Phospholipase B Is Critical for Cryptococcus neoformans Survival in the Central Nervous System.

Cryptococcus neoformans (Cn) is an opportunistic, encapsulated, yeast-like fungus that causes severe meningoencephalitis, especially in countries with high HIV prevalence. In addition to its well-known polysaccharide capsule, Cn has other virulence factors such as phospholipases, a heterogeneous group of enzymes that hydrolyze ester linkages in glycerophospholipids. Phospholipase B (PLB1) has been demonstrated to play a key role in Cn pathogenicity. In this study, we used a PLB1 mutant (plb1) and its reconstituted strain (Rec1) to assess the importance of this enzyme on Cn brain infection in vivo and in vitro. Mice infected with the plb1 strain survive significantly longer, have lower peripheral and central nervous system (CNS) fungal loads, and have fewer and smaller cryptococcomas or biofilm-like brain lesions compared to H99- and Rec1-infected animals. PLB1 causes extensive brain tissue damage and changes microglia morphology during cryptococcal disease, observations which can have important implications in patients with altered mental status or dementia as these manifestations are related to poorer survival outcomes. plb1 cryptococci are significantly more phagocytosed and killed by NR-9460 microglia-like cells. plb1 cells have altered capsular polysaccharide biophysical properties which impair their ability to stimulate glial cell responses or morphological changes. Here, we provide significant evidence demonstrating that Cn PLB1 is an important virulence factor for fungal colonization of and survival in the CNS as well as in the progression of cryptococcal meningoencephalitis. These findings may potentially help fill in a gap of knowledge in our understanding of cerebral cryptococcosis and provide novel research avenues in Cn pathogenesis. IMPORTANCE Cryptococcal meningoencephalitis (CME) is a serious disease caused by infection by the neurotropic fungal pathogen Cryptococcus neoformans. Due to the increasing number of cases in HIV-infected individuals, as well as the limited therapies available, investigation into potential targets for new therapeutics has become critical. Phospholipase B is an enzyme synthesized by Cn that confers virulence to the fungus through capsular enlargement, immunomodulation, and intracellular replication. In this study, we examined the properties of PLB1 by comparing infection of a Cn PLB1 mutant strain with both the wild-type and a PLB1-reconstituted strain. We show that PLB1 augments the survival and proliferation of the fungus in the CNS and strengthens virulence by modulating the immune response and enhancing specific biophysical properties of the fungus. PLB1 expression causes brain tissue damage and impacts glial cell functions, which may be responsible for the dementia observed in patients which may persist even after resolving from CME. The implications of PLB1 inhibition reveal its involvement in Cn infection and suggest that it may be a possible molecular target in the development of antifungal therapies. The results of this study support additional investigation into the mechanism of PLB1 to further understand the intricacies of cerebral Cn infection.

Acute Diarrhea in Adults.

Acute diarrheal disease accounts for 179 million outpatient visits annually in the United States. Diarrhea can be categorized as inflammatory or noninflammatory, and both types have infectious and noninfectious causes. Infectious noninflammatory diarrhea is often viral in etiology and is the most common presentation; however, bacterial causes are also common and may be related to travel or foodborne illness. History for patients with acute diarrhea should include onset and frequency of symptoms, stool character, a focused review of systems including fever and other symptoms, and evaluation of exposures and risk factors. The physical examination should include evaluation for signs of dehydration, sepsis, or potential surgical processes. Most episodes of acute diarrhea in countries with adequate food and water sanitation are uncomplicated and self-limited, requiring only an initial evaluation and supportive treatment. Additional diagnostic evaluation and management may be warranted when diarrhea is bloody or mucoid or when risk factors are present, including immunocompromise or recent hospitalization. Unless an outbreak is suspected, molecular studies are preferred over traditional stool cultures. In all cases, management begins with replacing water, electrolytes, and nutrients. Oral rehydration is preferred; however, signs of severe dehydration or sepsis warrant intravenous rehydration. Antidiarrheal agents can be symptomatic therapy for acute watery diarrhea and can help decrease inappropriate antibiotic use. Empiric antibiotics are rarely warranted, except in sepsis and some cases of travelers' or inflammatory diarrhea. Targeted antibiotic therapy may be appropriate following microbiologic stool assessment. Hand hygiene, personal protective equipment, and food and water safety measures are integral to preventing infectious diarrheal illnesses.