Streptolysin production and activity is central toin vivopathotype and disease outcome in GAS infections

Abstract

27Streptococcus pyogenes (GAS) is among the most diverse of all human pathogens, responsible 28 for a range of clinical manifestations, from mild superficial infections such as pharyngitis to 29 serious invasive infections such as necrotising fasciitis and sepsis. The drivers of these different 30 disease phenotypes are not known. The GAS cholesterol-dependent cytolysin, streptolysin O 31 (SLO), has well established cell and tissue destructive activity. We investigated the role of SLO 32 in determining disease outcome in vivo, by using two different clinical lineages; the recently 33 emerged hypervirulent outbreak emm type 32.2 strains, which result in sepsis, and the emm 34 type 1.0 strains which cause septic arthritis. Using clinically relevant in vivo mouse models of 35 sepsis and a novel septic arthritis model, we demonstrated that the amount and activity of SLO 36 is vital in determining the pathotype of infection. The emm32.2 strain produced large quantities 37 of highly haemolytic SLO that resulted in rapid development of sepsis. By contrast, the lower 38 levels and haemolytic activity of emm1.0 SLO led to translocation of bacteria to joints. 39 Importantly, sepsis associated strains that were attenuated by deletion or inhibition of SLO also 40 translocated to the joint, confirming the key role of SLO in determining infection niche. Our 41 findings demonstrate that SLO is key to in vivo pathotype and disease outcome. Careful 42 consideration should be given to novel therapy or vaccination strategies that target SLO. Whilst 43 neutralising SLO activity may reduce severe invasive disease, it has the potential to promote 44 chronic inflammatory conditions such as septic arthritis. 45 46 47 48 49 50 51 Group A Streptococcus (GAS), also called Streptococcus pyogenes, is a commensal of the 53 human upper respiratory tract and also an important human pathogen, accounting for over 750 54 million infections every year 1,2 . GAS is able to produce a variety of pyogenic infections that 55 range in severity and prevalence 3-5 . Diseases include pharyngitis, impetigo, cellulitis and more 56 life threating infections such as streptococcal toxic shock syndrome, necrotising fasciitis, and 57 sepsis 3,6 . The mechanisms that allow GAS to cause such diversity in disease types are 58 unknown, however a number of studies have shown that bacterial and host-specific components 59 may be involved 7 . 60 61 GAS strains are typed based on the sequence of the emm gene, which encodes the M-protein, 62 of which there are over 200 known emm types 8 . The epidemiology of GAS infections has been 63 changing globally over the last decade, with the emergence of new emm types and localised 64 outbreaks a main feature 9 . Within emm types of GAS, isolates may be causative of a range of 65 clinical outcomes, such that most lineages carry the potential for expression of a range of 66 phenotypes that may determine the course and nature of infection. Recent studies have shown 67 distinct correlations between the host niche of recovered GAS clin...