Biology subjects

Baltazar, M.

Publications and source records attributed to Baltazar, M..

6 recordsLinked to original sources

bioRxiv2026

Tripartite toxin-antitoxin system regulates the production and release of pneumolysin by Streptococcus pneumoniae.

The production of toxins is critical to the success of bacteria, with their targets and outcomes varying widely. Pneumolysin (Ply), produced by the major human pathogen Streptococcus pneumoniae, is a cytolytic pore forming toxin that plays many diverse roles including inducing tissue damage and inflammation, evasion of many aspects of the human immune system, invasion of the bacteria into deeper tissue, and transmission to new hosts. Despite its importance, many aspects of the biology of this toxin have to date remained unknown, in particular, what role of the three other genes that form part of the ply operon play in Ply production. Here we demonstrate that these genes encode a complex regulatory system, that includes a putative membrane destabilising protein (PlyA) and a MazEF-like toxin-antitoxin system (PlyB and PlyC), the toxin of which (PlyC) destabilises the Ply transcript. We propose a tripartite model whereby when the operon reaches relatively high levels of expression PlyA destabilises the S. pneumoniae membrane creating a stress that triggers a necessary negative feedback loop which results in the degradation of the PlyB antitoxin, release of the PlyC toxin and degradation of the ply transcript, thereby providing a means by which Ply production can be tightly regulated. Given the importance of Ply to the ability of S. pneumoniae to cause infection, identifying the factors that result in the shutdown of Ply production and release by the bacteria would seem promising target for future therapeutic strategies.

microbiology↗

bioRxiv2024

The effect of surfactants and film-forming polymers on pulmonary surfactant function measured in vitro is dose-rate dependent

Surfactants and film-forming polymers are common ingredients in consumer spray products such as cleaning products, hair care products, and anti-perspirants. Spraying eases application by creating aerosolised droplets of the product that can distribute evenly over the treated surface. However, these aerosols can potentially be inhaled during their normal application. Droplets that reach the alveoli can interact with the pulmonary surfactant; a complex mixture of phospholipids and proteins that regulates the surface tension at the air-liquid interface. This interaction could elevate the minimum surface tension at maximum compression and change the surface rheology of the pulmonary surfactant at the interface. We tested four surfactants and seven polymers for their ability to inhibit pulmonary surfactant function in vitro and investigated if the inhibition is dose-rate dependent i.e., the product of the concentration (mg/mL) and aerosolisation rate (mL/min). We found that independent of chemical class (surfactant or polymer) there was a clear dose-rate dependent inhibition of pulmonary surfactant function and that different chemicals inhibited function at different dose-rates. We compared the points of departure of inhibitory chemicals to a polymer with known dose-rate dependent lung toxicity. When assessing the risk of chemicals that might be inhaled, it is essential to ensure normal use would not inhibit pulmonary surfactant function leading to immediate effects on the lungs. Lay summarySpray products create a cloud of tiny droplets in the air when they are used. This cloud can be inhaled, and if it reaches the deepest parts of the lungs, it can interact with the thin layer of liquid, called pulmonary surfactant, that covers the cells. It protects the lung tissue during the constant movement of breathing. Droplets can sometimes disrupt the pulmonary surfactant function, making breathing difficult. Chemicals that are used in spray products must be tested to assess if they are harmful if inhaled. In this project we studied the effect of chemicals that are commonly found in spray products on the functioning of the pulmonary surfactant in vitro. The results can be combined with other in vitro methods to test if chemicals are harmful to inhale without testing on animals.

biophysics↗

bioRxiv2024

The Streptococcus agalactiae LytSR two-component regulatory system promotes vaginal colonisation and virulence in vivo

Streptococcus agalactiae (or Group B Streptococcus, GBS) is a leading cause of neonatal sepsis and meningitis globally. To sense and respond to variations in its environment, GBS possesses multiple two-component regulatory systems (TCSs) such as LytSR. Here, we aimed to investigate the role of LytSR in GBS pathogenicity. We generated an isogenic lytS knockout mutant in a clinical GBS isolate and used a combination of phenotypic in vitro assays and in vivo murine models to investigate the contribution of lytS to the colonisation and invasive properties of GBS. Deletion of the lytS gene in the GBS chromosome resulted in significantly higher survival rates in mice during sepsis, accompanied by reduced bacterial loads in blood, lung, spleen, kidney and brain tissue compared to infection with the wild-type strain. In a mouse model of GBS vaginal colonisation, we also observed that the lytS knockout mutant was cleared more readily from the vaginal tract compared to its wild-type counterpart. Interestingly, lower levels of proinflammatory cytokines were found in the serum of mice infected with the lytS mutant. Our results demonstrate that the LytSR TCS plays a key role in GBS tissue invasion and pathogenesis, and persistence of mucosal colonisation. ImportanceStreptococcus agalactiae (Group B strep, or GBS) is a common commensal of the female urogenital tract and one of WHOs priority pathogens. The bacterium has evolved mechanisms to adapt and survive in its host, many of which are regulated via two-component signal transduction systems (TCSs), however, the exact contributions of TCSs towards GBS pathogenicity remain largely obscure. We have constructed a TCS lytS-deficient mutant in a CC-17 hypervirulent GBS clinical isolate. Using murine models, we showed that LytSR regulatory system is essential for vaginal colonisation via promoting biofilm production. We also observed that lytS deficiency led to significantly attenuated virulence properties and lower levels of proinflammatory cytokines in blood. Our findings are of significant importance in that they unveil a previously unreported role for LytSR in GBS and pave the way towards a better understanding of its ability to transition from an innocuous commensal to a deadly pathogen.

microbiology↗

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↗