Degradation of nuclear and mitochondrial DNA after γ-irradiation and its effect on forensic genotyping.

Forensic genotyping can be impeded by γ-irradiation of biological evidence in the event of radiological crime; that is, criminal activity involving radioactive material. Oxidative effects within the mitochondria of living cells elicits greater damage to mitochondrial DNA (mtDNA) than nuclear DNA (nuDNA) at low doses. This study presents a novel approach for the assessment of nuDNA versus mtDNA damage from a comparison of genotype and quantity data, while exploring likely mechanisms for differential damage after high doses of γ-irradiation. Liquid (hydrated) and dried (dehydrated) whole blood samples were exposed to high doses of γ-radiation (1-50 kilogray, kGy). The GlobalFiler PCR Amplification Kit was used to evaluate short tandem repeat (STR) genotyping efficacy and nuDNA degradation; a comparison was made to mtDNA degradation measured using real-time PCR assays. Each assay was normalized before comparison by calculation of integrity indices relative to unirradiated controls. Full STR profiles were attainable up to the highest dose, although DNA degradation was noticeable after 10 and 25 kGy for hydrated and dehydrated blood, respectively. This was manifested by heterozygote imbalance more than allele dropout. Degradation was greater for mtDNA than nuDNA, as well as for hydrated than dehydrated cells, after equivalent doses. Oxidative effects due to water radiolysis and mitochondrial function are dominant mechanisms of differential damage to nuDNA versus mtDNA after high-dose γ-irradiation. While differential DNA damage was reduced by cell desiccation, its persistence after drying indicates innate differences between nuDNA and mtDNA radioresistance and/or continued oxidative effects within the mitochondria.

Short-read fastA files dataset from complexity-reduced genotyping by sequencing data of bacterial isolates from a public hospital in Australia.

This data article contains short-read sequences (length 30-69 bp) obtained from complexity-reduced genotyping by sequencing (GBS) of 165 samples bacterial isolates from hospital patients in the Australian Capital Territory, between 2013 and 2015. These samples represented 14 bacterial species. Data format is shown as filtered fastA files obtained from an Illumina HiSeq2500 sequencer. The experimental factors of this research used three complexity reduction methods with three combinations of restriction enzymes: PstI with MseI, PstI with HpaII and MseI with HpaII.

Identification of bacterial isolates from a public hospital in Australia using complexity-reduced genotyping.

Bacterial identification methods used in routine identification of pathogens in medical microbiology include a combination approach of biochemical tests, mass spectrometry or molecular biology techniques. Extensive publicly-available databases of DNA sequence data from pathogenic bacteria have been amassed in recent years; this provides an opportunity for using bacterial genome sequencing for identification purposes. Whole genome sequencing is increasing in popularity, although at present it remains a relatively expensive approach to bacterial identification and typing. Complexity-reduced bacterial genome sequencing provides an alternative. We evaluate genomic complexity-reduction using restriction enzymes and sequencing to identify bacterial isolates. A total of 165 bacterial isolates from hospital patients in the Australian Capital Territory, between 2013 and 2015 were used in this study. They were identified and typed by the Microbiology Department of Canberra Public Hospital, and represented 14 bacterial species. DNA extractions from these samples were processed using a combination of the restriction enzymes PstI with MseI, PstI with HpaII and MseI with HpaII. The resulting sequences (length 30-69 bp) were aligned against publicly available bacterial genome and plasmid sequences. Results of the alignment were processed using a bioinformatics pipeline developed for this project, Currito3.1 DNA Fragment Analysis Software. All 165 samples were correctly identified to genus and species by each of the three combinations of restriction enzymes. A further 35 samples typed to the level of strain identified and compared for consistency with MLST typing data and in silico MLST data derived from the nearest sequenced candidate reference. The high level of agreement between bacterial identification using complexity-reduced genome sequencing and standard hospital identifications indicating that this new approach is a viable alternative for identification of bacterial isolates derived from pathology specimens. The effectiveness of species identification and in particular, strain typing, depends on access to a comprehensive and taxonomically accurate bacterial genome sequence database containing relevant bacterial species and strains.

Small tumor necrosis factor receptor biologics inhibit the tumor necrosis factor-p38 signalling axis and inflammation.

