Modified capsule quellung test

Shuixiang XIE; Lianlan MA; Zhichun LIU

ABSTRACT

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.