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bacteria as causes of disease 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
Why are gram positive bacteria purple?
decolouriser dehydrates the cell wall and the crystal violet iodide gets trapped in the multi-layered petidoglycan
26
Why are gram negative bacteria pink?
decolouriser interacts with the lipids and cells lose their outer lipopolysaccharide membrane and the crystal violet-iodide complexes, thus they appear pink with counterstain
27
What are coliforms?
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
28
How do staphylococci specifically appear in gram stain?
gram positive cocci in CLUSTERS | think staff like to cluster in the staffroom
29
How do streptococci appear on gram stain?
gram positive cocci in CHAINS
30
Name a gram negative coccus geni and is it aerobic or anaerobic?
Neisseria | aerobic
31
Name gram positive cocci geni and are these listed aerobic or aerobic?
staphylococcus - aerobic | streptococcus - aerobic
32
Which bacterium is split into beta, alpha and gamma haemolysis?
streptococcus
33
Which bacteria are beta haemolytic?
streptococcus pyogenes | streptococcus agalactiae
34
Which bacteria are alpha haemolytic?
streptococcus pneumoniae streptococcus oralis streptococcus milleri streptococcus sanguis
35
Which bacteria are non-haemolytic?
streptococcus bovis | enterococcus faecalis
36
Which lancefield group is strep pyogenes
A
37
which lancefield group is strep agalactiae
B (begins with an a, so is in group B)
38
Which bacterium straphylococci or streptococci are catalase positive?
staphylococci
39
Give examples of a gram negative bacterium and a fungus that are catalase positive
E.coli | Aspergillus
40
what is the catalase test?
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
What is the aim of the coagulase test?
Distinguishes S. aureus (coagulase positive) from other staphylococci (coagulase negative)
42
Which staphylococcus species is coagulase positive?
S. aureus
43
What is the coagulase test and how does it work?
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
What test other than the coagulase and catalase test can be done to identify S. aureus?
latex test
45
Is staphylococcus epidermidis coagulase negative or positive?
coagulase negative
46
What is a curved rod called?
vibrio
47
what is a spiral rod called?
spirochaete
48
What do bacteria need to express to be able to break down red blood cells?
hemolysin
49
How is alpha haemolysis produced?
production of hydrogen peroxide oxidising hemoglobin to methemoglobin. The agar appears green
50
How is beta haemolysis produced
of lysis of red blood cells by hemolysin such as Streptolysin O produced by S. pyogenes
51
Which bacterium colony shows draughtsman colonies?
Strep. pneumoniae
52
Which bacterium is optochin sensitive?
Strep. pneumoniae
53
What type of haemolysis does Group A strep show?
beta haemolysis
54
What type of disc is used to test for penicillin sensitivity in Strep. pneumoniae?
oxacillin
55
What are the gram positive rods?
``` Clostridium (C. perfringens, C. tetani, C. botulinum, C. difficile) Corynebacterium (diptheriae) Listeria (monocytogenes) Bacillus (B. anthracis, B. cereus) Proprionibacterium (acnes) ```
56
What are the gram negative coliforms?
``` Escherichia Klebsiella Salmonella Shigella Proteus Yersinia ```
57
What are the gram negative geni?
``` Escherichia Klebsiella Salmonella Shigella Proteus Yersinia Campylobacter Helicobacter Haemophilus Bordetella Brucella Pseudomonas Bacterioides ```
58
What is MacConkey agar contain and what is it used for?
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
What is CLED media?
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
What are the classically lactose fermenting organisms?
E. coli, Klebsiella, Enterobacter
61
What are the non-lactose fermenting organisms?
``` Salmonella spp., Shigella spp., Yesrinia spp., Proteus spp Pseudomonas aeruginosa ```
62
Which bacterium produces swarming patterns on agar?
Proteus mirabilis
63
what is the oxidase test used for?
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
Which bacteria are oxidase positive?
Pseudomonas sp. Vibrio Campylobacter Helicobacter
65
Which bacteria are oxidase negative?
Enterobacteriaceae (coliforms)
66
What type of bacteria is the oxidase test used on?
G- bacilli and non-lactose fermenting
67
What type of bacteria are MacConkey, CLED or XLD plates (ie to test for lactose fermentation) used for?
G- bacilli
68
How would you initially differentiate between G+ cocci?
look at their appearance on the gram film and see whether they grow in clusters (staph) or chains (strep)
69
what do you look at do differentiate between streptococci?
haemolysis type on blood agar
70
What test is used to differentiate between alpha haemolytic strep and what is the result?
optochin test - sensistive = Strep. pneumoniae
71
What test would you use to differentiate between staphylococci and what is the result?
coagulase or DNAse test | coagulase or DNAse positive = S. aureus

Microbiology (12 decks)

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