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EMS - MoD > 9. Introduction to microbiology > Flashcards

9. Introduction to microbiology Flashcards

1
Q

Which bacteria do the hard surfaces of the teeth carry in large numbers?

A

Streptococcus mutans

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2
Q

Which bacteria do the soft tissues in the mouth and the tongue carry?

A

Streptococcus salivarius

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3
Q

Although considered a commensal bacterium, streptococcus mutans can also cause disease. Which disease?

A

Dental caries

particularly in people with diets rich in sugar

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4
Q

How are the microorganisms which cause disease described?

A

‘virulent’ or ‘pathogenic’

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5
Q

Give an example of how our gut commensals are beneficial?

A

Without them, we would require a continuous supply of vitamin K

Bacteria are responsible for supplying most of the ‘fixed’ nitrogen

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6
Q

Who set out the criteria used to decide if a microorganism caused a disease?

A

Robert Koch

Koch’s postulates

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7
Q

What do Koch’s postulates determine?

A

Whether a microorganism causes a disease

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8
Q

What are the 4 Koch’s postulates?

A
  • the causative organism must be isolated from every individual suffering from the disease
  • the causative organism must be cultivated artificially in pure culture
  • when the causative organism is inoculated from pure culture, the typical symptoms of the infection must result
  • the causative organism must be recoverable from individuals who are infected experimentally
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9
Q

In addition to Koch’s postulates, what would one also look for these days to determine whether a microorganism causes a disease?

A

Antibodies against the causative organism in natural cases and in individuals infected experimentally

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10
Q

What are the first 3 Koch’s postulates for genes?

A

Genes encode virulence factors:

  • the gene encoding the trait of interest should be present and transcribed/translated in a virulent strain
  • the gene encoding the trait of interest should NOT be present or should be silent in a strain that does not cause the disease
  • disruption of the gene in a virulent strain should result int he formation of a strain that is incapable of causing disease
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11
Q

What are the last 3 Koch’s postulates for genes?

A
  • introduction of the gene into a strain that previously did not cause disease should transform the strain into one that does cause disease
  • the gene must be expressed during infection
  • antibodies raised against the gene product or the appropriate cell-mediated immunity should protect experimental subjects against disease
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12
Q

What are the problems with Koch’s postulates?

A
  • difficulty isolating the causative agent
  • impossible to grow some pathogens in artificial culture
  • ethical objections
  • animal models not sufficient
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13
Q

Give a specific causative bacterium which is difficult to isolate from people who are infected with particular pathogens

A

Myobacterium tuberculosis

the cause of tuberculosis

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14
Q

Give a specific causative bacterium which cannot grow in artificial culture

A
  • Myobacterium leprae

(the cause of leprosy)

  • Treponema pallidum

(the cause of syphilis)

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15
Q

Why might there be ethical objections relating to Koch’s postulates?

A

Ethical issues with infecting subjects with infectious agents
(animal models not possible for all infections)

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16
Q

Give an example of where an animal model is not sufficient for testing the effect of a causative agent?

A

Salmonella typhi in mice causes gastroenteritis

Salmonella typhi in humans causes typhoid fever

(vice versa with salmonella typhimurium)

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17
Q

Are viruses living organisms?

A

This is debatable - they entirely rely upon other cells for their replication - they are obligate intracellular parasites

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18
Q

What is an ‘obligate intracellular parasite’?

A

Something that requires to live within a cell in its host

Viruses are obligate intracellular parasites

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19
Q

Who is affected by viruses?

A

Every class of organism, not just humans

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20
Q

What are viruses comprised of?

A

A nucleic acid core wrapped in a protein coat

Some viruses have an envelope, others are naked

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21
Q

What is the envelope of a virus made out of?

A

Lipid and usually derived from the cell in which they grow

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22
Q

What protects the nucleic acid core in the centre of a virus?

A

The protein coat

And sometimes the lipid envelope

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23
Q

Which nucleic acid do viruses contain?

A

Either DNA or RNA (but not both)

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24
Q

How are retroviruses unusual and different from normal viruses?

A

The virion carries an RNA copy of the genome but upon infection of a host cell, a cDNA copy of the virus genome is made using the enzyme reverse transcriptase

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25
Q

When a retrovirus infects a host cell, a cDNA copy of the virus genome is made from RNA. Which enzyme is required for this?

