Animal models for candidiasis

Induction of candidal vaginitis in diabetic mice and attempts to prevent the infection

In the present study on the induction and prevention of candidal vaginal infection in diabetic mice, ICR female mice were rendered diabetic by intraperitoneal injections of 160 mg kg-1 streptozotocin (SZ) which induced a stable non-lethal diabetic state apparent 2-7 days post-SZ injection. Diabetic mice and non-diabetic controls were inoculated intravaginally with 10(7)-10(10) Candida albicans yeasts. Infection was evaluated by the number of infected mice 3 days post-inoculation and the rate of clearance of infection during a 35-day follow-up. All C. albicans doses investigated induced vaginal infection in the diabetic mice, while in the non-diabetic controls only 40% of those inoculated with the lower (10(7) CFU) dose developed infection. The yeast load in the diabetic mice was 10-fold higher than in the controls and the duration of infection was longer. In an attempt to prevent infection intravaginal treatment with 5-40 mg of a chitin derivative (CSE) mouse-1 was given prior and pre- and post-inoculation with C. albicans. The optimal CSE treatment regimen was both pre- and post-administration of 10 or 20 mg CSE mouse-1 which significantly reduced the number of infected animals and also the duration of infection.

Animal models of oral candidiasis. A review

Candida albicans is the most common fungal infection of the human oral mucosa, yet much remains to be understood with respect to the pathogenesis of the disease. Numerous difficulties are inherent in designing studies that use human beings as subjects. The use of various animal species in experimental contexts has helped to provide insight with respect to this condition. A variety of manipulations of the system can be performed, including altering the host immune response, the mucosal environment, or the systemic environment. In addition, organism-related factors can be examined in a more controlled setting. The information obtained from such studies could not be obtained in an in vitro situation.

Comparison of a lesion-inducing isolate and a non-lesional isolate of Candida albicans in an immunosuppressed rat model of oral candidiasis

Two distinct strain-related patterns of organism-host interaction on dorsal tongue of immunocompetent rats have been identified for Candida albicans: some isolates induce mucosal lesions, while other isolates penetrate the keratin layer but do not produce a lesion. This study examined the behavior of each of the two types of isolates in a cyclosporin-immunosuppressed rat model. Groups B (normal) and D (cyclosporin) were orally inoculated with a lesion-inducing isolate of C. albicans, while a non-lesional isolate was given to Groups A (normal) and C (cyclosporin). A typical dorsal tongue lesion developed in 4/18 rats in Group B and in 13/16 in Group D (P = 0.00267). No significant difference in infection rate between the normal and cyclosporin-treated animals was seen for the non-lesional isolate. The lack of a host inflammatory response associated with the non-lesional isolate may represent an ecologic advantage for the organism.

Human submandibular-sublingual saliva promotes adhesion of Candida albicans to polymethylmethacrylate

The purpose of this study was to identify components of saliva that interact with Candida albicans in solution and that may modulate adhesion to dental acrylic (polymethylmethacrylate [PMMA]) surfaces. Saliva-derived pellicles extracted from C. albicans blastoconidia and hyphal-form cells mixed with fresh human submandibular-sublingual saliva (HSMSL) contained predominantly high- and low-molecular-weight mucins (MG1 and MG2, respectively). In contrast, few components from fresh human parotid saliva were adsorbed to yeast cells. Coating PMMA beads with HSMSL significantly enhanced (10-fold) adhesion of both growth forms of C. albicans compared with human parotid saliva (2-fold), suggesting a role for mucins in adhesion. HSMSL-enhanced adhesion was completely abolished by preadsorbing HSMSL with either blastoconidia or hyphal-form cells prior to coating PMMA. However, coating PMMA with purified salivary mucins or the addition of mucin to preadsorbed saliva did not enhance or restore adhesion to levels found with fresh HSMSL. Adhesion assays employing guanidine-treated fresh HSMSL showed a complete lack of Candida binding, suggesting that subjecting HSMSL to dissociating conditions may alter a property of salivary mucins crucial for C. albicans adhesion. Protease and glycosidase treatment of yeast cells significantly reduced adhesion to HSMSL-coated PMMA. In addition, preincubation of C. albicans with mannose and galactose inhibited adhesion to HSMSL-coated PMMA. These results suggest that mucins may play a role in C. albicans adhesion to saliva-coated PMMA and that a glycoprotein on the yeast surface may be involved in these events.

