Microbiology Practicals Flashcards
How is a gram stain prepared?
Come In And Stain
Crystal violet - primary stain
Iodine
Acetate/Alcohol - decolourise
Safranin - Counterstain
What colour do gram positive and gram negative bacteria stain?
Gram positive - Purple
Gram Negative - Pink
What is blood agar?
agar with horse/sheeps blood
used for growing lots of bacteria
least selective
What is chocolate agar?
heated to 80C for breakdown of haem & release of factors that grow organisms w/ fastidious growth requirements [H.influenzae]
What is CLED?
differentiates between organisms in urine & allows classification of lactose fermenting & non lactose fermenting gram-negative bacilli
What is MacConkey Agar?
grows gram negative bacilli (it has bile salts that inhibit the growth of gram positive). Has lactose & red dye
lactose fermenting = pink colonies
non lactose fermenting = white colonies
What is Gonococcus Agar?
Contains growth factors to promote the growth of Neisseria species as well as antibiotics & antifungal agents to inhibit the growth of other organisms.
What is Sabouraud’s Agar?
used to culture fungi. Has antibiotics to inhibit bacterial growth.
What is XLD Agar?
used to isolate Salmonella and Shigella [non lactose fermenting, gram negative]
Salmonella - Red with black centre (produces H2S)
Shigella - Red only
What colour will Staphylococcus aureus appear on blood agar and what colour would other staphylococcus species appear?
S.aureus - gold
S.other - white
What are the sterile sites of the body?
Blood
CSF
pleural fluid
Peritoneum
Joints
Urinary Tracts
Lower Respiratory Tract
How can you tell the difference between various Gram Positive bacteria?
+tve Catalase Test = Staphylococcus:
(if positive then do Coagulase Test:)
+tve = S.aureus
-tve = S.epidermidis/S.saprophyticus
-tve Catalase Test = Streptococcus
(if negative then do Haemolysis on blood agar)
alpha haemolysis (partial/green) = requirement for Optochin Test
Optochin Sensitive = S.pneumoniae
Optochin Resistant = S. viridans group
Beta haemolysis (full) = requirement for Lancefield grouping via serology)
A = S.pyogenes
B = S.agalactiae
A,C, G = Tonsilitis, pharyngitis, skin infection
B = Neonatal sepsis + meningitis
Gamma Haeomolgysis (none) = Enterococcus
How can you tell the difference between various Gram Negative bacteria?
MacConkey Agar for lactose fermentation Test:
+tve lactose fermentation = E.coli/Klebsiella
-tve Lactose fermentation = Requirement to do Oxidase Test
Oxidase Test:
+tve Oxidase = Pseudomonas, Aueruginosa
-tve Oxidase = Requirement to do XLD test:
Colonies on XLD which are Red with black centers = Salmonella
Colonies on XLD which are Red only = Shigella
What are the 2 main approaches to diagnosing viral infection?
Electron Microscopy / PCR
Serology Testing - ELISA, IF, Complement Fixation Test.
What is an advantage and disadvantage to EM testing?
Very specific and sensitive but too expensive and too long
What is an advantage and disadvantage to PCR?
Very fast but high risk of false positives as it is very sensitive and so can easily be contaminated.
What virus causes shingles and how does it present?
Varicella Zoster Virus (VZV)
Red painful rash conferred to a single dermatome
What virus causes Glandular fever (infectious mononucleosis)?
Epstein Barr Virus (EBV)
Ix: FBC - Atupical lymphocytes
Serology for EBV Igs - ELISA Test
What is a differential Diagnosis to Glandular fever and how is this ruled out?
S.pyogenes throat infection - Both EBV and S.pyogenes present with purulent (pus) infection over the tonsils
Take black charcoal swab to rule out S.pyogenes
What other Sx can be caused by EBV?
Tonsilitis,
Cough
Fever
Splenomegaly
What is BALF?
Bronchoalveolar lavage fluid
Fluid collected from the lungs
Bronchi are washed and this fluid is sent for analysis using PCR
What condition can cytomegalovirus cause?
CMV colitis
Characteristic finding is OWL EYE INCLUSION BODIES
What is the treatment for CMV infection?
IV ganciclovir
What HIV markers can be found in the blood
HIV Igs
HIV RNA
p24 antigen
How may a patient present with meningitis?
Headache
Fever
Photophobia
Neck stiffness
What Ix are required for suspected meningitis?
Take CSF sample.
CSF –> Increased WCC + protein
Determine type of meningitis based on CSF glucose, type of WCC and CSF appearance.
If viral then use PCR to determine specific type
