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Microbiology > Bacteria, Positive and Negative Grams > Flashcards

Bacteria, Positive and Negative Grams Flashcards

1
Q

Define a pathogen

A

A disease causing micro-organism

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2
Q

Define a commensal

A

Organism which colonises the host but doesn’t cause disease

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3
Q

Define virulence

A

Degree to which an organism is pathogenic

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4
Q

Define opportunist pathogen

A

Microbe that causes disease only if host is compromised

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5
Q

Define an asymptomatic carriage

A

Pathogen harmlessly carried at tissue site that doesn’t cause disease

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6
Q

What is the hierarchy of microbial size?

A

Protozoa –> Bacteria –> Viruses

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7
Q

How do you tell the difference between gram positive and negative bacteria including stain?

A

Positive: Thick peptidoglycan coating with single membrane, stains purple. Can also form spores
Negative: Thin peptidoglycan coating, double membrane carrying endotoxin

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8
Q

What organism is the Ziehl-Neesen used to stain for?

A

Mycobacteria

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9
Q

How is the stain carried out?

A

1) Apply crystal violet to heat fixed bacteria
2) Treat with iodine
3) Decolourise sample
4) Counterstain

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10
Q

What environmental factors affect bacterial growth?

A

Temp: -80 –> +80 degrees
pH: <4 - 9
Water/Desiccation
Light: UV

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11
Q

What are the 3 phases of bacterial growth?

A

Lag
Exponential
Stationary

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12
Q

What are 2 functions of pili and function of flagelli?

A

Pili: a) Plasmid exchange b) Adhere to surfaces
Flagelli: Locomotion propulsion

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13
Q

Which bacteria release exo and endo toxins?

A

Exotoxins: Both gram positive and negative
Endotoxins: Gram negative

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14
Q

What are endo and exotoxins?

A

En: Outer membrane component released when bacteria damaged (Heat stable, toxic to host and less specific)
Exo: Specific and heat labile proteins secreted by gram positive and negative

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15
Q

What are plasmids special ability?

A

Circular fragments of DNA that are able to carry genes for antibiotic resistance

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16
Q

How are staphylococci and streptococci arranged?

A

Sta: Clusters of Cocci
Str: Chains of Cocci (S Aureus –> G +ve)

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17
Q

What is the chemical test to distinguish the two types of gram positive bacteria?

A

Catalase Test: Detects for presence of catalase enzyme using hydrogen
peroxide
a) Sta: Cat +ve b) Str: Cat -ve

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18
Q

How do you distinguish further between the 2 sub types of bacteria:

A

Str: Blood Agar haemolysis (Serougrouping done if in B haemolysis group)
Sta: Coagulase Test: See if a fibrin clot has been produced

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19
Q

Where is staphylococcus found, spread and virulence factors?

A

Found: Nose and Skin
Spread: Aerosols and Touch
VF: Toxins, Proteases, Toxic shock syndrome toxin, Protein A

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20
Q

What are the 3 shapes of single cell bacteria?

A

1) Rod (Bacillus)
2) Cocci (+ve are Str and Sta)
3) Spirochetes

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21
Q

How is bacterial variation brought about?

A

1) Mutation: Del, Base Sub, Ins

2) Gene Tech: Transformation, Translation and Conjugation

22
Q

What are examples of gram negative and positive bacilli?

A

-: Shigella, salmonella, E. Coli, etc

+: Clostridium, bacillium, Corynebacterium

23
Q

What bacteria uses MacKonkey agar?

A

Gram negative bacilli

24
Q

What is found in MacKonkey agar?

A

Bile Salts, Lactose, pH indicator. (If lactose produced by organism, lactic acid produced and agar will be red/pink)

25
Q

What are 2 gram negative bacteria that produce a positive result for MacKonkey agar?

A

1) E. Coli

2) Klebsiella pneumoniae

26
Q

How does c.diptheriae spread?

A

Droplet

27
Q

Does shigella have an H antigen?

A

Has no flagellum as non-mobile therefore has no H antigen

No MacKonkey result as doesn’t ferment lactose

28
Q

Does salmonella contain an H antigen?

A

Salmonella motile, so has flagellum and an H antigen

No MacKonkey as doesn’t ferment

29
Q

Does E. Coli produce a positive MacKonkey agar result?

