emm gene diversity, superantigen gene profiles and presence of SlaA among clinical isolates of group A, C and G streptococci from western Norway

Abstract

In order to investigate molecular characteristics of beta-hemolytic streptococcal isolates from western Norway, we analysed the entire emm gene sequences, obtained superantigen gene profiles and determined the prevalence of the gene encoding streptococcal phospholipase A2 (SlaA) of 165 non-invasive and 34 contemporary invasive group A, C and G streptococci (GAS, GCS and GGS). Among the 25 GAS and 26 GCS/GGS emm subtypes identified, only emm3.1 was significantly associated with invasive disease. M protein size variation within GAS and GCS/GGS emm types was frequently identified. Two non-invasive and one invasive GGS possessed emm genes that translated to truncated M proteins as a result of frameshift mutations. Results suggestive of recombinations between emm or emm-like gene segments were found in isolates of emm4 and stG485 types. One non-invasive GGS possessed speC, speG, speH, speI and smeZ, and another non-invasive GGS harboured SlaA. speA and SlaA were over-represented among invasive GAS, probably because they were associated with emm3. speG(dys) was identified in 83% of invasive and 63% of non-invasive GCS/GGS and correlated with certain emm subtypes. Our results indicate the invasive potential of isolates belonging to emm3, and show substantial emm gene diversity and possible lateral gene transfers in our streptococcal population.

Fig. 1

Segments of a group A streptococci (GAS) and b group C/group G streptococci (GCS/GGS) M protein sequences differing in size mainly because of variation in the number of repeats in the hypervariable, variable and/or conserved regions. emm alleles encoding the M proteins are italicised in the left margin and alleles shown in bold type are exclusively associated with invasive isolates. Numerals representing the first amino acids of each line are placed to the left of the sequences. Dashes indicate deletions and dots indicate stop codons. To highlight our findings, repeated segments of varying sizes in the hypervariable/variable regions (pink or brown) and C-repeat sub-blocks of 28 (blue) or 7 (red, green) amino acids are shown

Fig. 2

Analysis of the full length emm gene sequences of a allele emm4.0–4 and b alleles stG485.0–1 and stg485.0–2. Genes or gene segments deposited in GenBank with close homology to the analysed genes are shown above the lines. The percentage of homology between these gene segments and segments of the genes analysed (indicated by base numbers) is shown below the lines. The GenBank accession numbers of the sequences referred to in the figure are DQ010939 (emm4.0), Z11602 (enn4), AF239717 (stG485.0), DQ522169 (stC74a.0), FJ531842 (stG166b.0), FJ531844 (stG245.0), DQ522164 (stC839) and DQ010924 (stG4222.1). The relatively low homology between the C-terminal segment of stG485.0–1 and other emm types was mainly due to a 21 bp deletion in stG485.0–1 compared with the corresponding segments of emm genes deposited in GenBank