Fatal systemic candidiasis of gastrointestinal origin: an experimental model in mice compromised by anti-cancer treatment

An experimental model of fatal systemic candidiasis originating from the gastrointestinal (GI) tract of compromised mice is presented. ICR female mice were compromised by a single anti-cancer treatment: irradiation (4 or 6 Greys i.e. 400-600 rads), methotrexate (MTX) (3 mg per mouse, intraperitoneally) or 5-fluorouracil (5FU) (200 mg kg-1, intravenously). Three days later, compromised and non-treated control mice were exposed to Candida albicans administered orally. Morbidity and mortality due to candidiasis were monitored for 30 days post-candidal inoculation. Increased and longer GI colonization was noted among the MTX and 5FU treated mice, or 6 Greys irradiated mice (up to 92.3% for over 30 days in anti-cancer treated mice). The stomach was found to be the major part of the GI tract involved in fungal colonization. A significant number (53.8-83.3%) of the anti-cancer treated mice developed systemic candidiasis originating from the GI tract, which was fatal in 30-80% of the infected animals. In systemically infected animals, candidal antigen was demonstrated in the serum, and fungal abscesses containing C. albicans were observed in the liver, kidneys and spleen. C. albicans was isolated from the infected organs. The severity of the infection, as reflected by the number of fungi in visceral organs, and by mortality during the 30 days post-candidal inoculation, indicated differences in the course and nature of the infection among the three treatment groups (i.e. MTX, 5FU, 6 Greys).(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of postoperative candidosis: no detectable fungemia during reoperations after abdominal surgery

Pathogenesis of systemic candidosis in surgical patients is unsettled. Results from animal models suggest that invasion from colonized intestine is the major portal of entry into circulation. To study the mechanisms of systemic candidosis in surgical patients after intestinal surgery, multiple blood cultures were taken during reoperations with manipulation of the intestinum to detect possible perioperative fungemia. The lysis centrifugation method (Isolator) was used for blood cultures. Of the 30 subjects in the material, 12 were demonstrated to be colonized with yeast before the reoperation. Three patients had positive blood cultures during reoperation, but no yeasts were found in the 146 perioperative blood cultures. Three patients had severe nonsuperficial yeast infection after reoperation, but none had disseminated candidosis. This finding in high risk patients supports the view that immediate perioperative fungemia and persorption from colonized intestinum is rare. However, persorption may occur later via healing wounds of the colonized intestinum. Both persorption and the exogenous route (e.g. vascular catheters) are possible in the pathogenesis of postoperative candidosis.

Candida albicans strain delineation

Candida albicans is a major opportunistic pathogen causing a wide spectrum of disease in human beings. Methods for strain delineation of this species to assess or predict virulence or to conduct epidemiologic or pathogenetic investigations have been developed. Although factors associated with virulence have been identified, there is no rapid system to quantitate them in a clinical laboratory. Therefore, many typing methods are based on variable phenotypic characteristics within this species including morphotyping, serotyping, antibiogram, resistogram typing, biotyping, biotyping based on commercial carbon assimilation patterns, enzyme profiles, sensitivity to yeast killer toxins, and typing based on protein variability. Phenotypically defined strains generally do not correlate with the pathogenic potential of a strain with the exception of morphotyping. However, these methods can be useful in epidemiologic investigations; for example, they have revealed that most individuals harbor one strain and that infections are frequently due to an endogenous strain. Problems with these methods usually relate to their discriminatory power. When this is maximized, reproducibility (especially between laboratories) suffers. Recently, methods based on differences in DNA structure (genotyping) for strain delineation have been developed, including electrophoretic karyotyping and restriction enzyme fragment length polymorphisms. The development of a computer-assisted data bank and analysis for these genotypic strain delineators will open investigations into the pathogenesis of this infection and permit epidemiologic studies previously not possible with this important human pathogen.

