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Infection > S1) Introduction to Microbes > Flashcards

S1) Introduction to Microbes Flashcards

1
Q

In size order, list the micro-organisms that cause human disease

A
  • Viruses (smallest)
  • Bacteria
  • Fungi
  • Parasites (biggest)
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2
Q

What happens when patients present with signs of infection (e.g. rash or fever) but you don’t know what’s going on, and it’s not apparent what is causing the infection ?

A
  • Go back to basics and think of what are the 4 major groups of infection organisms
  • Work through them one by one to work out what is going on
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3
Q

Name 8 groups of agents that can cause a disease that has characteristics of infection (In size order)

A
  1. Prions
  2. Proteins
  3. Viruses
  4. Mycoplasma, Chlamydiae, Rickettsiae (group of bacteria)
  5. Mitochondria
  6. Bacteria
  7. Eukaryotic cells (yeasts, protozoa, human cells
  8. Worms
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4
Q

What are prions?

A
  • Proteins that generate more proteins of the same type and cause symptoms which cause disease in individuals.
  • They are able to spread from individual to individual
  • They contain no nucleic acid
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5
Q

What is special about the mycoplasma, chamydiae and rickettsiae group of bacteria?

A
  • They are defective so only grow intracellularly as they require host cellular mechanisms to supplement a defective chromosome
  • They don’t have enough genes to be self replicating outside of the host cell
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6
Q

Name some obligate intracellular parasites

A
  • Viruses
  • Mycoplasma, chamydiae and rickettsiae group of bacteria
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7
Q

What good evidence is there about mitochondria?

A

Good evidence that Mitochondria are derived from bacteria

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8
Q

What are the 3 general shapes of worms?

A
  • Round
  • Flat
  • Elongated
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9
Q

Label A, B,C and D of this viral structure

A
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10
Q

What can you use to remember the viral structure?

A

M&M structure:

  • hard nut in middle = nucleic acid
  • Chocolate coat = envelope
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11
Q

How are viruses mostly classified?

A
  • According to the type of genetic material in their genome – DNA or RNA or whether they are have an envelope or not.
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12
Q

Describe the nature of the nucleic acid of the virus

A

Can be:

  • Sigle or double stranded
  • DNA or RNA
  • Right or left sided (or positive or negative sense)
  • Forms the genetic code of the virus
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13
Q

Variations in viruses exist. How many classes of viral nucleic acid are there?

A

7

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14
Q

Name the 3 classes of DNA viruses

A
  • Single-stranded, Non-enveloped
  • Double-stranded, Non-enveloped
  • Double-stranded, Enveloped
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15
Q

Give an example of a clinically important Single-stranded, non-enveloped DNA virus

A

Parvovirus

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16
Q

Give an example of 4 clinically important double-stranded, non-enveloped DNA viruses

A
  • Adenovirus
  • BK virus
    Human papilloma virus
  • JC virus
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17
Q

Give an example of 3 clinically important double-stranded, enveloped DNA viruses

A
  • Herpes viruses
  • Hepatitis B
  • Molluscum contagiosum
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18
Q

Name the 4 classes of RNA viruses

A
  • Single-stranded, Positive strand, Icosahedral, Non-enveloped
  • Single-stranded, Positive strand, Icosahedral or helical, Enveloped
  • Single-stranded, Negative strand, Helical, Enveloped
  • Double-stranded, Icosahedral, Non-enveloped
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19
Q

Give 5 examples of Single-stranded, Positive strand, Icosahedral, Non-enveloped RNA Viruses

A
  • Coxsackievirus
  • Echovirus
  • Enterovirus
  • Hepatitis A, E
  • Norovirus
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20
Q

Give 6 examples of Single-stranded, Positive strand, Icosahedral or helical, Enveloped RNA viruses

A
  • Human immunodeficiency virus (HIV)
  • Hepatitis C
  • Rubella virus
  • Encephalitis viruses (Japanese, St Louis, Tick- borne, Venezuelan equine)
  • Yellow fever virus
  • West Nile virus
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21
Q

Give examples of Single-stranded, Negative strand, Helical, Enveloped RNA viruses

A
  • Ebola, Lassa, Marburg
  • Measles, mumps Influenza, parainfluenza viruses
  • Respiratory syncytial virus (RSV)
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22
Q

Give an example of Double-stranded, Icosahedral, Non-enveloped RNA virus

A

Rota virus

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23
Q

What are bacteriophages?

A
  • Transferable DNA that infects bacteria with DNA which codes for virulence factors
  • It is not a virus that causes human infection
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24
Q

Label this 2D structure of a bacteriophage

A
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25
Q

Label this 3D structure of a bacteriophage

A
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26
Q

Which type of bacteria are we interested in?

A

Eubacteria - True bacteria

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27
Q

Give 6 examples of eubacteria

A
  • Thermotoga
  • Flavobacteria
  • Cyanobacteria
  • Purple bacteria
  • Gram-positive bacteria
  • Green non-sulfur bacteria
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28
Q

When learning about bacteria, what do we need to consider?

A
  • What shape are they?
  • Gram positive or gram negative
  • The arrangement
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29
Q

Label this structure of a generic bacteria

A
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30
Q

What is the cell envelope of bacteria?