Despite anti-TNF therapy advancements for inflammatory diseases such as rheumatoid arthritis, the burden of diseases remains high. An 11-mer TNF peptide, TNF70-80, is known to stimulate selective functional responses compared to the parent TNF molecule. Here, we show that TNF70-80 binds to the TNF receptor, activating p38 MAP kinase through TNF receptor-associated factor 2. Using truncated TNFR mutants, we identify the sequence in TNFRI which enables p38 activation by TNF70-80. Peptides with this TNFRI sequence, such as TNFRI206-211 bind to TNF and inhibit TNF-induced p38 activation, respiratory burst, cytokine production and adhesion receptor expression but not F-Met-Leu-Phe-induced respiratory burst in neutrophils. TNFRI206-211 does not prevent TNF binding to TNFRI or TNF-induced stimulation of ERK, JNK and NF-κB. TNFRI206-211 inhibits bacterial lipopolysaccharide-induced peritonitis, carrageenan-induced and antigen-induced paw inflammation, and respiratory syncytial virus-induced lung inflammation in mice. Our findings suggest a way of targeting TNF-p38 pathway to treat chronic inflammatory disorders.

Assessment of the Precision ID Ancestry panel.

AbstractThe ability to provide accurate DNA-based forensic intelligence requires analysis of multiple DNA markers to predict the biogeographical ancestry (BGA) and externally visible characteristics (EVCs) of the donor of biological evidence. Massively parallel sequencing (MPS) enables the analysis of hundreds of DNA markers in multiple samples simultaneously, increasing the value of the intelligence provided to forensic investigators while reducing the depletion of evidential material resulting from multiple analyses. The Precision ID Ancestry Panel (formerly the HID Ion AmpliSeq™ Ancestry Panel) (Thermo Fisher Scientific) (TFS)) consists of 165 autosomal SNPs selected to infer BGA. Forensic validation criteria were applied to 95 samples using this panel to assess sensitivity (1 ng-15 pg), reproducibility (inter- and intra-run variability) and effects of compromised and forensic casework type samples (artificially degraded and inhibited, mixed source and aged blood and bone samples). BGA prediction accuracy was assessed using samples from individuals who self-declared their ancestry as being from single populations of origin (n = 36) or from multiple populations of origin (n = 14). Sequencing was conducted on Ion 318™ chips (TFS) on the Ion PGM™ System (TFS). HID SNP Genotyper v4.3.1 software (TFS) was used to perform BGA predictions based on admixture proportions (continental level) and likelihood estimates (sub-population level). BGA prediction was accurate at DNA template amounts of 125pg and 30pg using 21 and 25 PCR cycles respectively. HID SNP Genotyper continental level BGA assignments were concordant with BGAs for self-declared East Asian, African, European and South Asian individuals. Compromised, mixed source and admixed samples, in addition to sub-population level prediction, requires more extensive analysis.

Singleplex quantitative real-time PCR for the assessment of human mitochondrial DNA quantity and quality.

Mitochondrial DNA (mtDNA) can provide a means for forensic identity testing when genotyping of nuclear DNA (nuDNA) targets is not possible due to degradation or lack of template. For degraded samples, an indication of the quantity and quality of mtDNA is essential to allow selection of appropriately sized targets for hypervariable region (HVR) analysis, which may conserve sample and resources. Three human-specific mtDNA targets of increasing length (86, 190 and 452 base pairs) were amplified by singleplex quantitative real-time PCR (qPCR), capable of providing an index of mtDNA degradation from fragment length information. Quantification was achieved by preparation of a standard curve for each target, using a purified mtDNA standard containing all three targets of interest, which produced a linear, accurate and precise result from 1×108 to 10 copies. These novel assays demonstrated excellent sensitivity, specificity and reproducibility in line with the minimum information for qPCR experiments (MIQE) guidelines. Further, a separate inhibition control reaction was included to guide sample clean-up and ensure the validity of degradation assays. This protocol assists the selection and analysis of appropriately sized targets to maximize the chance of obtaining an informative result in downstream assays like sequencing.

Characterization of Yersinia species by protein profiling using automated microfluidic capillary electrophoresis.

