microbiology

1. MICROBIOLOGY
AND
PARASITOLOGY
PITYRIASIS VERSICOLOR,
CANDIDIASIS, SCABIES

2. MALASSEZIA FURFUR (PITYRIASIS VERSICOLOR)

3. Morphology
 M. furfur appears as clusters of spherical or oval, thick-
walled yeastlike cells, 3 to 8 μm in diameter
 The yeast cells may be mixed with short, infrequently
branched hyphae that tend to orient end to end
 The yeastlike cells represent phialoconidia and show polar
bud formation with a “lip” or collarette around the point of
bud initiation on the parent cell
 In culture on standard media containing or overlaid with
olive oil, M. furfur grows as cream-colored to tan yeastlike
yeastlike colonies composed of budding yeastlike cells
 Malassezia can be isolated from normal skin and scalp and
are considered part of the cutaneous mycobiota
Note: other species as a causative agent of pityriasis
versicolor: Malassezia globosa, Malassezia sympodialis

5. Epidemiology
 Occurs worldwide, but it is most prevalent in tropical and subtropical regions
 Young adults are most commonly affected
 M. furfur is not found as a saprophyte in nature, and pityriasis versicolor has not been documented in
animals
 Human infection is thought to result from the direct or indirect transfer of infected keratinous material
from one person to another

6. Clinical syndromes
 Lesions of pityriasis versicolor are small hypopigmented or hyperpigmented macules
 Because M. furfur tends to interfere with melanin production, lesions are hypopigmented in dark-skinned
individuals
 In light-skinned individuals, the lesions are pink to pale brown and become more obvious when they fail to tan
to tan after exposure to sunlight
 Upper trunk, arms, chest, shoulders, face, and neck are most often involved, but any part of the body may be
affected
 Lesions are irregular, well-demarcated patches of discoloration that may be raised and covered by a fine scale
 Little or no host reaction occurs, and the lesions are asymptomatic, with the exception of mild pruritus in
severe cases.
 Complications (rare): folliculitis, perifolliculitis, dermal abscesses

7. Laboratory diagnosis
 Laboratory diagnosis of pityriasis versicolor is made by direct visualization of the fungal elements on
microscopic examination of epidermal scales in 10% potassium hydroxide (KOH) with or without
calcofluor white
 Yeast clusters & short curved septate hyphae = "spaghetti and meatballs"
 Organisms are usually numerous and may also be visualized with hematoxylin and eosin (H&E) or
periodic acid–Schiff (PAS) stains
 The lesions will also fluoresce with a yellowish color upon exposure to a Wood lamp
 Although not usually necessary for establishing the diagnosis, culture may be performed using synthetic
mycologic media supplemented with olive oil  growth of yeastlike colonies appear after incubation at
30° C for 5 to 7 days  microscopically, the colonies are comprised of budding yeastlike cells with
occasional hyphae

9. SARCOPTES SCABIEI (SCABIES)

10. Mites: tungau
Flea: pinjal
Ticks: caplak/sengkenit
Lice: kutu/tuma
LICE MITE

11. Of the 3000 species only a
dozen commonly attack
humans. The most
important species are the
rat flea, the human flea and
the cat flea
capitis

12. MITES
 small, eight-legged arthropods characterized by a saclike body and no antennae
 The number of mites that are considered true human parasites or present real medical problems is quite
small and include the human itch mite (Sarcoptes scabiei), the human follicle mite (Demodex
folliculorum), and the chigger mite
 Mites affect humans in 3 ways: by causing dermatitis, by serving as vectors of infectious diseases, and
by acting as a source of allergens.

13. ITCH MITES
 The itch mite (Sarcoptes scabiei) causes an infectious skin
disease variably known as scabies, mange, or the itch
 Sarcoptes scabiei undergoes four stages in its life cycle: egg,
larva, nymph and adult.
 Adult mites average 300 to 400 μm in length with an oval,
saclike body in which the first and second pairs of legs are
widely separated from the third and fourth pairs
 Male adults are slightly more than half bigger than female
adults
 The body has dorsal transverse parallel ridges, spines, and
hairs
 The ova (eggs) are oval and measure 100 to 150 μm
 Larva have 3 pairs of legs, nymphs have 4 pairs of legs

14. Epidemiology
 Cosmopolitan distribution ( can be found almost anywhere on the Earth)
 Estimated global prevalence is about 300 million cases
 The mite is an obligate parasite of domestic animals and humans; however, it may survive for hours to days away from
from the host, thus facilitating its spread
 Transmission is accomplished by direct contact or by contact with contaminated objects such as clothing. Sexual
transmission has been well documented.
 Transmission occurs primarily by the transfer of the impregnated females during person-to-person, skin-to-skin
contact.
 May occur in epidemic fashion among people in crowded conditions, such as day-care centers, nursing homes,
military camps, and prisons