A
  • The Cell Envelope is all the material external to and enclosing the cytoplasm.
  • It consists of several chemically and functionally distinct layers, the most prominent of which are the cytoplasmic membrane and the cell wall.
  • The cell envelope also includes the capsule, if present.
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31
Q

Describe the cell wall of the bacteria

A

ALL bacteria have a cell wall.

The common feature of the cell wall is a Peptidoglycan layer.

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. It is the target for several antibiotics.

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32
Q

What is the capsule of the bacteria and what material is it usually?

A
  • A sticky, viscous material that forms an extracellular coating around the cell.
  • The material is usually a polysaccharide.
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33
Q

What types of bacteria is the capsule present in?

A
  • Not all types of bacteria
  • Can be found in both gram positive and gram negative bacteria
34
Q

Name 4 important bacteria that contain a capsule

A

Streptococcus pneumoniae (pneumococcus)

Neisseria meningitidis (meningococcus)

 Group B streptococcus (GBS)

Haemophilus influenzae type b (Hib

35
Q

Describe the role of the spleen in dealing with the important bacteria with a capsule. Describe what occurs if a patient does not have a spleen

A
  • The spleen is especially important in recognising these particular bacteria and dealing with them.
  • If a patient does nothave a spleen then they are at an increased risk of infections from these bacteria.
  • Such patients will commonly need to be immunised against these bacteria (to be covered again later in the Unit) and/or receive prophylactic antibiotics.
36
Q

What is the difference. between ribosomes in prokaryotic and those in eukaryotic cells?

A

Bacteria/prokaryotic ribosomes are smaller 70s ribosomes, whereas in prokaryotic cells, there are 80s

37
Q

Describe the capsule of bacteria

A
  • Made up of polysaccharides
  • Immunogenic - can produce an antibody response or protect against an antibody response
38
Q

Describe the purpose of the bacterial flagellum

A
  • Some bacteria are motile so need flagellum
  • Others rely on other molecules in the environment to move them about
39
Q

Describe the nucleic of the bacteria

A
  • Double stranded
  • Contains genetic info for sustenance of the bacteria, including reproduction
40
Q

Describe the plasmid of the bacteria

A
  • Double stranded
  • Transferable/mobile DNA so can transfer from bacteria to bacteria
  • Before they transfer, they replicate, leaving a copy behind
41
Q

What are the 3 possible shapes of bacteria? Draw the shape of each

A
  • Coccus (plural - cocci) e.g. staphylococcus aureus
  • Spirilus (very few of these have real clinical importance) e.g. syphilis
  • Baccillus (plural - bacilli), also known as rods e.g. pneumonia

(insert image)

42
Q

Why are bacterial shapes really important from a diagnostic POV?

A
  • If you are doing a gram stain, you are looking at the shape of the bacteria cell wall and whether it is gram positive or gram negative
  • This can help us identify the likely pathogens and thus the most effective antibiotics until we have more information about what’s growing there
43
Q

What are the 2 ways cocci can be arranged? Draw them

A
  • Clusters
  • Chains
  • (insert images)
44
Q

If you look down a microscope at a blood culture and see gram positive cocci in chains, what can you be confident in?

A

That the patient has a streptococci infection, as those are the only thing that exist in chains

45
Q

If you look down a microscope at a blood culture and see gram positive cocci in clusters , what can you be confident in?

A

That the patient has a staphylococcus infection, as those are the only thing that exist in clusters

46
Q

What is this an image of? Label it

A

Gram positive bacteria

47
Q

What is this an image of? Label it

A

Gram negative bacteria

48
Q

Describe the process of gram staining

A
  1. Smear abit of bacteria onto the glass slide
  2. Fix it with bait of heat
  3. Put some chemical onto the glass slide
  4. Try and remove those chemicals with an alcohol-acetone combo
  5. Counter stain with another stain
49
Q

How does gram positive bacteria respond to gram staining?

A
  • It retains the colour of the first stain - the crystal violet dye (purple) because of the peptidoglycan (which is a very thick layer)
  • The peptidoglycan retains the purple colour and is not decolourised
50
Q

How does gram negative bacteria respond to gram staining?

A
  • Gram negative bacteria does not retain gram stain and is decolourised
  • Stains pink with the counter stain (commonly safranin or fuchsine)
51
Q

Describe gram positive bacteria

A
  • Have thick, multi-layered, peptidoglycan cell walls
  • That are exterior to the cytoplasmic membrane
52
Q

Describe gram negative bacteria

A
  • a more complex cell wall structure composed of two membranes (an outer membrane and an inner, that is, cytoplasmic, membrane).
  • The two membranes are separated by the periplasmic space, which contains the peptidoglycan layer.
  • In contrast to gram-positive cells, the peptidoglycan layer of gram-negative cells is thin, and the cells are consequently more susceptible to physical damage.
  • The outer membrane is distinguished by the presence of embedded lipopolysaccharide (LPS) The polysaccharide portion of LPS (O-polysaccharide) is antigenic and can, therefore, be used to identify different strains and species.
  • The lipid portion (called lipid A) is embedded in the membrane and is toxic to humans.
  • Because lipid A is an integral part of the membrane, it is called an endotoxin, as opposed to exotoxins, which are secreted substances
53
Q

Describe how the human body responds to lipopolysaccharide

A
  • Human body is very sensitive to LPS and detects even tiny quantities of it circulating in the bloodstream
54
Q

What is an example of what lipopolysaccharide can cause?

