Hsp90 governs dispersion and drug resistance of fungal biofilms

Fungal biofilms are a major cause of human mortality and are recalcitrant to most treatments due to intrinsic drug resistance. These complex communities of multiple cell types form on indwelling medical devices and their eradication often requires surgical removal of infected devices. Here we implicate the molecular chaperone Hsp90 as a key regulator of biofilm dispersion and drug resistance. We previously established that in the leading human fungal pathogen, Candida albicans, Hsp90 enables the emergence and maintenance of drug resistance in planktonic conditions by stabilizing the protein phosphatase calcineurin and MAPK Mkc1. Hsp90 also regulates temperature-dependent C. albicans morphogenesis through repression of cAMP-PKA signalling. Here we demonstrate that genetic depletion of Hsp90 reduced C. albicans biofilm growth and maturation in vitro and impaired dispersal of biofilm cells. Further, compromising Hsp90 function in vitro abrogated resistance of C. albicans biofilms to the most widely deployed class of antifungal drugs, the azoles. Depletion of Hsp90 led to reduction of calcineurin and Mkc1 in planktonic but not biofilm conditions, suggesting that Hsp90 regulates drug resistance through different mechanisms in these distinct cellular states. Reduction of Hsp90 levels led to a marked decrease in matrix glucan levels, providing a compelling mechanism through which Hsp90 might regulate biofilm azole resistance. Impairment of Hsp90 function genetically or pharmacologically transformed fluconazole from ineffectual to highly effective in eradicating biofilms in a rat venous catheter infection model. Finally, inhibition of Hsp90 reduced resistance of biofilms of the most lethal mould, Aspergillus fumigatus, to the newest class of antifungals to reach the clinic, the echinocandins. Thus, we establish a novel mechanism regulating biofilm drug resistance and dispersion and that targeting Hsp90 provides a much-needed strategy for improving clinical outcome in the treatment of biofilm infections

Sites of persistence of Fusobacterium necrophorum and Dichelobacter nodosus: a paradigm shift in understanding the epidemiology of footrot in sheep

Sites of persistence of bacterial pathogens contribute to disease dynamics of bacterial diseases. Footrot is a globally important bacterial disease that reduces health and productivity of sheep. It is caused by Dichelobacter nodosus, a pathogen apparently highly specialised for feet, while Fusobacterium necrophorum, a secondary pathogen in footrot is reportedly ubiquitous on pasture. Two prospective longitudinal studies were conducted to investigate the persistence of D. nodosus and F. necrophorum in sheep feet, mouths and faeces, and in soil. Molecular tools were used to detect species, strains and communities. In contrast to the existing paradigm, F. necrophorum persisted on footrot diseased feet, and in mouths and faeces; different strains were detected in feet and mouths. D. nodosus persisted in soil and on diseased, but not healthy, feet; similar strains were detected on both healthy and diseased feet of diseased sheep. We conclude that D. nodosus and F. necrophorum depend on sheep for persistence but use different strategies to persist and spread between sheep within and between flocks. Elimination of F. necrophorum would be challenging due to faecal shedding. In contrast D. nodosus could be eliminated if all footrot-affected sheep were removed and fade out of D. nodosus occurred in the environment before re-infection of a foot

Alveolar hypoxia, alveolar macrophages, and systemic inflammation

Diseases featuring abnormally low alveolar PO2 are frequently accompanied by systemic effects. The common presence of an underlying inflammatory component suggests that inflammation may contribute to the pathogenesis of the systemic effects of alveolar hypoxia. While the role of alveolar macrophages in the immune and defense functions of the lung has been long known, recent evidence indicates that activation of alveolar macrophages causes inflammatory disturbances in the systemic microcirculation. The purpose of this review is to describe observations in experimental animals showing that alveolar macrophages initiate a systemic inflammatory response to alveolar hypoxia. Evidence obtained in intact animals and in primary cell cultures indicate that alveolar macrophages activated by hypoxia release a mediator(s) into the circulation. This mediator activates perivascular mast cells and initiates a widespread systemic inflammation. The inflammatory cascade includes activation of the local renin-angiotensin system and results in increased leukocyte-endothelial interactions in post-capillary venules, increased microvascular levels of reactive O2 species; and extravasation of albumin. Given the known extrapulmonary responses elicited by activation of alveolar macrophages, this novel phenomenon could contribute to some of the systemic effects of conditions featuring low alveolar PO2

Factors Affecting the Invitro Adherence of Candida-Albicans to Acrylic Surfaces

The fitting surface of the upper denture is the main reservoir of yeasts in patients with chronic atrophic candidosis. Because little is known about the adhesion of Candida albicans to acrylic surfaces, an in-vitro technique was used to investigate the effect of sucrose, glucose, lactose, xylitol, mixed and parotid saliva, serum and Streptococcus salivarius on adhesion. Enhancement of candidal adhesion was seen on serum-coated acrylic strips and by yeasts incubated in sucrose, glucose and a dialysate of Strep. salivarius. Pre-coating acrylic strips with mixed saliva, 2 per cent chlorhexidine and Strep. salivarius reduced adhesion, while pre-coating strips with 0.2 per cent chlorhexidine and parotid saliva or pre-incubating yeasts in lactose and xylitol had no significant effect on adhesion. This study suggests that the factors involved in the adhesion of C. albicans to acrylic surfaces are complex, and that they may play an important role in the aetiology of chronic atrophic candidosis.link_to_subscribed_fulltex

Effect of Saliva and Serum On the Adherence of Candida Species to Chlorhexidine-Treated Denture Acrylic

The effect of saliva and serum on the adherence of five strains of Candida albicans and one each of C. tropicalis and C. glabrata to chlorhexidine-pretreated acrylic was measured in vitro. A four-fold dilution of saliva or serum significantly inactivated the fungicidal effect of chlorhexidine gluconate. Pretreatment of the acrylic with unstimulated mixed saliva for 30 min led to a reduced adherence for all the Candida strains tested, whilst a similar pretreatment with serum slightly increased adhesion. Moreover treatment of saliva- or serum-coated acrylic with chlorhexidine gluconate 2% reduced adherence by between 19% and 86%. The inhibition of yeast adherence by chlorhexidine persisted for up to 19 days after the exposure of the acrylic strips to the disinfectanct.link_to_subscribed_fulltex

Effect of chlorhexidine gluconate on the adherence of Candida species to denture acrylic

The effect of pretreatment of denture acrylic with chlorhexidine gluconate on the subsequent adherence of Candida albicans GDH 2346 was measured in vitro. Adherence was significantly reduced by pretreatment with chlorhexidine; maximal inhibition was achieved by incubation at room temperature for 30 min in 2% chlorhexidine. Inhibition of adherence was greatest when the organisms were grown in conditions that enhanced adherence the most, i.e., growth to stationary phase in high concentrations of galactose and sucrose. Yeasts grown in high concentrations of galactose, which were the most adherent to acrylic, were also the most sensitive to the fungicidal action of chlorhexidine gluconate, whereas those grown in a low concentration of glucose were the least adherent and also the most resistant. Adherence to acrylic of seven strains of C. albicans isolated from active infections (I strains) and grown in medium containing 500 mM sucrose was significantly higher than that of four strains obtained from asymptomatic carriers (C strains). A spectrum of adherence values was obtained when various yeasts other than C. albicans were tested.link_to_subscribed_fulltex