The Pore-Forming Toxin Listeriolysin O Mediates a Novel Entry Pathway of L. monocytogenes into Human Hepatocytes

Intracellular pathogens have evolved diverse strategies to invade and survive within host cells. Among the most studied facultative intracellular pathogens, Listeria monocytogenes is known to express two invasins-InlA and InlB-that induce bacterial internalization into nonphagocytic cells. The pore-forming toxin listeriolysin O (LLO) facilitates bacterial escape from the internalization vesicle into the cytoplasm, where bacteria divide and undergo cell-to-cell spreading via actin-based motility. In the present study we demonstrate that in addition to InlA and InlB, LLO is required for efficient internalization of L. monocytogenes into human hepatocytes (HepG2). Surprisingly, LLO is an invasion factor sufficient to induce the internalization of noninvasive Listeria innocua or polystyrene beads into host cells in a dose-dependent fashion and at the concentrations produced by L. monocytogenes. To elucidate the mechanisms underlying LLO-induced bacterial entry, we constructed novel LLO derivatives locked at different stages of the toxin assembly on host membranes. We found that LLO-induced bacterial or bead entry only occurs upon LLO pore formation. Scanning electron and fluorescence microscopy studies show that LLO-coated beads stimulate the formation of membrane extensions that ingest the beads into an early endosomal compartment. This LLO-induced internalization pathway is dynamin-and F-actin-dependent, and clathrin-independent. Interestingly, further linking pore formation to bacteria/bead uptake, LLO induces F-actin polymerization in a tyrosine kinase-and pore-dependent fashion. In conclusion, we demonstrate for the first time that a bacterial pathogen perforates the host cell plasma membrane as a strategy to activate the endocytic machinery and gain entry into the host cell

46. Racial and Ethnic Disparities in COVID-19 Incidence among Persons with HIV in a Multisite-Cohort

Abstract: Background: Little is known about how race and ethnicity, imperfect (albeit accessible) proxies for structural racism, impact COVID-19 incidence among people with HIV (PWH). We report the cumulative incidence and incidence rate ratios (IRR) for COVID-19 in a long-term multi-site cohort of PWH across the US Figure 1. Cumulative incidence of COVID-19 in the CNICS cohort Methods: We examined COVID-19 cumulative incidence and IRR among PWH in care between 3/1/2020 and 12/31/2020 at seven sites in the CFAR Network of Integrated Clinical Systems (CNICS) cohort. We define COVID-19 incident case as having a laboratory-confirmed (RT-PCR/Ag) SARS-CoV-2 positive result or diagnosis verified by chart review. Reinfections were excluded. Results are presented as monthly and quarterly cumulative incidence and IRR with 95% CI stratified by CD4 count, self-reported race/ethnicity, and site. Follow-up was censored on the earliest of diagnosis of COVID-19 disease, loss to follow up, or 12/31/2020 Results: Among 15,780 PWH in care in the CNICS cohort during the study period, 62% were non-white, with a median (IQR) age of 52 (IQR 40-59), 95% were on antiretroviral therapy, 17% had a CD4 count less than 350, and 6% less than 200. Overall, 651 PWH tested positive for COVID-19 for a cumulative incidence of 4.13%. COVID-19 cumulative incidence increased from 0.77% at the end of the first quarter to 4.12% by the end of December 2020. At the peak of the pandemic in December 2020, the cumulative incidence in Black PWH was 1.68 fold higher than in white PWH (p=.033) and 2.35 fold higher in Hispanics than in whites (P< .0001), figure 1. Similarly, the IRR for COVID-19 was 1.71 (95% CI 1.42-2.07) for Black and 2.40 (95% CI 1.91-3.01) for Hispanic PWH relative to white. Although there was variation across sites, reflecting geographic differences in pandemic waves and access to COVID-19 testing, overall individual trends remained the same. COVID-19 cumulative incidence was similar across CD4 cell count strata Conclusion: Our results suggest effects of structural racial disparities on COVID-19 incidence in this diverse population of PWH across the US, with higher and disproportionate rates of COVID-19 in Black and Hispanic PWH. Incidence estimates are conservative because testing was not uniform, and no systematic testing was conducted Disclosures: Edward R. Cachay, MD, MAS, Gilead Science (Grant/Research Support, Advisor or Review Panel member)Merck Sharp & Dohme Corp (Grant/Research Support) Adrienne Shapiro, MD, PhD, Vir Biotechnology (Scientific Research Study Investigator) Darcy Wooten, MD, MS, Nothing to disclose Rachel A. Bender Ignacio, MD MPH, Abbvie (Individual(s) Involved: Self): Consultant; SeaGen (Individual(s) Involved: Self): Consultant Greer A. Burkholder, MD, MSPH, Eli Lilly (Grant/Research Support) Heidi Crane, MD, MPH, ViiV (Grant/Research Support

