Morphology
Cultural characteristics
Pathogenesis
Labratory diagnosis
General knowledge
100
Which bacteria is it? And what about morphology of this bacteria?
Y.pestis is a short, plump, ovoid, gram negative bacillus, about 1.5*0.7mmin size, non motile, non spore forming and non acid fast bacteria
100
On which culture media will grow Y.pestis and which type of colonies they will produse?
Feature Description Best growth temperature 28–30°C (room temperature)
Blood agar Non-hemolytic, gray-white, smooth colonies
MacConkey agar Non-lactose fermenting (colorless colonies)
Nutrient agar “Fried-egg” appearance
100
Which host cells are primarily involved in the multiplication of Y. pestis?
Macrophages.
100
What clinical specimens are collected for laboratory diagnosis of plague?
➡️ Answer:
Bubonic plague: aspirate from lymph node (bubo)
Pneumonic plague: sputum, tracheal aspirate
Septicemic -blood
100
What are the main reservoirs of Y.pestis?
Wild rodents main natural reservoir, and fleas as vector that spread Y. pestis to other animals and humans.
200
Pathogenic species of Brucella?
Brucella melitensis
Brucella abortus
Brucella suis
200
Which bacteria's colony is it? on which culturural media? and optimum condition?
Bacillus anthracis, on blood agar, 37 degree
200
Why is Brucella considered an intracellular pathogen?
Because it replicates and persists inside macrophages, avoiding antibody-mediated destruction.
200
How long does it take for Brucella colonies to appear?
after 10 days to several weeks (slow-growing).
200
Plague, Black Dead
300
Which of these pathogens are facultative intracellular parasites?
Francisella tularensis and Brucella spp.
are facultative intracellular parasites.
300
What is the oxygen requirement of Bacillus anthracis?
Bacillus anthracis is an aerobic and facultative anaerobic bacterium.
This means:
It grows best in the presence of oxygen (aerobic conditions).
It can also grow without oxygen, but less efficiently.
Spore formation requires oxygen, which is why spores are produced only in the environment or culture, but not inside the host organism.
300
Name the main components of the anthrax toxin and their roles?
Protective antigen (PA) – binds to host cells and mediates entry. Edema factor (EF) – increases cAMP → tissue swelling. Lethal factor (LF) – causes macrophage lysis and tissue necrosis.
300
On which culture media does F.tularensis grow?
Requires cysteine-enriched media, such as:
Chocolate agar
Cysteine heart agar
Glucose–cysteine–blood agar
300
What is the main mode of transmission brucellosis?
Answer: Contact with infected animals or ingestion of unpasteurized dairy products.
400
Which bacteria is it? and morphology of this bacteria ?
Bacillus anthracis largest, gram positive, non acid fast, non motile, spore forming
400
Why is Francisella tularensis difficult to isolate in routine laboratories?
Francisella tularensis is very fastidious and highly infectious, which makes isolation in routine labs challenging.
Requires enriched media containing cysteine or cystine (e.g., cysteine-enriched agar).
Cannot grow well on standard blood or MacConkey agar.
Colonies are very small, slow-growing, often taking 2–5 days to appear.
Facultative intracellular bacterium → often inside macrophages, so free bacteria in clinical samples may be few.
400
Unlike Brucella and Francisella, is Bacillus anthracis intracellular or extracellular?
It is extracellular.
400
What are rapid antigen detection methods used for anthrax?
Direct fluorescent antibody (DFA) test for capsule and cell wall antigen.
ELISA for protective antigen (PA).
400
Which bacteria discovered by Sir David Bruce in 1887 from the spleen of a British soldier who died in Malta.
Brucella
500
A microbiology lab receives a clinical sample. The Gram stain shows small Gram-negative coccobacilli, difficult to see, and the culture requires cysteine-enriched agar. The patient has a history of tick bite and ulceroglandular lymphadenitis. Which bacterium is most likely, and how do its morphological features aid in diagnosis?
Francisella tularensis
500
Describe the growth requirements of Brucella spp. in culture?
Primary media: Blood agar, chocolate agar, Brucella agar.
Special enriched medium: Castaneda medium — a biphasic medium (solid + liquid phases) designed to improve isolation and enhance detection of Brucella from clinical samples (blood, bone marrow).
Liquid phase promotes bacterial growth.
Solid phase allows observation of colony morphology.
Facultative aerobe.
Many strains grow better with 5–10% CO₂ (capnophilic).
Colonies appear slowly, usually 3–7 days (sometimes up to 10 days).
Colonies are small, smooth, convex, non-hemolytic.
Optimal growth at 37°C (body temperature).
500
List the main routes of infection for Francisella tularensis.
inhalation of contaminated aerosols, ingestion of contaminated water or food, contact with infected animals or their tissues, and bites from infected arthropods like ticks, deer flies, and mosquitos. .
500
What molecular test can detect Brucella DNA?
PCR (highly specific and rapid).
500
Who developed the first anthrax vaccine?
Louis Pasteur in 1881.