Candida

• Normal Habitat: 
• mucosal membranes of human and other warm blooded animals.
• Also found in the gut, the vagina or also in the surface of the skin.
• Found in the digestive tract of birds also.
• Isolated from soil, animal, hospitals, in-animate objects and food.
• Worldwide distribution

• MORPHOLOGY
  
• Small, oval, measuring 2-4 µm in diameter.
• Yeast form, unicellular, reproduce by budding.
• Single budding of the cells may be seen.
• Both yeast and pseudo-hyphae are gram positive.
• Encapsulated and diploid, also form true hyphae.
• Polymorphic fungus (yeast and pseudohyphal form)
• Can form biofilms
• Normal condition: Yeast
• Special condition (pH, Temperature): Pseudohyphae
• 80-90% of cell wall is carbohydrate

• on SDA
• Creamy, pasty colonies, smooth after 24-48 hours at 25-37°C
• Yeast smell (odour)

Blood Agar

Candida albicans on Blood Agar

• White creamy colored
• Foot-like extensions from the margin.

• Opportunistic fungal pathogen that causes candidiasis in human
• Occurs in immunocompromised peoples such as HIV infected, transplant recipients, chemotherapy patients, etc.
• Mode of transmission:
• Mother to infant through childbirth
• Rarely through sexual contact
• People to people transmission in hospital settings

Stages of Infection

1. Colonization

• Epithelial adhesion
• Nutrient acquisition

2. Superficial Infection

• Epithelial penetration
• Degradation of host protein

3. Deep-Seated Infection

• Tissue penetration
• Vascular invasion
• Immune evasion or escape

4. Disseminated Infection

• Endothelial adhesion
• Infection of other host tissues
• Activation of coagulation and blood clotting cascades.

Types of Candidiasis

Mucosal Candidiasis

• Oral candidiasis: mucous membrane of mouth
• Denture related stomatitis: mild inflammation and redness of oral mucous membrane beneath a denture.
• Angular cheilitis: inflammation of one or both corners of the mouth
• Median rhomboid glossitis: redness and loss of lingual papillae
• Vulvovaginitis: white lesions on the epithelial surfaces of vulva, vagina and cervix
• Balanitis: infection of glans penis
• Esophageal candidiasis: infection of esophagus painful swallowing.

Cutaneous Candidiasis

• Candida folliculitis: infection and inflammation of hair follicles, rash may appear as pimples.
• Candidal intertrigo: infection of skin located between intertriginous folds of adjacent skin.
• Candidal paronychia: inflammation of the nail fold.
• Perianal candidiasis: irritation of the skin at the exit of the rectum.
• Chronic mucocutaneous candidiasis: immune disorder of T cells, deficient of CMI.
• Congenital cutaneous candidiasis: skin condition in new borne babies caused by premature rupture of membranes together with a birth canal infected with C. albicans.
• Diaper candidiasis: infection of a child’s diaper area.
• Erosio interdigitalis blastomycetia: characterized by an oval shaped area of macerated white skin on the web between and extending onto the sides of the fingers.
• Candidal onychomycosis: nail infection

Systemic Candidiasis

• Candidemia: leads of sepsis
• Disseminated candidiasis (organs)
• Endocarditis
• Gastro intestinal tract infection
• Respiratory tract infection
• Genitourinary candidiasis
• Hepatosplenic candidiasis (Chronic Disseminated Candidiasis)

Lab Diagnosis of Candida albicans

Specimens: Exudates, Tissues, Scrapings

1. Microscopy (Scraping)

• Examined in wet film in 10% KOH
• Visualization of pseudohyphae and budding yeast cells of candida
• Gram staining: Gram positive (+ve)

2. Culture

• SDA: Creamy white, smooth colonies
• CHROMAGAR: Green colonies

3. Identification of albicans

• Germ Tube Test: produce germ tube test within 2 hours when incubated in human serum at 37°C.
• Chlamydospores: produced by C. albicans on corn meal/rice agar at 25°C. They produces round thick walled chlamydospores borne terminally or laterally.
• Biochemical Tests: Glucose and maltose fermented with acid and gas production, sucrose and lactose not fermented, Pale pink coloration in Tetrazolium reduction medium

4. Serology

• Limited specificity
• Serum antibodies and cell mediated immunity are demonstrable in most people because of life long exposure to C. albicans.
• C. albicans antigen is a delayed hypersensitivity skin test, which is used as an indicator of functions of the CMI.
• ELISA and RIA: detection of circulating Candidial antigen either cell wall mannan or cytoplasmic constituents.

5. 1,3-beta-D-glucan assay

• Beta-D-glucan is a component of the cell wall of fungi.
• Detected by its ability to activate factor G of the horse-shoe crab coagulation cascade.
• Highly specific and sensitive test.

