The Integrative Conjugative Element ICESpyM92 Contributes to Pathogenicity of Emergent Antimicrobial-Resistant emm92 Group A Streptococcus.

Antimicrobial resistance-encoding mobile genetic elements (MGEs) may contribute to the disease potential of bacterial pathogens. We previously described the association of Group A Streptococcus (GAS) derived from invasive disease with increasingly frequent antimicrobial resistance (AMR). We hypothesized that a 65-kb AMR-encoding MGE (ICESpyM92), highly conserved among closely related emergent invasive emm92 GAS, contributes to GAS disease potential. Here, we provide evidence that a combination of ICESpyM92- and core genome-dependent differential gene expression (DGE) contributes to invasive disease phenotypes of emergent emm92 GAS. Using isogenic ICESpyM92 mutants generated in distinct emm92 genomic backgrounds, we determined the presence of ICESpyM92 enhances GAS virulence in a mouse subcutaneous infection model. Measurement of in vitro and ex vivo DGE indicates ICESpyM92 influences GAS global gene expression in a background-dependent manner. Our study links virulence and AMR on a unique MGE via MGE-related DGE and highlights the importance of investigating associations between AMR-encoding MGEs and pathogenicity.

Population Genomics Reveals Distinct Temporal Association with the Emergence of ST1 Serotype V Group B Streptococcus and Macrolide Resistance in North America.

Identified in the 1970s as the leading cause of invasive bacterial disease in neonates and young infants, group B Streptococcus (GBS) is now also recognized as a significant cause of morbidity and mortality among adults with underlying medical conditions and the elderly. Concomitant with the increasing incidence of GBS invasive disease in adults is the rise of resistance among GBS isolates to second line antibiotics. Previous research shows that among serotype V GBS, one of the most common capsular types causing adult invasive disease, sequence type 1 (ST1), accounts for an overwhelming majority of adult invasive disease isolates and frequently harbors macrolide resistance. In this study, using whole-genome sequencing data from strains isolated in the United States and Canada over a 45-year period, we examined the association of antimicrobial resistance with the emergence of invasive serotype V ST1 GBS. Our findings show a strong temporal association between increased macrolide resistance and the emergence of serotype V ST1 GBS subpopulations that currently co-circulate to cause invasive disease in adults and young infants. ST1 GBS subpopulations are defined, in part, by the presence of macrolide resistance genes in mobile genetic elements. Increased frequency of macrolide resistance-encoding mobile genetic elements among invasive GBS ST1 strains suggests the presence of such elements contributes to GBS virulence. Our work provides a foundation for the investigation of genetic features contributing to the increasing prevalence and pathogenesis of serotype V GBS in adult invasive disease.

Strain-Dependent Effect of Capsule on Transmission and Persistence in an Infant Mouse Model of Group A Streptococcus Infection.

Streptococcus pyogenes (group A Streptococcus [GAS]) is a human pathogen responsible for a wide range of diseases. Asymptomatic carriage of GAS in the human pharynx is commonplace and a potential reservoir for GAS transmission. Early studies showed that GAS transmission correlated with high bacterial burdens during the acute symptomatic phase of the disease. Human studies and the nonhuman primate model are generally impractical for investigation of the bacterial mechanisms contributing to GAS transmission and persistence. To address this gap, we adapted an infant mouse model of pneumococcal colonization and transmission to investigate factors that influence GAS transmission and persistence. The model recapitulated the direct correlation between GAS burden and transmission during the acute phase of infection observed in humans and nonhuman primates. Furthermore, our results indicate that the ratio of colonized to uncolonized hosts influences the rates of GAS transmission and persistence. We used the model to test the hypothesis that capsule production influences GAS transmission and persistence in a strain-dependent manner. We detected significant differences in rates of transmission and persistence between capsule-positive (emm3) and capsule-negative (emm87) GAS strains. Capsule was associated with higher levels of GAS shedding, independent of the strain background. In contrast to the capsule-positive emm3 strain, restoring capsule production in emm87 GAS did not increase transmissibility, and the absence of capsule enhanced persistence only in the capsule-negative (emm87) strain background. These data suggest that strain background (capsule positive versus capsule negative) influences the effect of capsule in GAS transmission and persistence and that as-yet-undefined factors are required for the transmission of capsule-negative emm types.

Identification of epidemic scarlet fever group A Streptococcus strains in the paediatric population of Houston, TX, USA.

Scarlet fever (SF) has recently been associated with group A streptococcal (GAS) strains possessing multidrug resistance and specific streptococcal exotoxins. We screened a local surveillance collection of GAS emm12 strains in Houston, TX, USA for antimicrobial resistance and identified a single isolate matching the antimicrobial resistance pattern previously reported for SF clones. Using whole-genome sequencing and combining genome sequence data derived from national surveillance databases, we identified additional emm12 GAS clones similar to those associated with prior SF outbreaks, emphasizing the need for continued surveillance for epidemic emergence in the USA.

Unexpected relationships between frequency of antimicrobial resistance, disease phenotype and emm type in group A Streptococcus.

Despite universal susceptibility to ß-lactams, resistance to second-line antimicrobials (e.g. erythromycin) is increasingly common among group A Streptococcus (GAS). To better understand the frequency of regional GAS antimicrobial resistance, we screened a previously described GAS strain collection from Houston, TX, USA, for resistance to commonly used antimicrobials. A total of 100/929 (10.8 %) showed resistance to at least one antimicrobial. Tetracycline resistance was identified in 52 (5.6 %) GAS strains. The cumulative frequency of erythromycin and clindamycin resistance [macrolide (M) and macrolide-lincosamide-streptogramin (MLS) phenotypes] was greatest among invasive GAS strains (9.9 %) compared to that of strains derived from any other infection type (5.9 %, P=0.045). We identified emm types 11, 75, 77 and 92 as the only emm types with high (e.g. >50 %) within-emm type resistance and contributing to the majority (24/26; 92 %) of erythromycin/clindamycin resistance in invasive GAS. High-frequency resistance emm types were also significantly overrepresented in invasive GAS strains as indicated by invasive index. We performed whole-genome sequencing to define genetic elements associated with resistance among emm types 11, 75, 77 and 92. Diverse mobile elements contributed to GAS resistance including transposons, integrative conjugative elements, prophage and a plasmid. Phylogenetic analysis suggests recent clonal emergence of emm92 GAS strains. Our findings indicate that less frequently encountered GAS emm types disproportionately contribute to resistance phenotypes, are defined by diverse mobile genetic elements and may favour invasive disease.

Identification of a chimeric emm gene and novel emm pattern in currently circulating strains of emm4 Group A Streptococcus.

Group A Streptococcus (GAS) is classified on the basis of the sequence of the gene encoding the M protein (emm) and the patterns into which emm types are grouped. We discovered a novel emm pattern in emm4 GAS, historically considered pattern E, arising from a fusion event between emm and the adjacent enn gene. We identified the emm-enn fusion event in 51 out of 52 emm4 GAS strains isolated by national surveillance in 2015. GAS isolates with an emm-enn fusion event completely replaced pattern E emm4 strains over a 4-year span in Houston (2013-2017). The novel emm-enn gene fusion and new emm pattern has potential vaccine implications.