emm typing and validation of provisional M types for group A streptococci

Managing toxic shock syndrome with antibiotics

Toxic shock syndrome (TSS) is a serious disorder with a worldwide prevalence of approximately 3/100,000 persons. TSS is mainly caused by Streptococcus pyogenes or Staphylococcus aureus. Thus, beta-lactam and lincosamides, such as clindamycin, are the first-line drugs. Yet, the mortality rate remains unacceptably high; highlighting the role of bacterial toxin-mediated activation of the inflammatory cascade in TSS pathogenesis. Further strategies should be targeted towards interfering with the interaction between bacterial toxins and host T cells. This paper aims to provide an overview of the epidemiology, pathomechanisms, and clinical presentation of TSS, and criteria for selecting drugs among available antibiotics.

Six-month multicenter study on invasive infections due to Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis in Argentina

During a 6-month period, 95 invasive infections due to Streptococcus pyogenes and group C or group G Streptococcus dysgalactiae subsp. equisimilis were recorded from 40 centers of 16 cities in Argentina. We describe here epidemiologic data available for 55 and 19 patients, respectively, associated with invasive infections due to S. pyogenes and S. dysgalactiae subsp. equisimilis. The associated isolates and 58 additional pharyngeal isolates were genotyped and subjected to serologic and/or antibiotic susceptibility testing. Group A streptococcal emm type distribution and strain association with toxic shock appeared to differ somewhat from results found within the United States; however, serologic characterization and sof sequence typing suggested that emm types found in both countries are reflective of shared clonal types.

Reemergence of emm1 and a changed superantigen profile for group A streptococci causing invasive infections: results from a nationwide study

Between 1999 and 2002, 496 invasive group A streptococcal (GAS) isolates from clinical microbiological departments in Denmark and subsequently 487 (98%) questionnaires from the clinicians treating the patients were received as part of a national surveillance. emm types and streptococcal superantigen (SAg) genes were determined. The incidence of invasive GAS infections was on average 2.3 per 100,000 per year. Bacteremia with no focal symptoms (27%) was together with erysipelas (20%) the most prevalent clinical diagnoses. Streptococcal toxic shock syndrome occurred in 10% of patients, of which 56% died. The overall case fatality rate within 30 days was 23%. In total, 47 different emm types were identified, of which emm1, emm3, emm4, emm12, emm28, and emm89 were identified in 72% of the 493 available isolates. During the 4-year period the presence of emm1 increased from 16% in 1999 to 40% in 2002. Concurrently, the presence of emm3 decreased from 23% in 1999 to 2% in 2002. The emm1 isolates predominantly carried speA, although the frequency decreased from 94% in 1999 to 71% in 2002, whereas the emm1-specific prevalence of speC increased from 25 to 53%. In a historical perspective, this could be interpreted as a reemergence of emm1 and could indicate a possible introduction of a new emm1 subclone. However, this reemergence did not result in any significant changes in the clinical manifestations during the study period. Our results show the complexity of invasive GAS infections, with time-dependent variations in the incidence and distribution of emm and SAg genes, which emphasizes the need for continuous epidemiological and molecular investigations.

Rapid identification and strain-typing of respiratory pathogens for epidemic surveillance

Epidemic respiratory infections are responsible for extensive morbidity and mortality within both military and civilian populations. We describe a high-throughput method to simultaneously identify and genotype species of bacteria from complex mixtures in respiratory samples. The process uses electrospray ionization mass spectrometry and base composition analysis of PCR amplification products from highly conserved genomic regions to identify and determine the relative quantity of pathogenic bacteria present in the sample. High-resolution genotyping of specific species is achieved by using additional primers targeted to highly variable regions of specific bacterial genomes. This method was used to examine samples taken from military recruits during respiratory disease outbreaks and for follow up surveillance at several military training facilities. Analysis of respiratory samples revealed high concentrations of pathogenic respiratory species, including Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pyogenes. When S. pyogenes was identified in samples from the epidemic site, the identical genotype was found in almost all recruits. This analysis method will provide information fundamental to understanding the polymicrobial nature of explosive epidemics of respiratory disease.

Comparison of emm typing and ribotyping with three restriction enzymes to characterize clinical isolates of Streptococcus pyogenes

A total of 336 Streptococcus pyogenes isolates recently recovered from patients with pharyngitis from 13 countries were characterized by emm typing and riboprinting using an automated Riboprinter (Dupont/Qualicon) based on the patterns produced by three restriction enzymes, EcoRI, PstI, and HindIII. Three enzymes were necessary to increase the discrimination of ribogroups formed by each enzyme. A total of 40 ribogroups and 38 emm sequences (not counting allelic variations) were identified. Multilocus sequence typing was performed on a sampling of the isolates, and those results were consistent with those of both emm typing and ribotyping. Correlations were observed among all three methods.

Antibiotic Resistance and Genotypic Characteristics of Group A Streptococci Associated with Acute Pharyngitis in Korea

Group A streptococci (GAS) is the most common pathogen of bacterial pharyngitis. GAS were isolated from pediatric outpatients with symptomatic acute pharyngitis. T typing and emm genotyping were performed for an epidemiologic study. The phenotypes of erythromycin (EM) resistance were evaluated, and the frequencies of ermB, ermTR(A), and mefA genes were determined by polymerase chain reaction. A total of 125 (50.8%) of 246 children yielded GAS. The two most frequent T types were T12 (35.2%) and T nontypeable (30.4%). The most frequent emm type was emm 12 (28.5%), followed by emm75 (18.7%), emm22 (13.0%), emm2 (12.2%), and emm8 (8.1%). The resistance rates to erythromycin and clindamycin were 44.8% and 19.2%, respectively. Among the EM-resistant strains, constitutive resistance, inducible resistance, and the M phenotype were observed in 42.1%, 0%, and 57.9%, respectively. The ermB, ermA, and mefA genes were present in 39.3%, 0%, and 58.9%, respectively. Most of the emm12 strains showed constitutive resistance, while emm18 and emm75 demonstrated the M phenotype. The organisms with other emm genotypes were susceptible to both EM and clindamycin. These results indicate that some emm genotypes might be associated with a specific mechanism of EM resistance.

