Nonoutbreak Surveillance of Group A Streptococci Causing Invasive Disease in Portugal Identified Internationally Disseminated Clones among Members of a Genetically Heterogeneous Population

Abstract

The typing of 160 invasive Streptococcus pyogenes isolates confirmed the importance of pulsed-field gel electrophoresis and multilocus sequence typing for defining clones. The results identified an extremely diverse population and highlighted the importance of both internationally disseminated and local clones not previously associated with invasive disease.A reemergence of invasive disease caused by Streptococcus pyogenes (a member of the group A streptococci [GAS]) has been noted since the late 1980s, both in North America and in Europe (3). This increase in the incidence of GAS infections has frequently been associated with specific clones, suggesting the possibility that the rise of particularly virulent clones is responsible for this reemergence. The identification of GAS clones in surveillance and epidemiological studies has frequently relied on serotyping using two variable surface antigens, the T antigen (T typing) and the M protein (M typing, or emm typing, as the protein is encoded by the emm gene) (3). Recent work suggests that emm typing alone is not sufficient to unambiguously identify GAS clones and that this method must be complemented with an analysis by either pulsed-field gel electrophoresis (PFGE) or multilocus sequence typing (MLST) (1). A total of 160 nonduplicate GAS isolates recovered from normally sterile sites (150 from blood, 7 from pleural fluid, and 3 from cerebrospinal fluid) were collected in 19 laboratories distributed throughout Portugal that were asked to submit all isolates between 2000 and 2005. The number of participating laboratories was not constant, and this variation was reflected in the number of isolates available in each of the study years Twelve different T serotypes (20) were identified, and 23 isolates (14%) were nontypeable (Simpson's index of diversity [SID] Ϯ 95% confidence interval [CI], 88.2% Ϯ 2.3%) (1), whereas 30 different emm types were identified (SID Ϯ 95% CI, 92.0% Ϯ 2.0%). The presence of genes encoding GAS pyrogenic toxins was studied by PCR (2, 9, 16, 18). As expected, the results confirmed the presence of the chromosomal genes speB and speF in all strains except one. Eleven different exotoxin gene profiles were identified (SID Ϯ 95% CI, 82.2% Ϯ 3.0%), but a significant fraction of the isolates (16%) were negative for all but the chromosomal genes ( Table 1).The dendrogram based on the PFGE profiles of SmaI-or Cfr9I-digested total DNA (1, 19) from the isolates identified 13 major clusters accounting for 86% of all isolates (SID Ϯ 95% CI, 92.0% Ϯ 2.1%) (Fig. 1). Among the 37 isolates characterized by MLST (5), four new alleles were identified and submitted to the S. pyogenes MLST database, namely, recP82, gki98, gtr73, and murI68, as well as seven new sequence types (STs; ST258 and ST406 to ST411) that are all single-locus variants of preexisting STs, except for ST258, which is a double-locus variant of three preexisting STs. The overall level of correspondence between PFGE clusters and emm types was high, with a Wallace coefficient of 0.890, meaning th...

emm1/Sequence Type 28 Strains of Group A Streptococci That ExpresscovRat Early Stationary Phase Are Associated with Increased Growth and Earlier SpeB Secretion

“…These results indicate that the emm1/ST28 strains should be highly homogenous, which supports the observations of previous studies (8,31,39). Importantly, emm1/ST28/PFGE type A is also the dominant type found in Canada, Portugal, and northern Taiwan, reinforcing its epidemiologic significance on a global scale (8,11,19). However, due to the limited geographical origin of these strains, the phenomenon of our finding requires further study on strains from different parts of the world.…”

Evidence for Rare Capsular Switching in Streptococcus agalactiae

“…The stability of several GBS clones, such as the hypervirulent ST17 clone found among serotype III isolates that is characterized by a specific combination of genetic markers, including mobile genetic elements and virulence genes, that are part of the variable genome and thus not shared by all GBS (2,4,21), suggests that the rate of gene exchange in this species may be lower than that of other streptococci. In fact, the PFGE analysis of collections of S. agalactiae isolates shows fewer clones than in other streptococcal species, such as Streptococcus pyogenes (14) and S. pneumoniae (37), a finding consistent with a less diverse clonal structure of the population. On the other hand, genomic analysis of eight fully sequenced strains of S. agalactiae provided evidence for the exchange of large chromosomal fragments, hinting at a high rate of gene exchange through an unusual mechanism (5).…”

Description of macrolide-resistant and potential virulent clones of Streptococcus pyogenes causing asymptomatic colonization during 2000–2006 in the Lisbon area

“…Interestingly, comparing both studies, we observed that the rise of the M phenotype was first detected in colonization isolates (in 2001; this study), and later in tonsillitis/pharyngitis isolates (in 2002) [22]. During these shifts, either in colonization (this study) or in tonsillitis/pharyngitis [22] the prevalence of lineage emm1/ST28 was observed, which is not exclusively, but is usually associated with severe S. pyogenes disease [23][24][25]. Nevertheless, this lineage is frequently reported as being macrolide susceptible among patients with severe disease [26].…”