Antibacterial activity of novel bacterial topoisomerase inhibitors against key veterinary pathogens.

Multidrug-resistant bacteria infect companion animals and livestock in addition to their devastating impact on human health. Novel Bacterial Topoisomerase Inhibitors (NBTIs) with excellent activity against Gram-positive bacteria have previously been identified as promising new antibacterial agents. Herein, we evaluate the antibacterial activity of these NBTIs against a variety of important veterinary pathogens and demonstrate outstanding in vitro activity, especially against staphylococci.

Adult zebrafish model of streptococcal infection.

Streptococcal pathogens cause a wide array of clinical syndromes in humans, including invasive systemic infections resulting in high mortality rates. Many of these pathogens are human specific, and therefore difficult to analyze in vivo using typical animal models, as these models rarely replicate what is observed in human infections. This unit describes the use of the zebrafish (Danio rerio) as an animal model for streptococcal infection to analyze multiple disease states. This model closely mimics the necrotizing fasciitis/myositis pathology observed in humans from a Streptococcus pyogenes infection. The use of a zoonotic pathogen, Streptococcus iniae, which replicates systemic infections caused by many streptococcal pathogens, including dissemination to the brain, is also described. Protocols describing both intraperitoneal and intramuscular infections, as well as methods for histological and quantitative measurements of infection, are also described.

SalY of the Streptococcus pyogenes lantibiotic locus is required for full virulence and intracellular survival in macrophages.

Streptococcus pyogenes utilizes numerous mechanisms for evading the host immune response but has only recently been found to survive in the intracellular environment. In this study, we demonstrate the requirement of a putative ABC transporter permease for intracellular survival in macrophages. The highly attenuated S. pyogenes mutant, SalY, was identified from a transposon mutagenesis screen, with over 200-fold attenuation in virulence in a zebrafish invasive-disease model. Sequencing of the region surrounding the insertion identified a locus that is highly conserved in other S. pyogenes genomes and is homologous to an operon involved in lantibiotic production. In vitro analysis demonstrated that the SalY mutant is deficient in intracellular survival in murine macrophages, a phenotype also observed in zebrafish macrophages in vivo. Macrophage crude cell lysates added to bacterial cultures resulted in the death of the SalY mutant but only growth inhibition of the wild-type strain. Specific depletion of zebrafish macrophages in vivo restored the ability of the SalY mutant to cause disease to wild-type levels. The SalY-infected, macrophage-depleted zebrafish exhibit large lesions and invasive dissemination at a rate and level similar to those of the wild type. In contrast, an M protein mutant with a degree of attenuation similar to that of the SalY mutant did not regain full virulence by in vivo depletion of macrophages. The putative SalY ABC transporter may be an example of the ability of S. pyogenes to adapt and evolve new survival strategies that allow dissemination and growth in previously uninhabitable sites.

Evolution of the zebrafish model: from development to immunity and infectious disease.

The successful zebrafish developmental model has now expanded to being used as a model for the analysis of host-pathogen interactions during infectious disease. Numerous pathogens have been demonstrated to infect zebrafish and new mechanisms of virulence, as well as host defense have been uncovered using this new model. In this review we summarize the literature on how the zebrafish infectious disease model is being used to decipher virulence mechanisms used by various pathogens and the host defense mechanisms initiated to combat infection.