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Medical Microbiology lectures > L.7 GPB: Corynebacterium spp. > Flashcards

L.7 GPB: Corynebacterium spp. Flashcards

1
Q

What shape are Corynebacterium spp.?

A

Pleomorphic, club-shaped Gram-positive rods

Often appear in ‘Chinese letter’ arrangements

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2
Q

Are Corynebacterium spp. motile or non-motile?

A

Non-motile

They are also non-spore-forming and non-capsulated

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3
Q

What type of respiration do Corynebacterium spp. exhibit?

A

Aerobic and facultative anaerobes

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4
Q

How many species of Corynebacterium are known?

A

46 species

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5
Q

How many species of Corynebacterium rarely cause human disease?

A

~30 species

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6
Q

Where are Corynebacterium spp. commonly found in humans?

A

Normal human microbiota, especially on skin and mucous membranes

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7
Q

What type of pathogens are many Corynebacterium spp.?

A

Opportunistic pathogens

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8
Q

What disease does Corynebacterium diphtheriae cause?

A

Diphtheria

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9
Q

What are diphtheroids?

A

Non-toxigenic Corynebacterium species, often commensals or contaminants

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10
Q

What is the life-threatening condition caused by C. diphtheria?

A

Acute respiratory or cutaneous condition

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11
Q

What type of infection can C. ulcerans cause?

A

Infection of throat occasionally clinically resembling diphtheria

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12
Q

Which Corynebacterium species is a pathogen of sheep and horses?

A

C. pseudotuberculosis

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13
Q

What is C. jeikeium known for?

A

Opportunistic pathogen in immunosuppressed, often antibiotic resistant

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14
Q

What unique membrane does C. diphtheria cause to form in the pharynx?

A

A tough leathery membrane

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15
Q

How many biotypes of C. diphtheria exist?

A

4 biotypes

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16
Q

Name one biotype of C. diphtheria.

A

C. diphtheria mitis

Other biotypes include C. diphtheria intermedius, C. diphtheria gravis, and C. diphtheria belfonti

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17
Q

What is the only known reservoir for C. diphtheria?

A

Humans

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18
Q

What is the main mode of transmission for C. diphtheria?

A

Respiratory droplets from coughing or sneezing

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19
Q

Can asymptomatic carriers spread C. diphtheria?

A

Yes

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20
Q

Fill in the blank: C. diphtheria can also spread through _______.

A

Direct contact with infected skin lesions

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21
Q

What are fomites in the context of C. diphtheria transmission?

A

Contaminated surfaces

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22
Q

How can C. diphtheria enter the body aside from respiratory routes?

A

Through open skin wounds

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23
Q

What is pharyngeal diphtheria?

A

Acute bacterial infection of the upper respiratory tract

Characterized by the formation of a grey, leathery pseudomembrane over the tonsils, pharynx, or larynx.

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24
Q

What are the symptoms of pharyngeal diphtheria?

A

Sore throat, bull neck, fever, malaise

Risk of airway obstruction may require emergency tracheostomy.

