다람쥐 (Eutamias sibiricus asiaticus)를 사용한 Candida albicans의 실험적 감염에 관한 연구

Abstract

[한글]

1751년 John Hill에 의하여 Candids가 최초로 관찰되었으며 Berkhout(1923)에 의하여 C

andida라 재명명된 이래 현재까지 100여종이 보고되어 있다. 이중Candida albicans만이

병원성을 나타낸다고 알려져 왔으나 근래에 와서 타Candida종들도 질병을 야기할 수 있다

는 보고가 있으며 각종 진균증의 감염 증가추세와 더불어 캔디다증 역시 증가하는 현상을

나타내고 있다. 이러한 진균증의 증가추세는 항생제의 남용, 면역억제제의 사용, 각종

종양 및 면역결핍성 질환 등 여러가지 소인에 의한다고 보고되어 있다.

현재까지 각종 진균증의 원인균에 대한 적당하고 우수한 실험동물이나 Candida species

에 대한 실험동물에 관한 연구는 별로 찾아볼 수 없으며 학자들 간에도 서로 다른 의견들

이 있는 실정이다.

따라서 본 연구에서는 연세의대 미생물학교실에서 연구 개발하여 현재까지 항산군증에

대하여 좋은 실험동물로서 보고된 한국산 다람저(Eutamias sibiricus asiaticus)를 사용

하여 세계적으로 널리 분포되어 있으며 심재성 진균증을 야기하는 진균의 일종인 Candida

albicans에 대한 감수성 여부를 규명하고 실험동물로서의 이용가능성 여부를 규명할 목

적으로 실험에 착수하여 다음과 같은 결과를 얻었다.

1. 정맥을 통하여 다람쥐에 Candida albicans를 감염시켰을 경우 LD^^50 는 1ml당 5.7

×10**4 cell 이었으며 다람쥐에서 100% 사망율을 나타낸 1ml당 3.2×10**5 cell에서의

마우스사망율은 20%이었다.

2. 정맥내로 주사한 다람쥐의 직접도말검경 및 배양성적에서는 균접종 4일 후부터는 신

장에서만 균검출이 가능하였다.

3. 각 장기에서의 생균수측정 결과는 신장을 제외하고는 균접종 1일내지 2일 이내에 최

고에 달하였다가 급속히 감소하였으나 신장에서는 31일까지도 균의 관찰이 가능하였다.

4. 혈액학적 검사성적에 있어서 백혈구의 수는 균접종전에 비하여 균접증 4일에 4배의

중가를 보였다.

5. 병리조직학적 소견을 보면 접종 초기에는 각 장기에서 조직 변화없이 군체의 관찰이

가능하였으나 균접종 31일에서는 신장에서 심한 다발성국소 농양 및 괴저를 초래한 현상

을 관찰함과 동시에 많은 균사체가 발견되었다.

이상의 실험결과를 종합하여 볼 때 한국산 다람쥐는 Candida albicans에 대하여 감수성

을 가지고 있는 동시에 실험동물로서의 가능성을 내포하고 있다고 사료된다.

[영문]

Introduction

In 1751, John Hill observed yeast-like organisms harvested from rotting

vegetation, which he named Monilia. But, the genus Monilia was erected by Persoon

in 1797 to encompass certain species of fungi isolated from rotting fruit. In 1923,

Berkhout reclassified the genus Candida and this name was accepted as a "nomen

conservandum'by the 8th Botanical Congress at Paris in 1954.

It is generally recognized that Candida albicans is the only species of Candida

known to be pathogenic to man and to a number of laboratory animals, but recently

it has been found that all of the Candida species may be involved in any from of

candidiasis. Presently, Candida albicans is one of the normal flora of the

alimentary tract, mucous membrane, oral cavity and skin of many mammals. The

incidence of human disease caused by this organism has increased steadily in recent

years due to the wider use of immuno-suppressive drugs and broad spectrum

antibiotics. The variety of predisposing factors, the range of the clinical

disease, and the poor antibiotic chemotherapy now avilable have made candidasis a

serious clinical problem. The need to understand the immunity, host-parasite

relationship and pathogenesis involved in human diseases due to Candida albicans

has made it desirable animal model for candidasis that mimics the systemic disease

seen in human.

Several animal models from disseminated candidiasis have been described. Baine et

al. (1974) used the rabbit to study systemic candidiasis and estab1ished that the

infection is of a chronic nature. Hurley and Winner (1963) described the

histological picture of experimental Candida albicans infection in the tissue of

mice. But up untill now, a properly susceptible and sensitive animal model for

experimental systemic candidiasis has not been found.

