ABSTRACT
BACKGROUND: Shigella dysenteriae type 1 (Sd1) causes recurrent epidemics of dysentery associated with high mortality in many regions of the world. Sd1 infects humans at very low infectious doses (10 CFU), and treatment is complicated by the rapid emergence of antibiotic resistant Sd1 strains. Sd1 is only detected in the context of human infections, and the circumstances under which epidemics emerge and regress remain unknown. RESULTS: Phylogenomic analyses of 56 isolates collected worldwide over the past 60 years indicate that the Sd1 clone responsible for the recent pandemics emerged at the turn of the 20th century, and that the two world wars likely played a pivotal role for its dissemination. Several lineages remain ubiquitous and their phylogeny indicates several recent intercontinental transfers. Our comparative genomics analysis reveals that isolates responsible for separate outbreaks, though closely related to one another, have independently accumulated antibiotic resistance genes, suggesting that there is little or no selection to retain these genes in-between outbreaks. The genomes appear to be subjected to genetic drift that affects a number of functions currently used by diagnostic tools to identify Sd1, which could lead to the potential failure of such tools. CONCLUSIONS: Taken together, the Sd1 population structure and pattern of evolution suggest a recent emergence and a possible human carrier state that could play an important role in the epidemic pattern of infections of this human-specific pathogen. This analysis highlights the important role of whole-genome sequencing in studying pathogens for which epidemiological or laboratory investigations are particularly challenging.
Subject(s)
Dysentery, Bacillary/epidemiology , Shigella dysenteriae/genetics , Anti-Bacterial Agents/pharmacology , Disease Outbreaks , Drug Resistance, Bacterial/drug effects , Dysentery, Bacillary/history , Evolution, Molecular , Genetic Variation , Genome, Bacterial , Genomics , High-Throughput Nucleotide Sequencing , History, 20th Century , Humans , Phylogeny , Sequence Analysis, DNA , Shigella dysenteriae/classification , Shigella dysenteriae/isolation & purificationABSTRACT
The severe and fatal human disease, tularemia, results from infection with the Gram-negative pathogen Francisella tularensis. Identification of surface outer membrane proteins, specifically lipoproteins, has been of interest for vaccine development and understanding the initiation of disease. We sought to identify Francisella live vaccine strain lipoproteins that could be a component of a subunit vaccine and have adjuvant properties as TLR2 agonists. We have identified a membrane lipoprotein of Francisella LVS isolated by sarkosyl extraction and gel filtration chromatography that is recognized by sera from LVS-vaccinated individuals and tularemia patients, indicating its potential diagnostic value. Sequencing of the protein by mass spectrometry indicated that it encodes the FTL_0645 open reading frame of F. holarctica LVS, which is 100% identical/homologous to FTT1416c of F. tularensis Schu S4. The predicted 137 amino acid lipoprotein encoded by FTL_0645 ORF, was expressed in Escherichia coli, purified, and demonstrated to be a lipoprotein. This recombinant lipoprotein, named Flpp3, was able to activate TLR2 and induce an immunogenic response in mice, suggesting that the E. coli-expressed Flpp3 is palmitoylated and closely resembles the native protein in structure and immunogenicity. Taken together, these data suggest that Flpp3 could be a candidate for inclusion in a F. tularensis vaccine.
Subject(s)
Bacterial Proteins/immunology , Bacterial Proteins/isolation & purification , Cloning, Molecular , Francisella tularensis/immunology , Gene Expression , Lipoproteins/immunology , Lipoproteins/isolation & purification , Tularemia/immunology , Amino Acid Sequence , Animals , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Base Sequence , Cell Line , Female , Francisella tularensis/chemistry , Francisella tularensis/genetics , Humans , Lipoproteins/chemistry , Lipoproteins/genetics , Mice , Mice, Inbred BALB C , Molecular Sequence Data , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/immunology , Recombinant Proteins/isolation & purification , Sequence Alignment , Tularemia/microbiologyABSTRACT
Francisella tularensis are the causative agent of the zoonotic disease, tularaemia. Among four F. tularensis subspecies, ssp. novicida (F. novicida) is pathogenic only for immunocompromised individuals, while all four subspecies are pathogenic for mice. This study utilized proteomic and bioinformatic approaches to identify seven F. novicida secreted proteins and the corresponding Type IV pilus (T4P) secretion system. The secreted proteins were predicted to encode two chitinases, a chitin binding protein, a protease (PepO), and a beta-glucosidase (BglX). The transcription of F. novicida pepO and bglX was regulated by the virulence regulator MglA. Intradermal infection of mice with F. novicida mutants defective in T4P secretion system or PepO resulted in enhanced F. novicida spread to systemic sites. Infection with F. novicida pepO mutants also resulted in increased neutrophil infiltration into the mouse airways. PepO is a zinc protease that is homologous to mammalian endothelin-converting enzyme ECE-1. Therefore, secretion of PepO likely results in increased production of endothelin and increased vasoconstriction at the infection site in skin that limits the F. novicida spread. Francisella human pathogenic strains contain a mutation in pepO predicted to abolish its secretion. Loss of PepO function may have contributed to evolution of highly virulent Francisellae.
