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Infection. > 1.2 - Introduction To Microbes > Flashcards

1.2 - Introduction To Microbes Flashcards

1
Q

What are the 4 main types on microbes

A

Viruses
Bacteria
Fungi
Parasites

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2
Q

Describe the structure of a virus

A

Circular, non membrane bound nucleic acid (DNA or RNA)

Protein Coat (provides resilience)

External Envelope (phospholipid bilayer)

Spikes ( proteins for attaching to specific cell surface)

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3
Q

How is the the genetic code of viruses stored?

A

DNA viruses

  • Single stranded non-enveloped (parvovirus 19)
  • Double stranded non-enveloped (Adenovirus)
  • Double stranded enveloped ( Hepatitis B)

RNA viruses
- Single stranded, positive strand, icosahedral, non-enveloped ( Hepatitis A and E)
- Single stranded positive strand icosahedral or helical, enveloped
(HIV, Hepatitis C, rubella)
- Single stranded, negative strand, helical, enveloped
(Ebola, Mumps, measles)
- Double stranded icosahedral, non enveloped.
(Rotavirus)

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4
Q

What are bacteriophages

A

Viruses that infect bacteria.

Can be used to treat bacterial infections.

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5
Q

Describe the bacterial cell structure

A 
Large circular wrapped DNA
Plasmids (small amounts of free DNA, cause antibody resistance as can transfer between different bacteria of the same and different species)
Plasma membrane
Cell wall
Capsule
Flagellum 
Pili
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6
Q

What are the three most common bacterial shapes?

A

Coccus
Spirillus
Bacillus

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7
Q

How can cocci bacterium be arranged?

A

In clusters (staphylococcus)

In chains (streptococcus)

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8
Q

What is the structural difference between gram positive and gram negative bacterium?

A

Gram positive = outer membrane consists of a plasma membrane, periplasmic space and a peptidoglycan coat

Gram negative = outer membrane consists of a plasma membrane, periplasmic space and a peptidoglycan coat and a LIPOPOLYSACCHARIDE layer

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9
Q

What are aerobes?

A

Bacteria that can survive in the presence of oxygen

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10
Q

What are obligate aerobes?

A

Bacteria that require oxygen for survival

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11
Q

What are anaerobes?

A

Bacteria that can survive in the absence of oxygen

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12
Q

What are obligate anaerobes?

A

Require an oxygen free environment for survival

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13
Q

What are important gram positive coccus bacterium?

A 
Staphylococcus aureus
Coagulase negative staphylococcus 
Streptococcus pyogenes
Streptococcus pneumonia
Enterococcus faecalis
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14
Q

What are important gram negative coccus bacterium?

A

Neisseria meningitidis

Neisseria gonorrhoeae

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15
Q

Name important gram positive bacillus bacterium

A

Listeria monocytogenes

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16
Q

Name important gram negative bacillus bacterium

A

Escherichia coli
Salmonella typhi
Haemophilia influenza
Pseudomonas aeruginosa

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17
Q

What are mechanisms of bacterial pathogenesis?

A

Virulence factors
– Host entry (e.g. polysaccharide capsule
– Adherence to host cells (e.g. pili and fimbriae)
– Invasiveness (e.g. enzymes such as collagenase)
– Iron sequestration (siderophores) •

Toxins
– Exotoxins (e.g.diphtheria toxin)
– Endotoxins (lipopolysaccharide)

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18
Q

How do eukaryote ribosomes vary from prokaryote ribosomes?

A

Prokaryotes have 70S ribosomes

Eukaryotes have 80S ribosomes and 70S ribosomes in organelles

19
Q

What are yeasts?

A

A type of single celled fungi

20
Q

Give some names of yeasts

A

Candida albicans

Cryptococcus neoformans

21
Q

What are moulds?

A

A form of multicellular fungi

22
Q

Give an example of a pathological mould

A

Aspergillus species

Dermatophytes

23
Q

What are helminths?

A

Multicellular parasites. Worms. Examples are roundworms, tapeworms, flukes.

24
Q

whats the difference between DNA virus and a RNA virus?