Yersinia pestis is a biological agent of high risk to national security due to its ability to be easily disseminated and transmitted among humans. If Y. pestis was to be utilized in a deliberate disease outbreak it would be essential to rapidly and accurately identify the agent. Current identification methods for Yersinia species are limited by their reliance on cultivation, the time taken to achieve results and/or the use of protocols that are not amenable for field use. Faster identification methods are urgently required. Microfluidic capillary electrophoresis was used to identify seven Yersinia species based on their protein profiles. Further objectives included determining if Yersinia species could be detected in mixtures of milk products and Escherichia coli, determining if Yersinia could be detected in a blinded identification and reproducibility across two platforms. Two characteristic protein bands were detected at 50 kilodaltons (kDa) and between 50 and 75 kDa for the Yersinia species. Individual Yersinia species could be differentiated from one another and distinguished from E. coli, Bacillus anthracis Sterne strain and Dipel (containing Bacillus thuringiensis). Due to the high protein content of milk products Yersinia could not be detected when mixed with these but was detected when mixed with E. coli. Species were correctly identified with 96% success in blinded procedures using 12 individuals. Whilst protein profile patterns were reproducible across platforms there was some discrepancy in protein sizing. This study demonstrates that protein profiling using microfluidic capillary electrophoresis is able to rapidly and reproducibly identify and characterize Yersinia species. Results show this technique is a powerful front-line, rapid and broad range screening method capable of identifying and differentiating biological agents, hoax agents and environmental bacterial species.

A simulation model to estimate the risk of transfusion-transmitted arboviral infection.

BACKGROUND: The arboviruses West Nile virus (WNV), dengue virus (DENV) and Ross River virus (RRV) have been demonstrated to be blood transfusion-transmissible. A model to estimate the risk of WNV to the blood supply using a Monte Carlo approach has been developed and also applied to Chikungunya virus. Also, a probabilistic model was developed to assess the risk of DENV to blood safety, which was later adapted to RRV. To address efficacy and limitations within each model we present a hybrid model that promises improved accuracy, and is broadly applicable to assess the risk of arboviral transmission by blood transfusion. MATERIAL AND METHODS: Data were drawn from the Cairns Public Health Unit (Australia) and published literature. Based on the published models and using R code, a novel 'combined' model was developed and validated against the BP model using sensitivity testing. RESULTS: The mean risk per 10,000 of the combined model is 0.98 with a range from 0.79 to 1.25, while the maximum risk was 4.45 ranging from 2.62 to 7.67 respectively. These parameters for the BP model were 1.20 ranging from 0.84 to 1.55, and 2.86 ranging from 1.33 to 5.23 respectively. CONCLUSION: The combined simulation model is simple and robust. We propose it can be applied as a 'generic' arbovirus model to assess the risk from known or novel arboviral threats to the blood supply.

Background frequency of Bacillus species at the Canberra Airport: A 12 month study.

Anthrax, caused by Bacillus anthracis, is a naturally occurring disease in Australia. Whilst mainly limited to livestock in grazing regions of Victoria and New South Wales, movement of people, stock and vehicles means B. anthracis could be present outside this region. Of particular interest is the "background" prevalence of B. anthracis at transport hubs including airports. The aim of this study was to determine the background frequency of B. anthracis and the commonly used hoax agent Bacillus thuringiensis at the Canberra Airport over a 12 month period. Samples were collected daily for seven days each month from August 2011-July 2012 and analyzed using species specific real-time polymerase chain reaction. Fourteen samples (of a total of 575) were positive for the B. anthracis PL3 genomic marker, 24 for the cya (pXO1) plasmid marker and five for the capB (pXO2) plasmid marker. Whilst five samples were positive for both PL3 and cya, no samples were positive for all three markers hence there is no evidence to suggest the presence of pathogenic B. anthracis strains. B. anthracis targets were detected primarily in February 2012 and B. thuringiensis peaked in October and November 2011 and again in April and May 2012. This study provides a rapid method to screen for, and differentiate, Bacillus species. Armed with this information investigators will be able to discriminate a "threat" from "background" frequencies should the need arise.

Nucleocytoplasmic transport of nucleocapsid proteins of enveloped RNA viruses.

Most viruses with non-segmented single stranded RNA genomes complete their life cycle in the cytoplasm of infected cells. However, despite undergoing replication in the cytoplasm, the structural proteins of some of these RNA viruses localize to the nucleus at specific times in the virus life cycle, primarily early in infection. Limited evidence suggests that this enhances successful viral replication by interfering with or inhibiting the host antiviral response. Nucleocapsid proteins of RNA viruses have a well-established, essential cytoplasmic role in virus replication and assembly. Intriguingly, nucleocapsid proteins of some RNA viruses also localize to the nucleus/nucleolus of infected cells. Their nuclear function is less well understood although significant advances have been made in recent years. This review will focus on the nucleocapsid protein of cytoplasmic enveloped RNA viruses, including their localization to the nucleus/nucleolus and function therein. A greater understanding of the nuclear localization of nucleocapsid proteins has the potential to enhance therapeutic strategies as it can be a target for the development of live-attenuated vaccines or antiviral drugs.

