Strain-Specific Association of Cytotoxic Activity and Virulence of Clinical Staphylococcus aureus Isolates

Staphylococcus aureus has been shown to invade and induce the death of various cell types. Here we investigate whether the cytotoxicity of intracellular S. aureus is a general feature or rather characteristic of individual S. aureus strains. The majority of 23 randomly collected clinical S. aureus isolates were killed inside keratinocytes and fibroblasts, indicating that the uptake of S. aureus represents an important mechanism of cell-autonomous host defense. However, seven independent S. aureus isolates survived intracellularly and induced significant cytotoxicity for their host cells. Subcloning analysis revealed that the ability or inability to kill host cells is a stable, apparently genetically determined trait of a given S. aureus isolate. We show that noncytotoxic strains but not cytotoxic strains colocalize with the lysosomal marker LAMP-1, suggesting that only cytotoxic strains escape degradation by the endolysosomal pathway. In a mouse septicemic model, cytotoxic S. aureus isolates produce significantly greater lethality (96%) compared to noncytotoxic strains (41%), which corresponds to 23-, 63-, and 30,000-fold increases of bacterial loads in the liver, spleen, and kidney, respectively. Finally, cytotoxic S. aureus strains produce clinically apparent arthritis in mice at a greater frequency than compared to noncytotoxic S. aureus strains. The results of our study unravel a previously unrecognized dichotomy of cytotoxic and noncytotoxic S. aureus isolates, which may play an important role in the dissemination of, and mortality induced by, S. aureus infection

Int. J. Dev. Biol.

Peptides are increasingly attracting attention as primary signals in the control of development. Even though a large number of peptides have been characterized in cnidarians, little experimental evidence addresses their endogenous role. The life cycle of Hydractinia echinata includes metamorphosis from planula larva into the adult stage of the polyp. This process of stage conversion includes internal signalling, which controls cell cycle activity, cell differentiation, cell death and proportion-controlled morphogenesis. LWamide peptides are considered to be part of the control system. We implemented methods to silence gene activity by dsRNAi in Hydractinia and show a substantial knock-down of LWamide gene activity. In addition, LWamide function was knocked-out pharmacologically by targeting the biosynthesis of amidated peptides and thus preventing functional LWamides. Here we show that extinction of bioactive LWamides from planulae causes loss of metamorphosis competence, a deficiency which can be rescued by synthetic LWamide peptides. Thus, it is shown that LWamides are indispensable and act by conveying outer metamorphosis stimuli to target cells within the animal. Considering non-availability of genetic analysis and the so-far limited success in expressing transgenes in hydroids, gene functions are difficult to analyse in hydroids. The approach as outlined here is suitable for functional analysis of genes encoding amidated peptides in hydroids

The role of alpha-amidated neuropeptides in hydroid development - LWamides and metamorphosis in Hydractinia echinata

Peptides are increasingly attracting attention as primary signals in the control of development. Even though a large number of peptides have been characterized in cnidarians, little experimental evidence addresses their endogenous role. The life cycle of Hydractinia echinata includes metamorphosis from planula larva into the adult stage of the polyp. This process of stage conversion includes internal signalling, which controls cell cycle activity, cell differentiation, cell death and proportion-controlled morphogenesis. LWamide peptides are considered to be part of the control system. We implemented methods to silence gene activity by dsRNAi in Hydractinia and show a substantial knock-down of LWamide gene activity. In addition, LWamide function was knocked-out pharmacologically by targeting the biosynthesis of amidated peptides and thus preventing functional LWamides. Here we show that extinction of bioactive LWamides from planulae causes loss of metamorphosis competence, a deficiency which can be rescued by synthetic LWamide peptides. Thus, it is shown that LWamides are indispensable and act by conveying outer metamorphosis stimuli to target cells within the animal. Considering non-availability of genetic analysis and the so-far limited success in expressing transgenes in hydroids, gene functions are difficult to analyse in hydroids. The approach as outlined here is suitable for functional analysis of genes encoding amidated peptides in hydroids