Supramolecular assemblies underpin turnover of outer membrane proteins in bacteria.

Gram-negative bacteria inhabit a broad range of ecological niches. For Escherichia coli, this includes river water as well as humans and animals, where it can be both a commensal and a pathogen. Intricate regulatory mechanisms ensure that bacteria have the right complement of ß-barrel outer membrane proteins (OMPs) to enable adaptation to a particular habitat. Yet no mechanism is known for replacing OMPs in the outer membrane, an issue that is further confounded by the lack of an energy source and the high stability and abundance of OMPs. Here we uncover the process underpinning OMP turnover in E. coli and show it to be passive and binary in nature, in which old OMPs are displaced to the poles of growing cells as new OMPs take their place. Using fluorescent colicins as OMP-specific probes, in combination with ensemble and single-molecule fluorescence microscopy in vivo and in vitro, as well as molecular dynamics simulations, we established the mechanism for binary OMP partitioning. OMPs clustered to form ∼0.5-µm diameter islands, where their diffusion is restricted by promiscuous interactions with other OMPs. OMP islands were distributed throughout the cell and contained the Bam complex, which catalyses the insertion of OMPs in the outer membrane. However, OMP biogenesis occurred as a gradient that was highest at mid-cell but largely absent at cell poles. The cumulative effect is to push old OMP islands towards the poles of growing cells, leading to a binary distribution when cells divide. Hence, the outer membrane of a Gram-negative bacterium is a spatially and temporally organized structure, and this organization lies at the heart of how OMPs are turned over in the membrane.

DNA vaccines encoding membrane-bound or secreted forms of heat shock protein 70 exhibit improved potency.

Traditional vaccine strategies are inefficient against challenge with complex pathogens including HIV; therefore, novel vaccine technologies are required. DNA vaccines are attractive as they are relatively cheap and easy to manufacture, but a major limitation has been their lack of immunogenicity in humans, which may be overcome with the incorporation of an adjuvant. HSP70 is a recognised damage-associated molecular pattern, which is a potential adjuvant. We investigated the immunogenicity of a DNA vaccine encoding HIV gag and HSP70; the latter was genetically modified to produce cytoplasmic, secreted or membrane-bound HSP70, the expression of which was controlled by an independent promoter. The DNA was administered to C57BL/6 mice to evaluate gag-specific T-cell responses. Our results demonstrated the ability of membrane-bound and secreted HSP70 to significantly enhance gag-specific T-cell responses and increase the breadth of T-cell responses to include subdominant epitopes. Membrane-bound or secreted HSP70 also significantly improved the multifunctionality of HIV-specific T cells and T-cell proliferation, which is important for maintaining T-cell integrity. Most importantly, the inclusion of membrane-bound HSP70, secreted HSP70 or a combination significantly increased protection in mice challenged with EcoHIV, a chimeric virus that replicates in mouse leukocytes in vivo.

Induction of antigen-positive cell death by the expression of perforin, but not DTa, from a DNA vaccine enhances the immune response.

The failure of traditional protein-based vaccines to prevent infection by viruses such as HIV or hepatitis C highlights the need for novel vaccine strategies. DNA vaccines have shown promise in small animal models, and are effective at generating anti-viral T cell-mediated immune responses; however, they have proved to be poorly immunogenic in clinical trials. We propose that the induction of necrosis will enhance the immune response to vaccine antigens encoded by DNA vaccines, as necrotic cells are known to release a range of intracellular factors that lead to dendritic cell (DC) activation and enhanced cross-presentation of antigen. Here we provide evidence that induction of cell death in DNA vaccine-targeted cells provides an adjuvant effect following intradermal vaccination of mice; however, this enhancement of the immune response is dependent on both the mechanism and timing of cell death after antigen expression. We report that a DNA vaccine encoding the cytolytic protein, perforin, resulted in DC activation, enhanced broad and multifunctional CD8 T-cell responses to the HIV-1 antigen GAG and reduced viral load following challenge with a chimeric virus, EcoHIV, compared with the canonical GAG DNA vaccine. This effect was not observed for a DNA vaccine encoding an apoptosis-inducing toxin, DTa, or when the level of perforin expression was increased to induce cell death sooner after vaccination. Thus, inducing lytic cell death following a threshold level of expression of a viral antigen can improve the immunogenicity of DNA vaccines, whereas apoptotic cell death has an inhibitory effect on the immune response.

A qualitative study of the incentives and barriers that influence preferences for rural placements during surgical training in Australia.

