/
Gram Positive Bacilli Flashcards
Save to my account
Sign up
Gram Positive Bacilli Flashcards
Gram Positive Bacilli Flashcards
Study
1
Question
What is Corynebacterium diphtheriae and why is it significant?
Answer
Corynebacterium diphtheriae is a gram-positive bacillus that causes diphtheria. It is the most important member of the Corynebacterium group due to its disease-causing ability.
2
Question
What are diphtheroids and how do they relate to Corynebacterium diphtheriae?
Answer
Diphtheroids are other species of corynebacteria that resemble C. diphtheriae in morphology and occur as normal flora on the skin and mucous membranes. Some can cause opportunistic infections, but they are distinct from toxigenic C. diphtheriae.
3
Question
Describe the characteristic arrangement and staining features of Corynebacterium diphtheriae on a Gram stain.
Answer
Corynebacterium diphtheriae are gram-positive bacilli arranged in a distinctive 'Chinese-letter' pattern. They appear club-shaped and pleomorphic under Gram staining.
4
Question
What role does the diphtheria toxin play in Corynebacterium diphtheriae's pathogenicity?
Answer
The diphtheria toxin is the virulence factor of C. diphtheriae. It inhibits protein synthesis in host cells, causing necrotic and neurotoxic effects. Its production depends on a specific bacteriophage, so only lysogenized strains are toxigenic.
5
Question
How is diphtheria primarily transmitted?
Answer
The most common form, tonsillar diphtheria, is transmitted via airborne droplets. Less common forms like conjunctival and skin diphtheria spread by direct contact.
6
Question
What is the pathogenesis of tonsillar diphtheria?
Answer
The organism colonizes the throat and tonsils, producing exotoxin that causes local inflammation and a pseudo-membrane. The toxin enters the bloodstream causing systemic toxicity (toxaemia) affecting heart, kidneys, liver, and nerves. The bacteria themselves do not enter the bloodstream.
7
Question
Why is immediate treatment crucial in suspected diphtheria cases?
Answer
Because the diphtheria exotoxin is powerful and rapidly fatal, prompt administration of antitoxin is essential to neutralize the toxin before irreversible damage occurs.
8
Question
What specimen is collected for the laboratory diagnosis of suspected tonsillar diphtheria?
Answer
A throat swab taken from the membrane on the tonsils or throat is collected for diagnosis.
9
Question
How does Albert stain help in identifying Corynebacterium diphtheriae?
Answer
Albert stain highlights the metachromatic (volutin) granules within the bacilli, making them appear beaded and assisting in the identification of C. diphtheriae.
10
Question
What is the medium used for primary isolation of Corynebacterium diphtheriae and what are its cultural characteristics?
Answer
Tellurite blood agar is used for primary isolation. C. diphtheriae produces grey to black colonies due to tellurite reduction.
11
Question
Is the presence of Corynebacterium diphtheriae enough to confirm diphtheria? Why or why not?
Answer
No. It is essential to demonstrate toxin production because only toxigenic strains cause diphtheria. Non-toxigenic strains do not cause disease.
12
Question
What is the standard treatment approach for diphtheria?
Answer
Treatment involves prompt administration of diphtheria antitoxin to neutralize toxin effects, and antibiotics like penicillin or erythromycin to inhibit bacterial growth and reduce toxin production. Airway maintenance is also critical.
13
Question
How does the diphtheria vaccine work, and what is its typical schedule?
Answer
The vaccine contains diphtheria toxoid, which induces immunity by stimulating antitoxin production. It is combined with tetanus and pertussis vaccines (DPT) and given at 2, 4, and 6 months, with boosters at 18 months and school age.
14
Question
Why are booster doses of diphtheria vaccine important for adults?
Answer
Booster doses with Td vaccines are important to maintain sufficient immunity, especially for adults traveling to areas where diphtheria is still endemic.
15
Question
What are the general characteristics of the genus Bacillus?
Answer
The genus Bacillus consists of large rectangular Gram-positive bacilli occurring in chains. They form central, oval, non-bulging spores that appear as unstained areas in Gram-stained films.
16
Question
Which member of the Bacillus genus is the most important pathogen?
Answer
Bacillus anthracis is the most important pathogenic member of the genus Bacillus.
17
Question
What types of Bacillus species are generally saprophytes, and which may act as opportunistic pathogens?
Answer
Most Bacillus species are saprophytes found in water, soil, and air and are called anthracoids. Among them, B. cereus and B. subtilis may act as opportunistic pathogens causing bacteraemia, endocarditis, and meningitis. B. cereus can also cause post-traumatic ophthalmitis and food poisoning due to enterotoxin production.
18
Question
What are the primary virulence factors of Bacillus anthracis?
Answer
The two main virulence factors are the polypeptide capsule, which has antiphagocytic action, and the anthrax toxin composed of three parts: lethal factor (LF), edema factor (EF), and protective antigen (PA).
19
Question
What are the three main modes of transmission and types of anthrax infection caused by Bacillus anthracis?
Answer
1) Contact - leads to cutaneous anthrax (malignant pustule). 2) Inhalation - leads to respiratory anthrax (wool sorter's disease). 3) Ingestion - leads to gastrointestinal anthrax.
20
Question
Describe the characteristics and common affected populations of cutaneous anthrax (malignant pustule).
Answer
Cutaneous anthrax occurs when the organism enters through skin abrasions, multiplies locally, and produces a malignant pustule. It mainly affects farmers, butchers, and veterinarians, and can also occur via shaving brushes made from infected animal hair.
21
Question
What is respiratory anthrax and how is it transmitted?
Answer
Respiratory anthrax, also known as wool sorter's disease, is transmitted by inhaling spores from infected animal wool or hairs. It can develop into pneumonia and is highly fatal.
22
Question
How common is gastrointestinal anthrax and how is it acquired?
Answer
Gastrointestinal anthrax is rare and is transmitted by eating meat from infected animals.
23
Question
What is septicaemic anthrax?
Answer
Septicaemic anthrax occurs when Bacillus anthracis invades the bloodstream in any of the forms of anthrax, leading to systemic infection.
24
Question
What specimens are used for laboratory diagnosis of suspected anthrax?
Answer
Specimens depend on the site of infection and include exudates or aspirates from skin lesions, sputum, stool, and blood.
25
Question
How do Bacillus anthracis appear in Gram-stained direct smears?
Answer
They appear as large, rectangular, capsulated Gram-positive bacilli arranged in chains.
26
Question
What culture conditions are used to grow Bacillus anthracis for diagnosis?
Answer
Cultures are done on nutrient or blood agar incubated at 35–37ºC for 24 hours.
27
Question
What are the characteristic colony features of Bacillus anthracis on culture?
Answer
The colonies are large with wavy margins, often described as Medusa head colonies.
28
Question
How does Bacillus anthracis appear microscopically after culture and staining?
Answer
After culture, Bacillus anthracis bacilli are non-capsulated and contain central, oval, non-bulging spores that appear as unstained areas in Gram stain. The spores stain pink with acid-fast spore stain.
29
Question
What are the recommended antibiotic treatments for cutaneous and pulmonary anthrax?
Answer
Cutaneous anthrax is treated with ciprofloxacin or tetracycline. Pulmonary anthrax treatment involves ciprofloxacin combined with rifampin or vancomycin.
30
Question
What are the key preventive measures for anthrax?
Answer
Prevention includes vaccination of domestic animals with live attenuated vaccine, proper disposal of animal carcasses, and autoclaving of animal products. The anthrax vaccine (Biothrax), containing protective antigen (PA), is used for humans at high risk such as veterinarians, lab workers, and livestock handlers.