Molecular heterogeneity among north Indian isolates of Group A Streptococcus

AIM

To monitor molecular heterogeneity among the clinical isolates of group A Streptococcus (GAS) from north India by Vir and emm typing.

METHODS AND RESULTS

GAS isolates, 31 from pharyngitis and nine from rheumatic fever (RF)/rheumatic heart disease (RHD) patients were differentiated into 16 Vir types (VT). These isolates were further discriminated into 23 emm types. Most of emm types were Vir type specific, except few (7.5%), which revealed different Vir types within same emm type. The most prevalent emm type found was emm 49 (15%) followed by 7.5% of emm 69, emm 71 and emm 75 which were different from emm type distribution reported from south India.

CONCLUSIONS

Analysis of data revealed 40% heterogeneity by Vir typing and 57.5% by emm typing among GAS isolates which is significant in view of small number of isolates studied. SIGNIFICANCE OF IMPACT OF THE STUDY: The molecular study for the first time demonstrates different emm types prevalent and circulating in northern region of India and such data may help in selection of types for vaccine development.

Mucosal vaccine made from live, recombinant Lactococcus lactis protects mice against pharyngeal infection with Streptococcus pyogenes

A novel vaccine (LL-CRR) made from live, nonpathogenic Lactococcus lactis that expresses the conserved C-repeat region (CRR) of M protein from Streptococcus pyogenes serotype 6 was tested in mice. Nasally vaccinated mice produced CRR-specific salivary immunoglobulin A (IgA) and serum IgG. Subcutaneously vaccinated mice produced CRR-specific serum IgG but not salivary IgA. A combined regimen produced responses similar to the salivary IgA of nasally vaccinated mice and serum IgG of subcutaneously vaccinated mice. Mice vaccinated nasally or with the combined regimen were significantly protected against pharyngeal infection following a nasal challenge with S. pyogenes M serotype 14. Mice vaccinated subcutaneously were not protected against pharyngeal infection. Mice in all three LL-CRR vaccination groups were significantly protected against the lethal effects of S. pyogenes. Only 1 of 77 challenged mice that were vaccinated with LL-CRR died, whereas 60 of 118 challenged mice that were vaccinated with a control strain or phosphate-buffered saline died. In conclusion, mucosal vaccination with LL-CRR produced CRR-specific salivary IgA and serum IgG, prevented pharyngeal infection with S. pyogenes, and promoted survival.

Natural selection and evolution of streptococcal virulence genes involved in tissue-specific adaptations

The molecular mechanisms underlying niche adaptation in bacteria are not fully understood. Primary infection by the pathogen group A streptococcus (GAS) takes place at either the throat or the skin of its human host, and GAS strains differ in tissue site preference. Many skin-tropic strains bind host plasminogen via the plasminogen-binding group A streptococcal M protein (PAM) present on the cell surface; inactivation of genes encoding either PAM or streptokinase (a plasminogen activator) leads to loss of virulence at the skin. Unlike PAM, which is present in only a subset of GAS strains, the gene encoding streptokinase (ska) is present in all GAS isolates. In this study, the evolution of the virulence genes known to be involved in skin infection was examined. Most genetic diversity within ska genes was localized to a region encoding the plasminogen-docking domain (beta-domain). The gene encoding PAM displayed strong linkage disequilibrium (P << 0.01) with a distinct phylogenetic cluster of the ska beta-domain-encoding region. Yet, ska alleles of distant taxa showed a history of intragenic recombination, and high intrinsic levels of recombination were found among GAS strains having different tissue tropisms. The data suggest that tissue-specific adaptations arise from epistatic coselection of bacterial virulence genes. Additional analysis of ska genes showed that approximately 4% of the codons underwent strong diversifying selection. Horizontal acquisition of one ska lineage from a commensal Streptococcus donor species was also evident. Together, the data suggest that new phenotypes can be acquired through interspecies recombination between orthologous genes, while constrained functions can be preserved; in this way, orthologous genes may provide a rich and ready source for new phenotypes and thereby play a facilitating role in the emergence of new niche adaptations in bacteria.

emm typing of M nontypeable invasive group A streptococcal isolates in Israel

We performed emm typing of M nontypeable invasive group A streptococcal (GAS) isolates collected in a prospective population-based study in Israel. One hundred twenty of 131 isolates (92%) had emm sequences compatible with GAS, consisting of 51 different emm types. Eleven isolates were found to be group G streptococcus. Of the 120 isolates, 55 (46%) belonged to 32 types for which there were no typing sera available in the Streptococcal Reference Laboratory in Israel. The other 65 (64%) isolates, consisting of 19 types, had sera available and therefore could have been serotyped. Forty-three isolates had T and emm types which were not correlated according to standard M-typing protocols and were therefore missed. The principal effect of emm typing was the addition of 32 types not previously identified in Israel and the discovery of new associations between emm and T types. emm typing did not significantly change the proportion of M types; the five most common types were 3, 28, 2, 62, and 41. Twenty different types comprised 80% of all isolates. No new emm sequences were discovered. emm typing emphasized the unusually low incidence of M1 strains causing severe disease in Israel. As serological typing of GAS becomes more problematic due to lack of sera and the appearance of new emm types, reference laboratories should replace M typing with emm sequence typing. Development of a GAS vaccine relies on the emm type distributions in different geographical locations. In our study, 7% of isolates (types 41 and 62) are not included in a 26-valent vaccine that is being studied.