Development of a forensic identity SNP panel for Indonesia.

Genetic markers included in forensic identity panels must exhibit Hardy-Weinberg and linkage equilibrium (HWE and LE). "Universal" panels designed for global use can fail these tests in regional jurisdictions exhibiting high levels of genetic differentiation such as the Indonesian archipelago. This is especially the case where a single DNA database is required for allele frequency estimates to calculate random match probabilities (RMPs) and associated likelihood ratios (LRs). A panel of 65 single nucleotide polymorphisms (SNPs) and a reduced set of 52 SNPs have been selected from 15 Indonesian subpopulations in the HUGO Pan Asian SNP database using a SNP selection strategy that could be applied to any panel of forensic identity markers. The strategy consists of four screening steps: (1) application of a G test for HWE; (2) ranking for high heterozygosity; (3) selection for LE; and (4) selection for low inbreeding depression. SNPs in our Indonesian panel perform well in comparison to some other universal SNP and short tandem repeat (STR) panels as measured by Fisher's exact test for HWE and LE and Wright's F statistics.

Dual proinflammatory and antiviral properties of pulmonary eosinophils in respiratory syncytial virus vaccine-enhanced disease.

UNLABELLED: Human respiratory syncytial virus (RSV) is a major cause of morbidity and severe lower respiratory tract disease in the elderly and very young, with some infants developing bronchiolitis, recurrent wheezing, and asthma following infection. Previous studies in humans and animal models have shown that vaccination with formalin-inactivated RSV (FI-RSV) leads to prominent airway eosinophilic inflammation following RSV challenge; however, the roles of pulmonary eosinophilia in the antiviral response and in disease pathogenesis are inadequately understood. In vivo studies in mice with eotaxin and/or interleukin 5 (IL-5) deficiency showed that FI-RSV vaccination did not lead to enhanced pulmonary disease, where following challenge there were reduced pulmonary eosinophilia, inflammation, Th2-type cytokine responses, and altered chemokine (TARC and CCL17) responses. In contrast to wild-type mice, RSV was recovered at high titers from the lungs of eotaxin- and/or IL-5-deficient mice. Adoptive transfer of eosinophils to FI-RSV-immunized eotaxin- and IL-5-deficient (double-deficient) mice challenged with RSV was associated with potent viral clearance that was mediated at least partly through nitric oxide. These studies show that pulmonary eosinophilia has dual outcomes: one linked to RSV-induced airway inflammation and pulmonary pathology and one with innate features that contribute to a reduction in the viral load. IMPORTANCE: This study is critical to understanding the mechanisms attributable to RSV vaccine-enhanced disease. This study addresses the hypothesis that IL-5 and eotaxin are critical in pulmonary eosinophil response related to FI-RSV vaccine-enhanced disease. The findings suggest that in addition to mediating tissue pathology, eosinophils within a Th2 environment also have antiviral activity.

Characterization of Bacillus strains and hoax agents by protein profiling using automated microfluidic capillary electrophoresis.

PURPOSE: In recent times, but especially since 2001, bioterrorism has been of increasing concern. In addition to the use of biological agents, including Bacillus anthracis (anthrax), there have been numerous hoax white powder "scares." It is imperative to rapidly and accurately identify any suspicious powder as hazardous or hoax. Classical methods for identification typically rely on time-consuming cultivation or highly specific molecular tests which are limited if the agent is unknown. Faster and field portable methods for analysis of suspicious powders are urgently required. METHODS: Potential hoax agents, including Bacillus species and household powders, were analyzed using automated microfluidic capillary electrophoresis to determine if protein profiling can distinguish between, and identify, samples. RESULTS: Distinctive protein profiles were produced for Bacillus species, with the presence and/or absence of certain bands, aiding identification. In particular B. anthracis Sterne strain contained a distinctive doublet band above 100 kDa which was not present in any other Bacillus species or hoax agents examined. The majority of powders produced distinctive banding that could enable the identification of the sample while simultaneously ruling out B. anthracis with a high degree of confidence. CONCLUSIONS: Results show automated microfluidic capillary electrophoresis can rapidly and reproducibly characterize Bacillus species and hoax agents based on protein profiles without the need for culture. Results were reproducible and there was enhanced resolution and rapidity compared to traditional protein profiling methods. Results show this technique is amenable to field use at a bioterrorism incident, thereby providing essential information to investigators regarding containment and treatment strategies.

Recovery and identification of bacterial DNA from illicit drugs.

