Biology subjects

Baltazar, M.

Publications and source records attributed to Baltazar, M..

3 recordsLinked to original sources

bioRxiv2023

Hypervirulent pneumococci display high levels of nasopharyngeal shedding and rapid onward transmission

Streptococcus pneumoniae serotype 1 is a major cause of invasive pneumococcal disease. Despite its high attack rate, serotype 1 exhibits a low carriage prevalence within the population, which raises important questions about the relationship between carriage and transmission of hypervirulent pneumococcal strains between individuals. We compared the transmission dynamics of serotype 1 sequence type ST217 to serotype 2 strain D39 using a novel model of transmission in young adult mice. Donor index mice were intranasally infected with ST217, D39 or isogenic pneumolysin-deficient mutants and co-housed with recipient naive contact mice. Three days later, all mice were infected with influenza A virus (IAV). Pneumococcal transmission was analysed during colonisation alone and co-infection with IAV by quantification of shedding and nasal colonisation in index and contact mice. The role of the toxin pneumolysin in shedding, transmission and colonisation, and the host nasopharyngeal immune response were investigated. We show that ST217 was shed in index mice at significantly greater levels compared to D39. Upon viral co-infection, ST217 was shed and transmitted at a faster rate to contact mice and displayed higher transmission levels compared to D39. Interestingly, the toxin pneumolysin did not play a role in shedding. However, upon acquisition by contact mice, pneumolysin-dependent macrophage recruitment was observed in the nasopharynx. Our results show that the rapid and high transmission rate of serotype 1 is a key factor in its ability to disseminate quickly within the population and cause disease outbreaks.

microbiology↗

bioRxiv2021

Streptococcus pneumoniae rapidly translocates from the nasopharynx through the cribriform plate to invade and inflame the dura

The entry routes and translocation mechanisms of bacterial pathogens into the central nervous system remain obscure. We report here that Streptococcus pneumoniae (Sp) or polystyrene microspheres, applied to the nose of a mouse, appeared in the meninges of the dorsal cortex within minutes. Recovery of viable bacteria from dissected tissue and fluorescence microscopy showed that up to at least 72h, Sp and microspheres were predominantly in the outer of the two meninges, the pachymeninx. No Sp were found in blood or cerebrospinal fluid. Evidence that this was not an artifact of the method of administration is that in mice infected by horizontal transmission, Sp were also predominantly in the meninges and absent from blood. Intravital imaging through the skull, and flow cytometry showed recruitment and activation of LysM+ cells in the dorsal pachymeninx at 5h and 10h following intranasal infection. Imaging of the cribriform plate suggested that both Sp and microspheres entered through its foramina via an inward flow of fluid connecting the nose to the pachymeninx. Our findings bring further insight into the invasion mechanisms of bacterial pathogens such as Sp into the central nervous system, but are also pertinent to the delivery of drugs to the brain, and the entry of air-borne particles into the cranium.

microbiology↗

bioRxiv2019

Streptolysin production and activity is central to in vivo pathotype and disease outcome in GAS infections

Streptococcus pyogenes (GAS) is among the most diverse of all human pathogens, responsible for a range of clinical manifestations, from mild superficial infections such as pharyngitis to serious invasive infections such as necrotising fasciitis and sepsis. The drivers of these different disease phenotypes are not known. The GAS cholesterol-dependent cytolysin, streptolysin O (SLO), has well established cell and tissue destructive activity. We investigated the role of SLO in determining disease outcome in vivo, by using two different clinical lineages; the recently emerged hypervirulent outbreak emm type 32.2 strains, which result in sepsis, and the emm type 1.0 strains which cause septic arthritis. Using clinically relevant in vivo mouse models of sepsis and a novel septic arthritis model, we demonstrated that the amount and activity of SLO is vital in determining the pathotype of infection. The emm32.2 strain produced large quantities of highly haemolytic SLO that resulted in rapid development of sepsis. By contrast, the lower levels and haemolytic activity of emm1.0 SLO led to translocation of bacteria to joints. Importantly, sepsis associated strains that were attenuated by deletion or inhibition of SLO also translocated to the joint, confirming the key role of SLO in determining infection niche. Our findings demonstrate that SLO is key to in vivo pathotype and disease outcome. Careful consideration should be given to novel therapy or vaccination strategies that target SLO. Whilst neutralising SLO activity may reduce severe invasive disease, it has the potential to promote chronic inflammatory conditions such as septic arthritis.

microbiology↗