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LF223: Microbial Pathogens > Lecture 1. Temperature Adaptation > Flashcards

Lecture 1. Temperature Adaptation Flashcards

1
Q

What is a pathogen?

A

A microorganism that is able to cause disease in a plant, animal or insect

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2
Q

What is pathogenicity?

A

The ability to produce disease in a host organism

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3
Q

How do microbes express their pathogenicity?

A

By means of their virulence

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4
Q

What does virulence mean?

A

The degree of pathogenicity of the microbe

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5
Q

What are the determinants of virulence of a pathogen?

A

Any of its genetic or biochemical or structural features that enable it to produce disease in a host

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6
Q

What is the relationship between a host and a pathogen?

A

Dynamic, since each modifies the activities and functions of the other

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7
Q

What does the outcome of an infection depend on?

A

The virulence of the pathogen and the relative degree of resistance or susceptibility of the host, due mainly to the effectiveness of the host defence mechanisms

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8
Q

What are the two broad broad qualities of pathogenic bacteria that underlie the means by which they cause disease?

A

The ability to invade tissues (invasiveness) and the ability to produce toxins (toxigenesis)

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9
Q

What is invasiveness?

A

Encompasses the mechanisms for colonisation (adherence and initial multiplication), ability to bypass or overcome host defence mechanisms, and the production of extracellular substances which facilitate invasion

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10
Q

What is an example of invasiveness?

A

Adhesins like fimbriae (filamentous proteins on the bacterial cell surface)

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11
Q

What two types of bacteria do bacteria produce?

A

Exotoxins and endotoxins

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12
Q

What are exotoxins?

A

Exotoxins are released from bacterial cells and may act at tissue sites removed from the site of bacterial growth

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13
Q

What are examples of exotoxins?

A

Botulinum or Cholera toxin

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14
Q

What are endotoxins?

A

Cell-associated substances that are structural components of the cell walls of Gram-negative bacteria

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15
Q

What are examples of endotoxins?

A

Capsule or LPS

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16
Q

For human pathogens, entry into the body can occur how?

A

Through the respiratory, gastrointestinal, urinary or genital tracts
By insect bites or by accidental or surgical trauma to the skin
Many opportunistic pathogens are carried as part of the normal human flora – acts as a ready source of infection in the compromised host

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17
Q

For primary pathogens what is transmission?

A

More complex

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18
Q

How is Bordetella pertussis (respiratory pathogen - whooping cough) transmitted?

A

Requires contact with infectious material since this organism survives poorly in the environment

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19
Q

How are sexually transmitted diseases (e.g Neisseria gonorrhoeae) transmitted?

A

Direct person-to-person mucosal contact is required
Man is the only natural host for N. gonorrhoeae which dies rapidly in the environment

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20
Q

What are examples of gastrointestinal pathogens?

A

Salmonella, Shigella and Campylobacter species

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21
Q

What are the primary source for many gastrointestinal pathogens?

A

Environmental, and infection follows ingestion of contaminated food or water

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22
Q

What is the environment can be colonised by a pathogen critical in determining?

A

The pathogen’s reservoirs and potential odes of transmission

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23
Q

What are individual bacteria not restricted to and why is this important?

A

Individual bacteria are not restricted to a single physiological state but can respond to environmental stimuli and undergo adaptive responses which confer improved capacity for survival in adverse conditions

24
Q

What are psychrophiles?

A

Microorganisms that grow best at relatively low temperatures
Minimum <0ºC, Optimum 10-15ºC, Maximum <20ºC

25
Q

What are psychrotrophs?

A

Microorganisms that are able to grow at low temperatures but prefer moderate temperatures
Minimum 0ºC, Optimum 15-30ºC, Maximum >25ºC

26
Q

What are mesophiles?

A

Most bacteria, especially those living in association with warm-blooded animals
Minimum 10-15ºC, Optimum 30-45ºC, Maximum <45ºC

27
Q

What are thermophiles?

A

Among all thermophiles is wide variation in optimum and maximum temperature
Minimum 45ºC, Optimum 45-70ºC, Maximum >100ºC (boiling)

28
Q

What is important to remember about growth curves of bacteria?

A

They are not symmetrical

29
Q

What happens in to the growth rate of bacteria as temperature increases?

A

There is a steady increase in growth rate between the minimum and optimum temperatures, but slightly past the optimum a critical thermolabile cellular event occurs, and the growth rates plunge rapidly as the maximum T is approached

30
Q

What does a downshift in temperature cause within bacteria?

A

Transient inhibition of most protein synthesis – causes a growth lag known as the acclimation phase

31
Q

What happens during the acclimation phase?

A

A group of cold shock proteins (Csp) are dramatically induced
Some of these cold shock proteins are essential for the cell to resume growth at low temperature

32
Q

What are the differences between class I and II E. coli shock proteins?

A

Class I Csp are involved in >10-fold induction, class II Csp are involved in <10-fold induction

33
Q

What is the role of many class I Csps (such as the CspA family)?

