Invasive group A Streptococcus (iGAS) is frequently associated with emm1 isolates, with an attendant mortality of around 20%. Cases occasionally arise in previously healthy individuals with a history of upper respiratory tract infection, soft tissue contusion, and no obvious portal of entry. Using a new murine model of contusion, we determined the impact of contusion on iGAS bacterial burden and phenotype.Calibrated mild blunt contusion did not provide a focus for initiation or seeding of GAS that was detectable following systemic GAS bacteremia, but instead enhanced GAS migration to the local draining lymph node following GAS inoculation at the same time and site of contusion. Increased migration to lymph node was associated with emergence of mucoid bacteria, although was not specific to mucoid bacteria. In one study, mucoid colonies demonstrated a significant increase in capsular hyaluronan that was not linked to a covRS or rocA mutation, but to a deletion in the promoter of the capsule synthesis locus, hasABC, resulting in a strain with increased fitness for lymph node migration.In summary, in the mild contusion model used, we could not detect seeding of muscle by GAS. Contusion promoted bacterial transit to the local lymph node. The consequences of contusion-associated bacterial lymphatic migration may vary depending on the pathogen and virulence traits selected.

Objectives: During a prospective study of S. aureus carriage in Royal Marines (RM) recruits, six S. argenteus strains were identified in four recruits undertaking military training together. As S. argenteus sepsis leads to mortality similar to S. aureus, we determined the potential for person-to-person transmission, to evaluate future outbreak risk. Methods: We used whole-genome sequencing to characterise S. argenteus and investigate phylogenetic relationships between isolates. Participant colonisation with S. aureus and skin and soft tissue infection acquisition were recorded. Results: All six S. argenteus strains were spa-type t5078, ST2250. Strains were detected in 4/40 recruits in the same troop (training cohort) in weeks 1, 6 or 15 of training. No mec, tsst or LukPV genes were detected. We identified differences of 10-35 core SNPs between S. argenteus from different recruits. In two recruits, two S. argenteus strains were isolated; these could be distinguished by 3 and 15 core SNPs in each case. S. argenteus was not identified in any one of the other 21 participating troops (1,012 recruits). Conclusions: The identification of S. argenteus within a single troop from the total recruit population supports a common source for transmission, supported by SNP analysis. The high number of SNPs between some isolates may indicate a common source of diverse isolates or a high level of S. argenteus mutation in carriage. S. argenteus ST2250 is a newly recognised lineage; a better understanding of the frequency of genetic changes during transmission and transition from asymptomatic carriage to disease is required.