Systemic mycosis (2) Candida

Mrs. Dalia Kamal Eldien

Msc in Microbiologylecture NO -11-

Objectives

Introduction to Candida Common speciesFactors predispose the candidiasis Pathogenicity of CandidaLaboratory diagnosis

Introduction

Candida is a genus of yeasts and is the most common cause of fungal infections worldwide.

This yeast can live as harmless commensal in many different body locations, and is carried in almost half of the population. However, in response to a change in the host environment, Candida can convert from a benign commensal into a disease-causing pathogen

Normal habitat is the mucosal membranes of humans and various other mammals including the mouth, gut, vagina, and sometimes the skin.

Candida belongs to the class Ascomycetes and the family, Saccharomycetaceae, reproduce by budding or binary fission, and some species can reproduce sexually.

When Candida reproduce by budding some time the generation fail to separate from the mother cell giving pseudo mycelium

Common species

• There are more than 163 species, only 20 can produce infection to man, the common species are:

C. albicansC. tropicalisC. psudotropicalisC. kruseiC. dubliniensisC. glabrata

Factors predispose candidiasis 

The major factors contributing to higher frequency of fungal infections

1- Excessive antibiotics consumption

2- Birth control devices  (e.g., oral contraceptives or estrogen therapy)

3- Excessive stress

4- Tap water consumption

5- Parasite and worms infection

6- Hypothyroid

7- Immunodeficiency

8- Hormonal imbalance

9-Diabetes  (with poor glycemic control)

10-Excessive alcohol consumption

Pathogenicity

Candida is considered an opportunistic pathogen (especially  C. albicans) because it can harmlessly colonize the human digestive tract, mouth, skin, and genitourinary tract, however, when the balance of normal bacteria is upset e.g after antibiotic treatment or the immune system of the host is weakened, Several areas of the body may be affected by fungal infection:-

Common disease caused by Candida

1-Oral candidiasis  Candida infections of the mouthAre widespread among humans,  which is

commonly identified by reddish lesions and crusting at the corners of the mouth, very painful, common in children and infant, and may clear spontaneously

In Adult oral candidasis occur usually due to use of broad-spectrum antibiotics or inhaled corticosteroids, and xerostomia (dryness of mouth) are all risk factors for oral candidiasis

Oral candidiasis

2-Candida vulvovagantitis: Are general terms that refer to the inflammation disease

of the vagina and/or vulva(the external genital organs of a woman).

Is not common before puppetry and after menposeVaginal thrush responsible for 50% of vaginal discharge,

whitish or whitish-gray cottage cheese-like , odor less. If the amount of discharge is increased without

treatment the thigh can affected. Candida balanitis : is an inflammation of the glans (the

rounded head) of the penis in men

Candida vulvovagantitis

3-Cutaneous candidasis:   Are a common phenomenon, affecting millions of people

worldwide, most cases occur in skin folds Major symptoms of cutaneous candidiasis include itching

(unrelenting and often intense) and an enlarging skin rash. Occasionally, the rash will be surrounded by smaller rashes

appearing along the outer edge of the main rash present on the surrounding healthy skin, with typical satellite lesions.

Predisposing factor include obesity, diabetes and wet skin . Diaper candidiasis is common in infants under unhygienic

conditions of chronic moisture and local skin maceration due to irregularly changed unclean diapers.

Cutaneous candidasis

4-Candida onychia and paraonchyia: The patient has a history of a painful and erythematous

area around the nail and nail bed of a finger or toenail.More frequently associated with immersion of the

hands in water and with diabetes mellitus.The nail be greenish or brown, luster less, latter

became irregular but not brittleUnlike the acute bacterial paronychia, which generally

involves a single finger, chronic fungal infection can affect a number of fingers simultaneously

Candida onychia and paraonchyia

5-Systemic Candida infection: Systemic candidiasis spreads throughout the body and

can be life-threatening. Infection might include the brain, heart, kidneys, eyes,

liver, genital tract and joints. This form occurs most often in people with low white

blood cell counts (neutropenia). up to 45% of people may die.

Laboratory diagnosis

Specimen:-According to the site of the infection. Include mouth swab,

vaginal swab, skin swab, vaginal secretion, infected nail, blood ,…….

Direct microscopy:-

1- wet mount preparation using10%KOH facilities the demonstration fugal elements, The fungal elements like bud yeast , pseudohyphae and or hyphae can be demonstrated by wet mount

2- Gram stain : Gram positive yeast cell, when ageing became gram variable

3- Other stains: PAS and Gomori’s methenamine silver stain

Direct microscopy KOH

Gram positive yeast cells

Culture1-Sabouraud Dextrose Agar with antibiotics produce

Cream, Pasty, Smooth colonies in 1-2days of incubation at 37 C aerobically

2- Cornmeal Agar : for identification of characteristic terminal chlamydospores, incubation at 25 C

3-Blood agar: non hemolytic, smooth, moderate colonies, resemble to Staph colonies

Blood agar

SDA

4-CHROMagar:

This is special media for Candida, use to identify the different species, each species colonies have a characteristic color

Candida albicans : light green to bluish green Candida glabrata : rose Candida krusei : rose pale Candida tropicalis : bleu-violet

CHROMagar

Biochemical tests: (to identifying the species )1. Zymogram test (Fermentation of Carbohydrates) The capacity of yeasts to use certain carbohydrates

as an energy source, result in produce acid and carbon dioxide

Acid production could be observed in a liquid growth medium with one carbohydrate by change of color& CO2 in Durham tubes.

C. albicans is Glucose and Maltose fermented with acid and gas production  in Durham tubes, sucrose and lactose not fermented.

Zymogram test

2- Germ tube test (Reynold’s-Braude Phenomenon) The abbreviation as GTT, provides a simple,

reliable and economical procedure for the presumptive identification of Candida albicans.

when culture in human serum from one to two hours, C. albicans produce germ tube like

GTT

3-Chlamydo spore formation: When C.albicans cultured on corn meal agar and

incubate at 26 C for 48-96 hrs, it produce chlamydo spore, while the other species are non producing

CHLAMYDO SPORE

4-Auxanograme:(Carbon and hydrogen assimilation test) Auxanogram was used to evaluate the capacity to

assimilate a different carbon source.Yeast suspension was incorporated into a synthetic base

free of carbon and solidified. After that 16 different carbohydrates were added to the

plate, which was then incubated at 35ºC for 24 and 48 hours.

Any visible growth, indicated by the spot of carbohydrate incorporation was defined as constituting positive assimilation.

Auxanograme

• Histological technique: for biopsy using H&E, PAS, or silver stain

• Immuno diagnosis used Southern blotting technique

• PCR based tests for Candida-DNA detection• Serological test if the antisera are available

ELISA, RIA, CIE, …..

Treatment

• Cutaneous candidiasis: Most localized cutaneous candidiasis infections may be treated with any number of topical antifungal agents (eg, clotrimazole, econazole, ciclopirox, miconazole, ketoconazole, nystatin).

• If the infection is a paronychia, the most important aspect of therapy is drainage of the abscess, followed by oral antifungal therapy with either fluconazole or itraconazole.

SOURCES

• (Merck Manual 2008; Cheng 2012; Douglas 2011