National Department of Defense surveillance data for antibiotic resistance and emm gene types of clinical group A streptococcal isolates from eight basic training military sites

Antibiotic resistance and emm gene types were examined from 692 Group A streptococci isolates from eight United States military basic training sites between 1998 and 2001. Macrolide resistance was associated with geographic sites and emm type. These data are useful for vaccine development initiatives and antimicrobial treatment considerations.

Molecular analysis of group A streptococcal isolates associated with scarlet fever in southern Taiwan between 1993 and 2002

Collected between 1993 and 2002 at a Taiwanese university hospital, 77 group A streptococcus isolates associated with scarlet fever were grouped by emm typing and pulsed-field gel electrophoresis. The predominance of an emm1 clone before 1996 and the presence of genetically diverse emm1 and emm4 strains thereafter were found.

Mass antibiotic treatment for group A streptococcus outbreaks in two long-term care facilities

Outbreaks of invasive infections caused by group A β-hemolytic streptococcus (GAS) may occur in long-term care settings and are associated with a high case-fatality rate in debilitated adults. Targeted antibiotic treatment only to residents and staff known to be at specific risk of GAS may be an ineffective outbreak control measure. We describe two institutional outbreaks in which mass antibiotic treatment was used as a control measure. In the first instance, mass treatment was used after targeted antibiotic treatment was not successful. In the second instance, mass treatment was used to control a rapidly evolving outbreak with a high case-fatality rate. Although no further clinical cases were seen after the introduction of mass antibiotic treatment, persistence of the outbreak strain was documented in one institution >1 year after cases had ceased. Strain persistence was associated with the presence of a chronically colonized resident and poor infection control practices.

Survey of emm gene sequences from pharyngeal Streptococcus pyogenes isolates collected in Spain and their relationship with erythromycin susceptibility

We conducted a nationwide survey of the variable 5' emm (M protein gene) sequences from 614 pharyngeal Streptococcus pyogenes isolates susceptible (299 isolates) and resistant (315 isolates) to erythromycin that were isolated in Spain from 1996 to 1999. Almost 98% of these isolates had emm sequences in agreement with previously recorded M antigen association. We only identified a new 5' emm sequence in 17 isolates. Nine different emm types accounted for 85% of the S. pyogenes isolates susceptible to erythromycin. By contrast, only 3 emm types accounted for 70% of the erythromycin-resistant isolates. Further characterization of these isolates by ribotyping and pulsed-field gel electrophoresis indicated that high frequency of erythromycin resistance in Spain is due to few clones.

Epidemiologic analysis of invasive and noninvasive group a streptococcal isolates in Hong Kong

Since the mid-1980s, there has been a resurgence of severe forms of invasive group A streptococcal (GAS) disease in many Western countries. In Hong Kong, a similar increase has also been observed in recent years. One hundred seven GAS isolates collected from 1995 to 1998 from individuals with necrotizing fasciitis, toxic shock syndrome, meningitis, or other type of bacteremic sepsis (invasive group, n = 24) as well as from individuals with minor skin and throat infections (noninvasive group, n = 83) were characterized through serologic and/or emm sequence typing. Thirty-two M protein gene sequence types were identified. Types M1, M4, and M12 were the most prevalent in both the invasive group and the noninvasive group; together they accounted for 70.8 and 37.3% of the isolates, respectively. No clear pattern of skin and throat infection M types was observed. Type M1 was overrepresented in the invasive and pharyngeal isolates. The same pulsed-field gel electrophoresis pattern was shared by most invasive and all pharyngeal M1 isolates. Overall, resistance to erythromycin (32%) and tetracycline (53%) was high, but M1 isolates were significantly less likely to have resistance to either antimicrobial agent than non-M1 isolates. One novel emm sequence type, stHK, was identified in an isolate from a patient with necrotizing fasciitis. Minor emm gene sequence alterations were noted for 31 isolates, and for 13 of these isolates, deletion, insertion, or point mutations were seen in the hypervariable 50 N-terminal residues.

emm Gene distribution among erythromycin-resistant and -susceptible Italian isolates of Streptococcus pyogenes

The phenotypes and genetic determinants for macrolide resistance were determined for 167 erythromycin-resistant Streptococcus pyogenes strains. A cMLS phenotype was shown in 18% of the erythromycin-resistant strains, while inducible resistance was apparent in 31% and the M phenotype was apparent in 50%. The emm gene type of this set of resistant isolates and that of 48 erythromycin-sensitive isolates were determined. emm2 and emm48 were recorded only in the resistant strains of the M phenotype, while approximately all of the strains harboring the emm22 gene had the cMLS phenotype. More than 80% of the emm89-positive strains had the iMLS phenotype, and the same portion of emm4 strains presented the M phenotype. emm3 is recorded only among sensitive strains. The distribution of frequencies of the genetic determinant for the virulence factor M protein was significantly different both among organisms of different types of resistance and between resistant and sensitive populations of S. pyogenes under study.

