BACKGROUND: Studies have confirmed that there is secreted protein out of cell wall of Candida albicans. However, in recent researches, we found there may be a capsule-like-structure within it.OBJECTIVE: To observe the capsule-like structure of Candida albicans by means of modified quellung test.DESIGN: A controlled observation experiment.SETTING: Department of Medical Microbiology, Gannan Medical College.MATERIALS: Candida albicans from 2 clinical specimens (C1, C2) identified by preserve center of Epiphyte strains of Chinese Academy of Science (Nanjing, China) and standard strains (CCCMC1a and ATCC14053) donated by preserve center of Epiphyte strains of Peking University (Beijing, China) were taken to quellung test. Experimental rabbits (weighing 2-2.5 kg) for preparing normal serum and antiserum were donated by Experimental Animal Center of Sun Yat-sen University. Antiserum was prepared by the book with experimental strains (C1, C2, CCCMC1a, and ATCC)respectively for later quellung tests.METHODS: This experiment was carried out in the Department of Medical Microbiology, Gannan Medical College in December 2005. ① Traditional Quellung test: The culture of Candida albicans (C1, C2, CCCMC1a, and ATCC) was spread on a slide respectively. Corresponding rabbit antiserum was added onto the slide (experimental group 1) and normal serum was added onto the slide (control group1). 1% methylene blue was added into each group, and then the slides were placed in a wet box at 37 ℃ for 20 minutes; the slides were taken out and covered with a cover-slip. Under the oil immersion, the count of Candida albicans was taken and the microscopic surveying instrument was used to measure the capsule thickness of cell of Candida albicans directly. The average thickness of capsule of 40 cells was taken. ②Modified quellung test: The culture of Candida albicans (C1, C2, CCCMC1a, and ATCC) was spread on a slide respectively. Corresponding rabbit antiserum was added onto the slide (experimental group 2) and normal serum was added onto the slide (control group 2), 1% methylene blue was not added into each group, but the slides were directly placed in a wet box et 37 ℃ for 20 minutes. The slides were taken out and dried naturally, but not covered with a cover-slip during the drying process. Hiss capsule staining was applied for them.The average thickness of capsule of 40 cells was taken.MAIN OUTCOME MEASURES: The average thickness of capsule in each experimental group in traditional and modified quellung tests.RESULTS: ① Traditional quellung test of Candida albicans was positive. The thickness of culture of Candida albicans C1, C2, CCCMC1a, and ATCC of experimental group1 was larger than that of the control group1, respectively [(0.558+0.081 ) vs. (0.225+0.061) μm; (0.530+0.081) vs. (0.252+0.038) μm; (0.475+0.081) vs. (0.200+0.072) μm;(0.600+0.068) vs. (0.225+0.046) μm,P ＜ 0.01] .② The thickness of culture of Candida albicans C1, C2, CCCMC1a, and ATCC of experimental group 2 was larger than that of the control group 2, respectively[(0.541 ±0.038) vs. (0.215±0.022)μm; (0.510±0.060)vs. (0.247±0.018) μm; (0.487±0.041) vs. (0.213±0.033)μm; (0.595±0.027) vs. (0.220±0.016) μm, P ＜ 0.01]. ③ The thickness of capsule of the control group 2 was smaller than that of control group 1 (P ＜0.01); The thickness of capsule of the experimental group 2 was smaller than that of experimental group 1 (P ＜ 0.01).CONCLUSION: As a quantitative analysis test, modified quellung test is more stable and accurate than traditional quellung test.

BACKGROUND: Previous studies have demonstrated that Candida albicans possesses capsule structure. Whether capsule structure is associated with the virulence of Candida albicans?OBJECTIVE: This study investigated the pathogenic difference between the standard strains of Candida albicans and the clinically isolated strains, verified whether capsule was the virulence factor of the Candida albicans, and analyzed the association between the animal pathogenicity of different strains and capsule thickness.DESIGN: A randomized controlled animal experiment.SETTING: Department of Pathogenic Biology, Gannan Medical College.MATERIALS: This study was performed at the Scientific Research Center, Gannan Medical College between May and June 2005. A total of 120 BALB/c mice and 72 healthy adult rabbits were included. Candida albicans strains (CCCMC1a and ATCC 14053) were used. The isolated and cultured 4 strains were numbered as C1-1, C1-2, C1-3,and C1-4.METHODS: All animals were randomly divided into 6 groups with 20 mice and 12 rabbits in each group, namely,CCCMC1a, ATCC 14053, C1-1, C1-2, C1-3, and C1-4 groups. Strains smeared in sabouraud ager medium for 36 hours were diluted into the bacterial solution with physiological saline. This solution was intravenously injected into rabbit ear edge, 1.5 mL per rabbit, and intraperitoneally injected into BALB/c mice, 0.5 mL per mouse. Six hours after administration, animal response was observed, and attack time, death time, and mortality were recorded.MAIN OUTCOME MEASURES: Rabbit nephridial tissue printing slices and mouse peritoneal fluid smears were made for Hiss capsule staining microscopy. The capsule thickness of 40 randomly selected yeast cells in each strain was measured using a microscope-micrometer, and the mean capsule thickness of each strain was compared.RESULTS: Compared with C1-1, C1-3, CCCMC1a, and ATCC 14053, C1-2 and C1-4 possessed stronger animal pathogenicity. The standard strains and clinically isolated strains could form capsule in the rabbit and mouse bodies. Capsule thickness differed due to different strains and animal genera (P < 0.05-0.01). The bacterial capsule thickness was greater in the rabbit renal infection focus than in the mouse abdominal cavity. The bacterial capsule thickness of rabbit renal infection focus and mouse abdominal cavity in the C1-1, C1-2, C1-3, and C1-4 groups was greater than that of the same genus in the CCCMC1a and ATCC 14053 groups. The bacterial capsule thickness of rabbit renal infection focus and mouse abdominal cavity was the greatest in the C1-2 and C1-4 groups.CONCLUSION: Candida atbicans C1-2 and C1-4 strains have strong animal pathogenicity. C1-2 and C1-4 strains possess greater bacterial thickness than other strains. It has been primarily confirmed that capsule is possibly a virulence factor of Candida albicans, and capsule thickness is closely associated with animal pathogenicity.