Genetically Diverse Group A Streptococci from Children in Far-Western Nepal Share High Genetic Relatedness with Isolates from Other Countries

Abstract

The genetic diversity of group A streptococci (GAS) throughout much of the world has not been adequately explored. To assess genetic variation among GAS in western Nepal, 120 noninvasive GAS, collected from eight different villages, were genetically characterized using emm typing, sof sequencing, and multilocus sequence typing (MLST). A high level of genetic diversity was observed among these isolates, with 51 genotypes based upon 51 multilocus sequence types (STs), 45 emm sequence types, and 28 sof sequence types. On the basis of shared ST-emm and sof-emm associations, 40 of the 51 genotypes were identical or highly related to genotypes characterized from locations outside of Nepal, even though most of the emm sequence and clonal types are rare among GAS within the United States. When analyzing all known STs highly related to Nepal STs, only one example of similar STs shared between a sof PCR-positive strain and a sof PCR-negative strain was observed. Since previous data indicate free exchange of MLST loci between sof-positive and sof-negative strains, there is possibly selection against the expansion of subclones resulting from horizontal transfers of sof or emm genes between sof-positive and sof-negative strains. All 45 emm types encountered in Nepal have also been documented from other countries. These data, together with data encompassing the past decade of emm type surveillance, support the possibility that most existing GAS emm types have been discovered. Similarly, since most (40/51) strain types were highly related to strains found elsewhere, it is likely that a major fraction of the existing GAS clonal complexes have been discovered.

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

“…A total of 11 different emm/st types were identified. Only three isolates were identified as st type, while the rest were emm types within the sequence of emm1 to emm124 typically encountered during investigations in other countries (9,14,25,27,28). These data are consistent with the prediction that most existing emm types within GAS have already been documented throughout the world, as described previously (25).…”

Polyclonal dissemination of tetracycline resistance among Streptococcus pyogenes paediatric isolates from Brazil

“…The opacity factor genotype was deduced from epidemiological data collected in several studies [29][30][31].…”

“…Isolates within a given emm-type usually display the same opacity factor genotype [28][29][30][31]. The opacity factor genotype was deduced from epidemiological data collected in several studies [29][30][31].…”

Streptococcus pyogenes Isolates Causing Severe Infections in Norway in 2006 to 2007: emm Types, Multilocus Sequence Types, and Superantigen Profiles

“…Multilocus sequence typing (MLST), a widely used method for genetic characterization of organisms of a bacterial species, which is based on the nucleotide sequence variation in seven housekeeping genes, provides unambiguous results that are easily comparable between laboratories (15). Although geographical and temporal variation has been described for GAS populations (15,35,47), strains with the same emm type isolated as much as 50 years apart may harbor identical allelic profiles (15) and share the same T type (23). Due to the clonal population structure of S. pyogenes strains, results obtained by T typing, emm typing, and MLST correlate with each other (15,23,53).…”