Evaluation of a murine model of hepatic candidiasis

A murine model of focal hepatic candidiasis which we suggest simulates certain conditions of this clinical variant of systemic candidiasis in leukemic patients is described. We have shown that outbred mice inoculated with Candida albicans by the oral-intragastric route as infants (6 days old) and then immunocompromised by cyclophosphamide and cortisone acetate treatment 2 weeks later demonstrate systemic spread of the opportunistic pathogen to the liver, lungs, spleen, and kidneys. Treatment with the immunosuppressive drugs cyclophosphamide and cortisone acetate resulted in alteration of the normal integrity of the mucosal epithelium of the gut as well as in granulocytopenia. Approximately 55% of the animals with C. albicans infections in the liver demonstrated hepatic abscesses. After these same infected, immunocompromised animals were treated with suboptimal dosages of antifungal agents (cilofungin or amphotericin B), either by intraperitoneal or subcutaneous (s.c.) routes, persistent hepatic abscesses were fewer in number and delimited by a distinct outer layer of host tissue but still contained large numbers of the viable pathogen. Blood cell counts indicated that these antifungal drug-treated animals had reestablished approximately the same number of leukocytes per microliter of blood as estimated prior to the immunocompromising drug treatment. Similar conditions in leukemic patients who were in remission and who were undergoing antifungal drug therapy for systemic candidiasis have been reported. Clearance of hepatic infections in mice was accomplished by using appropriate concentrations of amphotericin B administered by daily intraperitoneal or s.c. injection for 5 to 7 days or cilofungin by continuous s.c. infusion for 7 days. However, systemic antifungal therapy did not significantly reduce numbers of C. albicans cells in the stomach and esophagus. Persistent foci of gastrointestinal colonization by C. albicans, especially in the region of the cardial-atrium fold of the stomach of these mice, are reservoirs of the opportunistic pathogen from which reinfection may occur, leading to relapse of systemic candidiasis.

An animal model for oropharyngeal, esophageal and gastric candidosis

Conventional mice inoculated with Candida albicans by the oral-intragastric route as infants (6-day-old) have previously been shown to develop gastrointestinal (GI) candidosis which persists for at least 30-60 days post-challenge without the use of compromising procedures. Histological preparations of the stomachs of these animals reveal hyphae which have crossed the mucin barrier and are associated with the stratified squamous epithelium of the gastric mucosa primarily in the region of the cardial-atrium fold. Host inflammatory cells are frequently observed adjacent to these filaments and yeast cells. In this study, groups of neonates were challenged oral-intragastrically with either C. albicans strain CA30, or strain CA87. The two strains showed marked differences in the numbers of cells associated with tissue of the tongue, esophagus and stomach of non-immunocompromised mice at 20 days post-inoculation. After immunocompromising treatment by intraperitoneal administration of cyclosphosphamide and cortisone acetate, both groups of mice showed extensive colonization and tissue invasion of the tongue, proximal and distal portions of the esophagus, and cardial-atrium fold of the stomach. C. albicans-containing abscesses were occasionally observed on the tongue of these animals. Histological preparations of the cardiac antrum, located at the junction of esophagus and stomach, frequently revealed concentrations of hyphae and yeast cells associated with the stratified squamous epithelium. We suggest that these non-immunocompromised and immunocompromised mice with persistent C. albicans infections of oropharyngeal, esophageal and gastric tissue, initiated by oral-intragastric challenge at infancy, simulates conditions in different groups of chronically infected humans, and serves as a useful model for testing the efficacy of anti-Candida drugs in clearance of candidosis from the alimentary canal.

Candida albicans gastrointestinal colonization and invasion in the mouse: effect of antibacterial dosing, antifungal therapy and immunosuppression

Infant mice infected with Candida albicans by the oral-intragastric route became colonized in the gut and were persistently colonized into adulthood. Faecal levels of Candida were correlated with total gastrointestinal Candida and provided a useful means of detecting yeast overgrowth or elimination. Antibacterial agents promoting Candida overgrowth when given by the oral or parenteral route included ceftriaxone, augmentin and cefoperazone. Ceftizoxime had less effect. Ceftazidime and latamoxef produced raised levels only by the oral route. Gentamicin, vancomycin and metronidazole did not affect the Candida levels. Dosing with some antibacterials promoted an increase in gastrointestinal Candida and invasion to a greater extent than immunosuppression. Antifungal therapy to reduce gastrointestinal colonization was investigated using amphotericin B, nystatin, ketoconazole, intraconazole and fluconazole. Fluconazole was most effective at reducing faecal Candida.

