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IMED2001 UWA > Tutorial 3 > Flashcards

Tutorial 3 Flashcards

1
Q

What is the difference between bacteria and archaea?

A

Features that archaea have that bacteria don’t:

Have unique rRNA sequences

lack peptidoglycan in cell wall

Some have unusual metabolic characteristics

Many live in extreme environments

Features in bacteria that archaea lack:

Ubiquitous and some live in extreme environments

Cyanobacteria produce lots of oxygen

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2
Q

What are viroids and virusoids?

A

Infectious agents composed of RNA

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3
Q

What are prions?

A

Infectious proteins

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4
Q

What factors affect generation times between bacterial species?

A

Environmental pH

Oxygen level

Nutrient availability

Temperature

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5
Q

What are the ways to measure bacterial growth?

A

Direct method

Indirect method

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6
Q

What are the stages of the bacterial growth curve?

A

Lag phase

Exponential phase

Stationary phase

Death phase

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7
Q

What happens during lag phase?

A

Hardly any reproduction while bacteria are adjusting to their environment

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8
Q

What happens during exponential phase?

A

Constant growth provided nutrients are available in abundance

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9
Q

What happens during stationary phase?

A

Decreased availability of nutrients causes dying bacteria to equal bacteria reproduction rate

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10
Q

What happens during death phase?

A

Inversely correlates with log phase where logarithmic decline takes place

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11
Q

What are the categories of growth requirements?

A

Physical (temp pH osmotic pressure)

Chemical

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12
Q

What are obligate aerobes?

A

Require oxygen for growth

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13
Q

What are obligate anaerobes?

A

Cannot survive in presence of oxygen

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14
Q

What are facultative anaerobes?

A

Can grow with or without oxygen

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15
Q

What are aerotolerant microbes?

A

Grows in oxygen but doesn’t use it in metabolism

Microaerophile requires only low levels of oxygen for growth

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16
Q

What are some fastidious bacteria?

A

Mycobacterium tuberculosis (grown in vivo)

Haemophilus influenza (grown on chocolate agar)

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17
Q

What are the types of media?

A

Solid (agar)

Liquid (broth)

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18
Q

What is the difference between selective and differential media?

A

Selective medium contains ingredients that prohibit growth of some organisms

Differential medium contains ingredients that can differentiate between organisms

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19
Q

What are some direct methods of measuring bacterial growth?

A

Direct cell counts

Cell-counting instruments

Viable cell counts

Plate counts

Membrane filtration

Most probable number

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20
Q

What are some indirect methods of measuring bacterial growth?

A

Measuring biomass

Turbidity (most often used)

Total weight

Chemical constituents

Measuring cell products

Acids and gases produced

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21
Q

What does TSB contain? Why?

A

tryptone and peptone to support growth of many fastidious organisms

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22
Q

What are kings A and B used for?

A

To enhance of the fluorescein and pyocyanin pigments of pseudomonas. These broth cultures change to yellow to indicate fluorescein production and green to indicate pyocyanin production

23
Q

What is beta haemolysis?

A

Complete degradation of the red blood cells on the agar plate

24
Q

What is alpha haemolysis?

A

Partial degradation of red blood cells

25
Q

What is rogosa agar?

A

Selective medium for isolation of lactobacilli used to isolate lactobacilli in faeces, saliva, mouth rinsis and dairy products.

It contains acetate which lowers pH and allows lactic bacteria to grow alone.

Low magnesium, manganese and iron ensure optimal growth of lactobacilli. Glucose is used as carbon source

26
Q

What is Cysteine Lactose Electrolyte Deficient Agar?

A

Fermentation of lactose results in yellow colonies and L-cysteine causes alkaine reaction that results in blue colonies

27
Q

What kind of zone does alpha haemolysis produce?

A

Greenish coloured zones

28
Q

What is mannitol salt agar?

A

a selective-differential medium.

It uses a nutrition medium containing 7.5% salt a single major carbon source and an acid base indicator.

Result is growth of salt tolerant, mannitol fermentors of different kinds that show up in different colours

29
Q

What is CHROMagar Candida?

A

Selective/differential media for identification of yeasts.

Selective medium for isolation and presumptive isolation of yeasts and filamentous fungi

30
Q

What is CHROMagar Candida used to detect?

A

Yeasts and filamentous fungi

31
Q

What do yeasts look like in CHROMagar Candida culture?