A

RNA/DNA chaperone, making sure ribosome function properly by making sure proteins fold properly during cold shock

34
Q

What is the role of all Csps?

A

To make sure protein synthesis occurs in cold temperatures

35
Q

What is Listeria?

A

Non-spore forming Gram positive bacilli
Causes the disease Listeriosis

36
Q

Who are most at risk of getting a Listeria infection?

A

Pregnant women who have a Listeria infection later in their pregnancy can become ill and the baby may die or be born prematurely
Immunocompromised people may also become seriously ill if affected with Listeria

37
Q

Where is Listeria able to grow?

A

Listeria is widespread in the environment and is commonly found in vegetation, water, soil, wild or domestic animals, fish, birds as well as people.
Listeria is capable of growth over a wide range of temperatures (4-40ºC)

38
Q

How does Listeria spread?

A

Main method of becoming infected with Listeria is by eating contaminated foods that contain the bacteria
The infection can be transferred to an unborn child during pregnancy if the mother becomes infected

39
Q

What foodstuffs can be implicated by Listeria?

A

Meats, unpasteurised milk, contaminated vegetables (e.g coleslaw), seafood
Generally foods that require no further heat treatment or processing prior to being eaten and have a longer shelf life

40
Q

What virulence factors of Listeria are involved in the invasion of mammalian cells?

A

Internalin A and B

41
Q

What virulence factors of Listeria are required for escape from a single membrane vacuole?

A

LLO (listeriolysin) – a pore-forming cytotoxin
PI-PLC (PlcA) – an enzyme that removes charged head groups from phospholipids (esp. phophatidylinositol)

42
Q

What virulence factor of Listeria are required for movement through the cytoplasm, cell to cell spread?

A

ActA – interacts with host cell proteins to stimulate actin polymerisation
Actin tail forms at one end of the cell, propels the bacterium through the cytoplasm
Projections from the host cell surface caused by bacteria enter adjacent cells; bacteria inside double membrane vacuole

43
Q

What virulence factor of Listeria are required for movement through the cytoplasm, cell to cell spread?

A

PC-PLC (PlcB) – a phospholipase that cleaves the head group from many different kinds of lipids

44
Q

What virulence factor of Listeria regulates the other virulence factors?

A

PrfA – is a positive regulator of virulence genes, may respond to temperature

45
Q

How does listeria invade and spread?

A

ActA stimulates host cell proteins ARP and Profilin (which normally participate in nucleation of actin filaments to form host cell cytoskeleton) to polymerise actin at the surface of the bacterium (not the usual location)

Listeria polymerises actin at 1 end of the cell only

Ingestion leads to invasion of intestinal mucosa and subsequently systemic spread from macrophages to the liver

46
Q

How is Listeria unusual?

A

It can grow and multiply at normal refrigeration temperatures and can survive both freezing and relatively high cooking temperatures

47
Q

How can the number of Listeria be minimised in food?

A

Temperatures of at least 70ºC throughout a food or at least two minutes

48
Q

What other properties of food allow Listeria growth?

A

Grow in foods with 12% NaCl
Grow in food types with a pH range of 4.4- 9.8
Food preservatives have little effect on Listeria unless used in combination with other factors such as temperature and pH

49
Q

How can Listeria be controlled?

A

Commonly used disinfections and bactericidal cleaning agents are effective in controlling Listeria contamination of surfaces and equipment

50
Q

How can Listeria be prevented and treated?

A

Antibiotics not really useful unless disease diagnosed very early
Avoid products made with unpasteurised milk
Avoid coleslaw & deli meats
Cook meat thoroughly, & re-heat after refrigeration

51
Q

What is Legionella pneumophia?

A

Motile, aerobic Gram-negative rod that has complex nutritional requirements

52
Q

Where does L. pneumophila live?

A

Phagocytic cells esp. macrophages. Bacteria themselves avoid destruction by preventing fusion of the phagosome with lysosomes of the macrophage

53
Q

What are the normal environments L. pneumophila is found in?

A

Biofilms (particularly in air-conditioning cooling towers) or inside protozoa e.g. Acanthamoeba. Humans may well be ‘accidental’ hosts

54
Q

What does L. pneumophila cause?

A

Legionnaire’s disease – a form of bacterial pneumonia (first report was a group of elderly men attending an American Legion convention) – symptoms: fever and extensive lung damage

55
Q

How is L. pneumophila affected by temperature?

A

Cells express more flagellin RNA and protein and assemble more flagella when incubated at 30°C than at 37°C. Similarly, production of type IV pili and transcription of the pilBCD pilin locus occurs when bacteria are cultured at 30°C, but is minimal at 37°C.

56
Q

Why does the finding that L. pneumophila’s motility and adherence is optimal at temperatures less than 37ºC not surprising?

A

This result is consistent with a dominant role for the aquatic environment on the evolution of L. pneumophila as an intracellular parasite

LF223: Microbial Pathogens (15 decks)

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