Evolutionary pathway to increased virulence and epidemic group A Streptococcus disease derived from 3,615 genome sequences.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.We sequenced the genomes of 3,615 strains of serotype Emm protein 1 (M1) group A Streptococcus to unravel the nature and timing of molecular events contributing to the emergence, dissemination, and genetic diversification of an unusually virulent clone that now causes epidemic human infections worldwide. We discovered that the contemporary epidemic clone emerged in stepwise fashion from a precursor cell that first contained the phage encoding an extracellular DNase virulence factor (streptococcal DNase D2, SdaD2) and subsequently acquired the phage encoding the SpeA1 variant of the streptococcal pyrogenic exotoxin A superantigen. The SpeA2 toxin variant evolved from SpeA1 by a single-nucleotide change in the M1 progenitor strain before acquisition by horizontal gene transfer of a large chromosomal region encoding secreted toxins NAD(+)-glycohydrolase and streptolysin O. Acquisition of this 36-kb region in the early 1980s into just one cell containing the phage-encoded sdaD2 and speA2 genes was the final major molecular event preceding the emergence and rapid intercontinental spread of the contemporary epidemic clone. Thus, we resolve a decades-old controversy about the type and sequence of genomic alterations that produced this explosive epidemic. Analysis of comprehensive, population-based contemporary invasive strains from seven countries identified strong patterns of temporal population structure. Compared with a preepidemic reference strain, the contemporary clone is significantly more virulent in nonhuman primate models of pharyngitis and necrotizing fasciitis. A key finding is that the molecular evolutionary events transpiring in just one bacterial cell ultimately have produced millions of human infections worldwide.Knut and Alice Wallenberg Foundation Swedish Research Council Houston Methodist Hospital Fondren Foundatio

Bacterial Phenotype Variants in Group B Streptococcal Toxic Shock Syndrome1

Variants with markedly different expression of virulence factors can arise in invasive infection in humans

Streptococcus pyogenes infections and toxic shock syndrome : Molecular epidemiology and immunotherapy

Strepto coccus pyogenes , also known as group A streptococcus (GAS), is an important human pathogen causing a wide variety of diseases. One of the most severe diseases is streptococcal toxic shock syndrome (STSS), which is associated with high mortality rates. Toxic shock syndrome (TSS) may also be caused by Staphylococcus aureus. Superantigens have been identified as key mediators of STSS and staphylococcal TSS. Intravenous polyspecific immunglobulin (IVIG) has been suggested as adjunctive therapy in TSS, since it contains neutralising antibodies against streptococcal and staphylococcal superantigens, as well as bacterial opsonising antibodies. To assess the safety and efficacy of IVIG as adjunctive therapy in STSS, we conducted a multicenter placebo-controlled trial (paper I). The trial was prematurely terminated due to a low incidence of disease in the participating countries. Results were obtained from 21 enrolled patients; 10 of whom received IVIG and 11 placebo. The primary objective was mortality over 28 days, and a trend to decreased mortality was observed in the IVIG group, 10% versus 36% in the placebo group. A significant decrease in sepsis-related organ failure assessment (SOFA) score was noted in the IVIG-group, whereas no change was seen in the placebo group. The IVIG cases obtained a significantly increased plasma superantigen-neutralising activity against their own isolate following IVIG administration, whereas no change could be noted among patients in the placebo group. In paper II we tested whether superantigen-containing culture supernatants from streptococcal and staphylococcal severe sepsis isolates were inhibited to an equal extent by IVIG. Three different IVIG preparations were tested and found to be highly efficient in neutralising the superantigens. Most supernatants were completely inhibited at concentrations between 0.5 - 2.5 mg IVIG/ml. Importantly, culture supernatants from S. pyogenes isolates were consistently inhibited to a higher extent as compared to those of S. aureus isolates. In paper III and IV, results from active surveillance of invasive GAS infections in Denmark and Sweden during 2001-02 and 2002-04, respectively, are described. The yearly incidences were similar, 2.0-3.4 /100 0000 inhabitants, as was the prevalence of the severe manifestations STSS and necrotising fasciitis (NF), which were seen in approximately 10% of the cases. However, differences were observed in outcome with a mortality rate of 25% and 14.5% in Denmark and Sweden, respectively. Also the GAS type distribution varied between the two studies. emm1 was the most prevalent type (32%) in the Danish study in comparison to the new types emm89 (16%) and 81 (14%) that dominated in the Swedish study. Non-invasive GAS isolates were collected and analysed in parallel with the invasive in both studies, and the type distribution differed significantly from the invasive isolates. Differences in presence of superantigen genes were seen between isolates of different emm-types and also between invasive and non-invasive isolates. A combination of PFGE-analysis and superantigen profiling revealed subclones within the emm-types with higher invasiveness than others (paper IV). Further, IVIG treatment in patients with STSS was significantly associated with improved outcome. 20 out of 72 patients with STSS were given IVIG, with a mortality of 15% as compared to 48% among patients not receiving IVIG (paper IV) This thesis provides further support of IVIG therapy in STSS, and the in vitro analyses revealed that a higher dose of IVIG may be needed in staphylococcal TSS in order to achieve protective antibody levels. The thesis also provides new insights in the molecular epidemiology of invasive GAS disease

