Microbiology

Question 1

With gram stain, gram +ve cocci in clusters with lots of pus is most likely to be?

Answer 1

Staph. aureus

Question 2

With gram stain, gram +ve cocci in chains, with lots of pus is mostly likely to be which family of bacteria?

Answer 2

Streptococcus

Question 3

Larger cell bodies, gram +ve in clusters with pus?

Answer 3

Candida

Question 4

On a plate, if there is small clusters of gram +ve cocci with no pus and no inflammation, what is a likely diagnosis?

Answer 4

Gram +ve cocci are normal flora staph, and it’s most likely a viral infection

Question 5

What is the difference between gram +ve and gram -ve bacteria?

Answer 5

Gram +ve = thicker cell wall, more peptidoglycan, a little bit more resistant to drying, but more porous for antibodies

Gram -ve = complex structure, thinner cell wall, less resistant to drying, less porous to antibodies

Question 6

What’s the difference between enriched and enrichment media?

Answer 6

enriched: add additional nutrients to meet the requirement of certain bacteria
enrichment: a selective liquid medium that provides substrates that selectively favours a particular organism. May also suppress competitors

Question 7

What is chocolate horse blood agar used for?

Answer 7

it’s the same as horse blood agar but enriched by heating to 65-80 degrees. Used to grow fastidious organisms like Haemophilus spp. and Neisseria spp.

Question 8

What is the CLED medium used for

Answer 8

to support the growth of all urinary pathogens. The medium is included in the dip slide.

Question 9

what type of medium is HBA? What can it indicate

Answer 9

enriched medium, can indicate haemolysis

Question 10

What is beta-haemolysis? which organism typically does that (give 3)?

Answer 10

Clear haemolysis on HBA. Strep. pyogenes, Clostridium perfringens, Bacillus cereus

Question 11

What is alpha-haemolysis? which organism typically exhibit the behaviour

Answer 11

greening haemolysis

Strep. pneumoniae

Question 12

What is MAC?

Answer 12

a selective medium designed for intestinal bacterial pathogens

Question 13

What is the selective ingredients in MAC?

Answer 13

bile salt and only lactose

Question 14

If organism grows on MAC, what does that indicate?

Answer 14

it’s a lactose fermentor and resistant to bile salt

Question 15

What kind of organism has catalase

Answer 15

most aerobic and facultative anaerobic bacteria

Question 16

What does the catalase break down

Answer 16

H2O2

Question 17

How does a catalase positive test present?

Answer 17

gas production

Question 18

What is a coagulase test for?

Answer 18

a clotting test for Staphlococcus

more specific to test for staph. aureus

Question 19

What is an oxidase test for?

Answer 19

differential test for mainly aerobic and facultatively anaerobic groups of gram negative bacteria

Question 20

Which organism is typically oxidase positive?

Answer 20

Pseudomonas

Question 21

A gram +ve coccus, catalase positive, and coagulase positive organism is likely to be?

Answer 21

Staph. aureus

Question 22

gram +ve coccus, catalsse negative, b-haemolysis and no growth on MAC

Answer 22

Str. pyogenes

Question 23

gram +ve coccus, catalase -ve, greening on HBA, optochin sensitive?

Answer 23

Str. pneumoniae

Question 24

gram +ve rod, anaerobic, spore forming

Answer 24

Clostridium

Question 25

acid fast, weakly gram positive, requires NZ stain

Answer 25

Mycobacterium

Question 26

gram -ve rod, growth in air, no growth on MAC, requires blood to grow

Answer 26

Haemophilus

Question 27

What is the NBT test for?

Answer 27

test for phagocytic oxidative burst

Question 28

Gram -ve rod, growth in air, growth on MAC, oxidase positive, O-F test "O"

Answer 28

growth in air = aerobic or f. anaerobic growth on MAC = lactose fermentor and bile resistant oxidase positive = confirmed aerobic O-F test "O", so it's most likely Pseudomonas

Question 29

Gram -ve rod, growth in air, growth on MAC, oxidase negative, O/F test "F"

Answer 29

enterobacteria

Question 30

LFA-1 tests for macrophage's ability to migrate to site of infection. When is it not necessary?

Answer 30

When there is granuloma formation microscopically

Question 31

What are some signs showing neutrophil migration impairment?

Answer 31

neutrophilia, no puss at site of infection, CD18 -ve on antibody labelling

Question 32

What does a flow cytometry indicate?

Answer 32

presence of T and B cells

Question 33

What deficiency can impair B cell maturation? If B cell maturation is impaired, what will the patient's blood serology indicate? What is the treatment?

Answer 33

lack of CD40L expression High in IgM but low IgG Antibody transfusion

Question 34

When can the cysts of Pneumocystis jirovecci normally be found?

Answer 34

In classic T cell defects

Question 35

What is the common cold usually caused by

Answer 35

rhinovirus

Question 36

Why is epiglotitis life threatening? What shouldn't you do to diagnose it?

Answer 36

because it causes an obstruction in the airway. You shouldn't swab it, because that can cause complete obstruction

Question 37

Which of the resp. pathogens can be vaccinated against?

Answer 37

Pneumococcus, influenza, haemophilus influenzae (causative agent for epiglottitis), DPT, measles/mumps/rubella

Question 38

What is the most common cause tonsilitis/pharyngitis?

Answer 38

virus and strep pyogenes

Question 39

What are the complications of Strep. pyogenes infection?

Answer 39

rheumatic fever, rheumatic valvular disease

Question 40

What is the empirical treatment of Strep?

Answer 40

penicillin + tetracyclin/macrolide

Question 41

What makes hospital acquired pathogens resistant?

Answer 41

plasmid transfer and selection for antimicrobials

Question 42

Why is Klebsiella a likely pathogen in the hospital setting? Note Klesiella is gram -ve rod, oxidase negative, lactose fermentor

Answer 42

because it is only susceptible to gentamicin and imiperem, but resistant to common penicillin. This is likely due to plasmid transferred resistance

Question 43

What is the most common cause of bronchiolitis?

Answer 43

RSV

Question 44

What's the test used to identify influenza?

Answer 44

haemagglutination inhibition test

Question 45

What is conjugated vaccine used for? Give three examples of bacteria that require conjugate vaccine

Answer 45

for capsulated bacteria | Strep. pneumoniae, Haemophilus influenzae, Neisseria meningitidis

Question 46

Why do we need conjugate vaccine?

Answer 46

Because the pathogens have a poly s. capsule and cannot stimulate CD4 response

Question 47

What is the basis of conjugated vaccine?

Answer 47

attaching a protein on poly s. capsule that is able to induce B cell endocytosis of antigen, so it can be presented to activate CD4 response

Question 48

If a child under 1 exhibits resp. wheeze, what is the likely diagnosis? And what is it similar to?

Answer 48

bronchiolitis, symptoms like asthma

Question 49

What is the basis of haemagglutination inhibition test?

Answer 49

Add RBC into influenza infected cells. Because haemagglutinin is present, it can bind to RBC and clot Then, add specific antibody (H1N1, for example). This blocks HA binding site, so there will be no clotting.

Question 50

No growth on CAMP, no growth on selenite, gram -ve, lactose fermenting, PCR indicates positive for intimin, shiga toxin, what's the likely causative bacteria?

Answer 50

EHEC

Question 51

What is selenite broth good for?

Answer 51

isolate Salmonella. Looks red if positive