Medical Mycology.pptx

Mycology
Characteristics of fungi
Fungi are decomposers
They are very many species but 100 have been associated
with human disease
The cells vary from single to multicellular. Some multicellular
are large enough to be seen by naked eye
Fungi are eukaryotes with nuclear membrane and have
chromosome within their nucleus and organelles in cytoplasm
They have mitochondria, endoplasmic reticulum
Their cell structure contain a rigid cell wall and they also do
contain cytoplasmic cell membrane. Its content differs from the
mammalian cell i.e. they contain ergosterol.

Cont…
 The differs from that of mammal in that they
contain chitin, mannan and glucan.
 Chitins are also within the cell wall and are
inert compound that uncoats the rigidity of
the fungal cell wall.
 The fungal cells grow only in organic
compound, they only use carbcell wall of fungi
on as the source of energy and mostly found
in decaying organic matter

• The classification of fungi is based on the
– Mode of reproduction
– Micromorphology
• Mode of reproduction
– Perfect fungi: these reproduce both sexually and asexually.
They reproduce sexually by means of characteristic sexual
spores, which are used to classify fungi into four broad
classes, thus: Ascomycetes, Basidiomycetes, Zygomycetes,
Oomycetes
– Imperfect fungi: also called Deuteromycetes – these
reproduce only asexually
• Micromorphology
– Yeasts
– Molds
– Dimorphic
Classification of fungi

Most of the human fungi fall in the Deuteromycete group.
• Fungi can also be classified according to the tissue that they infect.
This is done using fungal diseases that they cause. They are:
– Superficial mycocete: they cause lession on the skin and
appendages. And they never invade the living tissues. The
organisms of these organism are dermatophytes. They have
preference for keratin because they produce an enzyme that
break down keratin. The enzyme is keratinase. There are three
(3) genera: i. microspora, ii. Epidemophyton, iii. Trichophyton.
They have septic hyphae and microconidia.
– Subcutaneous fungi: they cause diseases in the inner surface to
the skin. They can spread into the lymphatics. They are
introduced through the skin. Examples are: Sporotherix
schenkeii which causes sperotrichosis, Madunella mycetoma.

• Systemic fungi: they affect the internal organs i.e. lungs,
kidney e.t.c. they cause some of the most severe diseases in
human. Some of them are sub clinical in that there are no
clinical manifestation as such but those that cause clinical
characteristics are usually severe. Most are dimorphic in
nature and changes into yeast form in the body. Examples
are: Cryptococcus neoformans (pure yeast), Histoplasma
capsulatum (dimorphic), Blastomyces dermatitidis
(dimorphic), Coccidioides and Paracoccidioides (dimorphic)
• Opportunistic fungi: are occasional pathogens that attack a
patient depending on the prevailing conditions of the
patient. Example is Candida. They are termed as normal
flora, they do not cause disease unless they are allowed to
overgrow causing thrush. They form pseudohyphae in order
to penetrate the skin. Another one is the Aspergillus, it is
purely a mold and it does not change into other form. It
causes the respiratory tract infection (chest problem) and
they are toxin producers which affect the lung.

• Divided into 4 main classes:
• Phycomycetes: addition subdivide into the first six
classes. The six classes lack regular septa in their
hyphal filaments (coenocytic hyphae), resulting in
the presence of many nuclei in each cell filament.
Members of these six classes include organisms that
are infrequent causes of human disease even
though several genera in the class Zymomycetes do
cause occasional serious infection in debilitated or
immunologically compromised person.

• Ascomycetes: or sac fungi, form one or more sexual
spores within a saclike cell called ascus. The asexual
spores produced by the Ascomycetes are frequently
single-celled microconidia. Microconidia may be
produced in long chains extending from an aerial
hypha called conidiophore. Produce regular septa
which divide the mycelium into large number of
individual cells. Each septum, however, has ‘a hole’
which permits the free flow of cytoplasmic and
nuclear material between the cells. They grow only as
single – celled yeast, and by far the best known yeast in
this class are those of the genus Saccharomyces upon
which both the baking and the alcoholic beverage
industries are totally dependent.

