Biology subjects

Kadioglu, A.

Publications and source records attributed to Kadioglu, A..

9 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↗

bioRxiv2025

Resistance mutation supply modulates the benefit of CRISPR immunity against virulent phages

Only a fraction of bacterial genomes encode CRISPR-Cas systems but the selective causes of this variation are unexplained. How naturally virulent bacteriophages (phages) select for CRISPR immunity has rarely been tested experimentally. Here, we show against a panel of genetically and functionally diverse virulent phages that CRISPR immunity was not universally beneficial, and its fitness effect varied strongly between phages in predictable ways. In addition to mechanisms known to alter the effectiveness of CRISPR immunity, such as encoding a matching spacer or a protective nuclear shell, we show that the fitness effect of CRISPR immunity negatively correlated with the probability of evolving receptor-based resistance to the phage via spontaneous mutation. Supply of resistance mutations differed strongly between very closely related lipopolysaccharide-binding phages and was associated with variation at the C-terminus of the tail fibre protein altering residues involved in hydrogen bonding and the predicted binding site. Our results show that CRISPR immunity is more beneficial against virulent phages that are harder to evolve resistance to via receptor mutations, suggesting that virulent phage community composition and diversity will be important drivers of the prevalence of CRISPR immunity.

microbiology↗

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

Pseudomonas aeruginosa utilises host-derived polyamines to facilitate antimicrobial tolerance

Pseudomonas aeruginosa undergoes diversification during infection of the cystic fibrosis (CF) lung. Understanding these changes requires model systems that capture the complexity of the CF lung environment. We previously identified loss-of-function mutations in the two-component regulatory system sensor kinase gene pmrB, in P. aeruginosa from CF and from experimental infection of mice. Here, we demonstrate that whilst such mutations lower in vitro MICs for multiple antimicrobial classes, this is not reflected in increased antibiotic susceptibility in vivo. Loss of PmrB impairs aminoarabinose modification of lipopolysaccharide, increasing the negative charge of the outer membrane and promoting uptake of cationic antimicrobials. However, in vivo, this can be offset by increased membrane binding of other positively charged molecules present in lungs. The polyamine spermidine readily coats the surface of PmrB-deficient P. aeruginosa, reducing susceptibility to antibiotics that rely on charge differences to bind the outer membrane and increasing biofilm formation. Spermidine is elevated in lungs during P. aeruginosa infection in mice and during episodes of antimicrobial treatment in people with CF. These findings highlight the need to study antimicrobial resistance under clinically relevant environmental conditions. Microbial mutations carrying fitness costs in vitro may be advantageous during infection, where host resources can be utilised.

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↗

bioRxiv2021

Long term nasopharyngeal colonization by Staphylococcus aureus determinants of adaptation

Staphylococcus aureus nasal colonization is a risk factor for infection. A large proportion of the population are identified as potential S. aureus carriers yet we only partially understand the repertoire of genetic factors that promote long-term nasal colonization. Here we present a novel murine model of nasopharyngeal colonization that requires a low S. aureus inoculum and is amenable to experimental evolution approaches. We used this model to experimentally evolve S. aureus using successive passages in the nasopharynx to identify those genetic loci under selection. After 3 cycles of colonization, mutations were identified in mannitol, sorbitol, arginine, nitrite and lactate metabolism genes promoting key pathways in nasal colonization. Stress responses were identified as being under selective pressure, with mutations in DNA repair genes including dnaJ and recF and key stress response genes clpL, rpoB and ahpF. Peptidoglycan synthesis pathway genes also revealed mutations indicating potential selection for alteration of the cell surface. The infection model used here is versatile to assist decolonization and persistence studies.

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↗

bioRxiv2019

An alanine permease mutation or exposure to D-cycloserine re-sensitizes MRSA to beta-lactam antibiotics

Prolonging the clinical effectiveness of {beta}-lactams, which remain first-line antibiotics for many infections, is an important part of efforts to address antimicrobial resistance. We report here that inactivation of the predicted D-cycloserine (DCS) transporter gene cycA re-sensitized MRSA to {beta}-lactam antibiotics. The cycA mutation also resulted in hyper-susceptibility to DCS, an alanine analogue antibiotic that inhibits alanine racemase and D-alanine ligase required for D-alanine incorporation into cell wall peptidoglycan (PG). Alanine transport was impaired in the cycA mutant and this correlated with increased susceptibility to oxacillin and DCS. The cycA mutation or exposure to DCS were both associated with the accumulation of muropeptides with tripeptide stems lacking the terminal D-ala-D-ala and reduced PG crosslinking, prompting us to investigate synergism between {beta}-lactams and DCS. DCS re-sensitised MRSA to {beta}-lactams in vitro and significantly enhanced MRSA eradication by oxacillin in a mouse bacteraemia model. These findings reveal alanine transport as a new therapeutic target to enhance the susceptibility of MRSA to {beta}-lactam antibiotics.

microbiology↗