Factors Associated With Severity of COVID-19 Disease in a Multicenter Cohort of People With HIV in the United States, March-December 2020.

BackgroundUnderstanding the spectrum of COVID-19 in people with HIV (PWH) is critical to provide clinical guidance and risk reduction strategies.SettingCenters for AIDS Research Network of Integrated Clinic System, a US multisite clinical cohort of PWH in care.MethodsWe identified COVID-19 cases and severity (hospitalization, intensive care, and death) in a large, diverse HIV cohort during March 1, 2020-December 31, 2020. We determined predictors and relative risks of hospitalization among PWH with COVID-19, adjusted for disease risk scores.ResultsOf 16,056 PWH in care, 649 were diagnosed with COVID-19 between March and December 2020. Case fatality was 2%; 106 (16.3%) were hospitalized, and 12 died. PWH with current CD4 count <350 cells/mm 3 [aRR 2.68; 95% confidence interval (CI): 1.93 to 3.71; P < 0.001] or lowest recorded CD4 count <200 cells/mm 3 (aRR 1.67; 95% CI: 1.18 to 2.36; P < 0.005) had greater risks of hospitalization. HIV viral load and antiretroviral therapy status were not associated with hospitalization, although most of the PWH were suppressed (86%). Black PWH were 51% more likely to be hospitalized with COVID-19 compared with other racial/ethnic groups (aRR 1.51; 95% CI: 1.04 to 2.19; P = 0.03). Chronic kidney disease, chronic obstructive pulmonary disease, diabetes, hypertension, obesity, and increased cardiovascular and hepatic fibrosis risk scores were associated with higher hospitalization risk. PWH who were older, not on antiretroviral therapy, and with current CD4 count <350 cells/mm 3 , diabetes, and chronic kidney disease were overrepresented among PWH who required intubation or died.ConclusionsPWH with CD4 count <350 cells/mm 3 , and a history of CD4 count <200 cells/mm 3 , have a clear excess risk of severe COVID-19, accounting for comorbidities associated with severe outcomes. PWH with these risk factors should be prioritized for COVID-19 vaccination and early treatment and monitored closely for worsening illness

Food webs in Mediterranean rivers

River food webs are subject to two regimes of longitudinally varying ecological control: productivity and disturbance. Light-limited productivity increases as channels widen downstream. Time windows for growth, however, shrink as discharge increases, substrate particle size decreases, and the frequency of flood-driven bed mobilization increases downstream. Mediterranean rivers are periodically reset by hydrologic events with somewhat predictable timing. Typically, a rainy winter with high river discharge is followed by summer drought with little or no rainfall and slowly declining river flow. The magnitude and timing of winter floods and severity of subsequent summer drought can vary considerably from year to year, however. Episodic scouring floods or prolonged periods of drought are experienced as disturbances, stressors, or opportunities by river biota. The timing, duration, and intensity of these hydrologic controls affect performances of individuals, distribution and abundances of populations, and outcomes and consequences of species interactions. These interactions in turn determine how river food webs will assemble, develop, and reconfigure after disturbance. We discuss how spatial variation in solar radiation and spatial and temporal variations in disturbance affects river food webs under Mediterranean climate seasonality, focusing primarily on long-term observations in the Eel River of northwestern California, USA