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IVP > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is mycosis?

A

Infection of people or animals caused by a fungal organism.

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2
Q

What is mycotoxicosis?

A

Ingestion of preformed toxins produced by fungi e.g. perennial rye grass staggers.

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3
Q

What are some examples of microfungi?

A

Penicillium sp.

Altermaria sp.

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4
Q

Features of fungi:

A
  • Eukaryotes
  • Heterotrophic - require foodstuffs - no chlorophyll.
  • Saprophytes (live on dead matter) vs. parasites (living tissue)
  • Unicellular vs filamentous
  • Rigid cell walls (chitin) –> non-motile
  • Plasma membrane contains ergosterol
    (target of many anti-fungal drugs)
  • Reproduce by both sexual and asexual means
  • Exhibit mitosis
  • Mostly obligate aerobes
  • Generally insensitive to antibacterial antibiotics
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5
Q

What are the 2 morphologic types of fungi:

A 
1. Yeasts:
> Unicellular, 
> oval or round, 
> usually 3-5um diameter, 
> reproduce by budding
> e.g. Aspergillus
2. Moulds
> "filamentous fungi"
> hypha
> Many hyphae present --> colony = thallus
> e.g. Microsporum - ringworm
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6
Q

What are dimorphic fungi?

A

Fungi that form as either yeasts or moulds depending on the cultural conditions

  • Yeasts form at 37C
  • Mould form at room temp (25-27C)
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7
Q

What are bacteria?

A
  • The smallest self-contained organisms capable of self reproduction.
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8
Q

What are the common methods of study of bacteria?

A

1) Staining:
- Gram positive
- Gram negative
2) Electron Microscopy
- Shadowcasting
- Freeze etching
- Negative staining
- Thin Sections
3) Fractionation:
- Mechanical disintegration, selective digestion.
- Allows the study of chemical components and molecular organisation of specific components.

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9
Q

Outline principles of the gram stain

A
  1. Cells are fixed to the slide with heat and stained with a basic dye (crystal violet) which is taken up in similar amounts by all bacteria. This is then washed off with water
  2. Slides are treated with iodine-potassium iodide mixture to fix the stain. A dye-iodine complex forms within the cell cytoplasm. This is washed of with water
  3. Slides are washed in acetone/alcohol, which removes the dye iodine complex from the cells with Gram negative walls
  4. Cells are counterstained with a paler dye of a different colour e.g. safranin

Gram + retain initial violet stain
Gram - decolourised by the organic solvent and stained by the counterstain

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10
Q

Give an example of a Gram positive bacteria

A

Staphylococcus pseudintermedius
= Gram + cocci, Skin and mucous membranes, good pathogen, Intracellular e.g. skin infections, Infection in any body organ e.g. mastitis, otitis externa

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11
Q

Give an example of Gram negative bacteria

A

Pseudomonas aeroginosa
= Gram - rod, found EVERYWHERE, loves moist envt, not normal flora, Extracellular, wound infections (post burn, cystitis)

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12
Q

What is a mesosome

A

Large, convoluted, irregular invaginations of the cytoplasmic membrane in Bacteria.
>Gram + = large mesosomes
>Gram - = smaller mesosomes

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13
Q

Septal mesosomes

A

Help in cell division as they provide a site of attachment of bacterial chromosomes to the cytoplasmic membrane.

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14
Q

Lateral mesosomes

A

are attached to non-septal regions and have a function in secretion of enzymes etc.
e.g. associated with induction of beta lactamase excretion. They also have a function in electron transport and endospore formation.

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15
Q

What are the cytoplasmic contents of bacteria?

A

1) Mesosomes
2) Ribosomes
3) Granular inclusions

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16
Q

What are ribosomes?

A

Site for protein synthesis within bacteria. Roughly spherical, dense objects.
They have 2 subunits (50S and 30S).

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17
Q

What is the cell envelope made of?