M types of group a streptococcal isolates submitted to the National Centre for Streptococcus (Canada) from 1993 to 1999

The National Centre for Streptococcus (NCS) (Canada) determined the group A streptococcal (GAS) M types of 4,760 Canadian isolates submitted between 1993 and 1999 by classic serotyping. The 10 most frequently identified M types were M1 (26.4%), M12 (9.8%), M28 (8.9%), M3 (6.8%), M4 (6.2%), M11 (4.8%), M89 (3.1%), M6 (3.0%), M2 (2.6%), and M77 (1.9%). Nontypeable isolates accounted for 15.4% of the collection. The province of Ontario submitted 51.1% of the isolates, followed by Quebec (21.2%) and Alberta (13.9%). Together, these three provinces constituted 71.3% of the Canadian population in 1996. The numbers of M types M1, M12, M28, and M3 occurred most frequently in subjects whose ages were <1 to 15 years and 25 to 45 years, as well as in the elderly (60 to 90 years). Further analysis found that the four most frequently identified M types from blood, brain, and cerebrospinal fluid were M1 (28.2%), M28 (9.2%), M12 (9.1%), and M3 (8.2%), with 13.4% of isolates being nontypeable. The four isolates from throats most frequently identified were M1 (19.5%), M12 (15.3%), M3 (8.6%), and M28 (5%) with 19.4% of isolates being nontypeable. The sic gene of a subset of M1 strains (9.5% of the M1 collection) was sequenced. Of 36 sic types identified, the four most common were sic1.01 (22.8%), sic1.02 (14.9%), sic1.135 (10.5%), and sic1.178 (9.6%). Together these four sic types further characterized nearly 60% of the M1 strains sequenced. In summary, from the years 1993 to 1999, the NCS detected 54 M types, of which 10 different M types constituted 73.5% of the collection. M1 was the most common GAS M type circulating in the Canadian population, responsible for more than a quarter of the isolates typed. The most common throat isolates differed in M-type and proportion from those of invasive isolates. Sequencing the sic gene further characterized the most common M-type serotype 1 in a fashion that may be useful for epidemiologic investigations.

Prevention of invasive group A streptococcal disease among household contacts of case patients and among postpartum and postsurgical patients: recommendations from the Centers for Disease Control and Prevention

The Centers for Disease Control and Prevention hosted a workshop to formulate recommendations for the control of invasive group A streptococcal (GAS) disease among household contacts of persons with invasive GAS infections and for responding to postpartum and postsurgical invasive GAS infections. Experts reviewed data on the risk of subsequent invasive GAS infection among household contacts of case patients, the effectiveness of chemoprophylactic regimens for eradicating GAS carriage, and the epidemiology of postpartum and postsurgical GAS infection clusters. For household contacts of index patients, routine screening for and chemoprophylaxis against GAS are not recommended. Providers and public health officials may choose to offer chemoprophylaxis to household contacts who are at an increased risk of sporadic disease or mortality due to GAS. One nosocomial postpartum or postsurgical invasive GAS infection should prompt enhanced surveillance and isolate storage, whereas > or =2 cases caused by the same strain should prompt an epidemiological investigation that includes the culture of specimens from epidemiologically linked health care workers.

A locus of group A Streptococcus involved in invasive disease and DNA transfer

Group A streptococcus (GAS) causes diseases ranging from benign to severe infections such as necrotizing fasciitis (NF). The reasons for the differences in severity of streptococcal infections are unexplained. We developed the polymorphic-tag-lengths-transposon-mutagenesis (PTTM) method to identify virulence genes in vivo. We applied PTTM on an emm14 strain isolated from a patient with NF and screened for mutants of decreased virulence, using a mouse model of human soft-tissue infection. A mutant that survived in the skin but was attenuated in its ability to reach the spleen and to cause a lethal infection was identified. The transposon was inserted into a small open reading frame (ORF) in a locus termed sil, streptococcal invasion locus. sil contains at least five genes (silA-E) and is highly homologous to the quorum-sensing competence regulons of Streptococcus pneumoniae. silA and silB encode a putative two-component system whereas silD and silE encode two putative ABC transporters. silC is a small ORF of unknown function preceded by a combox promoter. Insertion and deletion mutants of sil had a diminished lethality in the animal model. Virulence of a deletion mutant of silC was restored when injected together with the avirulent emm14-deletion mutant, but not when these mutants were injected into opposite flanks of a mouse. DNA transfer between these mutants occurred in vivo but could not account for the complementation of virulence. DNA exchange between the emm14-deletion mutant and mutants of sil occurred also in vitro, at a frequency of approximately 10-8 for a single antibiotic marker. Whereas silC and silD mutants exchanged markers with the emm14 mutant, silB mutant did not. Thus, we identified a novel locus, which controls GAS spreading into deeper tissues and could be involved in DNA transfer.

Epidemiology of invasive group a streptococcus disease in the United States, 1995-1999

Severe invasive group A streptococcal (GAS) disease is believed to have reemerged during the past 10-20 years. We conducted active, laboratory, population-based surveillance in 5 US states (total population, 13,214,992). From 1 July 1995 through 31 December 1999, we identified 2002 episodes of invasive GAS (3.5 cases per 100,000 persons). Rates varied by age (higher among those <2 or >/=65 years old), surveillance area, and race (higher among black individuals) but did not increase during the study period. The 5 most common emm types (1, 28, 12, 3, and 11) accounted for 49.2% of isolates; newly characterized emm types accounted for 8.9% of isolates. Older age; presence of streptococcal toxic shock syndrome, meningitis, or pneumonia; and infection with emm1 or emm3 were all independent predictors of death. We estimate that 9600-9700 cases of invasive GAS disease occur in the United States each year, resulting in 1100-1300 deaths.

