Biology subjects

Massey, R. C.

Publications and source records attributed to Massey, R. C..

At least 19 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↗

bioRxiv2026

Human serum triglycerides promote Staphylococcus aureus biofilm formation and antibiotic tolerance

Biofilm formation and antibiotic tolerance are major contributors to the persistence of Staphylococcus aureus infections, yet how the host environment affects these phenotypes remains poorly understood. Here, we show that incubation in human serum primes S. aureus to form robust biofilms and tolerate vancomycin and daptomycin, last resort antibiotics for the treatment of antibiotic-resistant staphylococcal infections. Mechanistically, we demonstrate that the staphylococcal Geh lipase is essential for serum-induced biofilm formation by liberating glycerol from host lipids, which is then used to promote increased synthesis of D-alanylated wall teichoic acids, driving biofilm development. Inhibition of the Geh lipase or wall teichoic acid synthesis markedly reduces biofilm formation and restores antibiotic susceptibility, highlighting clinically achievable strategies to inhibit host-induced biofilm formation and prevent the associated antibiotic tolerance. Together, our findings reveal a host-driven mechanism of biofilm-associated antibiotic tolerance in S. aureus and provide rational targets for therapeutic intervention.

microbiology↗

bioRxiv2026

Copper as a central element critical to interkingdom interactions within a polymicrobial wound environment.

Staphylococcus aureus is a global health concern, estimated to cause over one million deaths each year. To colonise and survive in humans, S. aureus must overcome the host-immune system and compete with other native and invading microorganisms. As a frequent coloniser of wounds, it forms inter-kingdom polymicrobial biofilms, which are associated with impaired wound healing and poorer clinical outcomes. However, the microbial processes that contribute to the competitiveness of S. aureus within infection-related inter-kingdom communities are poorly understood. To address this, we established a polymicrobial in vitro wound-like model (WLM) consisting of two common bacterial pathogens Staphylococcus aureus and Pseudomonas aeruginosa, as well as a the fungal pathobiont Candida albicans. Using a collection of clinical S. aureus strains we then applied a genome-wide association study (GWAS) approach to identify bacterial factors that contribute to S. aureus fitness within this environment. Amongst the six S. aureus loci identified was copA, which encodes a copper exporter that prevents the accumulation of copper in the bacterial cytoplasm. Characterising the molecular processes involved, we identified a 4-way interaction, where C. albicans releases copper from the ceruloplasmin found in the human hosts plasma, which in turn causes a build-up of copper within the S. aureus cytoplasm, rendering the bacteria more susceptible to killing by P. aeruginosa. Human infection data validates the clinical relevance of this, where there is an association between mutations in copA and an origin of infection that is wound-based, highlighting the importance of understanding the entire infection ecosystem if improvements therapeutic approaches are to be developed.

microbiology↗

bioRxiv2026

Metabolic reprogramming promotes Staphylococcus aureus serum resistance during bacteraemia.

Staphylococcus aureus is a leading cause of bloodstream infections causing an estimated 300,000 deaths worldwide. Using a functional genomics approach, our group previously identified that adaptation of S. aureus to human serum is polygenic, with a clinically occurring non-synonymous mutation (V76I) in dihydrolipoamide dehydrogenase (lpdA1/pdhD) improving bacterial survival. In this work we establish that improved serum survival of strains expressing PdhD V76I is underpinned by enhanced resistance to host-derived antimicrobials including antimicrobial peptides and host-defence fatty acids which are prevalent in the bloodstream. Here we demonstrate that the PdhD V76I variant has enhanced diaphorase activity, with both clinical and laboratory strains expressing this variant recycling NADH to NAD+ without using respiration, leading to a reduction in membrane potential. This conferred persister / small colony variant (SCV) like phenotypes on strains expressing PdhD V76I including increased resistance to gentamicin, hydrogen peroxide, LL37, HNP-1 and arachidonic acid. However, strains which utilise PdhD V76I do not display growth defects typical of persisters and SCVs, with reduced NADH accumulation in serum leading to enhanced glycolysis/TCA cycle activity, enhancing bacterial replication in human serum. Whilst establishment of SCV and persister populations is a key survival strategy in the bloodstream, this work demonstrates how intermediate phenotypes can also be effective at promoting survival in this hostile environment. This highlights the heterogenous nature of S. aureus adaptation to the host-environment, with an improved fundamental understanding of these processes required to allow for the development of novel therapeutics which target this process of host-adaptation. IMPORTANCEThe establishment of a bloodstream infection requires the bacteria to be able to withstand the antibacterial factors found there. As one of the major global causes of these types of infections, S. aureus, utilises many diverse strategies to survive and replicate in the bloodstream, which can include modifications to either the cell envelope, or to core metabolic processes such that the hosts immune features are withstood. While extreme adaptations to metabolism can lead to the major growth defects associated with persisters and small colony variants, here we describe a clinically relevant adaption where metabolism was altered such that the bacteria could survive and replicate in serum, but where the growth characteristics of the bacteria were not affected. Mutation of the gene encoding the dihydrolipoamide dehydrogenase enzyme (lpdA1/pdhD) enhanced it diaphorase activity such that it could recycle NADH to NAD+ without using respiration, which led a reduction in membrane potential that conferred resistance to gentamicin, hydrogen peroxide, LL37, HNP-1 and arachidonic acid and human serum, but did not affect growth. This work uncovers a novel mean of adaptation to the bloodstream by S. aureus and highlights how it plasticity underlies its success as a major human pathogen.

