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Microbiome > Lecture 13: Saliva & Oral Yeast > Flashcards

Lecture 13: Saliva & Oral Yeast Flashcards

1
Q

What are the 2 basic structural forms of fungi?

A

Yeast & Mould

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2
Q

Which basic structural form of fungi is unicellular with spherical or ovoid bodies?

A

Yeast

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3
Q

Which basic structural form of fungi is multicellular with specialized structures to perform specific functions (different shapes, colors, sizes, etc btwn different genera)?

A

Moulds

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4
Q

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

A

Hyphae

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5
Q

________ is a mass of hyphae that form the mould colony

A

Mycelium

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6
Q

Which opportunistic fungi of the oral cavity is dimorphic?

A

C. albicans

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7
Q

Which opportunistic fungi of the oral cavity is Not dimorphic and is yeast?

A

Cryptococcus neoformans

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8
Q

Which opportunistic fungi of the oral cavity is Not dimorphic and is a mycelium

A

Aspergilus umigatus

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9
Q

What is the study of fungi called?

A

Mycology

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10
Q

What does yeast look like on a colony plate?

A

A smooth colony

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11
Q

What does branching hyphae look like on a colony plate?

A

fuzzy mold colony

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12
Q

How can you tell bacteria and fungi apart under a microscope?

A

fungi is bigger than bacteria (only need 40x undermicroscope)

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13
Q

How do fungi reproduce?

A

Asexually and Sexually (asexual mode is more clinically relevant)

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14
Q

What are the 3 classifications of Fungi?

A

Yeast
Filamentous fungi
Dimorphic fungi

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15
Q

How are Moulds identified?

A

based on color, texture, colony and microscope morphology, especially their specialized asexual structures

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16
Q

How are Yeasts identified?

A

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

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17
Q

What is the oxygen requirement of fungi?

A

majority are aerobic

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18
Q

Which Fungi species can grow in anaerobic conditions?

A

Candida

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19
Q

What are the growth mediums for fungi?

A

Sabouraud Dextrose Agar (SBD)
Potato Dextrose Agar (PDA)
Yeast Peptone Dextrose (YPD)

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20
Q

If using Peptone Dextrose in medium what kind of medium is it?

A

Complex medium b/c peptone extract is an undefined component

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21
Q

What are some special features of fungal growth medium?

A

high carbohydrate content
acidic pH
antibiotics

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22
Q

If there is a lot of candida present in the saliva what is there a higher risk for and why?

A

Higher risk for caries b/c of acidic pH

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23
Q

What species of fungi is most present in the oral cavity?

A

Candida

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24
Q

What genus could be the second most abundant fungi in the oral cavity?

A

Malassezia

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25
Q

What is Candidiasis?

A

infection (local or disseminated) in which Candida species are the primary infectious agents

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26
Q

Which species of candida is very similar to C. albicans?

A

C. dubliniensis

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27
Q

What is the primary candida species in candidiasis?

A

C. albicans

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28
Q

What are Localized candidiasis infection?

A

mucous (oropharyngeal candidiasis, OPC) burning or pain, alterted tased sensation, and difficulty swallowing liquids and solids (dysphagia); mucosal (skin, vaginal, and uro-genital) infection

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29
Q

What are Systemic Candidiasis infections?

A

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

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30
Q

What are the 2 most important localized infections and how do they differ?

A

Pseudomembranous (white patches, high microbial load)

Erythematous (red) Deture Stomatitis: more inflammation of tissue and less microbial load

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31
Q

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

A

C. albicans

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32
Q

How are Candidal Infections Triggered?

A

triggered by the attenuation of normal host immunity or disturbance of normal microbial flora

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33
Q

What is an exogenous infection?

A

introduction of pathogen is external

example is food poisoning

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34
Q

What is an endogenous infection?

A

introduction of pathogen is internal- you already hat it so when immune system when down, there is an increase in that pathogen

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35
Q

Are candidal infections usually endogenous or exogenous?

A

Endogenous

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36
Q

How does C. albicans go from harmless to a pathogen?

A
  • Rapid adaptation of C. albicans to the host environment mediated by cell-signalling
  • virulence genes are co-regulated with cell morphogenesis (yeast-hyphae transition)
  • Escape from surveillance of immune system
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37
Q

What are the immune deficiency factors that increase susceptibility to candida infections?

A

Neonates
Elderly
AIDS
Tumors

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38
Q

What are the mechanical factors that increase susceptibility to candida infections?

A

Burns
Oral prosthesis
Catheters
Hemodialysis

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39
Q

What are the pharmacology factors that increase susceptibility to candida infections?