Bacterial infections, including Bacillus anthracis (anthrax), are a common risk associated with illicit drug use, particularly among injecting drug users. There is, therefore, an urgent need to survey illicit drugs used for injection for the presence of bacteria and provide valuable information to health and forensic authorities. The objectives of this study were to develop a method for the extraction of bacterial DNA from illicit drugs and conduct a metagenomic survey of heroin and methamphetamine seized in the Australian Capital Territory during 2002-2011 for the presence of pathogens. Trends or patterns in drug contamination and their health implications for injecting drug users were also investigated. Methods based on the ChargeSwitch(®)gDNA mini kit (Invitrogen), QIAamp DNA extraction mini kit (QIAGEN) with and without bead-beating, and an organic phenol/chloroform extraction with ethanol precipitation were assessed for the recovery efficiency of both free and cellular bacterial DNA. Bacteria were identified using polymerase chain reaction and electrospray ionization-mass spectrometry (PCR/ESI-MS). An isopropanol pre-wash to remove traces of the drug and diluents, followed by a modified ChargeSwitch(®) method, was found to efficiently lyse cells and extract free and cellular DNA from Gram-positive and Gram-negative bacteria in heroin and methamphetamine which could then be identified by PCR/ESI-MS. Analysis of 12 heroin samples revealed the presence of DNA from species of Comamonas, Weissella, Bacillus, Streptococcus and Arthrobacter. No organisms were detected in the nine methamphetamine samples analysed. This study develops a method to extract and identify Gram-positive and Gram-negative bacteria from illicit drugs and demonstrates the presence of a range of bacterial pathogens in seized drug samples. These results will prove valuable for future work investigating trends or patterns in drug contamination and their health implications for injecting drug users as well as enabling forensic links between seizures to be examined.

Predicting the presence of hepatitis B virus surface antigen in Chinese patients by pathology data mining.

Hepatitis B virus (HBV) is a pathogen of worldwide health significance, associated with liver disease. A vaccine is available, yet HBV prevalence remains a concern, particularly in developing countries. Pathology laboratories have a primary role in the diagnosis and monitoring of HBV infection, through hepatitis B surface antigen (HBsAg) immunoassay and associated tests. Analysis of HBsAg immunoassay and associated pathology data from 821 Chinese patients applied 10-fold cross-validation to establish classification decision trees (CDTs), with CDT results used subsequently to develop a logistic regression model. The robustness of logistic regression model was confirmed by the Hosmer-Lemeshow test, Pseudo-R(2) and an area under receiver operating characteristic curve (AUROC) result that showed the logistic regression model was capable of accurately discriminating the HBsAg positive from HBsAg negative patients at 95% accuracy. Overall CDT sensitivity and specificity was 94.7% (± 5.0%) and 89.5% (± 5.7%), respectively, close to the sensitivity and specificity of the immunoassay, providing an alternative to predict HBsAg status. Both the CDT and logistic regression modeling demonstrated the importance of the routine pathology variables alanine aminotransferase (ALT), serum albumin (ALB), and alkaline phosphatase (ALP) to accurately predict HBsAg status in a Chinese patient cohort. The study demonstrates that CDTs and a linked logistic regression model applied to routine pathology data were an effective supplement to HBsAg immunoassay, and a possible replacement method where immunoassays are not requested or not easily available for the laboratory diagnosis of HBV infection.

Dengue virus therapeutic intervention strategies based on viral, vector and host factors involved in disease pathogenesis.

Dengue virus (DV) is the most widespread arbovirus, being endemic in over 100 countries, and is estimated to cause 50 million infections annually. Viral factors, such as the genetic composition of the virus strain can play a role in determining the virus virulence and subsequent clinical disease severity. Virus vector competence plays an integral role in virus transmission and is a critical factor in determining the severity and impact of DV outbreaks. Host genetic variations in immune-related genes, including the human leukocyte antigen, have also been shown to correlate with clinical disease and thus may play a role in regulating disease severity. The host's immune system, however, appears to be the primary factor in DV pathogenesis with the delicate interplay of innate and acquired immunity playing a crucial role. Although current research of DV pathogenesis has been limited by the lack of an appropriate animal model, the development of DV therapeutics has been a primary focus of research groups around the world. In the past decade advances in both the development of vaccines and anti-virals have increased in dramatically. This review summarises the current understanding of viral, vector and host factors which contribute to dengue virus pathogenesis and how this knowledge is critically important in the development of pharmaceutical interventions.

Applications of animal models of infectious arthritis in drug discovery: a focus on alphaviral disease.