A

Reverse transcriptase

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26
Q

Viruses have a nucleic acid core wrapped in a protein coat. What is this protein coat made of?

A

Units called capsomeres

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27
Q

What are capsomeres?

A

They are the units that make up the protein coat of a virus

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28
Q

What is a bacteriophage?

A

A special class of virus that attacks bacteria

Infects and replicates within the bacterium

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29
Q

What are some examples of shapes of viruses?

A
  • round
  • rod-shaped
  • icosahedral
  • brick-shaped
  • bullet-shaped
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30
Q

What are viroids?

A

Naked, infectious RNA molecules that are not associated with any proteins (the smallest infectious pathogens known)

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31
Q

What do viroids infect?

A

Plants

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32
Q

Give some spongiform encephalopathies

A
  • Creutzfeldt-Jakob disease
  • Srapie (sheep)
  • BSE (mad cow disease, cattle)
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33
Q

What are spongiform encephalopathies caused by?

A

Infectious proteins known as PRIONS

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34
Q

Are fungi prokaryotic or eukaryotic?

A

Eukaryotic

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35
Q

What is the cell wall of fungi made from?

A

Chitin

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36
Q

What is chitin?

A

A polymer of N-acetyl glucosamine

Makes up the cell wall of fungi

A major component of the exoskeleton of arthropods such as insects

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37
Q

While the cell wall of fungal cells are made up of chitin and other polymers, what is the cell wall of plants made from?

A

Cellulose

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38
Q

What is mould?

A

Fungi that grow in mats of tiny filaments known as hyphae or mycelia

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39
Q

What does hyphae mean?

A

Greek for thread

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40
Q

What does mycelia mean?

A

Greek for mushroom

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41
Q

Moulds may or may not be subdivided into separate compartments. By what?

A

Cross walls known as septa

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42
Q

Are moulds multicellular or unicellular?

A

Multicellular.

Unicellular fungi = yeasts

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43
Q

What is yeast?

A

Unicellular fungi

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44
Q

Which is the most familiar yeast?

A

Saccharomyces cerevisiae

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45
Q

How do yeasts grow and multiply?

A

By budding daughter cells off from a mother cell

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46
Q

What common, superficial infections do moulds cause?

A
  • ringworm

- athlete’s foot

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47
Q

What is the most common yeast infection?

A

Thrush, caused by candida albicans

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48
Q

What is thrush caused by?

A

Candida albicans

A yeast

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49
Q

What is tinea pedum?

A

Athlete’s foot

A mould infection

50
Q

What do some yeasts have the ability to develop under certain conditions?

A

Pseudomycelia

Cells cling together in chains resembling small true mycelia

51
Q

What are protists?

A

Unicellular eukaryotes

52
Q

What are the 4 classes of protista?

A
  • apicomplexa
  • flagellate protista
  • ciliate protista
  • amoebae
53
Q

What were apicomplexa protists formerly known as?

A

Sporozoa

54
Q

Give examples of how protists are spread

A
  • by insects
  • by human sexual contact
  • producing cysts to survive outside the body
55
Q

Give examples of infections caused by protists

A
  • toxoplasmosis
  • amoebic meningitis
  • malaria
  • trypanosomiasis
  • leishmaniasis (Kala-Azar)
  • amoebic dysentery
  • diarrhoea
56
Q

Which protist causes diarrhoea?

A

Cryptosporidium

57
Q

Which protist causes vaginal infections?

A

Trichomonas vaginalis - causes a foul-smelling vaginal discharge

58
Q

What effect does trichomonas vaginalis have in men?

A

Men can be asymptomatic carriers

But this protist can also cause balanitis

59
Q

Which fungus was previously thought to be a protist?

A

Pneumocystis carinii/jiroveci

60
Q

Pneumocystic carinii/jiroveci is a fungus, previously thought for many years to be a protist. What does it do?

A

Important for patients suffering from AIDS

Causes a type of pneumonia

61
Q

Are bacteria prokaryotes or eukaryotes?

A

Bacteria are prokaryotes, they lack a membrane-bound nucleus

62
Q

What proportion of bacteria causes disease?

A

Only a small minority of bacteria causes disease

63
Q

Which type of micro-organisms have an enormous range of metabolic capacities and can be found in some of the most extreme environments on earth?

