51) (for simplicity, the term prophage will be used to refer to prophages or prophage-like elements). The genome of each sequenced GAS strain is polylysogenic, and 23 distinct prophages have been described (1-6, 16, 38, 48, 51). Twenty of these 23 prophages encode one or two proven or putative extracellular virulence factors, including pyrogenic toxin superantigens (speA, speC, speH, speI, speK, speL, speM, and ssa), DNases (spd1, spd3, spd4, sdn, and sda), a phospholipase A 2 (slaA), macrolide resistance (mefA), and a novel cell surface protein of unknown function (1-5, 16, 37, 38, 48, 51).The contribution of serotype M28 GAS strains to human morbidity and mortality has often been underappreciated in part because serotypes such as M1 and M3 att...

The Intrinsic Immunoglobulin G Endopeptidase Activity of Streptococcal Mac-2 Proteins Implies a Unique Role for the Enzymatically Impaired Mac-2 Protein of M28 Serotype Strains

“…Since sequence similarities do not include the cysteine residue in position 257, these data imply that Mac-2 M28 represents a unique Mac-2 variant favoring receptor binding properties before IgG endopeptidase activity. Although streptococcal strains of the M1 serotype are currently most frequently associated with invasive streptococcal disease (e.g., see references 3, 8, and 15), M28 serotype strains are repeatedly reported as the leading cause of invasive and noninvasive disease (3,9,11,15,17). It is tempting to speculate whether the evolution (or preservation) of Mac M28 correlates with the reemergence of M28-associated pathogenesis: i.e., the prevalence of M28 serotypes in puerperal sepsis and/or neonatal infections (9).…”

Distribution of Phage-Associated Virulence Genes in Pharyngeal Group A Streptococcal Strains Isolated in Italy

“…1). With respect to these variables, the work of Green et al, which is the only study directly comparable to the present one, even if restricted to emm28 GAS, reported an m vir equal to 3.6 and an overall number of 46 profiles (12). Only 50 strains analyzed here could be classified in just 11 profiles represented in the scheme of Green et al…”

Genetic Analysis of Group A Streptococcus Isolates Recovered during Acute Glomerulonephritis Outbreaks in Guizhou Province of China

“…All isolates of the two outbreak types were analyzed for amplification of speA, speB, and speC genes using the primers speA-fw (5Ј-ACT TAA GAA CCA AGA GAT GG-3Ј) and speA-rev (5Ј-CTT TAT TCT TAG GTA TGA AC-3Ј), speB-fw (5Ј-GTC AAC ATG CAG CTA CAG GA-3Ј) and speB-rev (5Ј-AAT ACC AAC ATC AGC CAT CA-3Ј), and speC-fw (5Ј-TCT AGT CCC TTC ATT TGG TG-3Ј) and speC-rev (5Ј-GTA AAT TTT TCA ACG ACA CA-3Ј), respectively, as reported previously (11,30). The PCR cycle used for amplification was as follows: denaturation at 94°C for 15 s, annealing at 55°C for 30 s, extension at 72°C for 1 min for 30 cycles, and a final extension at 72°C for 5 min.…”