Biology subjects

Buchan, K. D.

Publications and source records attributed to Buchan, K. D..

4 recordsLinked to original sources

bioRxiv2026

Carbapenem-resistant Klebsiella pneumoniae lineage CG307 displays urinary tract tropism

Carbapenem-resistant (CR) Klebsiella pneumoniae (Kp) are designated by the WHO as a top-priority pathogen due to their antibiotic resistance profiles, capacity to disseminate resistance, and associated mortality. The prototypical CRKp clade, CG258, is associated with acute respiratory infections; however, urinary tract infections (UTIs) caused by CRKp are increasing, and frequently linked to the emergent clade CG307. Notably, CG307 isolates have extensive accessory genomes that may drive adaptation to the urinary tract, including a novel capsule gene cluster and high-affinity urea transporter. In this study, we show that UTIs caused by Kp are increasing across the Southern US and that in addition to CG307s circulating within Houston, TX hospital systems, the lineage was also detected in healthcare systems in the broader Gulf Coast region. Characterization of CG307 isolates demonstrate that while these strains exhibit similar mucoviscosity compared to the reference UTI strain TOP52, the lineage displays significantly higher i) growth in artificial urine, ii) urease activity, and iii) UTI in a mouse model. These results suggest that CG307 is spreading across the Southern US and encodes distinct pathogenic features that promote urinary tract tropism, underscoring a need for targeted surveillance and future studies that mechanistically examine the factors that promote UTI.

microbiology↗

bioRxiv2024

LiaR-dependent gene expression contributes to antimicrobial responses in group A Streptococcus

The ability to sense and respond to host defenses is essential for pathogen survival. Some mechanisms involve two-component systems (TCS) that respond to host molecules, such as antimicrobial peptides (AMPs) and activate specific gene regulatory pathways to aid in survival. Alongside TCSs, bacteria coordinate cell division proteins, chaperones, cell wall sortases and secretory translocons at discrete locations within the cytoplasmic membrane, referred to as functional membrane microdomains (FMMs). In Group A Streptococcus (GAS), the FMM or "ExPortal" coordinates protein secretion, cell wall synthesis and sensing of AMP-mediated cell envelope stress via the LiaFSR three-component system. Previously we showed GAS exposure to a subset of AMPs (-defensins) activates the LiaFSR system by disrupting LiaF and LiaS co-localization in the ExPortal, leading to increased LiaR phosphorylation, expression of the transcriptional regulator SpxA2, and altered GAS virulence gene expression. The mechanisms by which LiaFSR integrates cell envelope stress with responses to AMP activity and virulence are not fully elucidated. Here, we show the LiaFSR regulon is comprised of genes encoding SpxA2 and three membrane-associated proteins: a PspC domain-containing protein (PCP), the lipoteichoic acid-modifying protein LafB and the membrane protein insertase YidC2. Our data show phosphorylated LiaR induces transcription of these genes via a conserved operator, whose disruption attenuates GAS virulence and increases susceptibility to AMPs in a manner primarily dependent on differential expression of SpxA2. Our work expands understanding of the LiaFSR regulatory network in GAS and identifies targets for further investigation of mechanisms of cell envelope stress tolerance contributing to GAS pathogenesis.

microbiology↗

bioRxiv2020

Humanisation of the zebrafish C5a receptor confers targeting by human-specific staphylococcal virulence factors.

Staphylococcus aureus infects approximately 30% of the human population and causes a spectrum of pathologies ranging from mild skin infections to life-threatening invasive diseases. The strict host specificity of its virulence factors has severely limited the accuracy of in vivo models for the development of vaccines and therapeutics. To resolve this, we generated a humanised zebrafish model and determined that neutrophil-specific expression of the human C5a receptor conferred susceptibility to the S. aureus toxins PVL and HlgCB, leading to reduced neutrophil numbers at the site of infection and increased infection-associated mortality as a direct result of the interaction between S. aureus and the receptor. These results show that humanised zebrafish provide a valuable platform to study the contribution of human-specific S. aureus virulence factors to infection in vivo that could facilitate the development of novel therapeutic approaches and essential vaccines.

immunology↗

bioRxiv2018

A transgenic zebrafish line for in vivo visualisation of neutrophil myeloperoxidase

The neutrophil enzyme myeloperoxidase (MPO) is a major enzyme made by neutrophils to generate antimicrobial and immunomodulatory compounds, notably hypochlorous acid (HOCl), amplifying their capacity for destroying pathogens and regulating inflammation. Despite its roles in innate immunity, the importance of MPO in preventing infection is unclear, as individuals with MPO deficiency are asymptomatic with the exception of an increased risk of candidiasis. Dysregulation of MPO activity is also linked with inflammatory conditions such as atherosclerosis, emphasising a need to understand the roles of the enzyme in greater detail. Consequently, new tools for investigating granular dynamics in vivo can provide useful insights into how MPO localises within neutrophils, aiding understanding of its role in preventing and exacerbating disease. The zebrafish is a powerful model for investigating the immune system in vivo, as it is genetically tractable, and optically transparent. To visualise MPO activity within zebrafish neutrophils, we created a genetic construct that expresses human MPO as a fusion protein with a C-terminal fluorescent tag, driven by the neutrophil-specific promoter lyz. After introducing the construct into the zebrafish genome by Tol2 transgenesis, we established the Tg(lyz:Hsa.MPO-mEmerald,cmlc2:EGFP)sh496 line, and confirmed transgene expression in zebrafish neutrophils. We observed localisation of MPO-mEmerald within a subcellular location resembling neutrophil granules, mirroring MPO in human neutrophils. In Spotless (mpxNL144) larvae - which express a non-functional zebrafish myeloperoxidase - the MPO-mEmerald transgene does not disrupt neutrophil migration to sites of infection or inflammation, suggesting that it is a suitable line for the study of neutrophil granule function. We present a new transgenic line that can be used to investigate neutrophil granule dynamics in vivo without disrupting neutrophil behaviour, with potential applications in studying processing and maturation of MPO during development.

immunology↗