Corynebacteria and Bacillus Flashcards
(42 cards)
Outline key features of Corynebacteria.
◾ Gram-positive, non-motile, rod-shaped bacteria
◾ Under the microscope, they often appear as slender, slightly curved rods with clubbed ends, giving them a characteristic “V” or “Y” shape. They can also form palisades.
◾ Non-spore formers
◾ Non-motile
◾ Facultative anaerobes
◾ Not capsulated
What type of granules are found in the cytoplasm of Corynebacterium diphtheriae?
Corynebacterium diphtheriae contain metachromatic or volutin granules, which are a storage form of metabolites and tend to be concentrated at the ends of the bacillus.
How resistant is Corynebacterium diphtheriae to drying?
Corynebacterium diphtheriae is relatively resistant to drying and can retain viability for weeks in dust or on dry articles.
Is Corynebacterium diphtheriae susceptible to heat and disinfectants?
Yes, Corynebacterium diphtheriae is susceptible to heat and regularly used disinfectants.
What is the main virulence factor of Corynebacterium diphtheriae?
The main virulence factor is an exotoxin referred to as the diphtheria toxin.
What are the two types of Corynebacterium diphtheriae strains?
Corynebacterium diphtheriae strains can be either toxigenic or non-toxigenic.
What disease are toxigenic strains of Corynebacteria diphtheriae associated with?
Toxigenic strains are associated with the causation of diphtheria and are further classified according to the severity of associated clinical manifestations.
Can non-toxigenic strains of Corynebacterium diphtheriae cause infections?
Non-toxigenic strains may cause cutaneous infections, invasive infections [e.g. bacteremia, endocarditis] and upper respiratory tract infections. However, such incidences are rare, save for the cutaneous infections.
How is diphtheria transmitted?
Diphtheria is transmitted from person to person directly via the respiratory route or indirectly through contaminated items. The bacilli are released in secretions or droplets from the upper respiratory tract (URT) of an infected person and are acquired by the susceptible person through the URT.
Outline the clinical manifestations of diphtheria (5).
Outline possible complications of diphtheria.
(1) Obstruction of air passage [more likely where the pseudomembrane is extensive]
(2) Adverse effects of diphtheria toxin on internal organs:
◾ damage to the heart may result in myocarditis and/or arrhythmias
◾ degeneration of peripheral nerves may lead to loss of function [neuritis]
◾ damage to adrenal glands may interfere with production of hormones
Where is the specimen for laboratory tests in diphtheria obtained from?
The oropharynx, including infected material or part of the pseudomembrane or fluid.
List culture media that can be used to grow C. diphtheriae and make a brief note on each.
(1) Blood agar: It supports the growth of other organisms including other possible upper respiratory tract pathogens.
(2) Potassium tellurite blood agar (PTA): This media is more selective. Potassium tellurite suppresses the growth of upper respiratory tract normal flora. C. diphtheriae possess an enzyme that reduces tellurite and forms a dark colored product. Colonies hence appear grey or black in PTA. [Image 1]
(3) Tinsdale medium: also contains potassium tellurite. [Image 2]
(4) Loeffler agar: enhances the visibility of metachromatic granules in C. diphtheriae. Also, though it is not strictly selective for C. diphtheriae, it favours its growth over some other bacteria. [Image 3]
conditions for incubation of C. diphtheriae cultures
35° - 37°C for 18 - 24 hours
What methods are used to identify Corynebacterium diphtheriae?
Staining and microscopic morphology, colonial characteristics on potassium tellurite agar, presence of volutin granules, biochemical tests, and demonstration of diphtheria toxin production.
What stains can be used to demonstrate the presence of volutin granules in C. diphtheriae?
Albert’s stain, Neisser’s stain
What tests are used to demonstrate diphtheria toxin production?
The agar-gel precipitation technique and the Elek test are used to confirm diphtheria toxin production.
What are the specific treatments for diphtheria?
Antitoxin administration and antimicrobial treatment with agents like penicillin or erythromycin.
What are the prevention and control measures for diphtheria?
Detection and treatment of carriers and patients during an outbreak, managing hospitalized patients in separate rooms, and active immunization with the DPT vaccine.
What is the Schick test used for?
It is a skin test to detect the presence of circulating diphtheria antitoxin in predisposed people in a population.
State the mode of action of:
(a) penicillin
(b) erythromycin
(a) penicillin: this is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis. It binds to and activates penicillin-binding proteins located on the bacterial cell wall. This action prevents the cross-linking of peptidoglycan chains, which are essential for cell wall strength and rigidity. As a result, the bacterial cell wall weakens, leading to cell lysis and death.
(b) erythromycin: this is a macrolide antibiotic that inhibits bacterial protein synthesis. It binds to the 50S ribosomal subunit of the bacterial ribosome, preventing translocation of peptides during translation. This action effectively stops the growth of bacteria by inhibiting protein synthesis.
Outline key features of Bacillus.
◾ Gram-positive, rod-shaped bacteria that are arranged singly or in chains [Image 1] [Image 2] [Image 3]
◾ Aerobic or facultative anaerobes
◾ Form spores
◾ Majority of species are motile; B. anthracis is non-motile
◾ Most form colonies with complete zones of hemolysis on blood agar; B. anthracis is non-hemolytic
(a) What are anthracoides?
(b) List four examples of anthracoides.
(a) These are bacilli that closely resemble Bacillus anthracis in their morphological and cultural characteristics. Unlike Bacillus anthracis, they are generally motile and are haemolytic. Anthracoides are also generally less virulent and are often considered opportunistic pathogens.
(b) B. cereus, B. subtilis, B. pumilis, B. stearothermophilus
Discuss pathogenicity properties of Bacillus anthracis.
(1) The bacteria have a high resistance to heat. Spores are also relatively resistant to disinfectants and heat.
(2) Possession of capsule.
(3) Production of an extra-cellular toxin.