Pneumococcal Carriage in Children under Five Years in Uganda-Will Present Pneumococcal Conjugate Vaccines Be Appropriate?

Pneumonia is the major cause of death in children globally, with more than 900,000 deaths annually in children under five years of age. Streptococcus pneumoniae causes most deaths, most often in the form of community acquired pneumonia. Pneumococcal conjugate vaccines (PCVs) are currently being implemented in many low-income countries. PCVs decrease vaccine-type pneumococcal carriage, a prerequisite for invasive pneumococcal disease, and thereby affects pneumococcal disease and transmission. In Uganda, PCV was launched in 2014, but baseline data is lacking for pneumococcal serotypes in carriage.To study pneumococcal nasopharyngeal carriage and serotype distribution in children under 5 years of age prior to PCV introduction in Uganda.Three cross-sectional pneumococcal carriage surveys were conducted in 2008, 2009 and 2011, comprising respectively 150, 587 and 1024 randomly selected children aged less than five years from the Iganga/Mayuge Health and Demographic Surveillance Site. The caretakers were interviewed about illness history of the child and 1723 nasopharyngeal specimens were collected. From these, 927 isolates of S. pneumoniae were serotyped.Overall, the carriage rate of S. pneumoniae was 56% (957/1723). Pneumococcal carriage was associated with illness on the day of the interview (OR = 1.50, p = 0.04). The most common pneumococcal serotypes were in descending order 19F (16%), 23F (9%), 6A (8%), 29 (7%) and 6B (7%). One percent of the strains were non-typeable. The potential serotype coverage rate for PCV10 was 42% and 54% for PCV13.About half of circulating pneumococcal serotypes in carriage in the Ugandan under-five population studied was covered by available PCVs

Molecular and clinical characteristics of invasive group A streptococcal infection in Sweden

Background. The incidence and severity of invasive group A streptococcal infection demonstrate great variability over time, which at least, in part, seems to be related to group A streptococcal type distribution among the human population. Methods. An enhanced surveillance study of invasive group A streptococcal infection (746 isolates) was performed in Sweden from April 2002 through December 2004. Noninvasive isolates from either the throat or skin (773 isolates) were collected in parallel for comparison. Clinical and epidemiological data were obtained from 88% of patients with invasive disease and were related to isolate characteristics, including T type, emm sequence type, and the presence of 9 superantigen genes, as well as pulsed-field gel electrophoresis pattern comparisons of selected isolates. Results. The annual incidence was 3.0 cases per 100,000 population. Among the patients with invasive disease, 11% developed streptococcal toxic shock syndrome, and 9.5% developed necrotizing fasciitis. The overall case-fatality rate was 14.5%, and 39% of the patients with streptococcal toxic shock syndrome died (P < .001). The T3/13/B3264 cluster accounted for 33% of invasive and 25% of noninvasive isolates. Among this most prevalent type cluster, emm types 89 and 81 dominated. Combined results from pulsed-field gel electrophoresis, emm typing, and superantigen gene profiling identified subgroups within specific emm types that are significantly more prone to cause invasive disease than were other isolates of the same type. Conclusions. This study revealed a changing epidemiology of invasive group A streptococcal infection in Sweden, with emergence of new emm types that were previously not described. The results also suggest that some clones may be particularly prone to cause invasive disease