Saliva and oral yeast

study of fungi

mycology

fungi are

eukaryotic

2 basic structural forms

yeast and mold

dimorphic is

can exist in either for and can switch back and forth

yeast

unicellular with spherical or oviod bodies

molds

multicellular with specialized structures to perfrom specific function

hyphae

structural unit of mold; multicellular with each cell separated by a septa that has pores

mycellium

mass of hyphae that from mold colony

Dimorphic example

candida which is also opportunistic

fungi reproduction

both asexual and sexual modes; clinically only asexual is relevant

classification of yeast

yeast, filamentous fungi, dimorphic fungi

identification of yeast

biochemical reactions based on fermentation of and assimilation of carbohydrates and utilization of enzyme substrates and other metabolic activities

identification of molds

identified based on color, texture, colony, asexual structures and microscopic morphology

oxygen requirement - fungi

majority are aerobic can be anaerobic

growth medium for fungi

sabouraud dextrose agar, potato dextrose agar, yeast peptone dextrose

specialty features of fungal growth medium

high carbohydrate content, acidic pH, antibiotics

most common found fungi in the oral cavity

Candida, especially c. albicans

Accounts for 80% of all oral yeast isolated

C. albicans

oral carriage ranges from

35-55%

Candida is part of the oral flora

commensal or normal resident of the oral cavity

Candidiasis

local or disseminated infection

Localized

Burning or pain, altered taste sensation, and difficulty swallowing liquids and solids; mucosal infections

Systemic

Deep organ infection - 36-56% mortality, invasion of GI mucosa - passage across bowel wall - bloodstream (sepsis)

Erythematous - denture stomatitis

More inflammation of tissue as a response to the pathogen; less microbial load

What is a polymorphic fungus that normally colonizes at mucosal surfaces as harmless commensals?

Candida albicans

Candidal infections are triggered by?

Attenuation of normal host immunity or disturbance of normal microbial flora

Opportunistic infection is usually?

Endogenous but if it is exogenous its usually from mother to baby

Populations susceptible to candida injections

Immune deficiency, mechanical factors, pharmacology

Immune deficiency

Neonates, elderly, AIDS, tumors

Mechanical factors

Burns, oral prosthesis, catheters, hemodialysis, denture wearers

Pharmacology

Antibiotics, corticosteroids, antineoplastic, psycho-active

What triggers transformation from commensal to pathogenic forms?

Host-fungal interactions determine the outcome of Candida infection

From harmless to pathogen

Rapid adaptation of C.albicans to the host environment mediated by signaling, virulence genes are coregulated with cell morphogenesis, ecape from surveillance of immune system

Growth below 30C

Yeast

Growth at 37C

Hyphae

Germ tube test

Used in clinicallly diagnoses to distinguish C.albicans from other species

C.dubliniensis can form

Hyphae

Any change in signals can?

Up regulate the gene (bad)

Adherence of C.albicans

Relative cell surface hydrophobicity; expression of cell surface adhesion molecules

Evasion of host defenses

High frequency phenotypic switching; hyphal development; secreted aspartyl proteinase production; binding of complement molecules

Invasion and destruction of host tissue

Hyphal development; secreted aspartyl proteinase production; phospholipids production

Effect of adherence

Promotes rentention on the mouth

Effect of invasion of host defences

Promotes retention in the mouth

Effect of invasion and destruction of the host tissue

Enhances pathogenicity

Front line defense C.albicans

Rapidly acting, relatively non-specific

Beta-glucans and mannas on fungal cell wall interact with?

Receptors on host cells

What are the receptors called?

PRRs - pattern-recognition receptors (major class of these are toll-like receptors (TLRs))

What are responsible for recognizing fungal pathogens?

TLR2/4

What does TLR2/4 lead to?

Leads to activation of intracellular pathways leading to cytokines production, activation of the innate immune response and release of AMPs

Phagocytosis clearance of Candida by?

PMNs (neutrophils) and monocytes (macrophages)

Stimulation of macrophages are initiated by ?

Interaction of Dectin receptors (non TLR) on these fungal cell wall components like B-glucans

Cationic antimicrobial peptide

Antifungal peptides like histatins

C. Albicans cell wall triggers ?

Immune cell activation

What can change C. Albicans cell wall architecture and antifungal resistance?

Environmental change

Iron deprivation

Increases cell wall mannas and chitin while decreases B -1.3 glucan synthesis and thereby shows higher sensitivity to cell-wall damaging agents

B- 1.3 glucan masking

Decreases phagocytosis

B-1,3 glucan unmaking

Increases phagocytosis

Iron mediated cell wall remodeling alters C. Albicans what?

Phagocytic response

Iron deprivation enhances?

B-1,3 glucan masking and attenuates phagocytosis

Oral mucosa - keratinocytes

Physical barrier and secretion of antimicrobial peptides, such as B-defensins and calprotectin

Saliva - dual function

Flow dislodges yeasts and bacteria from oral cavity AND contains secreted fungicidal proteins (histatins, lysozymes and lactoferrin)

Salivary proteins and oral epithelial can aid?

C. Albicans growth by promoting adherence to oral tissues or inhibiting growth through immune exclusion by binding and aggregating fungal cells to facilitate their clearance by swallowing

What proteins prevent C.albicans growth?

Antifungal proteins, salivary histatins or calprotectin and B-defensins

Cationic proteins

15-20 amino acids with net positive charge of 2+ to 7+; to large numbers of basic amino acids; > 50% amino acids are hydrophobic

What makes the peptide more accessible to pathogens?

These properties plus an ionic microbial cell membrane and large transmembrane electrical potential

Group I - Cationic peptide classification

Linear, a-helical peptides without cysteines

Group II - Cationic peptide classification

Peptides with cysteines linked by disulfide bridges

Group III - Cationic peptide classification

Unusual high proportion of specific amino acids

What are Cationic salivary proteins that offer first line of defense against C.albicans?

Histatins

Hst 5

Most potent fungicidal activity against C.albicans at physiological concentration of 10-30 uM

Salvia secreted by salivary glands contain?

Antimicrobial proteins including Histatins 5

Hst 5 added to whole saliva exhibits how much of its in vitro fungicidal activity?

10-15%