microbiology↗

bioRxiv2025

Phosphate sensing by PhoPR regulates the cytotoxicity of Staphylococcus aureus

Staphylococcus aureus has evolved a complex regulatory network to coordinate expression of virulence factors, including cytolytic toxins, with host environmental signals. Central to this network are two-component systems, in which a histidine kinase senses an external signal and activates a response regulator via phosphorylation, leading to changes in gene expression. Using a comprehensive screen of transposon mutants in each of the non-essential histidine kinase and response regulatory genes in S. aureus, we demonstrate that 11 of these 16 systems regulate cytotoxicity. Further characterisation of a phoP mutant revealed that its impact on cytotoxicity is mediated through the Agr quorum-sensing system. Notably, we found that unphosphorylated PhoP is an activator of Agr activity, while phosphorylated PhoP also acts as a weak activator of Agr activity in high phosphate environments but as a repressor in low phosphate environments. Overall, we have demonstrated that phosphate sensing through PhoPR is a novel regulator of cytotoxicity in S. aureus. Moreover, our study challenges the canonical model of TCSs as simple on/off systems and highlights the importance of unphosphorylated response regulators in gene regulation. ImportanceThe production of cytolytic toxins is the major means by which bacterial pathogens damage host tissue and cause disease. Understanding the activity and regulation of these toxins is critical for the identification of means to block them and prevent the development of disease. In this study we focused on a specific regulatory mechanism, the two-component systems (TCSs), that enable bacteria to sense their environment and adapt accordingly. In the traditional model of a TCS, a response regulator (RR) is phosphorylated by a histidine kinase (HK), which enables it to activate or repress expression of target genes, which may include toxins or regulators of toxins. We found that 11 of S. aureus 16 TCSs affect toxin production, highlighting that S. aureus integrates a broad range of environmental cues to regulate toxicity. We focused on one of these TCSs, the PhoPR system and found that sensing of inorganic phosphate is a novel regulator of cytotoxicity in S. aureus. Furthermore, we found that the RR of this system acts as a strong activator of toxicity in its unphosphorylated form, challenging the traditional model of a TCS as only active upon signal activation.

microbiology↗

bioRxiv2025

Expression of mecA reduces the daptomycin susceptibility of Staphylococcus aureus

Staphylococcus aureus is a leading cause of bacteraemia and infections caused by methicillin-resistant strains (MRSA) are especially challenging to treat. MRSA strains are resistant to front-line beta-lactams due to PBP2a, a low-affinity penicillin-binding protein encoded by mecA. Daptomycin is used to treat MRSA infections but is not always effective and is associated with high rates of morbidity and mortality. Understanding why daptomycin fails is crucial to devising strategies to improve treatment outcomes. Here, using a panel of clinical bacteraemia isolates, we show that MRSA strains are less susceptible to daptomycin than methicillin-susceptible (MSSA) strains. This difference in susceptibility was due to mecA and was independent of any changes in surface properties previously associated with altered daptomycin susceptibility. Instead, using a mecA transposon mutant, we found that a lack of this gene led to higher activity of the Agr quorum sensing system, resulting in an increased release of the phenol-soluble modulin toxins. Increased levels of these surfactant-like toxins prevented daptomycin from being inactivated by lipids released by the bacteria, leading to enhanced susceptibility to the antibiotic. Additionally, the clinical MRSA strains tested produced lower levels of toxins than the MSSA strains and inactivated daptomycin to a greater extent, explaining their reduced susceptibility. Expression of mecA in clinical MSSA strains reduced toxin production, increasing daptomycin inactivation and thereby enhancing survival. Together, these results demonstrate that mecA does not only affect beta-lactam susceptibility but also compromises the efficacy of the last resort antibiotic daptomycin.

