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MEDICAL MICROBIOLOGY
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TWO MARKS:
1. What are the general characters of fungi?
1) Fungi are Eukaryotic organisms. Each fungal cells has Nucleus, Nuclear membrane,
Endoplasmic
Reticulum and Mitochondria.
2) Mycology is the study of Fungi.
3) Fungi are aerobic or facultatively anaerobic chemoheterotrophs.
4) Fungi synthesis lysine from alpha aminoadipic acid.
5) Many Fungal species produce flagellated, motile cells.
6) Fungi lack the property of photosynthesis.
7) They are found as saprophytes in the soil, they have the capacity to degrade the organic
matter.
2.Define Mhorphology of Fungi.
There are two forms of fungi that are Yeast and Molds.
YEAST
Yeast is round or oval shaped, 4-5micrometre in diameter. Some yeast is 24 micrometer in
dm. On SDA agar, yeast produce creamy opaque colonies, Eg: Cryptococcus neoformans
YEAST LIKE FUNGI
Some yeasts produce false hyphae during some time called pseudohyphae. These yeasts are
called yeast like fungi. Eg: Candida albicans
MOLDS
Multidellular fungi composed of filamentous or tubular structures called hyphae. The length
of single hyphae is about 5-50micrometre. Some hyphae have the cross walls called Septa.
Hyphae are branched and form a mat like structure is called as Mycelium. On SDA agar medium
molds produce cottony colonies.
FUNGAL CELL WALL
Cell wall is rigid and thick, 15% - 30% of the dry weight of fungal cell wall contains some
essential components such as polysaccharides and proteins, It provides rigidity, strength and it
protects the cell membrane form osmotic shock.
Cell wall of yeast thickness is about 200-300nm in dm and molds wall thickness is about
200nm in diameter.
3.What are the Fungal diseases?
1) Superficial Mycoses (Tineaversicolor)
2) Subcutaneous Mycoses (Sporotrichosis)
3) Cutaneous Mycoses (Tinea capitis)
4) Systemic Mycoses ( Histoplasmosis)
5) Oppurtunistic Mycoses (Candidiasis)
4)Give some economic importance of Fungi.
1) Saccharmyces and Trichoderma are used in the production of foods.
2) They are used for the biological control of pests.
3) Many fungal members cause spoilage of fruits, grains and vegetables and also cause plant
diseases.
4) Some of the fungus are used as a food (Mushroom)
5.Define Superficial Mycoses.
Superficial mycoses affect the skin, hair or nall. These infections are mild but sometimes
chronic in nature. Those fungi that cause superficial infections have the capability to digest
keratin and are saprophytes. It includes less inflammatory responses. There are two types of
superficial infections, Surface Mycoses and Cutaneous Myxoses.
In Surface infections, fungi surive only on dead layers of the skin. All the fungus involved in
the superficial mycoses is included under the group mold
Eg. Pityiasis versicolor(Tinea vesicolor)
Piedra (Trichosporosis)
Cutaneous Mycoses are observed slightly deeper portion of the Epidermis. In this case, the
fungi grown
in the cornified layer of the skin and cause inflammatory response
Eg. Dermatophytosis
Microsporum spp.
Trichophyton spp.
Epidermophyton spp.
6) Define Subcutaneous Mycoses.
These are a group of fungus involve in the Dermis and Subcutaneous tissue. These are
reffered as Mycoses of implantation because they are acquired when the pathogen is inoculated
through the skin by minor cuts or scratches or by thorns splinter wound. Etiological agents are
ubiquitous in nature and usually found in soil or on decaying vegetation. The infections occur on
the parts of the body that are most prone to be traumatized Eg. Feet, legs, and Buttocks.
Subcutaneous infections are slow in onset an lesions evolve over any months. Persistence may be
due to noninvasive properties of this group of organisms.
Infections are
1) Chromomycosis
2) Mycetoma
3) Sporotrichosis
4) Rhinosporidiosis
.
7) What is meant by Systemic Mycoses?
These are also called deep mycoses. They are acquired by inhalation. They are two types of
systemic mycoses, that are primary systemic mycoses and opportunistic systemic mycoses.
Those fungi that cause primary systemic mycoses are called primary pathogen.
Eg: Blastomycosis
Coccidioidomycosis
Some of the saprophytic fungi of the environment cause opportunistic systemic mycoses
and are called oppurtunuistic fungi.
Eg: Candidiosis
Aspergillosis
8) What are the laboratory diagnosis of fungal infections?
Fungi are significant, sometimes overlooked, human pathogens. Infection range is from
mild to life threatening. Clinical laboratories must be prepared to identify fungi and realize that
the range of new fungal species that causes diseases.
Diagnosis is based on a combination of clinical and laboratory investigations.
Laboratory procedure includes,
Demonstration of fungai by microscopy
Idetification by culture
Detection of specific humoral responses
Detection of fungal antigens and metabolites in body fluids.
Successful of laboratory diagnosis depends on the following
Specimen selection
Specimen collection
Specimen transport
Processing
Microscopic examination
Culturing.
9)Write the pathogenecity and laboratory diagnosis of Pityriasis versicolor.
Pathogenecity:
1) It affects external appearance of an individual
2) It produces non-inflammatory macular lesions with fine scaling
3) Lesions are not usually itchy.
4) Mycelial phase fungus is associated with Tinea versicolor.
5) Fungus interferes melanin production by the production of Dicarbolic acid.
6) Fubgus inhibits the activity of Tyrosinase, which is responsible for the synthesis of
melanin.
Laboratory diagnosis:
Specimen
Pus skin scrapings
Microscopy
1) Direct microscopic observations of the specimen with 10-20% KOH.
2) Short unbranched hyphae and spherical cells are observed.
3) Lesions also fluorescence under woods lamp test.
10)Define Dermatophyttosis.
Dermatophytosis is fungal infections that involve the superficial areas of the body. These
diseases are caused by the dermatophytes that invade the keratinized portion of the hair, skin and
nails.
Dermatophytes are transmitted by close contact and the organisms may spread rapidly
within families and enclosed communities. The dermatophytes can be conveniently classified
into three groups. On the basis of their reservoir and host preference.
1) Anthropophilic species are those which have man as their major host.
2) The zoophilic pathogens infect animals.
3) Geophilic organisms are found in soil but may infect animals and man.