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2.2 Microbiology > Denise - Corynebacteria > Flashcards

Denise - Corynebacteria Flashcards

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Biology 101 flashcards
1
Q

What type of bacteria are corynebacteria and listeria

A

Gram-positive non-endospore forming rods

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2
Q

Write about the corynebacterium species

A

Gram positive but some stain irregularly
“Chinese letter” appearance
Pleomorphic
Straight of slightly curved rods
May be club-shaped or show swellings
Non-motile
Non-capsulated
Aerobic or facultatively anaerobic
Several species in the genus

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3
Q

What are the reservoirs for corynebacterium

A

Exclusively human reservoir e.g. C. diptheriae

Throat and nasopharynx carriers and infected patients

Cow and animals are the main reservoir for corynebacterium

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4
Q

How is corynebacterium transmitted

A

Occurs via respiratory droplets

Asymptomatic carriers

Convalescents

Less common through direct contact or indirect contact with fomites

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5
Q

What are the four main biotypes of corynebacterium diphtheriae

A

Var gravis
Var intermedius
Var belfanti
Var mitis

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6
Q

Write about the pathogenesis of C. diptheriae

A

Early stages:
- sore throat
- low fever
- swollen neck glands

Late stages
- airway obstruction and breathing difficulty
- shocks

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7
Q

Write about the epidemiology of C. diptheriae

A

Acute respiratory or cutaneous condition
Life threatening
Rare due to immunisation with toxoid vaccine

Two cases of diphtheria in Ireland after almost 50 years compared to 2,625 in India in 2012

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8
Q

What are two telltale signs of localised respiratory diptheria

A

Bull neck - swollen
Pseudomembrane on tonsils

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9
Q

How does cutaneous diptheria present

A

May be mistaken for anthrax

Black necrosing swollen tissue at sight of cut

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10
Q

Write about the virulence of C. diptheriae

A

Releases exotoxins

Pseudomembrane on tonsils and pharynx

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11
Q

C. diphtheria releases exotoxins, what do they do

A

Facilitates:
- local tissue necrosis
- spread to affect heart -> death by myocarditis
- spread to peripheral nerves
- neurological complications

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12
Q

What is the function of the psudomembrane

A

Causes mechanical obstruction of the air passages

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13
Q

Write about Diphtheria exotoxin

A

Gene encoding DT (tox) is found on bacteriophage (B corynephage)

Only C. diphtheriae cells that contain the phage can produce the toxin - are toxigenic

Those unable to produce the toxin are toxigenic

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14
Q

How does diphtheria become toxigenic

A

Tox is of bacteriophage origin

Lysogenic integration of the phage genome into the bacterial chromosome occurs

A non toxigenic strain can be converted by lysogeny

Regulation of toxin production is under bacterial control

Iron metabolism

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15
Q

What is the diptheria exotoxin called

A

DT tox

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16
Q

What bacteriphage carries the Diphtheria tox

A

B corynephage

17
Q

What is the Diphtheria exotoxin’s mode of action

A

Bipartite protein molecule
Secreted across the bacterial cytoplasmic membrane as a proenzyme
Activated by proteolytic cleavage
ADP-ribosylating toxin
Hydrolysis of nicotinamide from NAD
Transfer the ADP-ribose to diphthamide reside on elongation factor 2
Inhibits protein synthesis

18
Q

What are the systemic effects of diptheria exotoxin

A

Local tissue destruction
Toxin carried via lymph and blood to other parts of the body

Can affect the heart and peripheral nerves

19
Q

How does exotoxin cause damafe

A
  1. A membrane receptor recognises and binds a portion of the toxin (fragment B)
  2. The toxin enters the cell by receptor-mediated endocytosis and dissociates into fragments A and B
  3. The A fragment is translocated to the cytosol, where is catalyses the transfer of adenosine diphosphate ribose (ADPR) from NAD+ to EF-2
  4. The ADPR-elongation factor complex is inactivated, and peptide synthesis stops
20
Q

Write about treatment and prevention of Corynebacterium

A

Prompt neutralisation of toxin using horse serum antitoxin or passive immunisation

Eradication of the microorganism through Erythromycin or Penicillin

Isolation of patient

Supportive care

Vaccination

21
Q

What antibiotics can be used to treat Corynebacterium

A

Erythromycin
Penicillin

22
Q

What are three other Corynebcaterium species

A

C. ulcerans
C. psudotuberculosis
C. jeikeium

23
Q

What infection does C. ulcerans cause

A

Infection of throat occasionally clinically resmebling diphtheria

24
Q

What infection does C. pseudotuberculosis cause

A

Pathogen of sheep and horses and very unusually a human pathogen

25
Q

What infection does C. jeikeium cause

A

Opportunistic pathogen is immunosuppressed, often antibiotic resistant

26
Q

What specimens is Corynebacterium seen in

A

Throat swabs
Nasopharynx swabs
Swabs from pseudomembrane
Skin swabs

27
Q

What media is Corynebacterium put up on on day 1

A

Blood agar
Hoyle’s medium
Tellurite agar

Incubate at 37 degrees for 24-48 hours

28
Q

Write about Corynebcaterium on hoyles medium

A

Highly selective medium
Inhibits most normal flora from respiratory tract

Diptheria = grey colonies

C. ulcerans = grey/black . very dry opaque colonies

29
Q

Write about the use of Tinsdale Medium

A

Contains L cystine, sodium thiosulphate and potassium tellurite

Diptheria = black colonies surrounded by brown halos

Organism produces cysteinase which released H2S which interacts with salts in medium

C. diptheriae, C. ulcerans and C. pseudotuberculosis give this reaction

30
Q

What produces the dark halo on tinsdale medium

A

Production of H2S from cystine, interacting with the tellurite salt

31
Q

What are the basic characteristics of corynebacterium

A

GPB (pallisades pelomorphic club shaped)
KoH negative
Catalase positive
Oxidase negative
No haemolysis

32
Q

What confirmatory tests are carried out on corynebacterium

A

Biohcemical identification
Toxin detection
Rapid screening Maldi TOF

33
Q

Write about the biochemical results for Corynebacterium

A

C. diphtheria:
- trehalose negative
- urease negative

C. ulcerans
- trehalose positive
- urease positive

Others
- Trehalose negative
- urease positive

34
Q

Write about the urease test

A

Detection of urease enzyme
Splitting of urea

Positive = pink
Negative = yellow

35
Q

Write about the laboratory detection of diphtheria toxin

A

Stains identified as C. diphtheriae must be investigated for toxin production through:
- in vivo tests
- in vitro tests
- Molecular methods of PCR

36
Q

Describe in vivo test for Diphtheria toxin

A

Using protected and unprotected guinea-pigs

37
Q

Describe in vitro test for Diphtheria toxin

A

Elek plate (immunoprecipitation method)

38
Q

Write about PCR used to detect diphtheria tocin

A

Detection of tox gene
PCR directed at the A subunit of the diphtheria toxin
It does not confirm toxin production

39
Q

What is an ELEK plate

A

Take a toxigenic C. diptheria strain and a non-toxigenic C. diptheria

Make two parallel lines across the plate

Add a piece of filter plate with diphtheria antittoxin across both lines

Lines of precipitin are formed is the strain is toxigenic

2.2 Microbiology (60 decks)

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