• Basidiomycetes: form their sexual basidospores
externally on club shaped cells called basidia. Asexual
reproduction may also occur by budding, microconidia,
or fragmentation of the hyphal filament. The hyphae
are usually aseptate. Causes few human disease but
many plant diseases. In this group is musshroom
• Deuteromycetes: (fungi imperfecti) comprise of a large
group of fungi for which no sexual states has been
demonstrated. Some members produce sexual spores
which mixed with the correct mating type and, as a
result , have acquired 2 names; one for sexual
classification and the other for older asexual name.
many of human pathogens belong to this group.
• Disease caused by deuteromycetes include superficial
infection, cutaneous infection and the subcutaneous
infection and deep seated systemic infection.

Mycoses
• Establishment of a mycotic infection depend on the
inoculums of the fungi and the resistance of the host.
• Severity of infection depend on immunological factors
of the host
• Some of the reasons why mycoses/fungal diseases are
prevalent are:
– Immune states of the patient because of HIV:
immunosuppressive drug
– The transplantation therapy
– Invasive procedures that are used today of tissue i.e.
operations

Diagnosis
• Wet mount: where this refers to wet preparations i.e. a drop a
liquid on a slide and cover it with a cover slip. It is a common
procedure for diagnosing dermatophytes. i.e. Skin scrapping,
mashilingi, hair cuttings.
• Prepare the wet mount and observe spores and conidia
morphology. In this, common light microscope is used. Staining
using electrophenol blue stain or use potassium hydroxide in
skin scrapping.
• Serological methods (Serology): here systemic infections are
detected. Some of the test are latex agglutination and
immunodiffusion.
• Direct flourescent microscopy: here you stain the specimen
with flourescent dyes before observing under the fluorescent
microscope.
Stain biopsy of specimens or section of body tissues

• The most definitive method is the culture the organism in a cultural
media. The most commonly used media for fungal culture cells is the
sabaroud dextrose agar (SDA). The incubation temperature depends
on the organism form whether it is a yeast form or a mold form. For
the yeast form, culture at 37 degrees centigrade, while for mold you
culture at a lower temperature at 25 degrees centigrade.
• After fungal isolation, look at the colonial morphology in terms of
color, texture, size and shape. After observation, you may want to
view it on the microscope without staining or stain usual
electrophenol blue. NEVER USE GRAM STAINING.
•

Zarqa Private UniversityBiology 4223 – The
Fungi
Fungal Diseases
• Mycosis- fungal infection
– < 100 cause human disease
– Not highly contagious
– Humans acquire from nature
• Groups based on degree on tissue involvement and
mode of entry

Fungi
Introduction
Fungal Infections
Superficial infections: involve outermost layers of skin
and its appendages [ nails or hair] ( Dermatophytosis)
• Cutaneous infections: involve deeper layers of skin
causing allergic or inflammatory response
• Subcutaneous infections: fungi with low virulence,
localized infection, or spread by mycelial growth
Systemic infections: caused by true pathogenic fungi or
opportunistic saprobes
Opportunistic infections

Fungi
Mycoses: diseases cause by fungi
• Superficial Cutaneous
• Subcutaneous Systemic
• Opportunistic

Fungi
FUNGAL DISEASES (Continued)
I. Cutaneous mycoses: Fungal infections of the skin, hair, and nails.
 Secrete keratinase, an enzyme that degrades keratin.
 Infection is transmitted by direct contact or contact with infected hair (hair
salon) or cells (nail files, shower floors).
 Examples:
– Ringworm (Tinea capitis and T. corporis)
– Athlete’s foot (Tinea pedis)
– Jock itch (Tinea cruris)

Fungi
Cutaneous Infections
Dermatophytic hyphomycetes
• 40 species
• Epidermophyton (2 species)
• Microsporum (17 species)
• Trichophyton (24 species)
• 50% of dermatophytes human specific

Fungi
Cutaneous Mycosis
Ringworm skin infection: Tinea corporis

Fungi
Cutaneous Mycosis
Candida albicans infection of the nails.

