Microbiology Flashcards
What samples can be tested for microbiology?
Blood cultures Urine CSF Fluids from joint or abscesses Tissues Swabs Line tips
What are the different colours of blood culture bottles?
Blue= aerobic Red= anaerobic
What are the 4 components of gram staining used for bacteria?
Crystal violet
-stains purple
Iodine
Alcohol
-will decolorise gram negative bacteria after staining with iodine
Safranin
-acts as counter stain for gram negative i.e. reason why gram negative are PINK
What colours do gram negative and gram positive bacteria stain and why?
Gram positive= PURPLE
-due to thick peptidoglycan cell wall leading to retention of crystal violet
Gram negative= PINK
-thin peptidoglycan cell wall leads to crystal violet washing out and then counterstaining with safranin
What is the difference in appearance of cocci and bacilli?
Cocci= clusters
Bacilli= rods
What are 3 examples of gram positive cocci?
What infections are they associated with?
Staphylococcus= clusters Streptococcus= chains of cocci Enterococcus= chains of cocci
Gram +ve bacteria tend to cause infections ABOVE the diaphragm
What are the 2 different types of staphylococcus sp?
What is the difference between their associated infections?
Staphylococcus aureus
- coagulase positive
- virulant organism leading to infection preseting w/i 1st 24 hrs
- associated with skin and soft tissue infections but can enter blood when skin barrier broken
Staphylococcus epidermidis
- coagulase negative]
- indolent infection= symptoms don’t present w/i 24hrs i.e. presents few months later
What are the 3 different forms of streptococcus?
Which form of streptococcus is associated with endocarditis?
What other infections are associated with streptococcus?
Streptococcus pneumoniae
Beta-haemolytic streptococci= groups A/B/C/G
Viridans streptococci
Streptococcus oralis (type of viridans) is associated with endocardititis -brushing teeth induces bacteraemia and poor dentention can lead to continual bacteraemia with the bacteria latching onto heart valves
Pneumonia
Skin + soft tissue
Abscesses i.e. liver and dental
What are the 2 main types of entercoccus and what is significant clinically about them?
What complications can occur secondary to enterococcus infection?
Enterococcus faecalis= amoxicillin sensitive
Enterococcus faecium= amoxicillin resistant
-need to treat with vancomycin
Endocarditis
-indolent infection, which sticks to valves
Intra-abdominal infections
What are 4 examples of gram positive bacilli?
What can occur when infected with these bacteria?
Actinomyces sp
-can occur with IUD (coil)
Bacillus cereus
-associated with reheating rice
Corynebacterium/C.diphtheriae
-highly infectious respiratory infection
Listeria monocytogenes
- can lead to meningitis which is resistant to cefrataxone i.e. need to treat with amoxicillin
- can lead to premature labour if in blood during pregnancy
What are 3 examples of gram negative cocci?
What infections are they associated with?
Neisseria meningitidis
- tends to occur when there is complement immunodeficiency
- causes meningitis
Neisseria gonorrhoeae
-can lead to reactive arthritis if infection becomes systemic due to infecting synovial fluid
Moraxella catarrhalis
-causes pneumonia
-
What are 3 examples of gram negatice bacilli?
What infections do these bacteria tend to cause?
Escherichia coli
Klebsiela pneumonia/Klebsiella oxytoca
Proteus mirabilis
Cause infections BELOW the diaphragm (due to being gram -ve)
- urosepsis
- GI infection
- intra-abdominal abscesses
What type of organism is detected by Ziehl-Neelsen stain and why?
When is Ziehl-Neelsen stain indicated?
What are the components of the stain and what would a positive result look like?
Detects acid-fast bacteria due to high lipid in cell membrane (mycolic acid) meaning impenetrable to normal gram staining
When gram +ve rods on culture and worried clinically about TB (mycobacterium tuberculosis)
Carbol fuchsin
Acid alcohol= used to remove anything not bound to acid-fast bacteria
Malachite gree/methylene blue= counterstain
TB +VE= red/pink rods on blue background
What is the difference between mycobacterium tuberculosis and non-tuberculous mycobacteria?
Non-tuberculous mycobacteria tends to only cause infection in immunosuppressed, bronchiectasis or patients with prosthetic materials
I.e. in patients who have parts of lung which will facilitate growth of bacteria
What are the 2 main types of virus and give examples of viruses for each?
RNA
- enterovirus
- rhinovirus
- rubella
- influenza
- measles
- mumps
- rabies
- HIV + HTLV
- rotavirus
DNA
- adenovirus
- Herpes= CMV/HSV/VZV/EBV
- Hep B
- Parvovirus B19
- Papillovirus + polyomavirus