A

Cytoplasmic membrane surrounded by a rigid cell wall

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18
Q

Structure and morphology of the cell envelope in GRAM POSITIVE bacteria

A

2 layers.

The cell membrane & Peptidoglycan

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19
Q

Structure and morphology of the cell envelope in GRAM NEGATIVE bacteria

A

3 layers:

a) Innermost cytoplasmic membrane
b) A thin layer (Corresponds with the thicker layer of gram positive cells) (basal layer)
c) Outer layer (Outer membrane resembles the typical unit membrane)

The outer 2 layers of gram negative bacteria are NOT visibly separated by EM thin sections.
Freeze etching has confirmed the presence of 2 layers in gram + organisms and 3 in gram - organisms.

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20
Q

What is lipopolysaccharide? (LPS)

A

LPS is also known as ENDOTOXIN. Found in gram negative bacteria. It is TOXIC and firmly bound to cells.
It provides or covers receptors for:
a) phage sites
b) host defence (incl. antibodies)
c) bacteriocin sites (glycoprotein)
D) impairs and excludes molecules
Therefore gram negative tend to gain more resistance to detergents and antibiotics.

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21
Q

The 2 gross forms of bacteria are:

A
  • Cocci (berry - spherical)

- Bacilli (rods)

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22
Q

What is the fine structure of bacteria?

A
  • Nuclear body i.e. nucleoid (DNA)
  • Cytoplasmic contents (mesosomes, ribosomes, granular inclusions)
  • Cell envelope (membrane & rigid cell wall)
  • Substances (enzymes, toxins)
  • Appendages: capsule, flagella and pili
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23
Q

What is the nucleoid of bacteria

A
  • not seen on routine gram stain. usually seen in EM
  • No nuclear membrane
  • Region filled with DNA fibrils thought of as a single chromosome closed loop of DNA
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24
Q

Bacterial Appendages:

Outline structure and function of a capsule?

A
  • firm gelatinous material
  • immediately in contact with cell wall
  • Mostly made of water and 2% solids (complex polysaccharides or polypeptide)
  • Produced by some fungi and
    bacteria (not always)
  • Little affinity for dyes

Function:

  • Protect against phagocytosis by host cells
  • Protects cell wall from attack (e.g. bacteriophages, lysozymes)
  • Protect against bacteriocidal polypeptide in animal tissue
  • important in determining immunological specificity in bacteria.

e.g. Strangles in horses:
Caused by streptococcus in lymph nodes. Capsules hides antigens, so can produce disease where high numbers of phagocytes are found (lymph nodes).

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25
Q

Bacterial Appendages:

What is the structure and function of flagellum(whip)?

A
  • Long, fine, wavy, filamentous appendages.
  • motility of bacteria
  • antigenicity in some bacteria

Can have peritrichous flagella, polar flagella
e.g. Otitis externa may involve bacteria Pseudomonas aeroginosa (Gram -) has many flagella

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26
Q

Bacterial Appendage:

Pili (Fimbrae)

A

Very small appendages seen only in EM

  • Pili (hairs) or Fimbriae (fringe)
  • Used for ADHESION
  • involved in bacterial conjugation
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27
Q

What is the basic structure and function of endospores and give examples of how certain bacteria use these defences.

A

Endospore = mesosome makes a wall around nuclear material
- Specialised units within certain G+ cells

  • Spores have no metabolic activity
  • much more resistant to effect of heat, drying, freezing, toxic chemicals and radiation – >main ecological role of spores is probably survival in the dry state.
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28
Q

How can bacteria acquire changes to their genome?

A
  • Mutation
  • Transposition
  • Recombination (Transformation, conjugation and transduction)
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29
Q

What are the types of genetic material in bacteria?

A
  1. Bacterial chromosome
  2. Plasmids
  3. Transposons
  4. Episomes
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30
Q

What is bacterial mutation?

A

Changes in the base sequence of bacterial DNA.

- Deletion, addition or inversion

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31
Q

How do antimicrobial agents work?

