Abstract
BackgroundThe major virulence factors determining the pathogenicity of streptococcal strains include M protein encoded by emm and emm-like (emmL) genes and superantigens. In this study, the distribution of emm, emmL and superantigen genes was analyzed among the streptococcal strains isolated from the patients of acute pharyngitis.MethodsThe streptococcal strains were isolated from the throat swabs of 1040 patients of acute pharyngitis. The emm and emmL genes were PCR amplified from each strain and sequenced to determine the emm types. The dot-blot hybridization was performed to confirm the pathogens as true emm nontypeable strains. The presence of eleven currently known superantigens was determined in all the strains by multiplex PCR.ResultsTotally, 124 beta-hemolytic streptococcal strains were isolated and they were classified as group A streptococcus (GAS) [15.3% (19/124)], group C streptococcus (GCS) [59.7% (74/124)] and group G streptococcus (GGS) [25.0% (31/124)]. Among 124 strains, only 35 strains were emm typeable and the remaining 89 strains were emm nontypeable. All GAS isolates were typeable, whereas most of the GCS and GGS strains were nontypeable. These nontypeable strains belong to S. anginosus [75.3% (67/89)] and S. dysgalactiae subsp. equisimilis [24.7% (22/89)]. The emm and emmL types identified in this study include emm12.0 (28.6%), stG643.0 (28.6%), stC46.0 (17.0%), emm30.11 (8.5%), emm3.0 (2.9%), emm48.0 (5.7%), st3343.0 (2.9%), emm107.0 (2.9%) and stS104.2 (2.9%). Various superantigen profiles were observed in typeable as well as nontypeable strains.ConclusionsMultiplex PCR analysis revealed the presence of superantigens in all the typeable strains irrespective of their emm types. However, the presence of superantigen genes in emm and emmL nontypeable strains has not been previously reported. In this study, presence of at least one or a combination of superantigen coding genes was identified in all the emm and emmL nontypeable strains. Thus, the superantigens may inevitably play an important role in the pathogenesis of these nontypeable strains in the absence of the primary virulence factor, M protein.
Highlights
The major virulence factors determining the pathogenicity of streptococcal strains include M protein encoded by emm and emm-like genes and superantigens
Characteristics of streptococcal isolates In the present study, 124 beta-hemolytic streptococcal strains were isolated and they were classified as group A streptococcus (GAS) [15.3% (19/124)], group C streptococcus (GCS) [59.7% (74/124)] and group G streptococcus (GGS) [25.0% (31/124)]
Of the 16 emmL positive strains, 10 strains were of GGS and the other 6 were GCS and these strains could be considered as emmL typeable
Summary
The major virulence factors determining the pathogenicity of streptococcal strains include M protein encoded by emm and emm-like (emmL) genes and superantigens. The distribution of emm, emmL and superantigen genes was analyzed among the streptococcal strains isolated from the patients of acute pharyngitis. Streptococcus pyogenes (group A streptococcus) is a Gram-positive bacterial pathogen. Extracellular surface molecules such as the M protein, hyaluronic acid capsule and fibronectin-binding proteins allow group A streptococcus (GAS) to adhere to, colonise, and invade human skin and mucus membranes under different disruption and bacterial transmission [3]. The major virulence factor reported in GAS is the M protein encoded by emm gene. A high rate of pharyngeal carriage of GCS and GGS in acute rheumatic fever (ARF) patients has been reported [11]
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