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25
What are the systemic effects of diphtheria toxin?
* Myocarditis * Acute tubular necrosis * Peripheral neuropathy (nerve demyelination, leading to paralysis) ## Footnote Systemic absorption of diphtheria toxin can lead to these serious conditions.
26
What is cutaneous diphtheria?
Entry via broken skin causing ulcerative skin lesions with grey membranes ## Footnote It is a form of diphtheria that affects the skin.
27
What is the epidemiology of diphtheria?
Rare infection due to immunization with toxoid vaccine ## Footnote No cases reported in 2024.
28
How does diphtheria enter the body?
Via respiratory droplets or direct contact ## Footnote Especially in unvaccinated or immunocompromised individuals.
29
What is the role of diphtheria toxin in pathogenesis?
Disrupts protein synthesis in host cells ## Footnote This leads to host damage.
30
What are the steps in the pathogenesis of diphtheria?
* Entry * Immune Evasion * Host Damage * Spread ## Footnote These steps outline how diphtheria infects and affects the host.
31
What is a key virulence factor of diphtheria?
Diphtheria toxin = cytotoxic endotoxin ## Footnote Encoded by β-phage (lysogenic bacteriophage inserts toxin gene into bacterial DNA).
32
What is the structure of diphtheria toxin?
AB toxin structure ## Footnote B subunit binds to host cell receptors; A subunit is the active component.
33
What does the A subunit of diphtheria toxin do?
Enters the cytosol and inhibits EF-2 via ADP-ribosylation ## Footnote This blocks protein synthesis and leads to cell death.
34
True or False: Diphtheria can spread through exhalation and person-to-person contact.
True ## Footnote This highlights the contagious nature of the disease.
35
What specimens are collected for pharyngeal diphtheria identification?
Throat swabs, Nasopharynx swabs, Swabs from pseudomembrane
36
What specimen is collected for cutaneous diphtheria?
Swab from cutaneous lesion
37
What type of organism is C. diphtheriae considered?
Fastidious organism
38
What type of culture media is used for C. diphtheriae?
Blood Agar
39
Describe the appearance of C. diphtheriae colonies on Blood Agar.
Small greyish, granular colonies
40
Is C. diphtheriae gravis haemolytic or non-haemolytic?
Non-haemolytic
41
What is the characteristic zone of haemolysis shown by other biotypes of C. diphtheriae?
Small zone of b-haemolysis
42
What components are included in Loeffler’s slope?
* Horse serum * Sodium chloride * Beef extract * Dextrose * Proteose
43
What does Loeffler’s slope enhance in C. diphtheriae?
Development of metachromatic granules
44
How can metachromatic granules be visualised?
By methylene blue stains (e.g. Albert’s/Neisser’s staining)
45
What is the shape of C. diphtheriae when viewed under a microscope?
Green club-shaped bacteria with metachromatic granules
46
Is Loeffler’s slope recommended by Public Health England?
Not recommended
47
What is the purpose of Hoyle’s medium?
Selective media that suppresses background flora
48
What does Hoyle’s medium inhibit?
Inhibits Gram negative and a variety of Gram positive bacteria
49
What does Hoyle’s medium help differentiate?
Biotypes based on colony morphology and tellurite reduction
50
What is the function of Tinsdale Agar?
Differentiates C. diphtheriae from diphtheroids
51
What selective and differential components does Tinsdale Agar contain?
* Tellurite (selective) * Cysteine (differential)
52
What is the appearance of C. diphtheriae on Tinsdale Agar?
Black halos due to the production of H2S from cysteine
53
What type of bacteria is indicated by microscopy on Day 2?
Gram Positive Bacilli ## Footnote This indicates the bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain used in the Gram staining procedure.
54
What characteristic shape do the bacteria exhibit under microscopy?
Club shaped & Chinese lettering ## Footnote This morphology is typical of certain bacterial species such as Corynebacterium diphtheriae.
55
What are the motility and endospore characteristics of the bacteria identified?
Non motile/Non endospore forming ## Footnote This indicates the bacteria do not have the ability to move independently and do not form spores, which are resistant structures for survival.
56
What are the results of the general biochemical tests for the bacteria?
Catalase Positive, Oxidase Negative, Koh Negative ## Footnote These biochemical tests help in identifying the metabolic characteristics of the bacteria.
57
What methods are used for confirmation of the bacteria on Day 3?
Biochemical Reactions (sugar fermentation, urease, nitrate reduction) ## Footnote These tests assess the bacteria's metabolic capabilities and help confirm its identity.
58
What is used to confirm the presence of toxigenic strains?
Elek plates ## Footnote These plates are used for toxin identification in bacteria, particularly for detecting diphtheria toxin.
59
What is the first step in the treatment of the identified bacterial infection?
Prompt action to eradicate bacteria ## Footnote Immediate treatment is crucial to prevent complications from the infection.
60
What is the recommended treatment for a patient identified with the infection?
Isolation of Patient ## Footnote Isolation helps prevent the spread of the infection to others.
61
What antibiotic is administered to treat the infection?
Pencillin G ## Footnote Penicillin G is commonly used to treat infections caused by Gram-positive bacteria.
62
What should be administered if the bacteria is found to be toxigenic?
Anti diphtheria toxin - Horse Serum antitoxin or Passive Immunisation ## Footnote This treatment neutralizes the effects of the toxin produced by the bacteria.
63
What is emphasized as a better approach than treating the disease?
Prevention better than cure ## Footnote Preventive measures can stop the disease before it occurs.
64
What type of vaccine is mentioned for prevention?
Toxoid vaccine (modified DT) ## Footnote This vaccine stimulates the immune response without causing disease.
65
At what age is the 6 in 1 vaccine given to children?
2 months - 6 years of age ## Footnote This vaccine schedule helps protect children from multiple diseases during early childhood.

Medical Microbiology lectures (10 decks)

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