microbiology↗

bioRxiv2024

PBP4 is required for serum-induced cell wall thickening and antibiotic tolerance in Staphylococcus aureus

The bacterial pathogen Staphylococcus aureus responds to the host environment by synthesising a thick peptidoglycan cell wall which protects the bacterium from membrane-targeting antimicrobials and the immune response. However, the proteins required for this response were previously unknown. Here, we demonstrate by three independent approaches that the penicillin binding protein PBP4 is crucial for serum-induced cell wall thickening. Firstly, mutants lacking various non-essential cell wall synthesis enzymes were tested, revealing that a mutant lacking pbp4 was unable to generate a thick cell wall in serum. This resulted in reduced serum-induced tolerance of the pbp4 mutant towards the last resort antibiotic daptomycin relative to wildtype cells. Secondly, we found that serum-induced cell wall thickening occurred in each of a panel of 134 clinical bacteraemia isolates, except for one strain with a naturally-occurring mutation that confers a S140R substitution in the active site of PBP4. Finally, inhibition of PBP4 with cefoxitin prevented serum-induced cell wall thickening and the resulting antibiotic tolerance in the USA300 strain and in clinical MRSA isolates. Together, this provides a rationale for combining daptomycin with cefoxitin, a PBP4 inhibitor, to potentially improve treatment outcomes for patients with invasive MRSA infections.

microbiology↗

bioRxiv2023

The mutational landscape of Staphylococcus aureus during colonisation

Staphylococcus aureus is an important human pathogen but is primarily a commensal of the human nose and skin. Survival during colonisation is likely one of the major drivers of S. aureus evolution. Here we use a genome-wide mutation enrichment approach to analyse a genomic dataset of 3,060 S. aureus isolates from 791 individuals to show that despite limited within-host genetic diversity, an excess of protein-altering mutations can be found in genes encoding key metabolic pathways, in regulators of quorum-sensing and in known antibiotic targets. Nitrogen metabolism and riboflavin synthesis are the metabolic processes with strongest evidence of adaptation. Further evidence of adaptation to nitrogen availability was revealed by enrichment of mutations in the assimilatory nitrite reductase and urease, including mutations that enhance growth with urea as the sole nitrogen source. Inclusion of an additional 4,090 genomes from 802 individuals revealed eight additional genes including sasA/sraP, pstA, and rsbU with signals adaptive variation that warrant further characterisation. Our study provides the most comprehensive picture to date of the heterogeneity of adaptive changes that occur in the genomes of S. aureus during colonisation, revealing the likely importance of nitrogen metabolism, loss of quorum sensing and antibiotic resistance for successful human colonisation.

genomics↗

bioRxiv2023

Lipoteichoic acid biosynthesis by Staphylococcus aureus is controlled by the MspA protein through competitive interference.

Staphylococcus aureus produces a plethora of virulence factors critical to its ability to establish an infection and cause disease. We have previously characterised a small membrane protein, MspA, which has pleiotropic affects on virulence and contributes to S. aureus pathogenicity in vivo. Here we report that mspA inactivation triggers overaccumulation of the essential cell wall component lipoteichoic acid (LTA) which, in turn, decreases autolytic activity and leads to increased cell size due to a delay in cell separation. We show that MspA directly interacts with the LTA synthesis enzymes UgtP, LtaA and LtaS, and competitively interferes with the association between LtaA and LtaS. While complementation of the mspA mutant with wild-type mspA reduces the amount of LTA, expression of a mutated version of MspA that does not interfere with the interactions between LtaA and LtaS does not. We suggest that MspA contributes to maintaining a physiological level of LTA in the cell wall by interacting with the LTA synthetic enzymes. In conclusion, this study uncovers the critical role of the MspA protein in regulating cell envelope biosynthesis and pathogenicity. IMPORTANCEThe S. aureus cell envelope, comprising of the cytoplasmic membrane, a thick peptidoglycan layer and the anionic polymers lipoteichoic acid and wall teichoic acids, is fundamental for bacterial growth and division, as well as being the main interface between the pathogen and the host. It has become increasingly apparent that the synthesis and turnover of cell envelope components also affect the virulence of S. aureus. In this study, we show that MspA, a novel effector of S. aureus virulence, contributes to the maintenance of normal levels of lipoteichoic acid in the cell wall, with implications on cell cycle and size. These findings further our understanding of the connections between envelope synthesis and pathogenicity and suggests MspA as a novel a target for therapeutic intervention.