Dissemination of the phage-associated novel superantigen gene speL in recent invasive and noninvasive Streptococcus pyogenes M3/T3 isolates in Japan

In Japan, more than 10% of streptococcal toxic shock-like syndrome (TSLS) cases have been caused by Streptococcus pyogenes M3/T3 isolates since the first reported TSLS case in 1992. Most M3/T3 isolates from TSLS or severe invasive infection cases during 1992 to 2001 and those from noninvasive cases during this period are indistinguishable in pulsed-field gel electropherograms. The longest fragments of these recent isolates were 300 kb in size, whereas those of isolates recovered during or before 1973 were 260 kb in size. These 260- and 300-kb fragments hybridized to each other, suggesting the acquisition of an about 40-kb fragment by the recent isolates. The whole part of the acquired fragment was cloned from the first Japanese TSLS isolate, NIH1, and its nucleotide sequence was determined. The 41,796-bp fragment is temperate phage phiNIH1.1, containing a new superantigen gene speL near its right attachment site. The C-terminal part of the deduced amino acid sequence of speL has 48 and 46% similarity with well-characterized erythrogenic toxin SpeC and the most potent superantigen, SmeZ-2, respectively. None of 10 T3 isolates recovered during or before 1973 has speL, whereas all of 18 M3/T3 isolates recovered during or after 1992 and, surprisingly, Streptococcus equi subsp. equi ATCC 9527 do have this gene. Though plaques could not be obtained from phiNIH1.1, its DNA became detectable from the phage particle fraction upon mitomycin C induction, showing that this phage is not defective. A horizontal transfer of the phage carrying speL may explain the observed change in M3/T3 S. pyogenes isolates in Japan.

Molecular analysis of group A Streptococcus type emm18 isolates temporally associated with acute rheumatic fever outbreaks in Salt Lake City, Utah

Acute rheumatic fever (ARF) and subsequent rheumatic heart disease are rare but serious sequelae of group A Streptococcus (GAS) infections in most western countries. Salt Lake City (SLC), Utah, and the surrounding intermountain region experienced a resurgence of ARF in 1985 which has persisted. The largest numbers of cases were encountered in 1985-1986 and in 1997-1998. Organisms with a mucoid colony phenotype when grown on blood agar plates were temporally associated with the higher incidence of ARF. To develop an understanding of the molecular population genetic structure of GAS strains associated with ARF in the SLC region, 964 mucoid and nonmucoid pharyngeal isolates recovered in SLC from 1984 to 1999 were studied by sequencing the emm gene. Isolates with an emm18 allele were further characterized by sequencing the spa, covR, and covS genes. Peak periods of ARF were associated with GAS isolates possessing an emm18 allele encoding the protein found in serotype M18 isolates. Among the serotype M18 isolates, the difference in the number of C repeats produced three size variants. Variation was limited in spa, a gene that encodes a streptococcal protective antigen, and covR and covS, genes that encode a two-component regulatory system that, when inactivated, results in a mucoid phenotype and enhanced virulence in mouse infection models. Pulsed-field gel electrophoresis showed a single restriction profile for serotype M18 organisms isolated during both peak periods of ARF. In SLC, the incidence of ARF coresurged with the occurrence of GAS serotype M18 isolates that have very restricted genetic variation.

Genome sequence and comparative microarray analysis of serotype M18 group A Streptococcus strains associated with acute rheumatic fever outbreaks

Acute rheumatic fever (ARF), a sequelae of group A Streptococcus (GAS) infection, is the most common cause of preventable childhood heart disease worldwide. The molecular basis of ARF and the subsequent rheumatic heart disease are poorly understood. Serotype M18 GAS strains have been associated for decades with ARF outbreaks in the U.S. As a first step toward gaining new insight into ARF pathogenesis, we sequenced the genome of strain MGAS8232, a serotype M18 organism isolated from a patient with ARF. The genome is a circular chromosome of 1,895,017 bp, and it shares 1.7 Mb of closely related genetic material with strain SF370 (a sequenced serotype M1 strain). Strain MGAS8232 has 178 ORFs absent in SF370. Phages, phage-like elements, and insertion sequences are the major sources of variation between the genomes. The genomes of strain MGAS8232 and SF370 encode many of the same proven or putative virulence factors. Importantly, strain MGAS8232 has genes encoding many additional secreted proteins involved in human-GAS interactions, including streptococcal pyrogenic exotoxin A (scarlet fever toxin) and two uncharacterized pyrogenic exotoxin homologues, all phage-associated. DNA microarray analysis of 36 serotype M18 strains from diverse localities showed that most regions of variation were phages or phage-like elements. Two epidemics of ARF occurring 12 years apart in Salt Lake City, UT, were caused by serotype M18 strains that were genetically identical, or nearly so. Our analysis provides a critical foundation for accelerated research into ARF pathogenesis and a molecular framework to study the plasticity of GAS genomes.

Influence of recombination and niche separation on the population genetic structure of the pathogen Streptococcus pyogenes

The throat and skin of the human host are the principal reservoirs for the bacterial pathogen Streptococcus pyogenes. The emm locus encodes structurally heterogeneous surface fibrils that play numerous roles in virulence, depending on the strain. Isolates harboring the emm pattern A-C marker exhibit a strong tendency to cause throat infection, whereas emm pattern D strains are usually recovered from impetigo lesions; as a group, emm pattern E organisms fail to display obvious tissue tropisms. The peak incidence for streptococcal pharyngitis and impetigo varies with season and locale, leading to wide spatial and temporal distances between throat and skin strains. To assess any impact of niche separation on genetic variation, the extent of recombinational exchange between emm pattern A-C, D, and E subpopulations was evaluated. Analysis of nucleotide sequence data for internal portions of seven housekeeping loci from 212 isolates provides evidence of extensive recombination between strains belonging to different emm pattern subpopulations. Furthermore, no fixed nucleotide differences were found between emm pattern A-C and D strains. Thus, despite some niche separation created by distinct epidemiological trends and innate tissue tropisms there is little evidence for neutral gene divergence between throat and skin strains. Maintenance of a relationship between emm pattern and tissue tropism in the face of underlying recombination suggests that tissue tropism is associated with emm or a closely linked gene.

