Molecular Epidemiology of sil Locus in Clinical Streptococcus pyogenes Strains

Abstract

Streptococcus pyogenes (group A Streptococcus [GAS]) causes a wide variety of diseases, ranging from mild noninvasive to severe invasive infections. Mutations in regulatory components have been implicated in the switch from colonization to invasive phenotypes. The inactivation of the sil locus, composed of six genes encoding a quorum-sensing complex, gives rise to a highly invasive strain. However, studies conducted on limited collections of GAS strains suggested that sil prevalence is around 15%; furthermore, whereas a correlation between the presence of sil and the genetic background was suggested, no link between the presence of a functional sil locus and the invasive status was assessed. We established a collection of 637 nonredundant strains covering all emm genotypes present in France and of known clinical history; 68%, 22%, and 10% were from invasive infections, noninvasive infections, and asymptomatic carriage, respectively. Among the 637 strains, 206 were sil positive. The prevalence of the sil locus varied according to the emm genotype, being present in >85% of the emm4, emm18, emm32, emm60, emm87, and emm90 strains and absent from all emm1, emm28, and emm89 strains. A random selection based on 2009 French epidemiological data indicated that 16% of GAS strains are sil positive. Moreover, due to mutations leading to truncated proteins, only 9% of GAS strains harbor a predicted functional sil system. No correlation was observed between the presence or absence of a functional sil locus and the strain invasiveness status.

Identification of a two-component Class IIb bacteriocin in Streptococcus pyogenes by recombinase-based in vivo expression technology

“…However, our analysis also indicates that the sil locus is not likely operational in MGAS8232 given the apparent truncation of silD . Interestingly, and as previously noted, most strains of S. pyogenes actually lack the majority of the sil locus38; however, other than S. pyogenes M1 serotypes which contain an 11-bp deletion resulting in a frame-shift mutation within the spbM coding sequence [e.g. strains SF37039, MGAS500540 and M1_47641], most sequenced S. pyogenes strains contain complete spbM and spbN sequences.…”

The Place of Group A Streptococci in Moroccan Children with Pharyngitis and Emm Type Distribution

“…The studies done by the French National Reference Center for Streptococci and Chen and al. linked this type of emm to invasive GAS infections (25,26). However, other studies showed that emm90 was involved in a severe epidemic of GAS pharyngitis (7,16).…”

Molecular epidemiology and genomics of group A Streptococcus

“…The sil locus is regulated by quorum-sensing, and the SilCR autoinducing peptide can be sensed across multiple streptococcal species (i.e., SDE) (Belotserkovsky et al, 2009). However, any involvement of sil in DNA transfer involving GAS is unlikely to be a universal mechanism because the sil locus is present in only a minority of GAS strains (Plainvert et al, 2014). …”