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bacteria as causes of disease Flashcards

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Biology 101 flashcards
1
Q

what is a pathogen?

A

organism that cause or is capable of causing disease

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2
Q

what is a commensal?

A

organism which colonises the host but causes no disease in normal circumstances

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3
Q

what is an opportunistic pathogen?

A

microbe that only causes disease if host defences are compromised

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4
Q

What is virulence/pathogenicity?

A

the degree to which a given organism is pathogenic

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5
Q

which is asymptomatic carriage?

A

when a pathogen is carried harmlessly at a tissue site where it causes no disease

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6
Q

What colour do gram negative bacteria turn on staining?

A

pink

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7
Q

What stain is used for TB?

A

Ziehl-Neelsen stain

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8
Q

What makes up the majority of the cell envelope of gram positive bacteria?

A

peptidoglycan

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9
Q

What is the substance that is specific to gram negative cell envelopes?

A

lipopolysaccharide

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10
Q

What is lipopolysaccharide made up of?

A

lipid A
O antigen
terminal sugars

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11
Q

What is the alternative name for lipoplysaccharide?

A

endotoxin

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12
Q

what are the three stages of bacterial cell growth in order?

A
  1. lag
  2. exponential
  3. stationary
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13
Q

Which type of bacteria have a slow growth rate?

A

mycobacteria

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14
Q

What is endotoxin?

A

component of the outer membrane of bacteria eg lipopolysaccharide in G- bacteria

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15
Q

What is exotoxin?

A

secreted proteins of gram positive AND gram negative bacteria

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16
Q

What type of molecule is an exotoxin?

A

protein

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17
Q

Can endotoxin be converted to a toxoid?

A

No- but exotoxin can

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18
Q

What type of genes does the plasmid contain?

A
  1. antibiotic or virulence determinent genes
  2. transfer promotion genes
  3. plasmid maintenance genes
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19
Q

What are the different methods of gene transfer in bacteria?

A

transformation via plasmid
transduction via phage
conjugation via sex pilus

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20
Q

Give examples of geni that are obligate intracellular bacteria

A

Chlamydia

Coxiella

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21
Q

Give the genus of bacteria that can be cultured on artificial media with no cell wall

A

Mollicutes

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22
Q

Give examples of bacteria that can grow as filaments and have a cell wall and can be cultured on media

A

streptomyces
actinomyces
nocardia

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23
Q

Give examples of geni of spirochaetes

A

treponema
leptospira
borrelia

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24
Q

How dod perform a gram stain?

A

Apply a primary stain such as crystal violet (purple) to heat fixed bacteria
Add iodide which binds to crystal violet and helps fix it to the cell wall
Decolorise with ethanol or acetone
Counterstain with safranin (pink)

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25
Q

Why are gram positive bacteria purple?

A

decolouriser dehydrates the cell wall and the crystal violet iodide gets trapped in the multi-layered petidoglycan

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26
Q

Why are gram negative bacteria pink?

A

decolouriser interacts with the lipids and cells lose their outer lipopolysaccharide membrane and the crystal violet-iodide complexes, thus they appear pink with counterstain

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27
Q

What are coliforms?

A

Coliform bacteria are defined as rod-shaped Gram-negative non-spore forming and motile or non-motile bacteria which can ferment lactose eg E.Coli

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28
Q

How do staphylococci specifically appear in gram stain?

A

gram positive cocci in CLUSTERS

think staff like to cluster in the staffroom

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29
Q

How do streptococci appear on gram stain?

A

gram positive cocci in CHAINS

30
Q

Name a gram negative coccus geni and is it aerobic or anaerobic?

A

Neisseria

aerobic

31
Q

Name gram positive cocci geni and are these listed aerobic or aerobic?

A

staphylococcus - aerobic

streptococcus - aerobic

32
Q

Which bacterium is split into beta, alpha and gamma haemolysis?

A

streptococcus

33
Q

Which bacteria are beta haemolytic?

A

streptococcus pyogenes

streptococcus agalactiae

34
Q

Which bacteria are alpha haemolytic?

A

streptococcus pneumoniae
streptococcus oralis
streptococcus milleri
streptococcus sanguis

35
Q

Which bacteria are non-haemolytic?

A

streptococcus bovis

enterococcus faecalis

36
Q

Which lancefield group is strep pyogenes

A

A

37
Q

which lancefield group is strep agalactiae

A

B (begins with an a, so is in group B)

38
Q

Which bacterium straphylococci or streptococci are catalase positive?

A

staphylococci

39
Q

Give examples of a gram negative bacterium and a fungus that are catalase positive

A

E.coli

Aspergillus

40
Q

what is the catalase test?

A

Flavoproteins reduce O2 using superoxide dismutase producing H2O2
Superoxide is converted in the following reaction by catalase2 H2O2 –> 2H2O+ O2
when a small amount of bacterial isolate is added to hydrogen peroxide, bubbles of oxygen are observed.