Fungi
– Cause common tinea (ringworm)
– Grow only on humans
– Reservoir not in soil or animals
– Reservoir in carpets and upholstery for up to two
years

Fungi
• Trichophyton rubrum
• Chronic infections of
the toe nails
Tinea corporis

Fungi
• Microsporum canis
– Reservoir in cat
– May move to humans or dogs
– Dies out after one or two person-person transfers

Fungi
• Disease process
– Fungus stimulates epithelial cells of skin to divide
more frequently
– Makes more keratin available to fungus
– Some species race specific in humans
– Some species body location specific

Fungi
II. Subcutaneous mycoses: Fungal infections beneath the skin.
 Caused by saprophytic fungi that live in soil or on vegetation.
 Infection occurs by implantation of spores or mycelial fragments into a
skin wound.
 Can spread to lymph vessels.
Superficial mycoses: Infections of hair shafts and superficial epidermal cells.
Prevalent in tropical climates.

Fungi
Subcutaneous mycoses
Subcutaneous infections - over 35 species produce chronic inflammatory disease of
subcutaneous tissues and lymphatics. e.g. sporotrichosis - ulcerated lesions at site of
inoculation followed by multiple nodules - caused by a dimorphic fungus: Sporotrix
schenckii.

Sporotrichosis
• Agent is Sporotherix schenkii
• It is a chronic infection of both the cuteneous and
subcutenous tissue. They tend to form ulcers that kind of
drain their fluids. Occasional mycetoma my be caused.
• It is transmitted through pricks i.e. thorns
• The most common parts of the body infected are the feet
(primary source of infection). From the primary source of
infection, the disease may pass on to the lymphatic system.
• Diagnosis: clinical specimens are pass, biopsy material or
sputum can be used incase pulmonary tract is infected.
Staining of biopsy material may be done in addition to
culture. No serological. NB// Fungi are not serologically Dx
because they are pure antigens

Fungi
Subcutaneous Infections
Chromoblastosis
• Common among barefoot peoples of the
tropics
• Soil hyphomycete species
• Enters human by thorns or wood slivers
– Fungus grows  host cells respond by rapid cell
division  wart-like growths on feet or legs

Fungi
Mycotic Mycetoma
• Disease of barefoot tropical people
• Entry: wound on foot
• Attacks various tissues
– Stimulates formation of tumor
– Compact fungal colonies form within tumor

Fungi
– Skin ruptures and
some colonies
extrude

Fungi
III. Systemic Mycoses
Introduction
• Caused by . . .
– Specialized pathogens
• Dimorphic
– One form outside the host
– Another form inside the host
– Opportunistic saprobes

Fungi
Systemic Mycoses
Dimorphic Pathogen Mycoses
• Histoplasmosis
– Histoplasma capsulatum
• Grows on bird droppings, chicken manure, bat guano
– Conidia inhaled  primary lung infection 
almost always fatal until recently

Histoplasmosis
The causative agent is Histoplasma capsulatum. It is a
primary systemic disease that affect the liver, spleen, bone
marrow and lung
• Its primary sign is spleenomegally. Spleenomegally appears
in children while in adult the primary sign is the pulmonary
tract having lesion.
• The porthole of entry for histoplasma is the lungs
• In places where histoplasma is a common organism, most
of the infections are subclinical
• Diagnosis: Specimen to be used for lab diagnosis depends
on the part of the body infected. For the dimorphic fungi,
one has to culture them two temperatures: 25 and 37
degrees centigrade. In serological test, the following can be
used: ELISA, Complement fixation test, Immunodiffusion.

Fungi
Systemic mycoses: Fungal infections deep within the body. Can affect a
number if tissues and organs.
 Usually caused by fungi that live in the soil and are inhaled. Not
contagious.
 Examples:
– Histoplasmosis (Histoplasma capsulatum): Initial infection
in lungs. Later spreads through blood to most organs.
– Coccidiomycosis (Coccidioides immites): Resembles
tuberculosis.

Fungi
Systemic Mycosis: Histoplasmosis
Disseminated Histoplasma capsulatum, lung infection.

