Biology subjects

McKeand, S. A.

Publications and source records attributed to McKeand, S. A..

3 recordsLinked to original sources

bioRxiv2023

Inhibition of Neisseria gonorrhoeae complement-mediated killing during acute gonorrhoea is dependent upon the IgG2:IgG3 antibody ratio

Excessive binding of antibodies to the bacterial cell surface can paradoxically increase resistance of some Gram-negative pathogens to complement-mediated killing (CMK). We examined CMK of 336 Neisseria gonorrhoeae clinical isolates sampled from participants recruited to a clinical trial. Serum bactericidal assays revealed 3% (9/336) of the autologous participant sera that were tested inhibited CMK. Gonococci isolated from these participants were resistant to the autologous host serum, sensitive to a pool of healthy control sera (HCS) and protected by the host serum in a 1:1 mixture with HCS. Analysis of the clinical metadata showed that there were a significantly higher proportion of inhibitory sera found in participants with urethral infections and from men within the transmission network of men who have sex with women (MSW), when compared to the whole cohort. Following antibody purification from selected participants with inhibitory sera (5/9), IgG and IgM protected the autologous isolates from HCS-mediated killing. Only three of these isolates were protected by purified IgA. A closer examination of IgG subclasses using whole gonococcal cell ELISAs revealed a strong correlation between increased IgG2 binding and decreased IgG3 binding to the bacterial cell surface of isolates that were resistant to CMK. This suggests that IgG2 prevents bactericidal IgG3 from initiating CMK and that the IgG2:IgG3 ratio is important for determining either inhibition or killing of isolates. We therefore reveal a previously unreported mechanism by which inhibitory antibodies prevent CMK of N. gonorrhoeae.

microbiology↗

bioRxiv2023

The inter-continental population dynamics of Neisseria gonorrhoeae

Neisseria gonorrhoeae is a globally distributed sexually transmitted bacterial pathogen. Recent studies have revealed that its evolution has been shaped by antibiotic use, while molecular surveillance efforts have demonstrated large changes in lineage composition over relatively short time-spans. However, the global population dynamics of N. gonorrhoeae remain unsatisfyingly characterized. To reconstruct recent large-scale population dynamics, we generated a dated phylogeny from 9,732 N. gonorrhoeae genomes and found the effective population size of the species to have expanded gradually over the past two centuries. While the effective population size of clades with reduced susceptibility to extended-spectrum cephalosporins started declining around 2010, a major clade containing a mosaic mtr operon associated with cephalosporin susceptibility and decreased azithromycin did not display any reduction in population size. Using ancestral trait reconstruction analyses, we delineated transmission lineages, defined as groups of sequences in which all the samples can be traced back to the same import event to a given location. Import, export and local transmission dynamics across two densely sampled locations (Norway and Victoria, Australia) were investigated in detail. Norway exhibited substantially higher rates of strain import and export compared to Victoria, where incidence was to a larger extent fuelled by locally transmitted lineages. Taken together, our work highlights the power of large-scale phylogenomic analyses to uncover the complex dynamics of lineage transmission in N. gonorrhoeae.

microbiology↗

bioRxiv2022

TraDIS-validate: a method for curating ordered gene-replacement libraries

In recent years the availability of genome sequence information has grown logarithmically resulting in the identification of a plethora of uncharacterised genes. To address this gap in functional annotation, many high-throughput screens have been devised with the goal of uncovering novel gene functions. Gene-replacement libraries are one such tool that can be screened in a high-throughput way to link genotype and phenotype and are key community resources. However, for a phenotype to be attributed to a specific gene, there needs to be confidence in the genotype. Construction of large libraries can be laborious and occasionally errors will arise. Here, we present a rapid and accurate method for the validation of any ordered gene-replacement library. We applied our method (TraDIS-Validate) to the well-known Keio library of Escherichia coli gene-deletion mutants. Our method identified 3,718 constructed mutants out of a total of 3,728 confirmed isolates. TraDIS-validate therefore had a success rate of 99.7% for identifying the correct kanamycin cassette position. This dataset provides a benchmark for the purity of the Keio mutants and a screening method for mapping the position of an antibiotic resistance cassette in any ordered library.

genetics↗