A

Antibiotics
Corticosteroids (asthma-inhalers)
Antineoplastic
Psycho-active drugs

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40
Q

What is Pseudohyphae?

A

the yeast form that keep multiplying by haven’t separated yet

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41
Q

What conditions are optimal for C. albicans in yeast form?

A

growth below 30C or pH 4

42
Q

What are the optimal conditions for C. albicans to transition from yeast to Pseudohyphae?

A

pH 6, 35C
Nitrogen limited growth on solid medium (SLAD)
High Phoshpate

43
Q

What are the environmental conditions that signal morpholigcal switching of C. albicans into Hyphae form?

A

Serum, greater than 34C
Lee’s medium 37C
pH 7, 37C

44
Q

The higher the temp goes the more ________ form in morpholigical switching in response to environmental signaling.

A

hyphae

45
Q

What test is used to distinguish C. albicans from other species?

A

Germ Tube Test

46
Q

What are the different mechanisms for the invasion of Candida at Host mucosal surfaces?

A

1st adherence has to happen before invasion mechs
-Germination
Persorption
Induced Phagocytosis

47
Q

What is Persorption?

A

invasion mechanism by which yeast can go through random leaks in membrane

48
Q

What are some enzymes that can damage the host tissue that help with invasion of candida at host mucosa surfaces?

A

Saps, Plb1p

49
Q

What are the stages of C. albicans epithelial colonization?

A
  1. Adherence
  2. Evasion of Host Defenses
  3. Invasion and Destruction of the Host tissue
50
Q

What are some of C. albicans virulence factors for its adhesion step in epithelial colonization?

A
  • Relative cell surface hydrophobicity: Non-specific adherence process
  • Expression of cell surface adhesion molecules: facilitates specific adhesion mechs
51
Q

What are C. albicans virulence factors for its Evasion of host defenses step in epithelial colonization?

A
  • High frequency phenotypic switching
  • Hyphal development
  • Secretes aspartyl proteinase production: secretory IgA destruction
  • Binding of complement molecules: antigenic masking
52
Q

What are C. albicans virulence factors for its Invasion & Destruction of host tissue stage in epithelial colonization?

A
  • Hyphal development-promotes invasion of oral epithelium
  • Secreted aspartyl proteinase production: host cell & extracellular matrix damage
  • Phospholipase production= damage to host cell
53
Q

What are responsible for phagocytic clearance of candida in the innate immunity against C. albicans?

A

Neutrophils (PMN) and Macrophages (monocytes)

-first line of defense in oral cavity

54
Q

The interaction of Dectin receptors in fungal cell wall components like B-glucans stimulates what?

A

macrophage initiation

55
Q

What is the Innate Response to Oral Candidaisis?

A
  • Phagocytic clearance of Candida by PMN (neutrophils) and monocytes (macrophages)
  • Stimulation of machrophages initiated by interaction of Dectin receptors on these with fungal cell wall components like B-glucan
  • Cationic antimicrobial peptides: antifungal peptides like histatins
56
Q

What components of the fungal cell wall interact with receptors on epithelial cells?

A

Beta-glucans and Mannans

57
Q

What receptors are responsible for recognizing fungal pathogens?

A

TLR2/4 (toll-like receptors)

58
Q

The interaction of fungal cell wall components (B-glucan & mannons) with TLR2/4 lead to what?

A

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

59
Q

What is innate immunity?

A

front-line defense, rapidly induced, relatively non-specific

60
Q

What innate peptides are secreted from the oral mucosa?

A

Keratinocytes and Calprotectin and B-defensins

61
Q

What is the function of the innate peptide Keratinocytes?

A

physical barrier

62
Q

What innate peptides are secreted by saliva and are fungicidal proteins?

A

Histatins, lysozymes, and lactoferrins

63
Q

What kills Candida by sequestering metals (copper & zinc)?

A

Calprotectin

64
Q

What 2 saliva components can bind candida and physically remove it?

A

mucins and IgA

65
Q

What antifungal protein secreted from the saliva can kill/prevent C. albican growth?

A

Hst 5

66
Q

How does mucins promote C. albicans growth?

A

When bound with PRPs, statherins and Tgase it binds candida and helps its adherence to the oral cavity

67
Q

What are Cationic peptides properties?

A

12-50 amino acids with a net positive charge (+2 to +7)

  • > 50% of amino acids are hydrophobic
  • these properties plus the anionic microbial cell membrane and large transmembrane electrical potential makes the peptide more accessible to pathogens
68
Q

What are the Cationic Peptide Classifications?

A

Group 1: linear a-helical peptides w/out cysteines
Group 2: linear peptides with cysteines linked by disulfide bridges
Group 3: linear with high proportion of specific amino acids

69
Q

What are Histatins?