Genomic localization of a T serotype locus to a recombinatorial zone encoding extracellular matrix-binding proteins in Streptococcus pyogenes

Streptococcus pyogenes is an important bacterial pathogen afflicting humans. A striking feature is its extraordinary biological diversity, evident in the wide range of diseases it can cause and the antigenic heterogeneity present on its surface. The T antigens form the basis of a major serological typing scheme that is often used as an alternative or supplement to M typing. Unlike M typing, the genetic basis for T typing is poorly understood. In this report, the tee6 gene is localized to a position approximately equal to 3.3 kb downstream from prtF1 (or sfbI), which encodes the Fn-binding protein, protein F, a key virulence factor. Comparison of this portion of the genome with those of four additional strains reveals the presence of genes encoding a collagen-binding protein (Cpa) and a second Fn-binding protein (PrtF2 or PfbpI). This chromosomal region--here designated the FCT region--is approximately 11 to 16 kb in length and is flanked at both ends by long stretches of highly conserved sequence. For each of the five strains, the FCT region contains a unique combination of semiconserved loci, indicative of extensive intergenomic recombination. The data provide evidence that the highly recombinatorial FCT region of the S. pyogenes genome is under strong selection for change in response to the host environment.

Extension of the Lancefield classification for group A streptococci by addition of 22 new M protein gene sequence types from clinical isolates: emm103 to emm124

Classic M protein serotyping has been invaluable during the past 60 years for the determination of relationships between different group A streptococci (GAS) strains and the varied clinical manifestations inflicted by these organisms worldwide. Nonetheless, during the past 20 years, the difficulties of continued expansion of the serology-based Lancefield classification scheme for GAS have become increasingly apparent. By use of a less demanding sequence-based methodology that closely adheres to previously established strain criteria while being predictive of known M protein serotypes, we recently added types emm94-emm102 to the Lancefield scheme. Continued expansion by the addition of types emm103 to emm124 are now proposed. As with types emm94-emm102, each of these new emm types was represented by multiple independent isolates recovered from serious disease manifestations, each was M protein nontypeable with all typing sera stocks available to international GAS reference laboratories, and each demonstrated antiphagocytic properties in vitro by multiplying in normal human blood.

Dynamic epidemiology of group A streptococcal serotypes associated with pharyngitis

BACKGROUND

Despite the past 15 years of heightened awareness of the disease-causing potential of group A streptococci, the possible epidemiological influence of rapid changes in prevalent serotypes has not been fully appreciated.

METHODS

We analysed throat cultures collected as part of routine medical care in a semi-closed community of nearly 500 children and adults between January, 1999, and April, 2000. beta-haemolytic streptococci from all positive cultures were characterised by serological grouping, T-agglutination pattern, and serotyping for M protein or opacity factor.

FINDINGS

We saw an increase in the number of symptomatic individuals with pharyngitis beginning in mid-1999. Between July 1 and Dec 31, 1999, 111 (29%) of 378 throat cultures yielded group A streptococci, 102 (92%) of which were serotype M1. Between Jan 1 and Mar 31, 2000, 126 (45%) of 277 throat cultures yielded group A streptococci. Unexpectedly, 106 (84%) of these throat isolates were serotype M6, and only 16 (13%) were M1. 20 (28%) of the 71 individuals with M1 infection subsequently acquired infection with M6.

INTERPRETATION

This rapid and almost complete shift in predominance of group A streptococcal serotype in this community draws attention to the dynamic epidemiology of these organisms. This change has important implications for further understanding the epidemiology of group A streptococcal infections, and for the development and use of a vaccine.

Isolated hypervariable regions derived from streptococcal M proteins specifically bind human C4b-binding protein: implications for antigenic variation

Antigenic variation in microbial surface proteins represents an apparent paradox, because the variable region must retain an important function, while exhibiting extensive immunological variability. We studied this problem for a group of streptococcal M proteins in which the approximately 50-residue hypervariable regions (HVRs) show essentially no residue identity but nevertheless bind the same ligand, the human complement regulator C4b-binding protein (C4BP). Synthetic peptides derived from different HVRs were found to retain the ability to bind C4BP, implying that the HVR corresponds to a distinct ligand-binding domain that can be studied in isolated form. This finding allowed direct characterization of the ligand-binding properties of isolated HVRs and permitted comparisons between different HVRs in the absence of conserved parts of the M proteins. Affinity chromatography of human serum on immobilized peptides showed that they bound C4BP with high specificity and inhibition experiments indicated that different peptides bound to the same site in C4BP. Different C4BP-binding peptides did not exhibit any immunological cross-reactivity, but structural analysis suggested that they have similar folds. These data show that the HVR of streptococcal M protein can exhibit extreme variability in sequence and immunological properties while retaining a highly specific ligand-binding function.

Binding of human C4BP to the hypervariable region of M protein: a molecular mechanism of phagocytosis resistance in Streptococcus pyogenes

The amino-terminal hypervariable region (HVR) of streptococcal M protein is required for the ability of this virulence factor to confer phagocytosis resistance. The function of the HVR has remained unknown, but the finding that many HVRs with extremely divergent sequences bind the human complement regulator C4b-binding protein (C4BP) has suggested that this ligand may play a role in phagocytosis resistance. We used the M22 system to study the function of bound C4BP and provide several lines of evidence that C4BP indeed contributes to phagocytosis resistance. First, the ability of anti-HVR antibodies to cause opsonization correlated with their ability to inhibit binding of C4BP. Secondly, a short deletion in the HVR eliminated C4BP binding and also reduced the ability of M22 to confer phagocytosis resistance. Thirdly, the addition of an excess of pure C4BP to a phagocytosis system almost completely blocked the effect of opsonizing anti-HVR antibodies. Together, our data indicate that binding of C4BP to the HVR of M22 plays an important role in phagocytosis resistance, but other properties of M22 also contribute. This study provides the first molecular insight into the mechanisms by which the HVR of an M protein confers phagocytosis resistance.