6. DNA probe and PCR

Treatments of Candida albicans

1. Oral candidiasis: Nystatin, miconazole, amphotericin B.
2. Cutaneous candidiasis: Clotrimazole, econazole, ciclopirox, miconazole, ketoconazole, nystatin.
3. Systemic and oral azoles: Fluconazole, itraconazole or posaconazole.
4. Vulvovaginitis: single dose of oral fluconazole, topical antifungals (butoconazole, clotrimazole, miconazole, nystatin, ticonazole, terconazole).
5. Blood infections: intravenous fluconazole or an echinocandin (caspofungin)
6. Candidemia: Fluconazole and Anidulafungin

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INTERFERONS (IFN)

INTERFERONS (IFN):

• GENERAL PROPERTIES:
• Is secreted out of host cell, usually found in a dimer or multimeric form.
• IFN goes out, binds to specific receptors on neighboring cells, and changes their transcription in such a way as to give them anti-viral properties.
• ds-RNA and LPS are both good inducers of IFN.
• FUNCTION: Suggested mechanism of action involves RNA endonuclease activity, and induction of transcription of new genes.
• IFN also prevents DNA synthesis and thus inhibits cell growth.
• ANTI-TUMOR: IFN's generally have some anti-tumor activity, particularly on leukemias and lymphomas. They induce the production of HLA antigens on tumor cells, thereby allowing the immune system to recognize the tumor cell.
• RESISTANT: CMV and VZV are resistant to IFN. Other viruses are mostly susceptible.
• INTERFERON-alpha: Produced by leukocytes.
• Receptor gene for IFN-alpha is on Chrom #21
• FNXN: Has been approved as a treatment for rare B-Cell Hairy Leukemia.
• INTERFERON-beta: Produced by fibroblasts.
• Receptor gene for IFN-beta is on Chrom #21
• INTERFERON-gamma: Produced by (1) unsensitized lymphoid cells, or (2) sensitized T_H1 cells.
• It is stronger than other two in its antiviral properties.
• Receptor gene for IFN-gamma is on Chrom #6

ANTIVIRAL CHEMOTHERAPY

• AMANTADINE and RIMANTADINE:
• ACTION: Inhibits the uncoating stage (part of binding) of Influenza A virus.
• Binds to M-Protein and blocks the pre-lysosomal uncoating, after attachment has already taken place.
• Viruses can acquire resistance with extended use.
• VIRUSES: Inhibits primarily the Influenza A virus, but also has activity against Influenza C, Sendai, Dengue, and Rubella viruses.
• Parainfluenza 1,2,3, Influenza B, and RSV are resistant
• SIDE-EFFECTS: In 10% of patients, CNS toxicity, nervousness, difficulty concentrating.
• CLINICAL: Use is restricted to certain subgroups: in epidemics, at-risk patients, hospitalized patients.
• RIBAVIRIN:
• ACTION: Inhibits viral transcription, by binding to and inhibiting enzymes involved in nucleic acid metabolism. Specifically inhibits inosine monodehydrogenase, involved in the synthesis of GTP.
• SIDE-EFFECTS: It is toxic in that it does not discriminate well between host cell and virus. Toxic to liver cells and can cause anemia.
• VIRUSES: RSV in infants, and Lassa Fever intravenously.
• ACYCLOVIR:
• ACTION: It is converted by HSV viral Thymidine Kinase into a monophosphate activated form. Host cell then converts monophosphate form into triphosphate form. This form then does two things:
• Binds and inhibits viral DNA polymerase
• It is incorporated into viral DNA, where it acts as a chain-terminator.
• RESISTANCE in HSV is due to mutations in two different viral proteins:
• Viral Thymidine Kinase, preventing conversion of acyclovir to the triphosphate form.
• Viral DNA polymerase, such that it doesn't bind the drug.
• VIRUSES: Specific for HSV infections: HSV-1, HSV-2, VZV, but not CMV or EBV.
• Resistance can occur, due to mutations in either Thymidine Kinase or viral DNA polymerase.
• ADENINE ARABINOSIDE (Ara A):
• ACTION: Binds to DNA-Polymerase -- cellular or viral, thus bad side effects.
• VIRUSES: Used to be used for HSV-Encephalitis cases. Now surpassed by Acyclovir.
• GANCICLOVIR:
• VIRUS: CMV, promising new treatment. Also works on HSV.
• Up to 80% of HIV patients will relapse if therapy is discontinued. CMV pneumonia does not respond as well as other CMV infections.
• ACTION: Nucleoside analog of guanosine, similar to Acyclovir.
• SIDE-EFFECTS: Reversible neutropenia, liver and CNS toxicity.
• AZIDOTHYMIDINE (AZT, ZIDOVUDINE):
• ACTION: Inhibits Reverse Transcriptase.
• AZT is phosphorylated first by host enzymes.
• VIRUS: HIV-1