A

Gram negative sepsis

55
Q

What is lipopolysaccaride very important in?

A

It is a very important virulence molecule

56
Q

Apart from physiological descriptions of bacteria, what else can you describe them by?

A

Oxygen tolerance

57
Q

What are the categories of oxygen tolerance of bacteria?

A
  • Aerobes
  • Anaerobes
58
Q

What are aerobes? Name and describe a subcatergory to aerobes

A
  • Any bacteria that can survive in the presence of oxygen e.g. ecoli
  • Obligate aerobes - absolutely require oxygen for survival and cannot survive in the atmosphere without oxygen
59
Q

What are anaerobes? Name and describe a subcatergory to an anaerobes

A
  • Any bacteria that can survive in the absence of oxygen (also e.g. ecoli)
  • Obligate anaerobes absolutely require an oxygen-free environment for survival (unless able to form spores)
60
Q

What are spores?

A

A bacterial cell surrounded by a very thick and hard coating.

They can protect bacteria from:

  • Very high temperatures
  • Dehydration
  • Oxygen
  • Chemicals normally used as disinfectants
61
Q

Where are spores found?

A

In parts of the body where there is an absence of oxygen, like the large bowel

62
Q

How do obligate anaerobes spread?

A

They pass through some kind of atmosphere which contains oxygen

They do that by producing some kind of bacterial life called a spore

63
Q

What do you call the method of naming bacteria, fungi and parasites?

A

Linnaean taxonomy

64
Q

Describe how linnaean taxonomy works, and explain using the example of Staphylococcus aureus

A
  • First you state the genus, then the species
  • The genus is basically the surname (which the organism shares with it’s family of organisms)
  • The species is like the first name
  • But you list the surname first before the first name

With Staphylococcus aureus, the genus is Staphylococcus and species is aureus

65
Q

When naming bacteria, fungi and parasites, what sometimes occurs?

A

Names are sometimes supplemented by adjectives describing growth, typing or antimicrobial susceptibility characteristics,

– E.g. E coli 0157, MRSA (meticillin resistant Staph aureus)

66
Q

What should you keep an eye out for in terms of naming microorganisms?

A

They names are subject to change sometimes, but everything else about it would be exactly the same

67
Q

What are the 2 main ways that bacteria cause disease (bacterial pathogenesis)?

A
  • Virulence factors
  • Toxins
68
Q

What are virulence factors?

A

Things that support the promotion of the bacteria causing disease

69
Q

Name 4 virulence factors

A
  • 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)
70
Q

Explain how iron acts as a virulence factor

A
  • Iron is a very important co factor in lots of biochemical process
  • Any organism that an efficiently absorb iron from the environment e.g. breaking down RBC’s and taking the haemoglobin gives it a selective advantage over organisms that are unable
71
Q

Explain how invasiveness is a virulence factor, using the example of enzymes such as collagenase

A
  • Collagenase breaks down collagen, that usually holds tissue together
  • If you can break down collagen, it allows the easy spread of bacteria through tissues
72
Q

What are exotoxins released to?

A

Into the environment

73
Q

What are endotoxins?

A

Toxins which cause disease when the bacterial cell breaks down

74
Q

Describe the differences between eukaryotes and prokaryotes

A

Insert image

75
Q

What are the 2 major groups that fungi come in?

A
  1. Yeasts (which are single-celled)
  2. Molds (multicellular)
76
Q

Name 3 yeasts and give examples

A
  • Candida albicans (organism that causes thrush and blood stream infection)
  • Cryptococcus neoformans (can cause a very fatal meningitis in immunosuppressed patients, particularly HIV)
  • Pneumocystis jiroveci (important cause of pneumonia in immunosuppressed)
77
Q

Name 2 moles and give examples

A
  • Aspergillus species - seen frequently in bone marrow transplant patents (important cause of pulmonary infection in the immunosuppressed)
  • Dermatophytes (ringworm, athlete’s foot) (can cause braisons on the skin and these allow bacteria to get in)
78
Q

Name the 2 classes of parasites

A
  • Protozoa (single-celled)
  • Helminths (worms, multi-cellular)
79
Q

Give 4 examples of Protozoa (single-celled)

A
  • Giardia lamblia
  • Cryptosporidium parvum
  • Plasmodium falciparum ( causative organism of malaria)
  • Trypanosoma cruzi
80
Q

Give 3 examples of Helminths (worms, multi-cellular)

A
  • Roundworms (e.g Enterobius vermicularis) - lots of children get this
  • Tapeworms (e.g. Taenia saginata) - not really in this country
  • Flukes (can cause significant liver and bladder disease, including chronic inflammation which leads to liver and bladder cancer) (e.g. Schistosoma mansoni)

Infection (9 decks)

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