41
Q

What is the aim of the coagulase test?

A

Distinguishes S. aureus (coagulase positive) from other staphylococci (coagulase negative)

42
Q

Which staphylococcus species is coagulase positive?

A

S. aureus

43
Q

What is the coagulase test and how does it work?

A

Coagulase is an enzyme produced by S. aureus that converts (soluble) fibrinogen in plasma to (insoluble) fibrin. Staphylococcus aureus produces two forms of coagulase, bound and free
Slide coagulase test is done to detect bound coagulase or clumping factor.
Tube coagulase test is done to detect free coagulase.
for slide coagulase add plasma to the bacterial suspension on the slide
for tube coagulase add bacterial colonises to plasma in a tube

44
Q

What test other than the coagulase and catalase test can be done to identify S. aureus?

A

latex test

45
Q

Is staphylococcus epidermidis coagulase negative or positive?

A

coagulase negative

46
Q

What is a curved rod called?

A

vibrio

47
Q

what is a spiral rod called?

A

spirochaete

48
Q

What do bacteria need to express to be able to break down red blood cells?

A

hemolysin

49
Q

How is alpha haemolysis produced?

A

production of hydrogen peroxide oxidising hemoglobin to methemoglobin. The agar appears green

50
Q

How is beta haemolysis produced

A

of lysis of red blood cells by hemolysin such as Streptolysin O produced by S. pyogenes

51
Q

Which bacterium colony shows draughtsman colonies?

A

Strep. pneumoniae

52
Q

Which bacterium is optochin sensitive?

A

Strep. pneumoniae

53
Q

What type of haemolysis does Group A strep show?

A

beta haemolysis

54
Q

What type of disc is used to test for penicillin sensitivity in Strep. pneumoniae?

A

oxacillin

55
Q

What are the gram positive rods?

A 
Clostridium (C. perfringens, C. tetani, C. botulinum, C. difficile)
Corynebacterium (diptheriae)
Listeria (monocytogenes)
Bacillus (B. anthracis, B. cereus)
Proprionibacterium (acnes)
56
Q

What are the gram negative coliforms?

A 
Escherichia
Klebsiella
Salmonella
Shigella 
Proteus 
Yersinia
57
Q

What are the gram negative geni?

A 
Escherichia
Klebsiella
Salmonella
Shigella 
Proteus 
Yersinia 
Campylobacter 
Helicobacter 
Haemophilus 
Bordetella 
Brucella 
Pseudomonas 
Bacterioides
58
Q

What is MacConkey agar contain and what is it used for?

A

Bile salts and crystal violet inhibit the growth of G+ bacteria and inhibits swarming of G- Proteus
contains an indicator called neutral red, sp that bacteria that ferment lactose (Lac+) appear pink/red
contains lactose
lactose for Lac+ organisms
peptone is used by Lac- organisms producing NH3 and a rise in pH

59
Q

What is CLED media?

A

electrolyte deficient media prevents swarming of Proteus
Bromothymol blue is indictor, lactose fermentation causes blue to yellow change
decarboxylation of L-cyteine results in blue colour
Used as media for urinary pathogens

60
Q

What are the classically lactose fermenting organisms?

A

E. coli, Klebsiella, Enterobacter

61
Q

What are the non-lactose fermenting organisms?

A 
Salmonella spp.,
Shigella spp.,
Yesrinia spp.,
Proteus spp
Pseudomonas aeruginosa
62
Q

Which bacterium produces swarming patterns on agar?

A

Proteus mirabilis

63
Q

what is the oxidase test used for?

A

to distinguish different types of bacteria in the non-lactose fermenters group (looks to see if a microorganism contains either of cytochrome oxidase or indophenol oxidase)

64
Q

Which bacteria are oxidase positive?

A

Pseudomonas sp.
Vibrio
Campylobacter
Helicobacter

65
Q

Which bacteria are oxidase negative?

A

Enterobacteriaceae (coliforms)

66
Q

What type of bacteria is the oxidase test used on?

A

G- bacilli and non-lactose fermenting

67
Q

What type of bacteria are MacConkey, CLED or XLD plates (ie to test for lactose fermentation) used for?

A

G- bacilli

68
Q

How would you initially differentiate between G+ cocci?

A

look at their appearance on the gram film and see whether they grow in clusters (staph) or chains (strep)

69
Q

what do you look at do differentiate between streptococci?

A

haemolysis type on blood agar

70
Q

What test is used to differentiate between alpha haemolytic strep and what is the result?

A

optochin test - sensistive = Strep. pneumoniae

71
Q

What test would you use to differentiate between staphylococci and what is the result?

A

coagulase or DNAse test

coagulase or DNAse positive = S. aureus

Microbiology (12 decks)

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