A

Ferments lactose –> Red/pink result (+ve)

Contains flagellum so motile and H antigen

30
Q

How do you detect differences between the different gram negative bacilli?

A

MacKonkey agar and Serology to detect presence of H antigen

31
Q

Why does E.Coli have pathogenic strains?

A

Due to recombinant strands of DNA from acquisition of other bacteria

32
Q

How does ETEC cause traveller’s diarrhoea?

A

1) ETEC heat labile toxin modifies Gs protein in “locked on” state
2) Adenylate cyclase activated so increased cAMP production
3) Increased Cl- secretion in the intestinal lumen
4) H2O follows down osmotic gradient causing traveller’s diarrhoea

33
Q

What effects do EPEC and EHEC e.coli have on mucosa?

A

Adhere to microvilli, rearrange actin leading to pedestal formation
EPEC: Chronic water diarrhoea
EHEC: Bloody diarrhoea

34
Q

What is the transmission, symptoms, AT advantage and action of Shigella?

A

T: Contaminated food/water, or person:person
S: Frequent passage, severe bloody diarrhoea
AT: Moves through V stomach pH without being destoryed and can infect the stomach
A: Induction of self uptake > Apoptosis > Cytokines released and neutrophils attracted causing inflammation then occurs in adjacent cells

35
Q

What bacteria causes salmonella and what are the 3 types of salmonella?

A

Bacteria: S. enterica

1) Gastroenteritis
2) Enteric fever
3) Bacteraemia

36
Q

What are gastroenteritis and enteric fever?

A

G: Freq. cause of food poisoning w/ 24 hr incubation period -> Highly infective dose
E: Typhoid fever (Systemic dose)

37
Q

What are the symptoms and dangers of v. cholerae?

A

S: Huge volumes of watery stools
D: Large amounts of water loss leads to hypovolemic and severe dehydration
- Grows at 18-42 degrees so withstands fever
- 8 alkaline pH sensitive so sensitive to the pH of the stomach

38
Q

How would haemophilus influenzae grow and what diseases does it cause?

A

Grow: Chocolate Agar (Needs Haem and NAD)
Diseases: Meningitis and Pneumonia

39
Q

What happens in the pathogenesis of gastro-enteritis?

A

1) Endocytosis
2) Chemokine release
3) Neutrophil recruitment and migration
4) Neutrophil induced tissue injury
5) Fluid and electrolyte loss –> Diarrhoea

40
Q

What happens in pathogenesis of enteric-fever?

A

1) Endocytosis
2) Migration to basolateral membrane
3) Survival in macrophage –> Systemic Spread

41
Q

What disease does Legionella cause?

A

Legionnaires disease (Immunocompromised Individuals)

42
Q

What type of bacteria are Neisseria? And what are 2 examples?

A

Gram negative diplocci

N. meningitidis and N. gonorrhoeae

43
Q

What is the transmission, pathogenesis and virulence of N.meningitidis?

A

T: Aerosol, with high risk in colonised
P: 1) Cross N-P epithelium and cross blood stream
2) Asymptomatic bacteraemia or septicaemia
V: Capsule (A-P), LPS and Pili (adherence to host cell)

44
Q

What are bacteroides?

A

Opportunistic, obligate anaerobes

45
Q

What are the consequences of N.gonorrhoeae infection?

A

STI - rectal, vaginal or oral inflammation.

46
Q

How is Chlamydia detected and how is it grown?

A

D: Serum antibodies/PCR
G: Not grown as an intracellular obligate parasite

47
Q

What are the 2 developmental stages of chlamydia’s unique growth cycle?

A

1) Elementary bodies (infective).
2) Reticulate bodies (intracellular multiplication).
(Reticulate bodies are converted back into elementary bodies and are released. The cycle continues)

48
Q

What are 2 bacteria found in the chlamydophila genre?

A

1) C.pneumoniae - respiratory tract infection.

2) C.psittaci - associated with birds.

49
Q

What sort of flagellum do spirochaete have?

A

Endoflagellum: Found between I and E membrane

50
Q

What spirochaete causes:

a) Lyme Disease
b) Syphillis

A

a) B. burgdoferi

b) T. pallidum

51
Q

What are the 3 stages of syphillis?

A
  1. Primary stage: localised infection.
  2. Secondary stage: systemic - skin, lymph nodes etc.
  3. Tertiary stage: CV syphilis and neuro syphilis.

Microbiology (6 decks)

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