microbiology↗

bioRxiv2023

Extensive re-modelling of the cell wall during the development of Staphylococcus aureus bacteraemia

Introductory Paragraph / AbstractThe bloodstream represents a hostile environment that bacteria must overcome to cause bacteraemia. To understand how the major human pathogen Staphylococcus aureus manages this we have utilised a functional genomics approach to identify a number of new loci that affect the ability of the bacteria to survive exposure to serum, the critical first step in the development of bacteraemia. The expression of one of these genes, tcaA, was found to be induced upon exposure to serum, and we show that it is involved in the elaboration of a critical virulence factor, the wall teichoic acids (WTA), within the cell envelope. The activity of the TcaA protein alters the sensitivity of the bacteria to cell wall attacking agents, including antimicrobial peptides, human defence fatty acids, and several antibiotics. This protein also affects the autolytic activity and lysostaphin sensitivity of the bacteria, suggesting that in addition to changing WTA abundance in the cell envelope, it also plays a role in peptidoglycan crosslinking. With TcaA rendering the bacteria more susceptible to serum killing, while simultaneously increasing the abundance of WTA in the cell envelope, it was unclear what effect this protein may have during infection. To explore this, we examined human data and performed murine experimental infections. Collectively, our data suggests that whilst mutations in tcaA are selected for during bacteraemia, this protein positively contributes to the virulence of S. aureus through its involvement in altering the cell wall architecture of the bacteria, a process that appears to play a key role in the development of bacteraemia.

microbiology↗

bioRxiv2022

A high-throughput cytotoxicity screening platform reveals agr-independent mutations in bacteraemia-associated Staphylococcus aureus that promote intracellular persistence

Staphylococcus aureus infections are associated with high mortality rates. Often considered an extracellular pathogen, S. aureus can persist and replicate within host cells, evading immune responses and causing host cell death. Classical methods for assessing S. aureus cytotoxicity are limited by testing culture supernatants and endpoint measurements that do not capture the phenotypic diversity of intracellular bacteria. Using a well-established epithelial cell line model, we have developed a platform called InToxSa (Intracellular Toxicity of S. aureus) to quantify intracellula cytotoxic S. aureus phenotypes. Studying a panel of 387 S. aureus bacteraemia isolates, and combined with comparative, statistical and functional genomics, our platform identified mutations in S. aureus clinical isolates that reduced bacterial cytotoxicity and promoted intracellular persistence. In addition to numerous convergent mutations in the Agr quorum sensing system, our approach detected mutations in other loci that also impacted cytotoxicity and intracellular persistence. We discovered that clinical mutations in ausA, encoding the aureusimine non-ribosomal peptide synthetase, reduced S. aureus cytotoxicity and increased intracellular persistence. InToxSa is a versatile, high-throughput cell-based phenomics platform and we showcase its utility by identifying clinically relevant S. aureus pathoadaptive mutations that promote intracellular residency.

microbiology↗

bioRxiv2022

Wall teichoic acids facilitate the release of toxins from the surface of Staphylococcus aureus.

A major feature of the pathogenicity of Staphylococcus aureus is its ability to secrete cytolytic toxins. This process involves the translocation of the toxins from the cytoplasm, through the bacterial membrane and the cell wall to the external environment. The process of their movement through the membrane is relatively well defined, involving both general and toxin-specific secretory systems. Movement of the toxins through the cell wall was considered to involve the passive diffusion of the proteins through the porous cell wall structures, however, recent work suggests that this is more complex, and here we demonstrate a role for the wall teichoic acids (WTA) in this process. Utilising a genome-wide association approach we identified a polymorphism in the locus encoding the WTA biosynthetic machinery as associated with the cytolytic activity of the bacteria. We verified this association using an isogenic mutant set and found that WTA is required for the release of several cytolytic toxins from the bacterial cells. We show this effect is mediated by a change in the electrostatic charge across the cell envelope that results from the loss of WTA. As a major target for the development of novel therapeutics, it is important that we fully understand the entire process of cytolytic toxin production and release. These findings open up a new aspect to this process that requires in-depth investigation, while also demonstrating that clinical isolates can utilise WTA production to vary their cytotoxicity, thereby altering their pathogenic capabilities. ImportanceThe production and release of cytolytic toxins is a critical aspect to the pathogenicity of many bacterial pathogens. In this study we demonstrate a role for wall teichoic acids, molecules that are anchored to the peptidoglycan of the bacterial cell wall, in the release of toxins from S. aueus cells into the extracellular environment. Our findings suggest this effect is mediated by a gradient of electrostatic charge the presence of the negatively charged WTA molecules create across the cell envelope. This work brings an entirely new aspect to our understanding of the cytotoxicity of S. aureus and demonstrates a further means by which this major human pathogen can adapt its pathogenic capabilities.