A

Bacteria, despite their simplicity

64
Q

Which shape are most bacteria?

A
  • round (cocci)
  • rod-shaped (bacilli)

A few are comma-shaped or spiral

65
Q

In the Gram reaction, what is being tested?

A

The cell’s ability to retain a crystal violet-iodine dye complex when the cell is treated with acetone or alcohol

66
Q

Which dye is used in the Gram reaction?

A

Crystal violet-iodine dye

67
Q

What colour will Gram-positive bacteria appear?

A

Violet

68
Q

What colour will Gram-negative bacteria appear?

A

Red/pink

69
Q

What is the counterstain used in Gram staining?

A

Safrinin or fuchsine (making all the Gram-ngeative bacteria red/pink)

70
Q

What does the envelope of Gram-positive bacteria consist of?

A

30-40 layers of a uniquely bacterial polymer “peptidoglycan”, interlinked sugar molecules and short peptides containing both D- and L- amino acids

71
Q

What does the envelope of a Gram-negative bacteria consist of?

A

Very little peptidoglycan

It posses an extra, complex “outer membrane”

72
Q

Rather than a peptidoglycan envelope, gram negative bacteria have an outer membrane. What is the structure of the outer membrane of Gram negative bacteria?

A

An outer leaflet containing lipopolysaccharides

73
Q

What is responsible for the symptoms of gram-negative shock?

A
  • sugars from the surface antigen of the bacterium
  • complex lipid, known as lipid A

(acts as endotoxin)

74
Q

Many bacteria are motile. What allows them to be motile?

A

Flagella

either surrounding the cell or clumped at one end of at both ends

75
Q

Which classification of bacteria contains fimbriae?

A

Gram-negative bacteria

76
Q

What are Gram-negative bacteria are surrounded by?

A

Hair-like structures known as fimbriae

77
Q

Gram-negative bacteria are surrounded by hair-like structures called fimbriae. What do these do?

A

Aid adhesion onto particular surfaces

78
Q

What are sex pili?

A

Tubes that join two cells together during conjugation

Used by gram-negative bacteria to exchange genetic material

79
Q

Which classification of bacteria have sex pili?

A

Gram-negative bacteria

80
Q

What are some bacteria enclosed by which they use to protect themselves?

A

A capsule

81
Q

What is the function of a capsule that some bacteria possess?

A

Protects the bacterium, even within phagocytes

Helps prevent the cell from being killed

82
Q

How does a capsule around a bacterium appear?

A

Revealed by negative staining

Appear as a halo around the producer cell

83
Q

What can some bacteria produce to help them stick to surfaces?

A

Slime

84
Q

What does the slime produced by Streptococcus mutans do?

A

Enables the bacterium to stick to the surface of teeth, where it helps to form plaque, leading eventually to dental caries

85
Q

What is the slime produces by bacteria usually made up from?

A

Polysaccharides

86
Q

Which bacteria causes infections associated with implanted plastic medical devices?

A

‘Coagulase-negative’ staphylococi

87
Q

‘Coagulase-negative’ staphylococci is associated with implanted plastic medical devices. Why?

A

It lives on the skin and some strains produce a slime that enables them to stick to plastics

88
Q

A few bacteria have the ability to produce highly resistant structures. What are these known as?

A

Endospores (or simply, spores)

89
Q

Endospores are produced by some bacteria and they are highly resistant. What do they resist?

A

A range of hazardous environments, and protect against heat, radiation, and desiccation (extreme dryness)

90
Q

How may an infection spread person-person?

A
  • inhalation of infectious droplets
  • faecal-oral route
  • sexual transmission
  • direct inoculation
  • animals
  • fomites
91
Q

How are airborne infections spread?

A

Through inhalation of infectious droplets

92
Q

Give an example of an airborne infection that is spread through inhalation of infectious droplets

A

Many viruses

eg. the common cold viruses

“coughs and sneezes spread diseases”

93
Q

What is the faecal-oral route a common means of spreading?

A

Gastrointestinal infections

  • typhoid
  • cholera
  • dysentery
  • hepatitis A
  • poliomyelitis
94
Q

What is dysentery

A

Infection of the intestines resulting in severe diarrhoea with the presence of blood and mucus in the faeces

95
Q

Many gastrointestinal infections are commonly spread through the faecal-oral route. What does this mean?