A

DNA viruses such as adenoviruses and poxviruses are more likely to be double-stranded whereas most RNA viruses are single-stranded.
DNA viruses like the poxvirus are packaged with their polymerase machinery so they can replicate in the host cytoplasm directly. RNA viruses infect cells by injecting RNA into the cytoplasm of the host cells to transcribe and replicate viral proteins. RNA viruses also include retroviruses which use reverse transcriptase to create DNA from RNA templates.

25
Q

how are microorganisms named?

A

Linnean taxonomy

26
Q

what are collagenases?

A

Collagenases are enzymes that break the peptide bonds in collagen. They assist in destroying extracellular structures in the pathogenesis of bacteria such as Clostridium.

27
Q

what are the differences between protozoa and helminths?

A

both are parasites

protozoa are single celled and helminths are multi-cellular

28
Q

give some examples of protozoa that are parasites

A

giardia lamblia
cryptosporidium parvum
plasmodium falciparum (malaria)

29
Q

what is agar?

A

a polysaccharide derived from seaweed

30
Q

what properties of agar make it suitable for its use in the culturing of bacterium?

A

clearer than gelatin
resists digestion by bacterial enzymes
can be inoculated at 40oC in its cooled molten state and incubated at 60oC without melting
can contain additional ingredients to help with bacterium growth

31
Q

why is the standard agar plate red?

A

due to the addition of blood

32
Q

what is chocolate agar?

A

Agara which contains lysed RBCs to release intracellular nutrients. Needed for the culture of haemophilus influenzae

33
Q

what is the main difference between prokaryotes and eukaryotes?

A

Cells that have a well-defined nucleus are called eukaryotic, whereas cells that lack a nucleus are called prokaryotic. All bacteria are prokaryotes

34
Q

what different layers can be contained within the cell envelope?

A

the cell wall
cytoplasmic membrane
envelope

35
Q

what is the cytoplasmic membrane?

A

also known as the cell membrane, it is composed of phospholipids and acts as a permeability barrier.

36
Q

the peptidoglycan layer is present in all bacterial cell walls. what is its function?

A

The peptidoglycan layer determines the shape of the cell. It is composed of a cross-linked polymeric mesh. The molecular structure of this layer helps render the bacterial wall resistant to host peptidases such as those in the intestine. This helps the bacteria survive in a hostile environment.

37
Q

why are gram negative bacterium more susceptible to physical damage than gram positive bacterium?

A

gram positive have a thick peptidoglycan cell wall.

gram negative cells have a thin peptidoglycan and therefore are more susceptible to physical damage.

38
Q

what can be used to identify different strains of gram negative bacterium?

A

the polysaccharide portion of the outer lipopolysaccharide layer is antigenic and can therefore be used to identify different strains of the bacterium

39
Q

what is the bacterial capsule?

A

the bacterial capsule is a sticky, viscous material that forms an extracellular coating around the cell. The material is usually a polysaccharide.

40
Q

what is the function of the bacterial capsule?

A
  • allows cells to adhere to surfaces
  • protect bacteria from antibodies and phagocytosis
  • act as diffusion barriers against some antibiotics thus contributing to the organisms’ pathogenicity
  • protect bacteria against desiccation, or drying, which facilitates transmission.
41
Q

what bacteria have a capsule?

A

streptococcus pneumoniae
neisseria meningitidis
Group B streptococcus
haemophilus influenzae type b

42
Q

what patients are at increased risk of an infection from encapsulated bacterium?

A

those that have undergone a splenectomy or have a defective spleen. The spleen has an important role in recognising and removing encapsulated bacterium

43
Q

what is a gram stain?

A

colouring of patient material prior to examination under a light microscope. Helps to distinguish between gram positive and gram negative bacterium

44
Q

what are the main principles of performing a gram stain?

A

treat with crystal violet
treat with iodine
gram positive purple microorganisms identified
treat with solvent (alcohol/acetone)
gram positive bacterium retain the stain, gram negative so not as the alcohol removes the external lipopolysaccharide
safranin stains the gram-ve bacterium pink

Infection. (10 decks)

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