For this reason, the author has also studied the course of an experimental

Candida albicans infection in the Korean chipmunks (Eutamias sibiricus asiaticus)

in order to establish whether this animal can be used as an experimental animal

model.

Materials and Methods

A. Materials

1. Experimental organism: Candida albicans ATCC 7491 was obtained from H.

Miyazaki (Juntendo University, Tokyo, Japan). It was maintained in our laboratory

by transfers on Sabouraud's glucose agar slant.

The morphological and biochemical characteristics of Candida albicans were

verified by microscopic observation and sugar fermentation reactions.

2. Animals: Wild chipmunks were obtained. They were maintained on a nutritional

diet and their adaptability to caged life was observed for 2 months prior to

inoculation with fungal suspension. Also, white ICR-mice were obtained from the

Institute of Leprosy, Japan and were used in all of the control studies.

B. Methods

1. Challenge Procedure: Aliquots of the stored Candida albicans suspension

diluted in saline were prepared to obtain the proper dose of administration. 0.2 ml

of the appropriate suspension were injected into the tail vein. Otherwise, 0.5 ml

of the suspension were injected intraperitoneally.

2. Enumeration of the Candida albicans Viab1e Unit: Chimmunks were sacrificed,

under aseptic condition. The appropriate organs were removed and weighed and placed

in tissue homogenizers. Sterile saline was added. Each organ was homogenized and

then number of Candida albicans viable units in the homogenate was determined by

the pour plate dilution method, using Sabouraud's glucose agar. Colony forming

units (CFU) were determined by counting the colonies used as a source of the

organisms.

3. Histopathological Study: Experimental animals Were sacrificed at 24 hours, 48

hours and 31 days after intarvenous inoculation of approximately 3.2×10**3

cell/ml. Sections of brain, lung, heart, liver, spleen and kidney were studied

after staining with hematoxylin eosin and Periodic acid-Schiff's reagent.

4. Hematological Study: Experimental chipmunks were infected with 3.2×10**3

cell/ml, and 0.5ml of whole blood were obtained daily for 5 days by cutting tail

vein. Blood was placed in tubes containing 0.3% sodium citrate solution, and white

blood cell(WBC), red blood cell (RBC) and hematocrit counts were determined with

Hema-Count TM System Model MK-3 type.

Results and Conclusions

1. Mortality Rate and Histopathological Study: In an attempt to produce a

disseminated infection, up to 3.2×10**5 cell/ml of Candida albicans were given

intravenously. With this inoculum, death of all animals was observed within 24

hours. The LD^^50 was determined as 5.7×10**4 cell/ml. Between the inocula of

2.0×10**4 cell/ml and 7.2×10**4 cell/ml mortality rose sharply, increasing from

10% to 90%.

Autopsies of animals given lethal and sublethal doses of Candida albicans

intravenous revealed disseminated microabscesses or inflammatory cell infiltrations

throughout the kidney, heart, lung, liver and spleen. Also, Candida albicans could

be cultured from these organs in the early stage of infection and cells in the

mycelial phase were demonstrated histopathologically in the renal and myocardial

abscesses after 31 days.

2. Course of Infection: For the study of the course of infection over time, a

sublethal dose of Candida albicans was given (3.2×10**4 cel1/ml) and animals were

autopsied at 24, 48, 72, 96, 120 hours and 31 days after injection, spleen, liver,

lung, heart and kidney were cultured. Over the next 5 days, colony counts revealed

a decreasing number of viable organisms in all tissues except the kidney. Between

24 hours and 48 hours the decline was rapid: between 96 hours and 120 hours all

nonrenal organs became sterile.

Although the initial renal colony counts was similar to colony counts in other

organs, there was gradual increase in renal colony count over the first 2 days of

infection, with maximal counts of viable organism of 7.0×10**5 CFU/gm tissue at 3

days. Subsequently, there was a gradual decline in colony count. By day 31, the

colony counts was 4.8×10**3 CFU/gm tissue.

3. Hematological Study: Paralleling the inefection, leukocytosis was observed 24

hours after injection and continued to rise until 4 days, when the total count of

(18.05±4.26)×10**3 WBC/cmm was seen. Blood cultures were positive for the

infecting organism for the entire 5 days period of the blood collection.

4. In summary of the above results, the chipmunk appears to be one of the most

susceptible to Candida albicans among all the experimental animals known to date.

Therefore this animal can be adopted as an expermental animal model for candidiasis

.