A

Produce different colours based on species:

Candida albicans green

Candida tropicalis small smooth metallic blue

Candid krusei large rough pale pink to mauve with white colony borders

Candida parapsilosis large smooth white to pale pink colonies

Candida guilliermondii large smooth dark purple with white colony borders

Candida stellatoidea small smooth deep greeny-blue colonies

32
Q

What is HEKTOEN ENTERIC AGAR?

A

Selective-differential medium for isolation of food poisoning organisms. Different bacteria produce different colored colonies

33
Q

How does Hektoen Enteric Agar work?

A

Contains various sugars as carbon sources which cannot be used by salmonella or shigella.

Peptone metabolism by salmonella and shigella results in an increase in pH turning the indicator blue.

Medium contains thiosulphate which forms black precipitate in presence of hydrogen sulphide and appears black/brown

Shigella does not produce hydrogen sulphide and so it looks green

34
Q

What is Xylose Lysine Deoxycholate Agar?

A

XLD agar is another selective+differential medium to isolate pathogens from enteric specimens

35
Q

How does XLD work?

A

Xylose is present which can be fermented by salmonella and decarboxylated to keep medium red however hydrogen sulphides make colonies have black center.

Shigella cannot ferment xylose and remains red.

E.coli ferment lactose and sucrose acidifying the medium resulting in yellow colonies

36
Q

What is MEGA (Membrane Enriched Enterococcus Glucoside Azide Agar)?

A

Medium used in the membrane filtration analysis of water samples to select for faecal streptococci.

37
Q

What does MEGA contain?

A

Sodium azide at a concentration inhivitory to coliform organisms and most other gram negative bacteria.

2, 3, 5 - triphenyl tetrazolium chloride which can be reduced by faecal streptococci to form formazan.

38
Q

What is MESLS?

A

Medium used in membrane filtration analysis of water samples to select for faecal coliforms.

39
Q

How does MESLS work?

A

Sodium lauryl sulfate acts to inhibit growth of non-coliform bacteria.

Lactose is the sole carbohydrate available and phenol red is the indicator of acidity

40
Q

How do bacteria selected for look like on MESLS agar?

A

Lactose fermenting colonies appear yellow while other non-coliform bacteria are pink

41
Q

What is E.coli used for?

A

indicator organism for monitoring faecal contamination of water sources.

42
Q

What are the features of ideal indicator organisms?

A

Present when pathogens are present

Present only when there is danger of pathogens

Occue in greater numbers than pathogens

Survive in the environment as long as the pathogens are present

Easy to detect

Should not multiply in water and thus distort numbers

43
Q

What are the limitations of using E.coli for monitoring pollution?

A

It does not reflect possible presence of protozoa and is not linked with possible viral contaminants such as enteroviruses

44
Q

What are slope cultures?

A

agar cultures that are liquid but not broths

45
Q

What are urea slopes?

A

slopes used for detection of organisms that can hydrolyse urea by producing urease.

All proteus species have urease which can be differentiated from other members of enterobacteraceae

46
Q

How does a capsule appear when stained with india ink?

A

Like a halo around bacteria

47
Q

What bacteria are detected using ZIEHL NEESON ACID-FAST stain?

A

Mycobacterium species such as M.tubercolosis or M.leprae

48
Q

What makes cell wall difficult to penetrate and how is that fixed with ZIEHL-NEELSON ACID-FAST stain?

A

Mycolic acid in cell walls make cell wall difficult to penetrate. Heat is used to permit entry of the stain.

Acid-fast because positive cells retain colour after being washed with acid

49
Q

How does kinyoun’s stain work?

A

Waxy mycolic acid in cell envelope is resistant to drying which improves survival in environment.

Mycolic acid binds with the stain carbol fuchsin and cannot be removed with acid-alcohol during decolourisation step.

50
Q

How is tuberculosis diagnosed?

A

Kinyoun’s stain on sample from sputum

51
Q

What are the staining reagents of kinyoun’s stain?

A

Kinyoun’s carbol fuchsin

3% acid alcohol

0.3% aqueous methylene blue counterstain

52
Q

What do acid fast bacteria look like on kinyoun’s stain?

A

Red against blue background

Non-acid fast bacteria stain blue/purple

53
Q

Endospore staining

A

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IMED2001 UWA (44 decks)

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