Animal models, which mimic human disease, are invaluable tools for understanding the mechanisms of disease pathogenesis and development of treatment strategies. In particular, animal models play important roles in the area of infectious arthritis. Alphaviruses, including Ross River virus (RRV), o'nyong-nyong virus, chikungunya virus (CHIKV), mayaro virus, Semliki Forest virus and sindbis virus, are globally distributed and cause transient illness characterized by fever, rash, myalgia, arthralgia and arthritis in humans. Severe forms of the disease result in chronic incapacitating arthralgia and arthritis. The mechanisms of how these viruses cause musculoskeletal disease are ill defined. In recent years, the use of a mouse model for RRV-induced disease has assisted in unraveling the pathobiology of infection and in discovering novel drugs to ameliorate disease. RRV as an infection model has the potential to provide key insights into such disease processes, particularly as many viruses, other than alphaviruses, are known to cause infectious arthritides. The emergence and outbreak of CHIKV in many parts of the world has necessitated the need to develop animal models of CHIKV disease. The development of non-human primate models of CHIKV disease has given insights into viral tropism and disease pathogenesis and facilitated the development of new treatment strategies. This review highlights the application of animal models of alphaviral diseases in the fundamental understanding of the mechanisms that contribute to disease and for defining the role that the immune response may have on disease pathogenesis, with the view of providing the foundation for new treatments.

Bacterial antigen expression is an important component in inducing an immune response to orally administered Salmonella-delivered DNA vaccines.

BACKGROUND: The use of Salmonella to deliver heterologous antigens from DNA vaccines is a well-accepted extension of the success of oral Salmonella vaccines in animal models. Attenuated S. typhimurium and S. typhi strains are safe and efficacious, and their use to deliver DNA vaccines combines the advantages of both vaccine approaches, while complementing the limitations of each technology. An important aspect of the basic biology of the Salmonella/DNA vaccine platform is the relative contributions of prokaryotic and eukaryotic expression in production of the vaccine antigen. Gene expression in DNA vaccines is commonly under the control of the eukaryotic cytomegalovirus (CMV) promoter. The aim of this study was to identify and disable putative bacterial promoters within the CMV promoter and evaluate the immunogenicity of the resulting DNA vaccine delivered orally by S. typhimurium. METHODOLOGY/PRINCIPAL FINDINGS: The results reported here clearly demonstrate the presence of bacterial promoters within the CMV promoter. These promoters have homology to the bacterial consensus sequence and functional activity. To disable prokaryotic expression from the CMV promoter a series of genetic manipulations were performed to remove the two major bacterial promoters and add a bacteria transcription terminator downstream of the CMV promoter. S. typhimurium was used to immunise BALB/c mice orally with a DNA vaccine encoding the C-fragment of tetanus toxin (TT) under control of the original or the modified CMV promoter. Although both promoters functioned equally well in eukaryotic cells, as indicated by equivalent immune responses following intramuscular delivery, only the original CMV promoter was able to induce an anti-TT specific response following oral delivery by S. typhimurium. CONCLUSIONS: These findings suggest that prokaryotic expression of the antigen and co-delivery of this protein by Salmonella are at least partially responsible for the successful oral delivery of C-fragment DNA vaccines containing the CMV promoter by S. typhimurium.

Impact of prior immunological exposure on vaccine delivery by Salmonella enterica serovar Typhimurium.

Recombinant Salmonella have been employed as vaccine vectors to deliver DNA and protein vaccines of viral, bacterial and parasitic origin. However, the effectiveness of Salmonella delivery may be hampered by prior immunological exposure to Salmonella. We investigated the effects of prior exposure to the Salmonella typhimurium aroAD strain BRD509 on its ability to deliver the non-toxic C fragment of tetanus toxin (TT). BALB/c mice were orally immunised with BRD509 containing the C fragment expression plasmid pTETtac4, C fragment DNA vaccine pAT153/Cfrag or BRD509 alone and, along with age matched un-vaccinated controls, were immunised again 6 months later with BRD509 (pTETtac4). Prior exposure to Salmonella was found to significantly reduce the ability of the bacteria to colonise the Peyer's patches and mesenteric lymph nodes, spread systemically to the liver and spleen and significantly impair antibody responses to Salmonella LPS and TT. Results show that prior exposure to Salmonella significantly compromises its efficacy as a vaccine vector and these negative effects do not diminish with time. In addition, findings suggest Salmonella vaccine vectors cannot be employed to deliver multiple doses of a vaccine antigen.