A

e. g. Mycoplasma haemofelis vs. Antimicrobial agents
- -> causes RBC lysis
1. Fluoroquinolones
- Bacteriocidal: Fragmentation of bacterial DNA and cell death
2. Tetracyclines
- Bacteriostatic: disruption of bacterial protein synthesis

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32
Q

How do organisms avoid effects of antimicrobial agents?

A

Bacteria can acquire resistance by either genetic mutation or by accepting antimicrobial resistant genes from other bacteria
- Usually by mutation, destruction/inactivation or efflux.

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33
Q

What is bacterial Transposition in relation to changing genome?

A

Transposition is relocation of portions of DNA in the genome ie. shuffling

34
Q

What is bacterial Recombination in relation to changing genome?

A

Genetic transfer by conjugation, transformation & transduction.
Conjugation: Specialised pili allow DNA exchange.
Transformation: Taking up free DNA directly from the surrounding media/envt.
Transduction: Transfer of genetic material via bacteriophages (viruses that multiply in bacteria & package DNA)

35
Q

What are the basic physical conditions required for bacterial growth?

A
  1. Suitable nutrients
  2. Optimal physical conditions. (Temp-varies, most commonly 37C, pH- 7.2-7.6, moisture, atmospheric req.- like dark best for growth)

Enriched Media - Blood agar
- Supplies basic nutrients required for the growth of many common bacteria

36
Q

What are the phases of bacterial growth?

A
  1. Lag phase
  2. Log or Exponential phase
  3. Stationary phase
  4. Death or decline phase

Antibiotic susceptibility testing is performed in log/exponential phase (increased cell division)

37
Q

What is a strict aerobe (bacteria)?

A

Can only grow with presence O2.

e. g. Pseudomonas aeroginosa commonly infects burn wounds.
e. g. Bordatella bronchiseptica

38
Q

Strict or obligate anaerobes (bacteria)?

A

Can only grow in non-oxygenated envt.

e.g. Porphyromonas gingivalis contributes to peridontal disease in cats, dogs and humans

39
Q

What are facultative anaerobes (bacteria)?

A

Grow either aerobically or anaerobically e.g. E.coli. But prefer O2 conditions
e.g. Bacteriodes fragilis

40
Q

What are microaerophilic bacteria?

A

Clostridia anaerobes in gas gangreen, need areas of low O2 tension e.g. necrosis

41
Q

what is Enriched media?

A

Basal media + substances which support and produce stronger growth. e.g. Blood agar

42
Q

What is Selective media?

A

Solid media containing inhibitory substances for certain organisms while permitting other organisms to grow.
e.g. MacConkeys agar - only bile-tolerant bacteria will grow (from git)

43
Q

What is Differential media?

A

Separation or differentiation of closely related organisms or groups of organisms.
e.g. MacConkeys agar used to divide members of the big family Enterobacteriaceae (E.coli, salmonella) contains bile salts, lactose and an indicator.

LACTOSE FERMENTER = BRIGHT PINK
NONLACTOSE FERMENTERS (salmonella and proteus) colonies do not change colour *yellow.
44
Q

What is transduction in bacteria?

A

Transfer of genetic material via bacteriophages.
–>”Recombination by transduction”.

  • Generalised transduction: Phage carry genetic info. as a length of nucleic acid accidentally fill with a length of host cell DNA (ie bacterial DNA) and carries it to a second cell.
  • Restricted or specialised transduction: bacteria may be infected by phages that hide their viral DNA by placing it into the bacterial chromosome –> viral DNA = prophage
45
Q

What is conjugation?

A

Bacterial conjugation is the one-way transfer of DNA between bacteria by a specialised ‘sex’ pilus which extends from the surface of the donor and a specific receptor protein in the wall of the recipient.
–> “Recombination of genome by conjugation”.

46
Q

Can fungi be strictly anaerobic?

A

NONE are strictly anaerobic.

Most fungi are obligate aerobes, some are facultatively anaerobic.

