Legionella pneumophila, the causative organism of Legionnaires' disease, is a fresh-water bacterium and intracellular parasite of amoebae. This study examined the effects of incubation in water and amoeba encystment on L. pneumophila strain JR32 and null mutants in dot/icm genes encoding a type IVB secretion system required for entry, delayed acidification of L. pneumophila-containing phagosomes, and intracellular multiplication when stationary-phase bacteria infect amoebae and macrophages. Following incubation of stationaryphase cultures in water, mutants in dotA and dotB, essential for function of the type IVB secretion system, exhibited entry and delay of phagosome acidification comparable to that of strain JR32. Following encystment in Acanthamoeba castellanii and reversion of cysts to amoeba trophozoites, dotA and dotB mutants exhibited intracellular multiplication in amoebae. The L. pneumophila Lvh locus, encoding a type IVA secretion system homologous to that in Agrobacterium tumefaciens, was required for restoration of entry and intracellular multiplication in dot/icm mutants following incubation in water and amoeba encystment and was required for delay of phagosome acidification in strain JR32. These data support a model in which the Dot/Icm type IVB secretion system is conditionally rather than absolutely required for L. pneumophila virulence-related phenotypes. The data suggest that the Lvh type IVA secretion system, previously thought to be dispensable, is involved in virulence-related phenotypes under conditions mimicking the spread of Legionnaires' disease from environmental niches. Since environmental amoebae are implicated as reservoirs for an increasing number of environmental pathogens and for drug-resistant bacteria, the environmental mimics developed here may be useful in virulence studies of other pathogens.Legionnaires' disease is a potentially fatal pneumonia acquired by inhalation of aerosols containing Legionella pneumophila from standing-water reservoirs of man-made origin (10,11,47). L. pneumophila, the causative organism (58), is a freshwater bacterium capable of entry and intracellular multiplication in aquatic amoebae (38,39). In response to environmental stress, amoebae containing internalized bacteria can form cysts that resist killing by water purification treatment (32,39,49,70). In this fashion, L. pneumophila housed within amoeba cysts is proposed to enter domestic water supplies. Subsequent aerosolization and inhalation of encysted bacteria by susceptible persons is proposed to lead to Legionnaires' disease via entry, intracellular multiplication, and killing of alveolar macrophages by L. pneumophila.Virulence genes in L. pneumophila have been identified by screening for defective phenotypes following infection of macrophages and amoebae with bacteria cultured to stationary phase in rich medium. This approach identified mutants in the dot/icm (defective organelle trafficking/intracellular multiplication) genes (9,12,72,96). Based on homology of dot/icm genes to plasmid conjug...
Introduction —An arteriovenous fistula between the subclavian artery and the internal jugular vein represents a rare iatrogenic injury that has almost exclusively been described on the right side. We describe the case of an arteriovenous fistula between the left subclavian artery and the left internal jugular vein after attempted central venous cannulation. The initial duplex ultrasound exam established the definitive diagnosis. Patient Description —A 72-year-old man had a central venous catheter inadvertently placed in the arterial system during attempted cannulation of the left internal jugular vein. After the catheter was removed, a duplex ultrasound exam of the left common carotid artery was requested to evaluate for injury. Methods —A carotid duplex ultrasound exam was performed using an Acuson Antares Ultrasound System with a VFX 9–4 MHz probe. The left common, internal, and external carotid arteries were evaluated with grayscale imaging; color Doppler, and spectral flow analysis. The left vertebral artery and subclavian arteries were also evaluated sonographically. Results —The duplex ultrasound did not detect an injury to the left common carotid artery; however, a color flow bruit was noted in the surrounding tissue. Further investigation clearly demonstrated a high-flow vascular communication between the left subclavian artery and the left internal jugular vein consistent with an arteriovenous fistula. The arteriovenous fistula was treated with an endovascular intervention that involved placing a stent graft in the left subclavian artery to cover the arterial origin of the arteriovenous fistula. The completion arteriogram and follow-up duplex ultrasound showed that the stent graft completely excluded the arteriovenous fistula. Conclusion —This case describes an extremely rare iatrogenic arteriovenous fistula between the left subclavian artery and the left internal jugular vein. The images obtained with duplex sonography were detailed enough to definitively diagnose the injury and plan for treatment.
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