Genetic and phenotypic features of Streptococcus pyogenes strains isolated in Brazil that harbor new emm sequences

In the present study, 37 group A Streptococcus (GAS) strains belonging to 13 new emm sequence types identified among GAS strains randomly isolated in Brazil were characterized by using phenotypic and genotypic methods. The new types were designated st204, st211, st213, st809, st833, st854, st2904, st2911, st2917, st2926, st3757, st3765, and st6735. All isolates were susceptible to the antimicrobial agents tested, except to tetracycline. They all carried the speB gene, and 94.6% produced detectable SpeB. Most strains belonging to a given emm type had similar or highly related pulsed-field gel electrophoresis profiles that were distinct from profiles of strains of another type. The other characteristics were variable from isolate to isolate, although some associations were consistently found within some emm types. Unlike the other isolates, all type st213 isolates were speA positive and produced SpeA. Strains belonging to st3765 were T6 and opacity factor (OF) negative. Individual isolates within OF-positive emm types were associated with unique sof gene sequence types, while OF-negative isolates were sof negative by PCR. This report provides information on new emm sequence types first detected in GAS isolates from a geographic area not extensively surveyed. Such data can contribute to a better understanding of the local and global dynamics of GAS populations and of the epidemiological aspects of GAS infections occurring in tropical regions.

Directional gene movement from human-pathogenic to commensal-like streptococci

Group A streptococci (GAS) are highly pathogenic for humans, and their closest genetic relatives, group C and G streptococci (GCS and GGS, respectively), are generally regarded as commensals, although they can be found in association with human disease. As part of an effort to better understand the evolution of virulence, the phylogenetic relationships between GAS, GCS, and GGS were examined. The nucleotide sequence was determined for an internal portion of seven housekeeping (neutral) loci among >200 isolates of GAS and 34 isolates of GCS or GGS obtained from human subjects. Genotypic analysis failed to show support for the separation of GCS and GGS into two distinct populations. Unlike GAS, there was poor concordance between emm type and genetic relatedness among GCS and GGS. All housekeeping genes within GAS displayed relatively low levels of sequence diversity. In contrast, individual GCS and GGS strains had mosaic genomes, containing alleles at some loci that were similar or identical to GAS alleles, whereas the alleles at other loci were about 10 to 30% diverged. The data provide evidence for a history of recent interspecies transfer of neutral genes that exhibits a strong net directionality from GAS donors to GCS and GGS recipients. A model for the evolution of GAS and of GCS and GGS is described.

Outbreak of scarlet fever caused by an erythromycin-resistant Streptococcus pyogenes emm22 genotype strain in a day-care center

We report an outbreak of scarlet fever and pharyngeal colonization with Streptococcus pyogenes in a day-care center in Mexico City. The outbreak strain was resistant to erythromycin but susceptible to clindamycin. T-type 11,12 serotype was found in eight isolates, from two patients and six carriers, which had the emm22 gene. The recognition of streptococci resistant to macrolides causing outbreaks has implications for infection control and for improving antibiotic prescribing patterns in the day-care setting.

Group A streptococcal genotypes from pediatric throat isolates in Rome, Italy

In a study assessing genetic diversity, 114 group A streptococcus (GAS) isolates were recovered from pediatric pharyngitis patients in Rome, Italy. These isolates comprised 22 different M protein gene (emm) sequence types, 14 of which were associated with a distinct serum opacity factor/fibronectin binding protein gene (sof) sequence type. Isolates with the same emm gene sequence type generally shared a highly conserved chromosomal macrorestriction profile. In three instances, isolates with dissimilar macrorestriction profiles had identical emm types; in each of these cases multilocus sequence typing revealed that isolates with the same emm type were clones having the same allelic profiles. Ninety-eight percent of the pharyngeal isolates had emm types previously found to be highly associated with mga locus gene patterns commonly found in pharyngeal GAS isolates.

Epidemiological usefulness of anti-opacity factor antibody screening in schoolchildren

The presence of the anti-opacity factor (anti-OF) antibody (Ab) in the serum used for identifying the OF antigen (Ag) type represents previous or current infection with group A streptococci (GAS) of the OF Ag type. Throat cultures were taken from 172 elementary schoolchildren in Chinju, Korea, and venous blood samples were collected at the same time to screen for the frequency of the anti-OF Ab. After isolation of GAS, the OF Ag of each GAS was identified by inhibition of the opacity reaction with recognized anti-OF sera. The anti-OF Abs in the sera were screened with the six most common OF Ag types. OF22 and OF28 were high in prevalence (28.2 and 20.5%, respectively) among OF Ag types, while anti-OF types 4, 28, and 22 were frequently identified (39.5, 29.7, and 15.7%, respectively) in the sera. Thirty-two of 39 (82.1%) OF Ag-producing GAS carriers, 25 of 34 (73.5%) GAS carriers not producing OF Ag, and 72 of 99 (72.7%) throat culture-negative children harbored the anti-OF Ab. Forty-five (26.2%) of 172 children had two different anti-OF Abs, and 11 (6.4%) had more than three anti-OF Abs. Seventy-five percent of 172 elementary schoolchildren were shown to be previously or currently infected with GAS. The percentages of children positive for the anti-OF Ab were very high regardless of the result of throat culture or OF Ag production of GAS. We could also demonstrate (i) that the prevalent strains of GAS changed according to the time span by determining the difference between the frequencies of OF Ag and anti-OF Ab and (ii) that repeated infections were not uncommon in schoolchildren, as one-third had more than two different anti-OF Abs.

