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Flashcards in Microbiology Deck (33):
1

Give the 2 main species of mycobacteria 

M. Tuberculosis (1/4th leading infection that results in death. - wasting, fever & bloody cough) 

M. Leprae (affects skin, mucous membranes & nerves, can lead to disformaties and disfigurement in severe cases) 

2

How do you stain for mycobacteria? 

Ziehl-Neelsen stain 

Their cell wall has a thick lipid layer which is pale staining in gram stains due to the mycolic acids in the wall. 

Need acid fast stain

Ziehl-Neelsen: carbon fuchsin, acid alcohol, methylene blue. 

AFB are resistant to destaining so stay pink/red

3

Explain how the immune system tries to prevent an infection due to a mycobacterium 

Mycobacterium (AFB) phagocytosed by macrophages & enter a phagolysosome. 

Host aims to degrade AFB and display the antigens for T-cells. 

CD4 cells generate IFN-gamma for macrophages for intracellular killing. IL-12 stimulates T Helper and IFN-gamma. 

 

 

4

Explain how a mycobacterium can lead to in infection 

Signalling pathways are required to attract macrophages for killing. 

Problems in the signalling pathways can lead to infection.

  • genetic defects in IL-12/INF-g/signaling 
  • CD4 (HIV) 
  • TNF inhibitors (rheumatoid arthritis, inflammatory bowel disease) 
  • Immunosuppresed patients 

5

Explain how granulomas form in mycobacterial infections 

Lesions that try and contain mycobacteria 

Macrophages:

 - become epitheliod cells 

- M0 fuse to form giant multinucleated cells 'langhans giant cells' 

Central part may necrose = caseating granuloma 

Granuloma? Rule out TB 

6

Which of the following is true?

a) Mycobacteria are not immunogenic 

b) Mycobacteria are highly immunogenic 

 

Mycobacteria are highly immunogenic 

Due to mycobacterial lipids 

7

How can you test exposure to TB?

Which is the most useful test and why?

Tuberculin skin test - intradermal injection of purified proteins, difficult to tell if immunitiy to BCG/TB 

Interferon gamma release assays IGRAs - ELLISPOT/TSOT use antigens specific for M. tuberculosis. Demonstrate exposure but not active infection. - more useful 

8

For the following give the main reason for the tissue damage 

a) Tuberculoid leprosy 

b) Lepromatous leprosy 

a) Tuberculoid leprosy - too much immune response -tissue hypersensitivity and granulomata 

b) Lepromatous leprosy - Too little immune response - tissue damage to uncontrolled bacilli & poorly formed granulomata 

9

What are the principles of mycobacterial treatment?

Prolonged treatment as slow growing bacteria 

Can grow in different locations - intra/extracellular

Combination of drugs

Resistance (big problem) - need to target all populaions and mutants - MDR & XDR

Compliance is essential 

10

In primary tuberculosis where are the bacilli most likely to settle and why?

a) Carina of trachea 

b) Apex of lung 

c) Lower legft and right lobes

d) Right main broncus 

Bacilli settle in the apex of the lung and form granuloma. 

This is because the apex has more air and less blood supply (fewer defending WBC) 

11

With TB which doesn't makes up the primary complex?

a) granuloma 

b) lymphatics 

c) lymphnodes 

d) capillary beds 

Primary Complex = Granuloma + Lymphatics + Lymph nodes 

 

 

12

Describe how laten TB can become active 

Latent TB = no clinical disease 

Vigorous T cell control 

Detectable cell mediated immunity of IGRA/tuberculin test 

May become active if there is a compromise to the immune system - aging, HIV, malnutrition, diabetes 

Control lost by the T cells 

13

Which bacteria is being described?

Purple on gram stain. Negative catalase test with chains of cocci.  Appears yellow on a haemolysis test. 

a) Beta haemolytic stretococcus

b) Streptococcus pneumoniae 

c) Staphlococcus pneumonia 

d) Staphlococcus aureus 

Beta haemolytic stretococcus

Purple on gram stain = +ve 

Negative catalase test with chains of cocci = Streptococcus 

Appears yellow on a haemolysis test = beta haemolytic 

14

Which of the following are being described?

Purple on gram stain. Clusters of cocci that are catalase +ve and coagulase +ve. 

a) Beta haemolytic stretococcus

b) Streptococcus pneumoniae 

c) Staphlococcus pneumonia 

d) Staphlococcus aureus 

Staphlococcus aureus 

Purple on gram stain = gram postive  

Clusters of cocci that are catalase +ve = Staphlococcus 

Coagulase +ve = S. aureus 

15

Which of the following are being described?