47
Q

How do anaerobes grow when O2 is present?

A
  • They find an ecological niche that provides them with nutrients and protects from O2
    e. g. Periodontal pocket, GIT, necrotic tissue
  • Presence of physical factors eg. skin folds, tartar
  • Vary in O2 tolerance
  • Synergy with aerobes and anaerobes
48
Q

Who are the non-spore forming anaerobes (NSFA)?

A
  • Large group of morphologically diverse bacteria
    Cocci, Bacilli, Filamentous, Branching rods
  • Some are G+, other G-
  • Most are part of normal flora

e. g. Lactobacillus (G+)
e. g. Bacteroides (G-)

49
Q

What signs are suggestive for a NSFA as the cause of disease?

A
  • Foul smell
  • Location of infection (proximity to mucosal surface)
  • Produce gas
  • Black discolouration
  • suggestive history
50
Q

Give an example of an oral disease associated with NSFA.

A
  • Periodontal disease
  • Cat fight abscess
  • Pyothorax in cats and dogs
  • Equine Pleuropneumonia
51
Q

Give an example of a foot problem associated with NSFA.

A
  • Foot abscesses
  • Ovine footrot

Other diseases associated with NSFA: Mastitis, Diarrhoeal disease

52
Q

Gingivitis manifests clinically as swelling and reddening of the gingival margin. What happens if it is left untreated?

A
  • Reversible inflammation of gingiva
  • Bacteria in gingival sulcus stimulate inflammatory reaction
  • G+ bacteria predominate
  • If left untreated
  • -> irreversible changes = PERIODONTITIS
  • -> Irreversible destruction of tooths supporting structures
  • Switch to primarily G- bacteria
  • soft tissue damage
53
Q

How would you treat fungal disease?

A

DRAIN = remove infectious agents, foreign material and by products of the inflammatory response
DEBRIDE = remove devitalised tissue and areas of potential “media” or ecological niches for bacteria. Allow access for further drainage over the following few days.
LAVAGE = flush with lots of sterile saline
ANTIMICROBIALS

54
Q

What are the clinical signs of Pyothorax/Pleuropneumonia?

A
  • Increased respiratory effort (dyspnea)
  • +/- Fever
  • Lethargy
  • Anorexia
  • Lung sounds (increase dorsally, decrease ventrally)
55
Q

How does bacteria get to the thorax in pyothorax/Pleuropneumonia?

A
  • Extension of pneumonia
  • Secondary URTI
  • Direct inoculation
  • Parasitic migration
  • Direct extension
  • Haematogenous
56
Q

How do viruses differ to bacteria and fungi?

A
  • Smaller than bacteria/fungi
  • Require metabolic processes/ host for replication
  • lack enzymes for metabolism and no ribosomes for making their own proteins.
    = OBLIGATE INTRACELLULAR PARASITES
57
Q

What is the structure of a virus?

A
  • Protein shell = CAPSID
  • May be helical, cubical (icosahedral) or complex in shape
  • Many have ENVELOPES which surround the capsid
58
Q

What is a virion?

A

A completely assembled infective virus particle.

  • ->In general, viruses without envelopes are more resistant to environmental desiccation or the action of lipid solvents/detergents than enveloped viruses
  • GLYCOPROTEINS - viral proteins often aid in attachment to cellular receptors
59
Q

List 2 ways viruses are classified?

A
  1. Nature of nucleic acid (DNA/RNA) and genome type (ds/ss)

2. Presence of envelope

60
Q

What are the features of Canine parvovirus?

A
  • Non-enveloped DNA virus
  • DNA stable, less prone to mutate, most replicate in nucleus
  • non-enveloped viruses are stable and RESILIENT. More resistant to heat, cold, acid etc. Exit host cells only by LYSIS
  • Usually require Antibody (acquired or passive) directed at virus.
61
Q

What are some features of Influenza virus?`

A
  • Enveloped RNA virus
  • RNA is unstable, most replicate in cytoplasm, prone to mutation
  • Enveloped viruses are FRAGILE
  • usually don’t survive adverse conditions. Exit host cell by LYSIS or BUDDING and SYNCYTIA. Usually require both cell-mediated and humoral immunity
62
Q

What is viral tropism?