microbiology↗

bioRxiv2021

Self-sensitisation of Staphylococcus aureus to the antimicrobial factors found in human blood.

Introductory ParagraphFor opportunistic pathogens, the switch from a commensal to an invasive lifestyle is often considered an accidental event. But with plentiful opportunity, what leads one accidental event to result in an invasive infection, and another not to? And how much of this apparent stochasticity is driven by bacterial factors? To answer these questions, here we focussed on the major human pathogen Staphylococcus aureus, which can both reside asymptomatically as a member of our respiratory microbiome, or become invasive and cause infections as severe as bacteraemia. Survival upon exposure to the antibacterial factors found in serum is a critical aspect of their ability to cause bacteraemia, and across a collection of 300 clinical isolates we found there to be significant variability in this capability. Utilising a GWAS approach we have uncovered the genetic basis of much of this variability through the identification and functional verification of a number of new polymorphic loci that affect serum survival: tcaA, tarK, gntR, ilvC, arsB, yfhO, and pdhD. The expression of one of these genes, tcaA, was found to be induced upon exposure to serum, while simultaneously enhancing the sensitivity of S. aureus to serum through a process involving the ligation of wall teichoic acids into the cell wall. As blood-stage infections are a transmission dead-end for the bacteria, that S. aureus actively responds to serum to produce a protein which specifically limits their ability to survive in this environment demonstrates that the switch from the commensal to the invasive lifestyle is complex, and that TcaA may contribute to the long-term success of S. aureus by restricting the bacteria to their more readily transmissible commensal state.

microbiology↗

bioRxiv2021

Significant Variability exists in the Toxicity of Global Methicillin-resistant Staphylococcus aureus Lineages.

Staphylococcus aureus is a major human pathogen where the emergence of antibiotic resistant lineages, such as methicillin-resistant S. aureus (MRSA), is a major health concern. While some MRSA lineages are restricted to the healthcare setting, the epidemiology of MRSA is changing globally, with the rise of specific lineages causing disease in healthy people in the community. In the past two decades, community-associated MRSA (CA-MRSA) has emerged as a clinically important and virulent pathogen associated with serious skin and soft-tissue infections (SSTI). These infections are primarily toxin driven, leading to the suggestion that hyper-virulent lineages/multi-locus sequence types (STs) exist. To examine this, we compared the toxic activity of 475 MRSA isolates representing five major MRSA STs (ST22, ST93, ST8, ST239 and ST36) by employing a monocyte-macrophage THP-1 cell line as a surrogate for measuring gross cytotoxicity. We demonstrate that while certain MRSA STs contain highly toxic isolates, there is such variability within lineages to suggest that this aspect of virulence should not be inferred from the genotype of any given isolate. Furthermore, by interrogating the accessory gene regulator (Agr) sequences in this collection we identified several Agr mutations that were associated with reduced toxicity. Interestingly, the majority of isolates that were attenuated in toxin production contained no mutations in the agr locus, indicating a role of other undefined genes in S. aureus toxin regulation.

microbiology↗

bioRxiv2021

The MpsB protein contributes to both the toxicity and immune evasion capacity of Staphylococcus aureus.

