Priority effects dictate community structure and alter virulence of fungal-bacterial biofilms

Polymicrobial biofilms are a hallmark of chronic wound infection. The forces governing assembly and maturation of these microbial ecosystems are largely unexplored but the consequences on host response and clinical outcome can be significant. In the context of wound healing, formation of a biofilm and a stable microbial community structure is associated with impaired tissue repair resulting in a non-healing chronic wound. These types of wounds can persist for years simmering below the threshold of classically defined clinical infection (which includes heat, pain, redness, and swelling) and cycling through phases of recurrent infection. In the most severe outcome, amputation of lower extremities may occur if spreading infection ensues. Here we take an ecological perspective to study priority effects and competitive exclusion on overall biofilm community structure in a three-membered community comprised of strains of Staphylococcus aureus, Citrobacter freundii, and Candida albicans derived from a chronic wound. We show that both priority effects and inter-bacterial competition for binding to C. albicans biofilms significantly shape community structure on both abiotic and biotic substrates, such as ex vivo human skin wounds. We further show attachment of C. freundii to C. albicans is mediated by mannose-binding lectins. Co-cultures of C. freundii and C. albicans trigger the yeast-to-hyphae transition, resulting in a significant increase in neutrophil death and inflammation compared to either species alone. Collectively, the results presented here facilitate our understanding of fungal-bacterial interactions and their effects on host-microbe interactions, pathogenesis, and ultimately, wound healing.Subject terms: Fungi, Biofilms, Microbial ecology, Pathogenesis     

Prepubertal changes in the hypothalamic-pituitary axis of Holstein bulls

We investigated the nature and sites of changes in the hypothalamic-pituitary axis associated with the onset of high-frequency, high-amplitude discharges of luteinizing hormone (LH) in young bulls during the transition from the infantile to the prepubertal phase of development. Blood serum and neuroendocrine tissues from bulls killed at 1, 6, 10, 14, or 18 wk of age were evaluated. Concentrations of LH in serum from bulls 1 or 6 wk old averaged less than 0.25 ng/ml and only one episodic discharge of LH was detected for 10 bulls. At 10, 14, or 18 wk, 14 of 15 bulls had episodic discharges of LH. Concentrations of testosterone in serum were progressively higher at 10, 14, and 18 wk, but the concentration of estradiol was maximal at 6 wk. The concentrations of gonadotropin-releasing hormone (GnRH) in the anterior hypothalamus, posterior hypothalamus, or median eminence were not influenced by age. However, concentration of GnRH receptors in the anterior pituitary gland increased 314% between 6 and 10 wk and the concentration of LH increased 67%. Between 6 and 10 wk, concentrations of estradiol receptors in the anterior and posterior hypothalamus declined by 68% and 46%, but the concentration of estradiol receptors in the anterior pituitary gland increased by 103%. For most characteristics, there was no major change between 10 and 18 wk. We postulate that between 6 and 10 wk of age, there is 1) removal of an estradiol-mediated block of GnRH secretion and 2) an estradiol-mediated, and possibly GnRH-mediated, increase in pituitary GnRH receptors. Together, these changes result in greatly increased stimulation of the anterior pituitary gland by GnRH between 6 and 10 wk of age and stimulation of the discharges of LH characteristic of bulls in the early prepubertal phase of development.     

Pituitary gonadotropin-releasing hormone (GnRH) receptor: structure, distribution and regulation of expression

Reproduction in mammals is controlled by interactions between the hypothalamus, anterior pituitary and gonads. Interaction of GnRH with its cognate receptor is essential to regulating reproduction. Characterization of the structure, distribution and expression of GnRH receptors (GnRH-R) has furthered our understanding of the physiological consequences of GnRH stimulation of pituitary gonadotropes. Based on the putative topology of the amino acid sequence of the GnRH-R and point mutation studies, key elements of the GnRH-R have been identified to play a role in ligand recognition and binding, G-protein activation and internalization. Normally, reproductive function is mediated by GnRH-R expressed only on the membranes of pituitary gonadotropes. The density of GnRH-R on gonadotropes determines their ability to respond to GnRH. This density is highest just prior to ovulation and likely is important for complete expression of the pre-ovulatory surge of LH. Therefore, knowledge regarding what regulates the density of GnRH-R is essential to understanding changes in pituitary sensitivity to GnRH and ultimately, to expression of the LH surge. Regulation of GnRH-R gene expression is influenced by a multitude of factors including gonadal steroid hormones, inhibin, activin and perhaps most importantly GnRH itself.     

The distribution and evolutionary history of the PRP8 intein

Background  

We recently described a mini-intein in the PRP8 gene of a strain of the basidiomycete Cryptococcus neoformans, an important fungal pathogen of humans. This was the second described intein in the nuclear genome of any eukaryote; the first nuclear encoded intein was found in the VMA gene of several saccharomycete yeasts. The evolution of eukaryote inteins is not well understood. In this report we describe additional PRP8 inteins (bringing the total of these to over 20). We compare and contrast the phylogenetic distribution and evolutionary history of the PRP8 intein and the saccharomycete VMA intein, in order to derive a broader understanding of eukaryote intein evolution. It has been suggested that eukaryote inteins undergo horizontal transfer and the present analysis explores this proposal.     

Review of techniques for diagnosis of catheter-related Candida biofilm infections

Recent evidence shows that many hospital-acquired infections, including most device-associated infections, involve the persistence of sessile organisms in the form of biofilms that are attached to a device surface and encased in an extracellular matrix. The cells in this environment exhibit an altered phenotype with respect to antimicrobial resistance and thus are extraordinarily difficult to eradicate without device removal. Although a number of implantable and topical devices are at risk for Candida biofilm formation, this review focuses on the diagnosis of the most common of these infections, biofilm growth on the surface of central venous catheters and urinary catheters.     

Blastomyces dermatitidis serine protease dipeptidyl peptidase IVA (DppIVA) cleaves ELR+CXC chemokines altering their effects on neutrophils

Blastomycosis elicits a pyogranulomatous inflammatory response that involves a prominent recruitment of neutrophils to the site of infection. Although neutrophils are efficiently recruited to the site of infection, this event is paradoxically coupled with the host's inability to control infection by Blastomyces dermatitidis, the causative agent. The mechanisms underlying this characteristic pyogranulomatous response and inability of neutrophils to kill the yeast are poorly understood. We recently reported that the fungal protease dipeptidyl peptidase IVA (DppIVA) promotes B. dermatitidis virulence by cleaving a dipeptide from the N‐terminus of C–C chemokines and granulocyte/macrophage‐colony stimulating factor, thereby inactivating them. Herein, we present evidence that DppIVA can also truncate the N‐terminus of members of the ELR⁺CXC chemokine family, which are known to modulate neutrophil function. We show that the DppIVA cleaved form of human (h) CXCL‐2, for example, hCXCL‐2 (3‐73), is a more potent neutrophil chemoattractant than its intact counterpart, but hCXCL‐2 (3‐73) is conversely impaired in its ability to prime the reactive oxygen species response of neutrophils. Thus, DppIVA action on ELR⁺CXC chemokines may promote the pyogranulomatous response that is typical of blastomycosis, while also explaining the inability of neutrophils to control infection.