Multilocus sequence typing of Streptococcus pyogenes and the relationships between emm type and clone

Multilocus sequence typing (MLST) is a tool that can be used to study the molecular epidemiology and population genetic structure of microorganisms. A MLST scheme was developed for Streptococcus pyogenes and the nucleotide sequences of internal fragments of seven selected housekeeping loci were obtained for 212 isolates. A total of 100 unique combinations of housekeeping alleles (allelic profiles) were identified. The MLST scheme was highly concordant with several other typing methods. The emm type, corresponding to a locus that is subject to host immune selection, was determined for each isolate; of the >150 distinct emm types identified to date, 78 are represented in this report. For a given emm type, the majority of isolates shared five or more of the seven housekeeping alleles. Stable associations between emm type and MLST were documented by comparing isolates obtained decades apart and/or from different continents. For the 33 emm types for which more than one isolate was examined, only five emm types were present on widely divergent backgrounds, differing at four or more of the housekeeping loci. The findings indicate that the majority of emm types examined define clones or clonal complexes. In addition, an MLST database is made accessible to investigators who seek to characterize other isolates of this species via the internet (http://www.mlst.net).

Role for a secreted cysteine proteinase in the establishment of host tissue tropism by group A streptococci

Primary infection of the human host by group A streptococci (GAS) most often involves either the epidermis of the skin or the oropharyngeal mucosa. A humanized in vivo model for impetigo was used to investigate the basis for host tissue tropism among GAS. Disruption of the speB gene (encoding for a secreted cysteine proteinase) led to a loss of virulence for two impetigo-derived strains (M-types 33 and 53), as evidenced by a diminution in tissue damage and a lack of reproductive growth. The level of cysteine proteinase activity in overnight cultures was associated with the extent of gross pathological changes induced by strains displaying varied degrees of virulence in the impetigo model. Moreover, high levels of secreted cysteine proteinase activity correlated with a genetic marker for preferred tissue site of infection at the skin (emm pattern D). The addition of exogenous SpeB to a speB mutant (emm pattern D) or to an avirulent throat-like strain (emm pattern A) led to increased bacterial reproduction at the skin. The data provide both experimental and epidemiological evidence for a critical role of a secreted bacterial protease in promoting host tissue-specific infection.

Genetic relatedness and superantigen expression in group A streptococcus serotype M1 isolates from patients with severe and nonsevere invasive diseases

The relatedness of group A streptococcal (GAS) strains isolated from 35 Canadian patients with invasive disease of different severity was investigated by a variety of molecular methods. All patients were infected with M1T1 strains and, based on clinical criteria, were classified as severe (n = 21) and nonsevere (n = 14) invasive GAS infection cases. All the M1 strains studied had the emm1.0 allele and the same streptococcal pyrogenic exotoxin (Spe) genotype, speA(+) speB(+) speC speF(+) speG(+) speH smeZ(+) ssa. All isolates had the same speA allotype, speA2. The randomly amplified polymorphic DNA banding pattern with two different primers was identical for all strains, and pulsed field gel electrophoresis analysis showed that 33 and 30 isolates had identical banding patterns after DNA digestion with SfiI or SmaI, respectively; the nonidentical isolates differed from the main pattern by only one band. A relatively high degree of polymorphism in specific regions of the sic gene was observed among isolates; however, this polymorphism was not associated with disease severity. Likewise, although the phenotypic expression of SpeA, SpeB, and SpeF proteins varied among the M1T1 isolates, there was no correlation between the amount of Spe expressed and disease severity. Importantly, mitogenic and cytokine responses induced by partially purified bacterial culture supernatants containing a mixture of expressed superantigens were very similar for isolates from severe and nonsevere cases (P > 0.1). Together, the data indicate that highly related invasive M1T1 isolates, some indistinguishable, can cause disease of varying severity in different individuals. These findings underscore the contribution of host factors to the outcome of invasive GAS infections.

emm and sof gene sequence variation in relation to serological typing of opacity-factor-positive group A streptococci

Approximately 40-60% of group A streptococcal (GAS) isolates are capable of opacifying sera, due to the expression of the sof (serum opacity factor) gene. The emm (M protein gene) and sof 5' sequences were obtained from a diverse set of GAS reference strains and clinical isolates, and correlated with M serotyping and anti-opacity-factor testing results. Attempts to amplify sof from strains with M serotypes or emm types historically associated with the opacity-factor-negative phenotype were negative, except for emm12 strains, which were found to contain a highly conserved sof sequence. There was a strong correlation of certain M serotypes with specific emm sequences regardless of strain background, and likewise a strong association of specific anti-opacity-factor (AOF) types to sof gene sequence types. In several examples, M type identity, or partial identity shared between strains with differing emm types, was correlated with short, highly conserved 5' emm sequences likely to encode M-type-specific epitopes. Additionally, each of three pairs of historically distinct M type reference strains found to share the same 5' emm sequence, were also found to share M serotype specificity. Based upon sof sequence comparisons between strains of the same and of differing AOF types, an approximately 450 residue domain was determined likely to contain key epitopes required for AOF type specificity. Analysis of two Sof sequences that were not highly homologous, yet shared a common AOF type, further implicated a 107 aa portion of this 450-residue domain in putatively containing AOF-specific epitopes. Taken together, the serological data suggest that AOF-specific epitopes for all Sof proteins may reside within a region corresponding to this 107-residue sequence. The presence of specific, hypervariable emm/sof pairs within multiple isolates appears likely to be a reliable indicator of their overall genetic relatedness, and to be very useful for accurate subtyping of GAS isolates by an approach that has relevance to decades of past M-type-based epidemiological data.