Understanding the role specific bacterial factors play in the development of severe disease in humans is critical if new approaches to tackle such infections are to be developed. In this study we focus on genes we have found to be associated with patient outcome following bacteraemia caused by the major human pathogen Staphylococcus aureus. By examining the contribution these genes make to the ability of the bacteria to survive exposure to the antibacterial factors found in serum, we identify three novel serum resistance associated genes, mdeA, mpsB and yycH. Detailed analysis of an MpsB mutant supports its previous association with the slow growing SCV phenotype of S. aureus, and we demonstrate that the effect this mutation has on membrane potential prevents the activation of the Agr quorum sensing system, and as a consequence the mutant bacteria do not produce cytolytic toxins. Given the importance of both toxin production and immune evasion to the ability of S. aureus to cause disease, we believe these findings explain the role of the mpsB gene as a mortality-associate locus during human disease.

microbiology↗

bioRxiv2021

A Functional Menadione Biosynthesis Pathway is Required for Capsule Production by Staphylococcus aureus.

Staphylococcus aureus is a major human pathogen that utilises a wide array of pathogenic and immune evasion strategies to cause disease. One immune evasion strategy, common to many bacterial pathogens, is the ability of S. aureus to produce a capsule that protects the bacteria from several aspects of the human immune system. To identify novel regulators of capsule production by S. aureus we applied a genome wide association study (GWAS) to a collection of 300 bacteraemia isolates that represent the two major MRSA clones in UK and Irish hospitals: CC22 and CC30. One of the loci associated with capsule production, the menD gene, encodes an enzyme critical to the biosynthesis of menadione. Mutations in this gene that result in menadione auxotrophy induce the slow growing small-colony variant (SCV) form of S. aureus often associated with chronic infections due to their increased resistance to antibiotics and ability to survive inside phagocytes. Utilising such an SCV we functionally verified this association between menD and capsule production. Although the clinical isolates with polymorphisms in the menD gene in our collections had no apparent growth defects, they were more resistant to gentamicin when compared to those with the wild-type menD gene. Our work suggests that menadione plays a critical role in the production of the S. aureus capsule, and that amongst clinical isolates polymorphisms exist in the menD gene that confer the characteristic increased gentamicin resistance, but not the major growth defect associated with SCV phenotype.

microbiology↗

bioRxiv2020

Targeted control of toxin production by a mobile genetic element in Streptococcus pneumoniae.

Streptococcus pneumoniae is a major human pathogen that can cause severe invasive diseases such as pneumonia, septicaemia and meningitis. Young children are at a particularly high risk, with an estimated half a million deaths worldwide in those under five attributable to invasive pneumococcal disease each year. The cytolytic toxin pneumolysin (Ply) is a primary virulence factor for this bacterium, yet despite its key role in pathogenesis, immune evasion, and transmission, the regulation of Ply production is not well defined. Using a genome-wide association approach we identified a large number of potential affectors of Ply activity, including a gene acquired horizontally on the antibiotic resistance conferring Integrative and Conjugative Element (ICE) ICESp23FST81. This gene encodes a novel modular protein, ZomB, which has an N-terminal UvrD-like helicase domain followed by two Cas4-like domains with potent ATP-dependent nuclease activity. We found the regulatory effect of ZomB to be specific for the ply operon, potentially mediated by its high affinity for the BOX repeats encoded therein. Using a murine model of pneumococcal colonisation, we further demonstrate that a ZomB mutant strain colonises both the upper respiratory tract and lungs at higher levels when compared to the wild type strain. While the antibiotic resistance conferring aspects of ICESp23FST81 is often credited with contributing to the success of the S. pneumoniae lineages that acquire it, its ability to control the expression of a major virulence factor implicated in bacterial transmission is also likely to have played an important role.

microbiology↗

bioRxiv2019

A small membrane protein critical to both the offensive and defensive capabilities of Staphylococcus aureus.

Staphylococcus aureus is a major human pathogen, where the widespread emergence of antibiotic resistance is making infections more challenging to treat. Toxin induced tissue damage and resistance to the hosts immune system are well established as critical to its ability to cause disease. However, recent attempts to study S. aureus pathogenicity at a population level have revealed significant complexity and hierarchical levels of regulation. In an effort to better understand this we have identified and characterized a principle effector protein, MasA. The inactivation of this small highly-conserved membrane protein simultaneously disrupts toxin production and impairs S. aureus ability to resist several aspects of the innate immune system. These pleiotropic effects are mediated by both a change in the stability of the bacterial membrane and the dysregulation of iron homeostasis, which results in a significant impairment in the ability of S. aureus to cause infection in both a subcutaneous and a sepsis model of infection. That proteins with such major effects on pathogenicity remain unidentified in a bacterium as well studied as S. aureus demonstrates how incomplete our understanding of their ability to cause disease is, an issue that needs to be addressed if effective control and treatment strategies are to be developed.

microbiology↗