Cryptococcus neoformans Capsular Enlargement and Cellular Gigantism during Galleria mellonella Infection

We have studied infection of Cryptococcus neoformans in the non-vertebrate host Galleria mellonella with particular interest in the morphological response of the yeast. Inoculation of C. neoformans in caterpillars induced a capsule-independent increase in haemocyte density 2 h after infection. C. neoformans manifested a significant increase in capsule size after inoculation into the caterpillar. The magnitude of capsule increase depended on the temperature, being more pronounced at 37°C than at 30°C, which correlated with an increased virulence of the fungus and reduced phagocytosis at 37°C. Capsule enlargement impaired phagocytosis by haemocytes. Incubation of the yeast in G. mellonella extracts also resulted in capsule enlargement, with the polar lipidic fraction having a prominent role in this effect. During infection, the capsule decreased in permeability. A low proportion of the cells (<5%) recovered from caterpillars measured more than 30 µm and were considered giant cells. Giant cells recovered from mice were able to kill the caterpillars in a manner similar to regular cells obtained from in vivo or grown in vitro, establishing their capacity to cause disease. Our results indicate that the morphological transitions exhibited by C. neoformans in mammals also occur in a non-vertebrate host system. The similarities in morphological transitions observed in different animal hosts and in their triggers are consistent with the hypothesis that the cell body and capsular responses represent an adaptation of environmental survival strategies to pathogenesis

<i>In vitro</i> capsule and cellular enlargement of <i>C. neoformans</i> in <i>G. mellonella</i> extracts.

<p>Larvae were homogenized and different extracts were prepared as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0024485#s4" target="_blank">Material and Methods</a>. <b>A</b>) Growth curves in Sabouraud (▴), 10% Sabouraud diluted in 50 mM MOPS pH 7.3 (•), total <i>G. mellonella</i> extract (<b>x</b>), Upper phase of <i>G. mellonella</i> extract, containing polar lipids (♦) and PBS (*) at 37°C during 3 d. <b>B</b>) Distribution of total cell size, cell body size and capsular diameter of <i>C. neoformans</i> cells in Sabouraud (Sab), Sabouraud buffered with MOPS (10%Sab pH 7.3), <i>G. mellonella</i> extract (Gal), upper phase of <i>G. mellonella</i> lipid extraction (Upper phase) and PBS at 37°C for 10 d. T-test comparing cells in different media to cells grown in Sabouraud broth and scatter plot graphs were done using Graph Pad Prism 5. The line in each sample denotes the average of the distribution. <i>P</i><0.05 is indicated with an asterisk.</p

Haemocyte density in larvae after <i>C. neoformans</i> injection.

<p><b>A</b>) Ten larvae were inoculated with 10⁴ cells from H99 strain and haemocyte densities were assessed at different times (2 h, 2 d and 5 d). Black bars show haemocyte density of larvae injected with PBS and white bars of larvae injected with <i>C. neoformans</i>. <b>B</b>) Ten larvae per group were inoculated with 10⁴ cells from H99, B3501 and the <i>cap59</i> mutant (C536) and haemocyte densities were assessed after 2 h after inoculation as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0024485#s4" target="_blank">Material and Methods</a>. In both A and B, significant differences (<i>p</i><0.05) in haemocyte density relative to that in the PBS treated larvae are indicated with an asterisk. Experiments were repeated 3 times.</p

Role of the capsule on phagocytosis by haemocytes.

<p><b>A</b>) Cells with small (grown in Sabouraud) and large capsule (incubated in 10% Sabouraud buffered with 50 mM MOPS pH 7.3) were stained with Calcofluor and used to infect caterpillars. Bars show the average phagocytosis at 2 h. <i>p</i><0.05 is indicated with an asterisk. The experiment was repeated twice in triplicates. <b>B</b>) Survival curves of <i>G. mellonella</i> infected with 10⁴ cells of <i>C. neoformans</i> grown in Sabouraud broth and in 10% Sabouraud diluted in MOPS pH 7.3. <b>C</b>) <i>In vivo</i> phagocytosis using H99, B3501 and <i>cap59</i> (C356) strains was performed as described in section A and quantified after 2 h of infection. Bars show phagocytosis average after 2 h. <i>P</i> value below 0.05 is indicated with an asterisk.</p

<i>Cryptococcus neoformans</i> forms giant cells in <i>Galleria mellonella</i>.

<p><b>A</b>) Figure shows photographs of <i>C. neoformans</i> cells suspended in India ink after overnight growth in Sabouraud broth and giant cells recovered from <i>G. mellonella</i> after 6 d of infection. Scale bar applies to both panels. <b>B</b>) Binding of wheat germ agglutinin to <i>C. neoformans</i> as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0024485#s4" target="_blank">Material and Methods</a>. Upper panels show cells grown in Sabouraud browth and lower panels show a representative cell recovered from caterpillars after 6 d of infection.</p

Morphogenesis of <i>C. neoformans</i> during infection in <i>G. mellonella</i>.

<p>Distribution of total cell size, cell body size and capsule diameter of <i>C. neoformans</i> cells grown in Sabouraud (T = 0) and recovered from <i>G. mellonella</i> caterpillars at different times after inoculation of 10⁴ yeast cells. Total cell size was defined as the diameter of the complete cell including the capsule. The capsule diameter was calculated as the difference between the whole cell size and the cell body size. T-test and scatter plot graphs were obtained using Graph Pad Prism 5. The bar denotes the average of the distribution. Asteriks indicate <i>p</i><0.05.</p

Temperature dependent virulence and morphogenesis of <i>C. neoformans</i> in <i>G. mellonella</i>.

<p><b>A</b>) Survival curves of <i>G. mellonella</i> infected with 10⁴ H99 cells. Sixteen larvae per group were incubated at 30°C (▾) and 37°C (▴). A group of larvae were injected with PBS and kept at 30°C (•) and at 37°C (▪) to control the trauma of the injection. <b>B</b>) Growth curves of H99 strain at 30°C (Black line) and at 37°C (grey dotted line) during 48 h. <b>C</b>) <i>In vivo</i> phagocytosis was performed as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0024485#s4" target="_blank">Material and Methods</a> and quantified after 2 h of incubation of the larvae at 30°C and 37°C. <i>P</i><0.05 is indicated with an asterisk. <b>D</b>) Distribution of total cell size, cell body size and capsule diameter of <i>C. neoformans</i> cells grown in Sabouraud (Sab) and recovered from <i>G. mellonella</i> caterpillars at different temperatures after 6 d of infection. T-test and scatter plot graphs were performed using Graph Pad Prism 5. The line in each sample denotes the average of the distribution.</p

Effects of pre-operative isolation on postoperative pulmonary complications after elective surgery: an international prospective cohort study an international prospective cohort study

We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05–1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4–7 days or ≥ 8 days of 1.25 (1.04–1.48), p = 0.015 and 1.31 (1.11–1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care. We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05–1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4–7 days or ≥ 8 days of 1.25 (1.04–1.48), p = 0.015 and 1.31 (1.11–1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care