不同氧浓度对新生隐球菌荚膜的影响

Effects of oxygen concentration on the capsule of Cryptococcus neoformans

目的探讨不同氧浓度对新生隐球菌荚膜的影响。方法以厌氧、微需氧和CO2产气袋建立不同氧浓度（分别为0、8％、15％）培养条件，以大气氧浓度（21％）为正常氧浓度培养条件，以新生隐球菌标准株5株（BLS71、BLS63、ATCC32609、ATCC34874、YD53，分别为血清型A、B、C、D、AD）、临床株1株为研究对象，以常规沙氏液体培养基和含3-（N吗啡啉）丙磺酸（MOPS）的10％沙氏液体培养基（pH7．3）为非诱导和诱导培养基，在37℃下培养3d，观察不同氧浓度培养条件下新生隐球菌的荚膜形成及大小。结果除菌株YD53（血清型AD）外，其余受试菌株均可形成明显的荚膜。在非诱导培养条件下，菌株BLS71、BLS63、ATCC32609和临床株在4种氧浓度培养条件下荚膜大小差异有统计学意义（P〈0．01）。在诱导培养条件下，菌株BLS71、BLS63和临床株在厌氧培养条件下的荚膜厚度比其余氧浓度条件下的荚膜明显变小（P〈0．05）。结论缺氧可能抑制新生隐球菌荚膜的形成。

Objective To investigate the effect of oxygen concentration on the capsule of Cryptococcus neoformans. Methods Three concentrations （15%, 8%, 0） of oxygen were achieved by using AnaeroPack system. The atmospheric oxygen level （21%） served as the normal oxygen concentration. Five standard strains, including BLS71 （serotype A）, BLS63 （serotype B）, ATCC32609 （serotype C）, ATCC34874 （serotype D） and YD53 （serotype AD）, as well as one clinical isolate of C. neoformans were cultured on either traditional Sabouraud medium （non-inducing conditions） or 10% Sabouraud medium buffered to pH 7.3 with 10 mmol/L 3-（N- morpholino） propanesulfonic acid （capsule-inducing conditions） at 37 ℃ under the four oxygen concentrations for three days. An Olympus microscope was used to observe the formation of capsules, and the size of capsules was measured. Results With the exception of YD53, all the strains formed obvious polysaccharide capsules under the four oxygen levels. Under non-inducing conditions, there was a significant difference in the size of capsules formed by the standard strains BLS71, BLS63, ATCC32609 and the clinical isolate between the four oxygen concentrations （all P 〈 0.01 ）. The standard strains BLS71, BLS63 and the clinical isolate formed smaller size of capsules under the anaerobic condition （no oxygen） compared with the other three oxygen concentrations （21%, 15%, 8%, all P 〈 0.05）. Conclusion Hypoxia may inhibit the formation of capsules by C. neoformans.