15. Life cycle
 Adult mites enter the skin, creating serpiginous burrows in the upper layers of the epidermis (never below the stratum
stratum corneum). Burrows appear as tiny raised serpentine lines that are grayish or skin-colored and can be a
centimeter or more in length
 Female mite lays her eggs in the skin burrows (2-3 eggs per day)
 Eggs hatch in 3 to 4 days
 Larvae migrate to the skin surface and burrow into the intact stratum corneum to construct almost invisible, short
burrows called molting pouches (larval stage has only 3 pairs of legs and lasts about 3 to 4 days)
 The larvae molt resulting in nymphs
 Nymphs molts into slightly larger nymphs before molting into adults (Larvae and nymphs may often be found in
molting pouches or in hair follicles and look similar to adults, only smaller)
 Mating occurs after the active male penetrates the molting pouch of the adult female. Mating takes place only once
once and leaves the female fertile for the rest of her life. Impregnated females leave their molting pouches and
wander on the surface of the skin until they find a suitable site for a permanent burrow.
 When the impregnated female mite finds a suitable location, it begins to make its characteristic serpentine burrow,
laying eggs in the process. After the impregnated female burrows into the skin, she remains there and continues to
lengthen her burrow and lay eggs for the rest of her life (1-2 months)
 Males are rarely seen; they make temporary shallow pits in the skin to feed until they locate a female’s burrow and
mate.
 Characteristically, the preferred sites of infestation are the interdigital and popliteal folds, the wrist and inguinal
regions, and the inframammary folds
 The presence of the mites and their secretions cause intense itching of the involved areas.

17. Clinical syndromes
 Intense itching, usually in the interdigital folds and sides of the fingers, buttocks, external genitalia,
wrists, and elbows
 Uncomplicated lesions appear as short, slightly raised cutaneous burrows. At the end of the burrow,
there is frequently a vesicle containing the female mite
 Intense pruritus usually leads to excoriation of the skin secondary to scratching, which in turn produces
crusts and secondary bacterial infection
 Patients experience their first symptoms within weeks to months after exposure; however, the incubation
period may be as little as 1 to 4 days in persons sensitized by prior exposure

18. Diagnosis
 Clinical diagnosis of scabies is based on the characteristic lesions and their distribution
 Definitive diagnosis of scabies depends on the demonstration of the mite in skin scrapings. Because the
the adult mite is most frequently found in the terminal portions of a fresh burrow, it is best to make
scrapings in these areas
 Scrapings are placed on a clean microscope slide, cleared by the addition of 1 or 2 drops of a 20%
solution of potassium hydroxide, covered with a coverslip, and examined under a low-power microscope
 mite or mite eggs or fecal matter (scybala) recognized
 Skin biopsy may also reveal the mites and ova in tissue sections.

20. OTHER MITES

21. HUMAN FOLLICLE MITES
Structure
 Includes two species of the genus Demodex: D. folliculorum and D.
brevis
 0.1 to 0.4 mm, wormlike body, four pairs of stubby legs, and an
annulate abdomen
 D. folliculorum parasitizes the hair follicles of the face of most adult
humans
 D. brevis is found in the sebaceous glands of the head and trunk
Epidemiology
 Cosmopolitan distribution
 Infestations are uncommon in young children and increase at the time of
puberty
 It is estimated that 50% to 100% of adults are infested with these mites.

22. Clinical syndromes
 Role of Demodex species in human disease is uncertain
 They have been associated with acne, blackheads, blepharitis, abnormalities of the scalp, and truncal rashes
 Extensive papular folliculitis resulting from Demodex infestation has been described in people with acquired
immunodeficiency syndrome
 Factors such as poor personal hygiene, increased sebum production, mite hypersensitivity, and immunosuppression
may increase host susceptibility and enhance the clinical presentation of Demodex infestation.
 Most people infested with these mites remain asymptomatic
Diagnosis
 Demonstrated microscopically in material expressed from an infested follicle
Treatment
 single application of 1% gamma benzene hexachloride

23. CHIGGER MITES
Structure and physiology
 Family Trombiculidae
 Adult trombiculid mites infest grass and bushes, and their larvae
(i.e., chiggers) attack humans and other vertebrates, producing
severe dermatitis
 Larvae have three pairs of legs and are covered with
characteristic branched, feather-like hairs
 Larvae appear as minute, barely visible, reddish dots attached to
the skin, where they use their hooked mouth parts to ingest
tissue fluids
 Chiggers typically attach to the skin areas where clothing is tight
or restricted, such as the wrists, ankles, armpits, groin, and
waistline
 After feeding, the engorged larvae fall to the ground where they
molt and undergo development into nymphs and adults.