A

Acquired through drinking water contaminated with human faeces for example

96
Q

The pathogens that cause sexually transmissible infections are vulnerable. What does this mean?

A

They rapidly die when exposed to conditions outside the body

In order to spread, these pathogens require the most intimate of human contact

97
Q

Which type of pathogens are ‘vulnerable’

A

Pathogens that cause sexually transmissible infections - they cannot survive outside of the body

98
Q

Who is most at risk from acquiring infections by direct inoculation?

A

Intravenous drug users who share dirty needles

99
Q

Give examples of infections that can spread by direct inoculation

A

Hepatitis and HIV

100
Q

Why is donated blood screened?

A

It is screened for blood-borne infections to minimise risk of infection following transfusion

101
Q

Give an example of an infection that is spread by animals. What animal is it spread by?

A

Malaria

Malaria is spread by the female anopheles mosquito

102
Q

Malaria is spread by the female anopheles mosquito. What is malaria caused by?

A

Protists of the genus Plasmodium

103
Q

Animals can be the reservoir for bacteria. What bacteria can they hold and what are such infections referred to as?

A

Bacteria such as Salmonella enterica

Such infections are referred to as “zoonoses”

104
Q

What is a zoonosis?

A

An infection which can be transmitted from animals to humans

The animals act as a reservoir for the bacteria

105
Q

As well as humans, animals and microorganisms, what else may act as the vector for infection?

A

Inanimate objects such as paper, pens, surgical instruments etc.

106
Q

What are “fomites”

A

Any object capable of carrying infectious organisms and hence transferring them.

Skin cells, hair, clothing, and bedding are common hospital sources of contamination

107
Q

What does controlling infection depend upon?

A
  • identifying the mode of spread

- interrupting the cycle of infection, replication, and spread

108
Q

What does the cycle of infection require?

A
  • pathogenic microorganisms to encounter and adhere to a host
  • to multiply within the host
  • to be dispersed to encounter other hosts
109
Q

What does a pathogen need more of, the deeper it penetrates into the body?

A

The deeper pathogens penetrate into the body, the greater the defences they need to protect them from our immune defences

110
Q

What are the traits that pathogens use to complete the cycle of infection referred to as?

A

Virulence factors

111
Q

What is unusual about cases of intoxicating illnesses such as tetanus, botulism and ergotism?

A

The victim does not need to encounter live microorganisms as the disease results from exposure to a toxin (exotoxin) rather than a living micro-organism

112
Q

“Lockjaw” is an alternative name for which disease?

A

Tetanus

Since the toxin causes muscles to go rigid, firstly those of the face

113
Q

By what mechanisms do bacteria causes disease?

A
  • production of structures that enable the microorganism to attach to the surface at which they cause the disease
  • production of toxins
  • production of aggressins
  • initiating undesirable consequences of the host defences
114
Q

In what way do microorganisms produce structures that enable the microorganism to attach to the surface at which they cause disease?

A
  • pili and fimbriae (hair-like structures that enable bacteria to stick to surfaces through a specific mechanism)
  • slime (eg. produced by streptococcus mutans that allows it to stick firmly to the enamel of the tooth)
115
Q

What two types of toxins may bacteria produce?

A
  • exotoxins (such as that responsible for tetanus)

- endotoxins (the cause of Gram-negative shock)

116
Q

What is a circulating immune complex?

A

A combination of soluble antigen produced by bacteria and antibodies.

117
Q

How can circulating immune complexes cause problems?

A

They can become trapped in vessels and compromise their function - an example = glomerulonephritis, kidney damage following streptococcus pyogenes infection

118
Q

How does the autoimmune disease rheumatic fever result?

A

Following streptococcal pyogenes infection, antibodies raised against the bacterial antigens cross-react with the antigens produced by human tissue, leading to autoimmune disease

119
Q

What is an aggressin?

A

Any substance, produced in the body by a pathogenic bacterium, that enhances the virulence of the bacteria

120
Q

What is the characteristic lesion of tuberculosis called?

A

The tubercle

121
Q

How does mycobacterium tuberculosis produce disease?

A

By over-stimulation of our immune response to infection - the tubercle consists of giant cells and activated macrophages and lymphocytes

122
Q

What does the tubercle in tuberculosis consist of?

A

Mixture of giant cells formed by the fusion of several macrophages, as well as activated macrophages and lymphocytes

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