Gastrointestinal and systemic candidosis in immunocompromised mice

Oral-intragastric inoculation of 6-day-old outbred Crl:CFW(SW) BR mice with Candida albicans can lead to colonization of the gastrointestinal (GI) tract. We have shown that in the absence of an immunocompromising treatment, Candida is primarily localized in the stomach and intestines of mice at 20 days post-inoculation. Cultures of homogenates of the esophagus of most animals tested, and homogenates of the liver, lungs, spleen and kidneys of all animals tested, proved negative for C. albicans. Previous histological examinations of the GI tract of these colonized, non-immunocompromised mice showed hyphal elements associated with the stratified, squamous epithelium of the stomach in the region of the cardial-atrium fold. In this study, mice were immunocompromised by intraperitoneal injection of cyclophosphamide and cortisone acetate 11-14 days after oral-intragastric challenge with C. albicans and then sacrificed 20 days post-challenge. A high density of invasive hyphae was observed in the same, cardial-atrium region of the stomach of these animals. Cultures of the homogenized stomach showed a 100-fold increase in colony forming units (c.f.u.) of C. albicans compared with stomach homogenates of infected but non-immunocompromised controls. In addition, homogenates of the esophagus and selected body organs of most immunocompromised mice examined were positive for C. albicans by plate culture. When the immunocompromising drug treatment was delayed 3-5 weeks after oral-intragastric challenge, proliferation of C. albicans in the stomach and intestines was still evident, although fewer mice showed systemic spread and lower numbers of c.f.u. were recovered from body organ homogenates. Abscesses which contained both C. albicans hyphae and yeast cells were frequently observed in the liver and occasionally in the lungs and kidneys of immunocompromised mice sacrificed 20 days post-inoculation. The frequent occurrence of abscesses in the liver simulates a clinical variant of this mycosis, referred to as focal hepatic candidosis, which has been recognized with increasing frequency in immunocompromised patients. We suggest that the animal model described here may be particularly useful both for exploring methods which may prevent dissemination of C. albicans from localized foci of colonization in the GI tract after exposure of the host to immunocompromising drugs, and for testing the efficacy of anti-Candida drugs in clearance of the pathogen from body organs with established fungal abscesses.

Morphological aspects of gastrointestinal tract invasion by Candida albicans in the infant mouse

The infant mouse has proved to be a useful model for examination of various aspects of gastrointestinal and systemic candidosis. Oral-intragastric inoculation of 5-6-day-old mice with yeast of a virulent strain of Candida albicans (CA30) resulted in systemic spread within 30 min after challenge. Histological examinations of the gastrointestinal (GI) tract have shown that the highest frequency of invasion of the mucosa by yeast cells occurred in the region of the jejunum 1-3 h after inoculation. Results of ultrastructural examinations of sites where the fungus invaded the bowel wall suggested that C. albicans yeast cells are capable of progressive extracellular digestion of the intestinal mucus barrier and microvillus layer, followed by intracellular invasion of columnar epithelial cells. Minimal disruption of cytoplasmic contents of the host epithelial cells appears to result from invasion and transmigration of the pathogen. The infant mouse model is suggested to be well suited for localization of extracellular products of C. albicans yeast in vivo which may play pivotal roles in the invasion of host tissue during GI candidosis.

Dynamic expression of cell surface hydrophobicity during initial yeast cell growth and before germ tube formation of Candida albicans

Expression of cell surface hydrophobicity (CSH) during initial growth of Candida albicans was monitored. CSH of hydrophobic and hydrophilic yeast cells changed within 30 min upon subculture into fresh medium. Morphologic evidence of germination was preceded by expression of CSH. These results indicate that CSH expression is important in C. albicans growth.

Proteinase production and pathogenicity of Candida albicans. I. Invasion into chorioallantoic membrane by C. albicans strains of different proteinase activity

In order to investigate a role of proteinase in the pathogenesis of Candida infections, invasion of C. albicans strains of different proteinase activity into the chorioallantoic membrane (CAM) of developing chicks was studied. Eight strains were used after examining the inducible proteinase activity in the culture containing bovine serum albumin as the sole source of nitrogen. Six were proteinase-producing strains (type I) and two were proteinase-deficient ones (type II). Type I strains were subdivided into type Ia strains in which the proteinase activity persisted for a week in the in vitro culture and type Ib ones in which the enzyme activity was lost by the 7th day after inoculation. By inoculation onto CAM, the type I strains could invade the tissue in which secreted proteinase was detected on the periphery of the invading Candida cells by immunohistochemical method. At an early stage of the infection, proteinase secretion was detected on the surface of the yeast cells before their entry into the tissue. The type II strains remained on the surface of the CAM and did not invade the tissue where the secretion of the enzyme was not detected. The mortality rate of the chick embryo was not correlated with the degree of proteinase production of these strains. Two type Ib strains invaded the CAM tissue and elicited some tissue reactions by the host, yielding a low mortality rate of the chick embryos. These results suggested that the secretion of proteinase was an important factor for the invasion of CAM but other factors were also involved for the pathogenicity of C. albicans.