BACKGROUND: Rural exposure of long durations during clinical training is positively associated with rural career uptake and is a central strategy to addressing the geographical maldistribution of Australia's surgical workforce. However, the incentives and barriers to trainees undergoing surgical training preferencing repeated rural placements in Australia are not well understood. This qualitative study explores the incentives and barriers that influence preference for rural placements during surgical training in Australia. METHODS: This qualitative study employed online semi-structured in-depth interviews. Participants were recruited using an online survey, and interviews were conducted between October 2020 and November 2020. Transcripts were transcribed and de-identified, and thematically analysed. RESULTS: Twenty-nine semi-structured interviews were conducted with trainees and 12 Fellows. Twenty-five participants identified as male, and four identified as female. Four main incentives identified were: (1) broad scope of learning opportunities, (2) quality of supervision, (3) positive work environment and (4) lifestyle. Seven barriers identified were: (1) inadequate preparation for placement, (2) limited case mix to support learning outcomes, (3) lack of formally structured learning opportunities, (4) workload and safe hours concerns, (5) lack of peer support, (6) childcare and educational needs and (7) partner career development. CONCLUSION: The strategy of encouraging trainees to undertake rural placements to address the maldistribution of the surgical workforce should include initiatives that support learning outcomes across their training levels. In addition, improving trainees' ability to prepare adequately for placements may also improve the number and duration of rural placements trainees undertake during their training.

Impact of COVID-19, gender, race, specialty and seniority on mental health during surgical training: an international study.

BACKGROUND: Superior patient outcomes rely on surgical training being optimized. Accordingly, we conducted an international, prospective, cross-sectional study determining relative impacts of COVID-19, gender, race, specialty and seniority on mental health of surgical trainees. METHOD: Trainees across Australia, New Zealand and UK enrolled in surgical training accredited by the Royal Australasian College of Surgeons or Royal College of Surgeons were included. Outcomes included the short version of the Perceived Stress Scale, Oxford Happiness Questionnaire short scale, Patient Health Questionnaire-2 and the effect on individual stress levels of training experiences affected by COVID-19. Predictors included trainee characteristics and local COVID-19 prevalence. Multivariable linear regression analyses were conducted to assess association between outcomes and predictors. RESULTS: Two hundred and five surgical trainees were included. Increased stress was associated with number of COVID-19 patients treated (P = 0.0127), female gender (P = 0.0293), minority race (P = 0.0012), less seniority (P = 0.001), and greater COVID-19 prevalence (P = 0.0122). Lower happiness was associated with training country (P = 0.0026), minority race (P = 0.0258) and more seniority (P < 0.0001). Greater depression was associated with more seniority (P < 0.0001). Greater COVID-19 prevalence was associated with greater reported loss of training opportunities (P = 0.0038), poor working conditions (P = 0.0079), personal protective equipment availability (P = 0.0008), relocation to areas of little experience (P < 0.0001), difficulties with career progression (P = 0.0172), loss of supervision (P = 0.0211), difficulties with pay (P = 0.0034), and difficulties with leave (P = 0.0002). CONCLUSION: This is the first study to specifically describe the relative impacts of COVID-19 community prevalence, gender, race, surgical specialty and level of seniority on stress, happiness and depression of surgical trainees on an international scale.

Loss of long term protection with the inclusion of HIV pol to a DNA vaccine encoding gag.

Traditional vaccine strategies that induce antibody responses have failed to protect against HIV infection in clinical trials, and thus cell-mediated immunity is now an additional criterion. Recent clinical trials that aimed to induce strong T cell responses failed to do so. Therefore, to enhance induction of protective T cell responses, it is crucial that the optimum antigen combination is chosen. Limited research has been performed into the number of antigens selected for an HIV vaccine. This study aimed to compare DNA vaccines encoding either a single HIV antigen or a combination of two antigens, using intradermal vaccination of C57BL/6 mice. Immune assays were performed on splenocytes, and in vivo protection was examined by challenge with a chimeric virus, EcoHIV, able to infect mouse but not human leukocytes, at 10 days (short term) and 60 days (long term) post final vaccination. At 60 days there was significantly lower frequency of induced antigen-specific CD8(+) T cells in the spleens of pCMVgag-pol-vaccinated mice compared with mice which received pCMVgag only. Most importantly, short term viral control of EcoHIV was similar for pCMVgag and pCMVgag-pol-vaccinated mice at day 10, but only the pCMVgag-vaccinated significantly controlled EcoHIV at day 60 compared with pCMV-vaccinated mice, showing that control was reduced with the inclusion of the HIV pol gene.