24. Epidemiology
 Chiggers that are important in North America include the larvae of Eutrombicula alfreddugesi
and Eutrombicula splendens
 In Europe, the important species is the harvest mite, Trombicula autumnalis
 Chiggers are a particular problem for outdoor enthusiasts, such as campers and picnickers
 In Europe and the Americas, they are associated with intensely pruritic lesions; however, in
Asia, Australia, and the western Pacific rim, they serve as vectors of the rickettsial disease
scrub typhus or tsutsugamushi fever (Rickettsia tsutsugamushi)

25. Clinical syndromes
 Saliva injected into the skin at the time of mite attachment produces an intense pruritus and dermatitis
 Skin lesions appear as small erythematous marks that progress to papules and may persist for weeks
 Mite larvae may be visible in the center of the reddened, swollen area
 Irritation may be so severe that it auses fever and sleep disruption
 Secondary bacterial infection of the excoriated lesions may occur.
Treatment, prevention, control
 Treatment: antipruritics, antihistamines, and steroids
 Prevention: insect repellents such as N,N-9-diethyl-m-toluamide (DEET)

26. CANDIDA

27. CANDIDA
 Candida spp are the most important group of opportunistic fungal pathogens, the third most common
cause of central line–associated bloodstream infections (BSI)
 C. albicans is the species most commonly isolated from clinical material and generally accounts for 90%
to 100% of mucosal isolates and 40% to 70% of isolates from BSI
 Approximately 95% of all Candida BSI are accounted for by four species: C. albicans, C. glabrata, C.
parapsilosis, and C. tropicalis
 The remaining 5% of Candida BSI encompasses 12 to 14 different species, including C. krusei, C.
lusitaniae, C. dubliniensis, and C. rugosa among other

28. Morphology
 All Candida species exist as oval yeastlike forms (3 to 5 μm)
that produce buds or blastoconidia
 Species of Candida other than C. glabrata also produce
pseudohyphae and true hyphae
 C. albicans forms germ tubes
 In histologic sections, all Candida spp. stain poorly with
hematoxylin and eosin (H&E) and well with the periodic acid–
Schiff (PAS), Gomori methenamine silver (GMS), and Gridley
fungus stains
 In culture, most Candida spp. form smooth, white, creamy,
domed colonies

29. Epidemiology
 Candida spp. are known colonizers of humans and other warm-blooded animals
 The primary site of colonization is the GI tract from mouth to rectum
 May also be found as commensals in the vagina and urethra, on the skin and under the fingernails and
toenails
 Most types of candidiasis represent endogenous infection in which the normally commensal host flora
take advantage of the “opportunity” to cause infection  there must be a lowering of the host’s anti-
Candida barrier
 Among the various species of Candida capable of causing human infection, C. albicans predominates in
in most types of infection

30. Clinical syndromes
 Candida spp. can cause clinically apparent infection
of virtually any organ system
 Mucosal infections caused by Candida spp. (known
as “thrush”) may be limited to the oropharynx or
extend to the esophagus and the entire GI tract. In
women, the vaginal mucosa is also a common site
of infection
 Candida spp. may cause localized skin infection in
areas where the skin surface is occluded and moist
(e.g., groin, axillae, toe webs, breast folds). These
infections present as a pruritic rash with
erythematous vesiculopustular lesions. Smaller,
satellite pustules are common

32. Laboratory diagnosis
 Laboratory diagnosis of candidiasis involves the procurement of appropriate clinical material followed by
direct microscopic examination and culture
 Scrapings of mucosal or cutaneous lesions may be examined directly after treatment with 10% to 20%
potassium hydroxide (KOH) containing calcofluor white
 Culture on standard mycologic medium will allow the isolation of the organism for subsequent
identification to species
 Selective chromogenic medium such as CHROMagar Candida allows the detection of mixed species of
Candida: C. albicans (green colonies) , C. tropicalis (blue colonies), C. krusei (pale pink colonies)
 Visualization of characteristic budding yeasts and pseudohyphae is sufficient for the diagnosis of
candidiasis

34. REFERENCES
 Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2013). Medical microbiology. Philadelphia:
Elsevier/Saunders.
 Riedel, S., Morse, S., Mietzner, T., & Miller, S. (2019). Jawetz Melnick & Adelbergs Medical Microbiology 28
E (28th ed.). McGraw-Hill Education / Medical.
 CDC - Scabies - Biology. (2010). U.S. Centers for Disease Control and Prevention.
https://www.cdc.gov/parasites/scabies/biology.html