Purple on gram stain. Catalase test -ve. Green haemolysis test. Optochin sensative. 

a) Beta haemolytic stretococcus

b) Streptococcus pneumoniae 

c) Staphlococcus pneumonia 

d) Staphlococcus aureus 

Streptococcus pneumoniae 

Purple on gram stain = +ve 

Catalase test -ve = Streptococcus 

 Green haemolysis test = alpha haemolysis 

Optochin sensative = S.pneumoniae

16

Name the sterile parts of the body?

Sterile parts of the body 

Blood, CNS, joints, peritoneal cavity, pleura fluid, lower respirary tract, urinary tract 

17

Which of the following could be being described here?

Pink on gram film. Yellow appearence on MacConkey agar. Oxidase test +ve. 

a) Shigella / salmonella 

b) Pseudomonas 

c) E.coli 

Pseudomonas 

Pink on gram film = -ve 

Yellow appearence on MacConkey agar = non-lactose fermentors

Oxidase test +ve =  Pseudomonas 

18

Which of the following could be being described?

Pink on gram stain. Pink/red appearence on MacConkey agar 

a) Shigella / salmonella 

b) Pseudomonas 

c) E.coli 

d) Staphlococcus 

Pink on gram stain = GNB 

Pink/red appearence on MacConkey agar = lactose fermentors = enterobacteriaceae = E.coli 

19

What are protozoa?

Protozoa are single cells eukaryotic organisms 

Consumers of bacteria, algae + microfungi 

20

What type of infection is malaria?

Parasitic protozoa 

Sporozona -> plasmodium spp. 

21

How is malaria transmitted?

On the bite of an anophele mosquito 

22

Which is the most dangerous type of malaria?

Plasmodia falciparum 

23

Explain the life cycle of malaria 

Malaria bites an infected human - takes up gametocytes 

Gamaetocytes to sporozoites in mosquito salivary gland 

Mosquito bites human  

Human liver into merozites - released into blood stream

Merozites invade RBC, divide and destroy them 

 

A image thumb
24

Explain the difference in lifecycles of P.ovale and P.vivax

P.ovale & P.vivax have an additional hypnozoite stage in the liver

They are also not eradicated by conventional anti-malarial treatments  

25

P.falciparum is known as 'cerebral malaria' and can be fatal. 

Explain how it can cause tissue hypoxia. 

The parasite matures in RBC and forms knobs on the surface. 

These bind to receptors on endothelial cells & other RBC (rosetting) 

Sequestration in small vessels (including brain, lung)

 = Microcirculation obstructed: tissue hypoxia

26

A 32 year old presents with fever, chills and sweats, fatigue, headaches and diarrhea. 

On history you find that they have been in Kenya 2 months ago. 

What could be the diagnosis?

Malaria 

 

Fever and they have been to a tropical contry... think Malaria 

27

What are the following clinical features describing?

Fever, coma, ARDS, renal failure and shock 

P.falciparum malaria 

28

Broadly explain how antimicrobials work

Antimicrobials work by binding to target sites on a bacteria. 

Defined as points of bichemical reactions that are crucial to the survival of the bacteria. 

The crucial binding site varies with each class of antimicrobials. 

29

Give examples of beta lactams and explain how they act as antimicrobials

Beta-lactams: 

Penicillin based - penicillin, amoxicillin - cephamycin, cephalosporins ...

They bind to penicilin binding proteins in the cell wall and prevent cell wall synthesis 

Glycoptpties also work by this mechanism 

30

Give the correct antimicrobial mechanism of action for the fluroquinolones

a) Inhibition of ribosomal acivity & protein synthesis 

b) Interference with nucleic acid synthesis/function 

c) Binding to cell wall and inhibiting cell wall synthesis 

d) Inhibition of DNA gyrase (topoisomerase II) 

The antimicrobial mechanism of action for the fluroquinolones

Inhibition of DNA gyrase (topoisomerase II) 

31

Give the correct antimicrobial mechanism of action for the aminoglycosids and tetracyclins

a) Inhibition of ribosomal acivity & protein synthesis 

b) Interference with nucleic acid synthesis/function 

c) Binding to cell wall and inhibiting cell wall synthesis 

d) Inhibition of DNA gyrase (topoisomerase II) 

The antimicrobial mechanism of action for the aminoglycosids and tetracyclins = 

Inhibition of ribosomal acivity & protein synthesis 

32

Give the correct antimicrobial mechanism of action for metronidazole & rifampicin 

a) Inhibition of ribosomal acivity & protein synthesis 

b) Interference with nucleic acid synthesis/function 

c) Binding to cell wall and inhibiting cell wall synthesis 

d) Inhibition of DNA gyrase (topoisomerase II) 

The antimicrobial mechanism of action for metronidazole & rifampicin = 

b) Interference with nucleic acid synthesis/function

33