Corynebacteria and Bacillus Flashcards
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.
Discuss the anthrax toxin.
◾ This is a tripartite protein complex composed of three distinct components:
Protective antigen (PA), Edema factor (EF), and Lethal factor (LF).
◾ PA facilitates the formation of a pore in the host cell membrane that facilitates entry of EF and LF into the cells.
◾ EF is an adenylate cyclase enzyme that increases the levels of cyclic AMP within host cells. The elevated cAMP levels disrupt cellular signaling and water homeostasis, leading to edema and other manifestations of anthrax.
◾ LF induces cell death and impairs immune responses.
Which animals are primarily affected by anthrax?
Cattle and sheep
How do human infections with Bacillus anthracis typically occur?
Human infections occur accidentally, often through contact with infected animals or contaminated animal products.
What are the primary infective agents of Bacillus anthracis?
The spores
Through which routes are Bacillus anthracis bacilli shed from infected animals?
Through the animal’s nose and mouth or in feces
What are the primary sources of Bacillus anthracis infection for humans?
(1) contaminated soil
(2) infected animals:
◾ direct handing of skin, bones, wool, meat, carcasses
◾ eating improperly handles or improperly cooked meat
Name four different presentations of B. anthracis infection.
(1) Cutaneous anthrax/Black eschar
(2) Pulmonary anthrax/Inhalation anthrax/Woolsorter’s disease
(3) Gastro-intestinal anthrax
(4) Septicaemic anthrax
What specimens are examined in the laboratory investigation of human anthrax?
Fluid or pus from cutaneous lesions, blood, and sputum.
What staining methods are used in the smear examination for anthrax?
Gram’s stain to demonstrate Gram-positive bacilli and polychrome methylene blue stain for capsular material.
(a) What is the Ascoli test used for in anthrax investigation?
(b) What indicates a positive result in the Ascoli test?
(a) To detect the presence of B. anthracis by mixing extracts of infected tissues with immune serum.
(b) Formation of a precipitate.
(a) What growth media are used for the isolation and identification of Bacillus anthracis?
(b) At what temperature and for how long should Bacillus anthracis be incubated?
(a) Blood agar (BA) and nutrient agar.
(b) In air at a temperature of 35 to 37 degrees Celsius for 18 to 24 hours.
What is the appearance of Bacillus anthracis colonies on agar plates?
Greyish opaque with a wavy margin and small projections, referred to as Medusa head colonies.
What is the size and surface texture of Bacillus anthracis colonies?
About 2 to 5 mm in diameter with a rough surface.
Are Bacillus anthracis colonies hemolytic on blood agar?
No
What biochemical test is useful for identifying Bacillus anthracis, and what is the expected result?
The gelatin liquefaction test, which should show a positive result.
Which antibiotics is Bacillus anthracis susceptible to?
Penicillin, doxycycline, and ciprofloxacin.
What is one specific measure to prevent human infections with Bacillus anthracis?
Decontamination or sterilization of animal products before use.
Identify the lesions: [Image].
anthrax eschars
