20 Questions
What is the diameter of Corynebacteria?
0.5-1 µm
Which granules are mainly composed of high molecular weight polyphosphate?
Sulfur granules
Which granules are stained deep blue and found in the cytoplasm?
Volutin granules
How do individual Corynebacteria in stained smears typically appear?
At acute angles to one another
What is a characteristic appearance of Corynebacteria?
L- or Y-forms
Which method is not used for bacteriological diagnosis?
Genetic sequencing
What type of examination involves the use of a microscope?
Smear examination
Which of these sugars is not fermented by C. diphtheriae?
Lactose
Which type of bacteria is Corynebacterium?
Non-spore-forming, gram-positive bacilli
Where is Corynebacterium commonly found?
Skin and mucous membranes
Which biochemical property is true for C. diphtheriae?
Catalase positive
C. diphtheriae ferments which of the following with acid production?
Maltose
What is a common contaminant of clinical specimens that Corynebacterium is known for?
Contaminants of clinical specimens
What severe disease can the exotoxin produced by Corynebacterium cause?
Diphtheria
For what purpose is Corynebacterium often submitted?
For diagnostic evaluation
What is the initial appearance of C. diphtheriae colonies on Löffler's medium?
Small, opaque, white circular disks with a regular border
Which of these characteristics is true regarding the C. diphtheriae colonies on blood agar?
Small, granular, and gray with irregular edges
What is a characteristic of C. diphtheriae colonies as they evolve on Löffler's medium?
The center becomes elevated and yellow in color
What is one of the criteria used to classify the four biotypes of C. diphtheriae?
Colony morphology
Which of the following is NOT a recognized biotype of C. diphtheriae?
hemolyticus
Study Notes
Morphology and Identification
- Corynebacteria are 0.5-1 µm in diameter, non-motile, and do not have capsules.
- They have an irregular shape, appearing "club-shaped" due to the presence of granules at one end.
- They are carotenoid-positive and have irregularly distributed granules within the cell.
- Metachromatic granules or Babes-Ernst granules are composed of high molecular weight polyphosphate and can be present at one or both ends of the cell.
- Volutin granules stain deep blue and are found in the cytoplasm.
- Stained smears of corynebacteria often show parallel or acute angles between individual cells.
Diagnostic Laboratory Tests
Characterizations of C. diphtheriae
- C. diphtheriae grows poorly on Löffler's medium, leading to pleomorphism and distinct morphology.
- Colonies on Löffler's medium are small, opaque, white, and circular with a regular border that later becomes crenated and elevated with a yellow center.
- On blood agar, colonies are small, granular, and gray with irregular edges, and may have small zones of hemolysis.
- There are four recognized biotypes of C. diphtheriae: gravis, mitis, intermedius, and belfanti, classified based on growth characteristics, biochemical reactions, and disease severity.
Diagnostic Laboratory Tests
- Sterile swabs are taken from the lesion site and can include a portion of the pseudomembrane.
- Bacteriological diagnosis methods include smear examination, cultural examination, and pathogenicity tests.
Biochemical Reactions
- C. diphtheriae ferments glucose, galactose, maltose, and dextrin with acid production.
- It does not ferment lactose, sucrose, or mannitol.
- It does not liquefy gelatin.
- It is H2S-positive and catalase-positive.
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