A

cationic salivary proteins that offer first line of defense against C. albicans

70
Q

What has the most potent fungicidal activity against C. albicans?

A

Hst 5

71
Q

What is Hst 5 and what does it do?

A

its a positively charged cationic salivary protein with killing activity against C. albicans
-requires Dur3 (transporter protein) to enter the cell and has multi-targets inside the cell

72
Q

Hst 5’s activity is masked when what binds to it?

A 
salts
sugars
metals (iron)
host proteins (salivary mucins)
proteins secreted by pathogens (Saps and Msb2)
73
Q

What protease secreted by C. albicans reduces Hst 5 activity?

A

Sap 6

74
Q

How does the concentration of salivary mucin affect Hst 5 activity?

A

High mucin concentration reduces Hst 5 activity because it can bind to it and trap it

75
Q

How can mucins indirectly reduce Hst 5 activity?

A

mucins can also bind candida and clump it together so its like a biofilm so it makes it harder for Hst 5 to penetrate the big clumps of candida

76
Q

What are the characteristics of Adaptive immunity to Candida?

A

slow growing B and T cells require up to 7 days to mature
hallmarks are specificity, inducibility, and discrimination of self vs non-self (dendritic cell-mediatied T cell response)

77
Q

How does Th1 cell respond in the adaptive immunity to candida?

A

activation of antimicrobial functions, respiratory burst, degranulation, isotype switching of Ab

78
Q

What is Th2 cell response in adaptive immunity to candida?

A

eosinophilia, hyper-IgE, Hyper-IgG4 production which exacerbate the symptoms

79
Q

Which T-helper cell response exacerbates the symptoms in the adaptive immunity to candida infection ?

A

Th2 cell response

80
Q

Which T-helper cell response is more protective in the adaptive immunity to candida?

A

Th1 cell response

81
Q

IL-12 mediates which T-helper cell response?

A

Th1

82
Q

IL-6 mediates which T-helper cell response?

A

Th17

83
Q

IL4,5,10 mediate which T-helper cell response?

A

Th2

84
Q

What is the connection between oral candidiasis and HIV?

A

T-helper cells because T-cells are affected in HIV

-see a lot of oral candida in HIV patients

85
Q

What antifungal agent targets fungal cell walls?

A

Echinocandins

86
Q

What antifungal agent targets fungal cell membranes?

A

Polyene

87
Q

What antifungal agent targets sterol synthesis?

A

Azoles

88
Q

What antifungal agent targets DNA and RNA synthesis?

A

Flucytosine

89
Q

What antifungal agent targets protein synthesis?

A

Sordarins

90
Q

What antifungal agent targets microtubule assembly?

A

Griseofulvin

91
Q

What antifungal agents are frequently used in dental practice for oral infections?

A

Polyene and

Azoles

92
Q

What are some examples of Polyene drugs?

A

Amphotericin B and Nystatin (mycostatin)

93
Q

What is the mode of action of Polyene drugs?

A

binds to fungal ergosterol and leads to membrane disruption by making it porous

94
Q

What are some examples of Azole drugs?

A

Clotrimazole (mycelex)
Etoconazole (nizoral)
Fluconazole (diflucan)

95
Q

What is the mode of action of Azole drugs

A

intracellular target to inhibit synthesis of ergosterols
leads to inhibition of sterol in fungal membranes
Fungistatic but not fungicidal, therefore treat underlying condition with this therapy

96
Q

What are the Therapeutics of Candidiasis?

A

a broad spectrum to susceptible species

  • less toxicity to mammalian cells
  • combination therapy-effects on 2 or more disparate targets
  • Systemic treatment (HAART) (highly active antiretroviral therapy) in HIV patients
97
Q

Why could Hst 5 be a possible future therapeutic for candidiasis?

A

its broad spectrum

has multi-targets so could be effective killer

98
Q

How can one analyze host-pathogen interactions in candida infections?

A

Candida Gene mutants: in vitro assessment-altered growth rate and morphological defect of mutant strain- can see if that protein is the target of killing
Animal Models: in vivo assessment- survival and organ burdens after C. albicans infection

99
Q

What are some animal models?

A

oro-esophageal candidiasis in transgenic mice expressing HIV-1

  • Congenitally immunodeficient mice w/ individual or combined immune defects
  • mice immunocompromised with steroid administration (most advantagenous one)
100
Q

What are the advantages of animal model studies in candida infections?

A

clinical relevance- closely mimic clinical and pathological features of candida infections in humans
-cause-and-effect analysis of host-candida interactiosn

101
Q

What makes Hst 5 activity against candida more efficient?

A

Hst5-Spd

Microbiome (6 decks)

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