Systemic Mycoses
Coccidiomycosis
• Coccidioides immitis
• Also a pulmonary disease and most of the patients in
which it occurs, it will resolve on their own (60%). It is
mainly found in USA and also S. America, N. America
• The organisms are mostly found in desert soils and
rodent barrows.
• Diagnosis: the clinical specimens are the sputum, and
pass from the skin since it affects the skin also.
Serological test can be done similar to histoplasma.

Fungi
Systemic Mycoses
• Infection, disease process, and clinical
symptoms similar to histoplasmosis
• Can be effectively treated with fluconazole

Paracoccidiomycosis
• Agent is Paracoccidioides brasiliensis.
• It affects the mucus membrane and the skin.
• Diagnosis: can be done by KOH microscopy on
sputum specimen or on skin scrapping and
also on pass. The organism can also be
cultured at 25 degrees centigrade using SDA
as the medium culture. Serological test used is
the immodiffusion.

Fungi
IV. Opportunistic mycoses:
Caused by organisms that are generally harmless unless individual has
weakened defenses:
– AIDS and cancer patients
– Individuals treated with broad spectrum antibiotics
– Very old or very young individuals (newborns).
 Examples:
– Aspergillosis: Inhalation of Aspergillus spores.
– Yeast Infections or Candidiasis: Caused mainly by Candida
albicans. Part of normal mouth, esophagus, and vaginal
flora.

Fungi
Opportunistic Pathogens/Disease
General
• Pathogens all grow well at 37C
• None cause disease in well individuals
• Require breakdown in resistance system
• Complication of diabetes, AIDS, advanced
cancer, sequel to steroid or antibiotic
treatments

Fungi
Zygomycosis
• Species of Zygomycota
– Rhizopus, Mucor, Rhizomucor
• Rhinocerebral mycosis
– Spores enter through sinuses
– Grows rapidly outward to the eyes and inward
towards the brain

Fungi
Aspergillosis
• Aspergillus sp.
• Bronchiopulmonary aspergillosis
– Mucus within the bronchi  severe allergic
reaction
• Aspergilloma
– Forms a mycelia ball in lung cavity formed from
earlier TB

Aspergillosis
Aspergilus cause a variety of diseases. One of them being allergic reaction due to
the hypersensitivity of aspergillus spores
• The organism can invade the lungs the disease my invade other organs like the
heart causing endocardiasis. They may also invade the bones
• There is also fungal ball: this is when the apergillus organisms invade the
carvities that are left by tuberculosis (TB). Hepatitis: toxins produced by
Aspergillus accumulate in the liver.
• There are many species of Aspergillus but only 3 are associated with human
diseases namely: A. flavus, A. Niger and A. fumigatus
• Aspergillus are worldwide distributed found in soil e.t.c. They also cause
opportunistic diseases rather than frank infections/true.
• To culture Aspergilllus, depends on the part of tissue from which the specimen
is taken.
• The incubation period is 3 weeks because some are slow growers and others
fast growers

Fungi
– Surgical intervention often required
• Invasive aspergillosis
– Severely debilitated
– Immunosuppressed (AIDS)
• Almost always fatal until recently

Fungi
AIDS and Mycoses
• Aspergillosis
• Candidiases (Candidiasis seen in 2/3 of AIDS
patients
• Cryptococcosis
• Zygomycosis
• Esophogeal candidiasis and cryptococcosis are
strong indicators of AIDS

Fungi
PRIMARY ANTI-FUNGAL AGENTS
1. Polyene derivatives
– Amphotericin B
– Nystatin
2. Azoles
– Ketoconazole
– Fluconazole
– Itraconazole
– Voriconazole

Fungi

Fungi
Azoles
There are a few rare serious side
effects from Itraconazole and
Fluconazole

Fungi
5-fluorocytosine
(5-FC)
Interferes With RNA Synthesis

Fungi
MECHANISMS OF ACTION
• Polyenes
• Azoles
• Griseofulvin
• 5 - FC
• Ergosterol in cell
membrane
• Interfere with
ergosterol synthesis
• Forms a barrier to
fungal growth
• Inhibits RNA synthesis

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