Functional analysis of Salmonella Typhi adaptation to survival in water.

Contaminated water is a major risk factor associated with the transmission of Salmonella enterica serovar Typhi (S. Typhi), the aetiological agent of human typhoid. However, little is known about how this pathogen adapts to living in the aqueous environment. We used transcriptome analysis (RNA-seq) and transposon mutagenesis (TraDIS) to characterize these adaptive changes and identify multiple genes that contribute to survival. Over half of the genes in the S. Typhi genome altered expression level within the first 24 h following transfer from broth culture to water, although relatively few did so in the first 30 min. Genes linked to central metabolism, stress associated with arrested proton motive force and respiratory chain factors changed expression levels. Additionally, motility and chemotaxis genes increased expression, consistent with a scavenging lifestyle. The viaB-associated gene tviC encoding a glcNAc epimerase that is required for Vi polysaccharide biosynthesis was, along with several other genes, shown to contribute to survival in water. Thus, we define regulatory adaptation operating in S. Typhi that facilitates survival in water.

Respiratory syncytial virus in the Western Pacific Region: a systematic review and meta-analysis.

BACKGROUND: Respiratory syncytial virus (RSV) is the leading cause of viral pneumonia and bronchiolitis, especially in younger children. The burden of RSV infection in adults, particularly in the older age group, is increasingly recognised. However, RSV disease burden and molecular epidemiology in the World Health Organization (WHO) Western Pacific Region (WPR) has not been reviewed systematically. The aim of this systematic review is to investigate the epidemiological aspects of RSV (incidence, prevalence, seasonality and hospitalisation status) and the associated molecular data in the WPRO countries. METHODS: A systematic search was conducted in international literature databases (MEDLINE, EMBASE, Scopus and Web of Science) to identify RSV-related publications from January 2000 to October 2017 in the WPR countries. RESULTS: A total of 196 studies from 15 WPR countries were included. The positivity rate for RSV among respiratory tract infection patients was 16.73% (95% confidence interval (CI) = 15.12%-18.4%). The RSV-positive cases were mostly found in hospitalised compared with outpatients (18.28% vs 11.54%, P < 0.001), and children compared with adults (20.72% vs 1.87%, P < 0.001). The seasonality of RSV in the WPR countries follows the latitude, with the peak of RSV season occurring in the winter in temperate countries, and during the rainy season in tropical countries. The molecular epidemiology pattern of RSV in WPR countries was similar to the global pattern, with NA1 (RSV A) and BA (RSV B) being the predominant genotypes. CONCLUSIONS: The available data on RSV are limited in several countries within the WPR, with most data focusing on children and hospitalised patients. Further studies and surveillance, incorporating laboratory testing, are needed to determine the burden of RSV infection in the WPR countries.

Rapid transcriptional responses to serum exposure are associated with sensitivity and resistance to antibody-mediated complement killing in invasive Salmonella Typhimurium ST313.

Background: Salmonella Typhimurium ST313 exhibits signatures of adaptation to invasive human infection, including higher resistance to humoral immune responses than gastrointestinal isolates. Full resistance to antibody-mediated complement killing (serum resistance) among nontyphoidal Salmonellae is uncommon, but selection of highly resistant strains could compromise vaccine-induced antibody immunity. Here, we address the hypothesis that serum resistance is due to a distinct genotype or transcriptome response in S. Typhimurium ST313. Methods: Six S. Typhimurium ST313 bloodstream isolates, three of which were antibody resistant, were studied. Genomic content (single nucleotide polymorphisms and larger chromosomal modifications) of the strains was determined by Illumina and PACBIO sequencing, and functionally characterized using RNA-seq, transposon directed insertion site sequencing (TraDIS), targeted gene deletion and transfer of selected point mutations in an attempt to identify features associated with serum resistance.   Results: Sequence polymorphisms in genes from strains with atypical serum susceptibility when transferred from strains that were highly resistant or susceptible to a strain that exhibited intermediate susceptibility did not significantly alter serum killing phenotype. No large chromosomal modifications typified serum resistance or susceptibility. Genes required for resistance to serum identified by TraDIS and RNA-seq included those involved in exopolysaccharide synthesis, iron scavenging and metabolism. Most of the down-regulated genes were associated with membrane proteins. Resistant and susceptible strains had distinct transcriptional responses to serum, particularly related to genes responsible for polysaccharide biosynthesis. There was higher upregulation of wca locus genes, involved in the biosynthesis of colanic acid exopolysaccharide, in susceptible strains and increased expression of fepE, a regulator of very long-chain lipopolysaccharide in resistant strains. Conclusion: Clinical isolates of S. Typhimurium ST313 exhibit distinct antibody susceptibility phenotypes that may be associated with changes in gene expression on exposure to serum.

Characterisation of a live Salmonella vaccine stably expressing the Mycobacterium tuberculosis Ag85B-ESAT6 fusion protein.

A recombinant Salmonella enterica serovar Typhimurium (S. Typhimurium) vaccine strain was constructed that stably expressed the Mycobacterium tuberculosis fusion antigen Ag85B-ESAT6 from the chromosome. Live oral vaccination of mice with the Salmonella/Ag85B-ESAT6 strain generated a potent anti-Ag85B-ESAT6 T(H)1 response with high antibody titres with a IgG2a-bias and significant IFN-gamma production lasting over a 120-day period. When mice primed with the Salmonella/Ag85B-ESAT6 vaccine were mucosally boosted with the Ag85B-ESAT6 antigen and adjuvant the IFN-gamma responses increased markedly. To determine the protective efficacy of this vaccine strain, guinea pigs were immunised and followed for a 30-week period after aerosol challenge with M. tuberculosis. The heterologous prime-boost strategy of live Salmonella vaccine followed by a systemic boost of antigen and adjuvant reduced the levels of M. tuberculosis bacteria in the lungs and spleen to the same extent as BCG. Additionally, this vaccination regimen was observed to be statistically equivalent in terms of protection to immunisation with BCG. Thus, live oral priming with the recombinant Salmonella/Ag85B-ESAT6 and boosting with Ag85B-ESAT6 plus the adjuvant LTK63 represents an effective mucosal vaccination regimen.