Denise - Corynebacteria Flashcards
What type of bacteria are corynebacteria and listeria
Gram-positive non-endospore forming rods
Write about the corynebacterium species
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
What are the reservoirs for corynebacterium
Exclusively human reservoir e.g. C. diptheriae
Throat and nasopharynx carriers and infected patients
Cow and animals are the main reservoir for corynebacterium
How is corynebacterium transmitted
Occurs via respiratory droplets
Asymptomatic carriers
Convalescents
Less common through direct contact or indirect contact with fomites
What are the four main biotypes of corynebacterium diphtheriae
Var gravis
Var intermedius
Var belfanti
Var mitis
Write about the pathogenesis of C. diptheriae
Early stages:
- sore throat
- low fever
- swollen neck glands
Late stages
- airway obstruction and breathing difficulty
- shocks
Write about the epidemiology of C. diptheriae
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
What are two telltale signs of localised respiratory diptheria
Bull neck - swollen
Pseudomembrane on tonsils
How does cutaneous diptheria present
May be mistaken for anthrax
Black necrosing swollen tissue at sight of cut
Write about the virulence of C. diptheriae
Releases exotoxins
Pseudomembrane on tonsils and pharynx
C. diphtheria releases exotoxins, what do they do
Facilitates:
- local tissue necrosis
- spread to affect heart -> death by myocarditis
- spread to peripheral nerves
- neurological complications
What is the function of the psudomembrane
Causes mechanical obstruction of the air passages
Write about Diphtheria exotoxin
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
How does diphtheria become toxigenic
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
What is the diptheria exotoxin called
DT tox
What bacteriphage carries the Diphtheria tox
B corynephage
What is the Diphtheria exotoxin’s mode of action
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
What are the systemic effects of diptheria exotoxin
Local tissue destruction
Toxin carried via lymph and blood to other parts of the body
Can affect the heart and peripheral nerves
How does exotoxin cause damafe
- A membrane receptor recognises and binds a portion of the toxin (fragment B)
- The toxin enters the cell by receptor-mediated endocytosis and dissociates into fragments A and B
- The A fragment is translocated to the cytosol, where is catalyses the transfer of adenosine diphosphate ribose (ADPR) from NAD+ to EF-2
- The ADPR-elongation factor complex is inactivated, and peptide synthesis stops
Write about treatment and prevention of Corynebacterium
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
What antibiotics can be used to treat Corynebacterium
Erythromycin
Penicillin
What are three other Corynebcaterium species
C. ulcerans
C. psudotuberculosis
C. jeikeium
What infection does C. ulcerans cause
Infection of throat occasionally clinically resmebling diphtheria
What infection does C. pseudotuberculosis cause
Pathogen of sheep and horses and very unusually a human pathogen
What infection does C. jeikeium cause
Opportunistic pathogen is immunosuppressed, often antibiotic resistant
What specimens is Corynebacterium seen in
Throat swabs
Nasopharynx swabs
Swabs from pseudomembrane
Skin swabs
What media is Corynebacterium put up on on day 1
Blood agar
Hoyle’s medium
Tellurite agar
Incubate at 37 degrees for 24-48 hours
Write about Corynebcaterium on hoyles medium
Highly selective medium
Inhibits most normal flora from respiratory tract
Diptheria = grey colonies
C. ulcerans = grey/black . very dry opaque colonies
Write about the use of Tinsdale Medium
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
What produces the dark halo on tinsdale medium
Production of H2S from cystine, interacting with the tellurite salt
What are the basic characteristics of corynebacterium
GPB (pallisades pelomorphic club shaped)
KoH negative
Catalase positive
Oxidase negative
No haemolysis
What confirmatory tests are carried out on corynebacterium
Biohcemical identification
Toxin detection
Rapid screening Maldi TOF
Write about the biochemical results for Corynebacterium
C. diphtheria:
- trehalose negative
- urease negative
C. ulcerans
- trehalose positive
- urease positive
Others
- Trehalose negative
- urease positive
Write about the urease test
Detection of urease enzyme
Splitting of urea
Positive = pink
Negative = yellow
Write about the laboratory detection of diphtheria toxin
Stains identified as C. diphtheriae must be investigated for toxin production through:
- in vivo tests
- in vitro tests
- Molecular methods of PCR
Describe in vivo test for Diphtheria toxin
Using protected and unprotected guinea-pigs
Describe in vitro test for Diphtheria toxin
Elek plate (immunoprecipitation method)
Write about PCR used to detect diphtheria tocin
Detection of tox gene
PCR directed at the A subunit of the diphtheria toxin
It does not confirm toxin production
What is an ELEK plate
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