A

The capacity to enter and interact with a host to cause disease.

63
Q

What are the types of viral mutations?

A
  • Point mutations: may alter codons for amino acids.
  • Deletion and insertions
  • The host genomic DNA may also be included in the viral genome e.g. some herpesviruses and retroviruses - may facilitate oncogenesis
64
Q

What is antigenic drift?

A

A gradual accumulation of point mutations leading to a new strain of virus (common).

65
Q

What is antigenic shift?

A

Acquisition of a new gene from another virus - particularly common in influenza due to recombination and assortment (relatively rare).
e.g. how bacteria exchange plasmids, though viruses cannot do this the same way they can CO-INFECT.

66
Q

T/F: Non-enveloped RNA viruses such as FMD are resistant in the environment making them harder to eradicate.

A

True

67
Q

T/F: Enveloped viruses do NOT require antibody and cell-mediated immunity to protect against disease?

A

False. Enveloped viruses require both cell mediated and humoral immunity.

68
Q

What are the types of virus-cell interactions that occur?

A
  1. Lytic infections (aka cytocidal): e.g. canine parvovirus
  2. Persistent infection:
    - Productive and cytocidal e.g. FMD
    - Productive (non-cytocidal) eg. rabies, distemper
    - Latent e.g. herpes, retrovirus
    - Non-productive but transforming e.g. retrovirus
69
Q

What is a persistent, productive and cytocidal viral disease?

A

FMD.

Persistent in the population, productive (produce virus) and cell killing.

70
Q

What is a persistent, productive and non-cytocidal viral disease?

A

Rabies.

not cell-killing, hide from blood stream in nerves

71
Q

What is a persistent, latent virus

A

Herpesvirus.

72
Q

What is an example of a persistent, non-productive but transforming infection?

A

Equine Sarcoids.

73
Q

What are some effects of viral infection on cell morphology?

A
  1. Cytopathic effect (CPE)
  2. Inclusion bodies
  3. Alteration of the cellular membranes
  4. Formation of syncytia
  5. Haemadsorption
74
Q

What is the meaning of Cytophathic effect due to viral infections?

A

CPE -
In vitro, CPE occurs in monolayer cell cultures when inoculated with lytic viruses. Virion infected cells release progeny virions that spread through cell culture supernatant fluid to infect other cells in the culture.

75
Q

What is the meaning of inclusion bodies due to viral infection?

A

Morphological changes:
Intranuclear inclusion bodies - DNA viruses e.g. herpes, adeno & parvo
Intracytoplasmic inclusion bodies - RNA viruses e.g. Rabies

76
Q

What is meant by alteration of cell membranes in relation to viral infection on cell morphology?

A
  • Increase permeability
  • Altered ion exchange
  • Proliferation and rearrangement
  • Insertion of viral glycoproteins
77
Q

What is meant by haemadsorption in relation to viral infection on cell morphology?

A

Cell in culture affected with some viruses may be able to absorb RBC due to presence of glycoproteins in the plasma membrane

78
Q

How do viruses damage cell?

A
  • Cell lysis
  • Inhibit host cell nucleic acid synthesis
  • Shutdown host cell protein synthesis
  • Cytopathic effects of toxic viral products
  • Cytolysis
79
Q

What is “viral interference”

A
  • Occurs when a virus infected cell population resists superinfection with the same or a different virus
    1. Superinfection exclusion (virus being selfish)
    2. Interference mediated by interferon (host interference)
80
Q

What are Interferons?

A
  • Members of the large family of normal cellular regulatory proteins called CYTOKINES.
    3 classes = alpha, beta and gamma
  • INF is released from infected cells and binds to specific receptors on the plasma membrane of other cells.

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