We provide insights into the in vivo evolution of colistin resistance in a series of XDR A. baumannii isolates recovered during therapy of infections and emphasize the importance of antibiotic stewardship and surveillance.
BackgroundBacteriophages specific for Yersinia pestis are routinely used for plague diagnostics and could be an alternative to antibiotics in case of drug-resistant plague. A major concern of bacteriophage therapy is the emergence of phage-resistant mutants. The use of phage cocktails can overcome this problem but only if the phages exploit different receptors. Some phage-resistant mutants lose virulence and therefore should not complicate bacteriophage therapy.Methodology/Principal FindingsThe purpose of this work was to identify Y. pestis phage receptors using site-directed mutagenesis and trans-complementation and to determine potential attenuation of phage-resistant mutants for mice. Six receptors for eight phages were found in different parts of the lipopolysaccharide (LPS) inner and outer core. The receptor for R phage was localized beyond the LPS core. Most spontaneous and defined phage-resistant mutants of Y. pestis were attenuated, showing increase in LD50 and time to death. The loss of different LPS core biosynthesis enzymes resulted in the reduction of Y. pestis virulence and there was a correlation between the degree of core truncation and the impact on virulence. The yrbH and waaA mutants completely lost their virulence.Conclusions/SignificanceWe identified Y. pestis receptors for eight bacteriophages. Nine phages together use at least seven different Y. pestis receptors that makes some of them promising for formulation of plague therapeutic cocktails. Most phage-resistant Y. pestis mutants become attenuated and thus should not pose a serious problem for bacteriophage therapy of plague. LPS is a critical virulence factor of Y. pestis.
BackgroundInfections by pan-drug resistant Acinetobacter baumannii plague military and civilian healthcare systems. Previous A. baumannii pan-genomic studies used modest sample sizes of low diversity and comparisons to a single reference genome, limiting our understanding of gene order and content. A consensus representation of multiple genomes will provide a better framework for comparison. A large-scale comparative study will identify genomic determinants associated with their diversity and adaptation as a successful pathogen.ResultsWe determine draft-level genomic sequence of 50 diverse military isolates and conduct the largest bacterial pan-genome analysis of 249 genomes. The pan-genome of A. baumannii is open when the input genomes are normalized for diversity with 1867 core proteins and a paralog-collapsed pan-genome size of 11,694 proteins. We developed a novel graph-based algorithm and use it to assemble the first consensus pan-chromosome, identifying both the order and orientation of core genes and flexible genomic regions. Comparative genome analyses demonstrate the existence of novel resistance islands and isolates with increased numbers of resistance island insertions over time, from single insertions in the 1950s to triple insertions in 2011. Gene clusters responsible for carbon utilization, siderophore production, and pilus assembly demonstrate frequent gain or loss among isolates.ConclusionsThe highly variable and dynamic nature of the A. baumannii genome may be the result of its success in rapidly adapting to both abiotic and biotic environments through the gain and loss of gene clusters controlling fitness. Importantly, some archaic adaptation mechanisms appear to have reemerged among recent isolates.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0701-6) contains supplementary material, which is available to authorized users.
Brucellae are gram-negative intracellular pathogens which can survive and multiply within the phagocytic cells of their hosts and are resistant to the bactericidal action of serum. Brucella melitensis is considered the principal cause of human brucellosis (40,41) and is more virulent than B. abortus (42). These species may occur as either smooth or rough variants depending on the expression of O-polysaccharides (OPS) as a component of the bacterial outer membrane lipopolysaccharide (LPS). In rough strains expression of OPS is limited or absent and attenuation in virulence is generally observed (1,4,19,26,31,35). Our previous studies demonstrated that smooth B. melitensis and B. abortus strains bind fewer complement components on their surface than their corresponding roughmutant organisms (13) obtained by disruption or deletion of the wboA gene (13,26,37,40). However, OPS-deficient strains derived from smooth, virulent B. melitensis 16M are as resistant as the wild type to the bactericidal action of nonimmune human serum (HS) and bind less complement than OPS-deficient strains derived from B. abortus 2308 (13). Since rough mutants of B. melitensis are protected from extracellular complement-mediated killing, we decided to investigate whether the attenuation in virulence previously observed in these strains was associated with differences in their interaction with macrophages.The green fluorescent protein (GFP) from the jellyfish Aequorea victoria is a self-fluorescing protein that requires no substrates and emits bright green fluorescence at 509 nm (3). We took advantage of the properties of the GFP to study the interaction of fluorescent rough and smooth B. melitensis strains with human mononuclear phagocytes and to evaluate the importance of the presence of OPS in the pathogenesis of brucellosis. We introduced plasmid pBBR1MCS-6Y (29) expressing GFP into 16M, OPS-deficient ⌬wboA B. melitensis strain WRR51, and WRR51 complemented with wboA and examined interactions of the fluorescent bacteria with human and murine macrophages by fluorescent and electron microscopy, flow cytometry, and release of lactate dehydrogenase (LDH). We found that infection of mononuclear phagocytes with WRR51 was followed by host cell apoptosis and bacterial death. In contrast, infection with either 16M or wboA-complemented WRR51 led to intracellular bacterial replication but not host cell apoptosis. Moreover, infection with the latter
To gain insights into the origin and genome evolution of the plague bacterium Yersinia pestis, we have sequenced the deep-rooted strain Angola, a virulent Pestoides isolate. Its ancient nature makes this atypical isolate of particular importance in understanding the evolution of plague pathogenicity. Its chromosome features a unique genetic make-up intermediate between modern Y. pestis isolates and its evolutionary ancestor, Y. pseudotuberculosis. Our genotypic and phenotypic analyses led us to conclude that Angola belongs to one of the most ancient Y. pestis lineages thus far sequenced. The mobilome carries the first reported chimeric plasmid combining the two species-specific virulence plasmids. Genomic findings were validated in virulence assays demonstrating that its pathogenic potential is distinct from modern Y. pestis isolates. Human infection with this particular isolate would not be diagnosed by the standard clinical tests, as Angola lacks the plasmid-borne capsule, and a possible emergence of this genotype raises major public health concerns. To assess the genomic plasticity in Y. pestis, we investigated the global gene reservoir and estimated the pangenome at 4,844 unique protein-coding genes. As shown by the genomic analysis of this evolutionary key isolate, we found that the genomic plasticity within Y. pestis clearly was not as limited as previously thought, which is strengthened by the detection of the largest number of isolate-specific single-nucleotide polymorphisms (SNPs) currently reported in the species. This study identified numerous novel genetic signatures, some of which seem to be intimately associated with plague virulence. These markers are valuable in the development of a robust typing system critical for forensic, diagnostic, and epidemiological studies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.