Microbiology & Immunology Pracs Flashcards
What kind of environment can a Gram +ve bacterium survive in (due to its cell wall)
It can survive in a dry environment due to its thick peptidoglycan cell wall
- What are the two diseases caused by Varicella Zoster Virus?
- What are the layman’s terms for these diseases?
- How does it cause two diseases?
Varicella = Chickenpox (primary infection)
Herpes Zoster = Shingles (reactivation of latent virus)
What is the distinctive colour of Psuedomonas Aeruginosa?
Green
What is the difference between primary and secondary immunodeficiencies?
Primary immunodeficiencies: the result of inherent congenital defects in the components of the immune system/their products
Secondary immunodeficiencies: the effects of external agents or alterations in other body systems
What are some causes of secondary immunodeficiencies?
Extremes of age
Malnutrition
Anatomic barrier dysfunction (including medical devices)
Non infectious diseases e.g. diabetes, tumours
Infections e.g. Malaria, HIV
Cytotoxic drugs/irradiation
Immunosuppressive drugs
Explain the technique of flow cytometry
Tag a cell population with a fluorecent dye (react with a fluorescently labelled monoclonal antibody) so it can be easily recognised and analysed
e.g. you can tag leukocytes to see if they are deficient in numbers, or see of certain cell populations are overabundant.
A 2 month old baby presented with swelling and discharge around her umbillical cord stump (the stump had not yet separated). On examination she had a fever, Swabs were taken from the serosanguineous discharge around the stump. On further investigation she was found to be infected by S. Aureus.
What is the significance of the discharge being serosanguineous?
Serosanguineous = blood & serum but NO PUS
No pus = No white blood cells
S. Aureus often causes a purulent discharge.
This should raise suspicion of an immunological deficiency
Leukocyte Adhesion Deficiency (LAD) is a primary immunodeficiency. Explain its pathogenesis
There is a normal number of T cells & monocytes but the individual lacks the ability to make certain adhesion molecules = Lack of leukocyte integrin CD18.
The tight binding for B2 integrins to ICAM-1 cannot occur therefore there is no migration, no attachment, no diapedesis and therefore the immune cells cannot get to the site of infection.
A young child is suspected to have a primary immunodeficiency.
Upon analysis of his antibodies, the following results were found:
IgG - Low
IgM - High
IgA - None detected
CD40L - Low
Explain these results.
The child’s antibodies are not undergoing isotype switching.
CD40L is required to activate B cells for isotype switching, memory B cells, and stimulating macrophages.
(Diagnosis: Hyper IgM Syndrome)
When collecting a sample to test for septicaemia, why should three sets of blood cultures be taken?
Bacteraemia is usually intermittent, rather than continuous
What does a catalase test, test for?
The bacteria’s ability to break down H2O2 and therefore its ability to survive in phagocytes
The enzyme catalase is present in most aerobic and faculative anaerobic bacteria.
What does a coagulase test look at?
The bacteria’s ability to clot fibrinogen to fibrin.
If the colonies on MAC were found to be pink, what does this indicate?
They are lactose fermenters
TRUE OR FALSE?
Upper respiratory tract infections are predominantly caused by bacteria.
FALSE!! They are predominantly caused by viruses
Common cold: viral
Sore throat: predominantly viral
Sinusitis: predominantly bacterial (often after viral infection)
Otitis media: bacteria
What are some syndromes associated with Lower Respiratory tract infections?
Croup (laryngotracheobronchitis) Whooping cough Bronchiolitis Bronchitis - acute, and acute exacerbation of chronic bronchitis Pneuomonoa
When diagnosing organisms found in the lower respiratory tract, how do we ensure it isn’t just contaminants from the upper respiratory tract in our sample?
Macroscopically it should be thick mucus
Microscopically there should be NO epithelial squamous cells
Microorganisms that have invaded the LRT would be in greater numbers than in the URT (infection is often associated with isolated of particular microorganism in numbers greater than 10 ^ 7 /ml of sputum)
There should be the prescence of inflammatory cells
What are the most common causes of pharyngitis and tonsillitis?
Viruses, but also Strep Pyogenes
What antibiotic is Strep. Pyogenes ALWAYS susceptible to?
Penicillin
What type of bacteria is not susceptible to pencillin?
Beta lactamase producing bacteria
How does Klebsiella evade the immune system?
With its capsule - it will look shiny in colonies
What causes the majority of bronchiolitis?
How should it be managed?
Respiratory Syncitial Virus (RSV)
DON’T USE ANTIBIOTICS - can only provide symptomatic treatment (oxygen, fluid, rest…)
In bacterial contamination of food, what are the symptoms normally due to?
Ingesting the toxins produced by the pathogens in the contaminated food.
Common offenders include: Steph aureus, Bacillus cereus and Clostridium botulinum
Compare the differences in likely pathogens between developing and developed countries that cause gastroenteritis w. diarrhoea
Developing countries: Most likely to be viruses, less likely to be bacteria, least likely to be protozoa
Developed countries: Most likely to be bacteria, less likely to be viruses, least likely to be eukaroytic parasites
A group of friends went to have lunch together. The next day over half of them were unwell. By the following night, they all showed signs of gastroenteritis.
The doctor decided the pathogen was NOT Staph Aureus.
Why?
This case demonstrated a long incubation period.
Staph aureus is associated with a short incubation period (only 4-6 hours) as it produces toxins directly in the food.
