Microbiology

Question 1

Define commensal

Answer 1

Organism which colonise the host but cause no disease in normal circumstances

Question 2

Define oppurtunist pathogen

Answer 2

Microbe that only causes disease if host defences are compromised

Question 3

Define asymptomatic carriage

Answer 3

Pathogen is carried harmlessly at tissue site without causing disease

Question 4

What is the relationship between gram stain and membrane of bacteria?

Answer 4

Gram +ve = single membrane
Gram -ve = double membrane

Question 5

Describe the process of gram staining

Answer 5

Come In And Stain
1. Crystal violet
2. Iodine
3. Alcohol/acetone
4. Safranin

Question 6

How do gram +ve and gram -ve bacteria appear?

Answer 6

Gram +ve - purple
Gram -ve - pink

Question 7

When would Ziehl-Neelsen stain be used?

Answer 7

Mycobacteria
-acid-fast bacilli do not take up gram stain

Question 8

How do Ziehl-Neelsen stain?

Answer 8

• Acid-fast bacilli = Red (mycobacterium)
• Non acid-fast bacilli = Blue

Question 9

What is the catalase test?

Answer 9

1. Add peroxide to bacteria and see for bubbling reaction
2. Used to differentiate between staphylococci (+ve) and streptococci (-ve)

Question 10

What is a haemolysis test?

Answer 10

1. Haemolysis = ability of bacteria to break down RBCs in blood agar
2. Expression of haemolysin dependent
3. Used to classify streptococci

Question 11

What is alpha haemolysis?

Answer 11

1. Indistinct zone of partial destruction of RBC
2. Medium discolouration to greenish brown

Question 12

Give some examples of alpha haemolytic bacteria

Answer 12

1. Strep. Pneumoniae
2. Strep. Viridans

Question 13

What is beta haemolysis?

Answer 13

1. Clear colourless zone appears around colonies; RBCs have undergone complete lysis

Question 14

Give some examples of beta haemolytic bacteria

Answer 14

1. Strep. pyogenes
2. Staph. aureus

Question 15

How can you differentiate between strep. and staph. aureus in beta haemolysis?

Answer 15

Staph aureus beta haemolysis will appear creamy yellow on blood agar

Question 16

What is gamma haemolysis?

Answer 16

No haemolysis occurs

Question 17

What is the Optochin test?

Answer 17

1. Tests to differentiate between Strep. pneumoniae and viridans strep. and other alpha haemolytic strep.
2. Optochin soaked disc placed in agar, growth observed

Question 18

How does the Optochin test?

Answer 18

-Sensitive = strep. pneuomniae = clear zone of no growth around disc
-Resistant = Viridans strep. and other alpha haemolytic strep. grow around disc

Question 19

How does the oxidase test?

Answer 19

• oxidase +ve = blue (aerobic) = V. cholerae
• oxidase -ve = no colour change = bacteria may be aerobic or anaerobic

Question 20

What is the use of Macconkey agar?

Answer 20

1. Only grows gram -ve bacilli
2. Useful to differentiate between lactose fermenting and non-lactose fermenting gram -ve bacilli
3. pink/red = lactose fermenting = E.Coli
4. White/transparent = non lactose fermenting = Salmonella

Question 21

What is the use of XLD agar?

Answer 21

1. Differentiate salmonella vs shigella
2. Red/pink colonies with some black spots = Salmonella
3. Red/pink colonies = Shigella

Question 22

How to find, diagnose and treat Staph. aureus

Answer 22

Clinical presentation
- Pain in shoulder
- Elevated temperature
- Osteomyelitis (bone infection) C6 & C7
Diagnose
- Blood culture shows staph. aureus
- Coagulase +ve
Treat
- FLUCLOXACILLIN 3 MONTHS

Question 23

What is the cause,test and treatment of impetigo, boils, cellulitis, endocarditis, toxic shock syndrome?

Answer 23

CAUSE - Strep. Aureus
TEST - Gram +ve, Coagulase +ve
TREAT - Flucloxacillin, co-amoxiclav, macrolides

Question 24

What is the cause,test and treatment of MRSA?

Answer 24

CAUSE - Staph. Aureus
TEST - Gram +ve, Coagulase +ve
TREAT - Gentamicin, vancomycin

Question 25

What is the cause,test and treatment of surgical wound infections, septicaemia, endocarditis?

Answer 25

CAUSE - Strep. epidermidis TEST - Gram +ve, Coagulase -ve TREAT - Co-Amoxiclav

Question 26

What is the cause,test and treatment of acute cystitis?

Answer 26

CAUSE - Strep. saphrophiticus TEST - Gram +ve, Coagulase -ve TREAT - Nitrofurantoin, Trimethoprim

Question 27

What are the key differences between gram +ve and -ve bacteria?

Answer 27

- Gram +ve = single cytoplasmic membrane, large amount of peptidoglycan, no endotoxin, STAIN PURPLE - Gram -ve = Inner & outer membrane, small amount of peptidoglycan, endotoxin present, STAIN PINK

Question 28

State the different types of antibiotics

Answer 28

1. Beta lactams glycopeptides 2. Metronidazole and Rifampicin 3. Fluroquinolones 4. Aminoglycosides,Tetracyclines, Macrolides, Chloramphenicol 5. Sulphonamides, Trimethoprim

Question 29

How do beta lactam gylcopeptide antibiotics work?

Answer 29

1. Bind to bacterial cell wall 2. Inhibition of cell wall synthesis

Question 30

How do Metronidazole and Rifampicin antibiotics work?

Answer 30

Interfere with nucleic acid synthesis or function

Question 31

How do Fluroquinolones antibiotics work?

Answer 31

Inhibit DNA gyrase

Question 32

How do Aminoglycosides, Tetracyclines, Macrolides, Chloramphenicol antibiotics works?

Answer 32

Inhibit ribosomal activity and protein synthesis

Question 33

How do Sulphonamides and Trimethoprim antibiotics work?

Answer 33

Inhibit folate synthesis

Question 34

What are the 4 species of protazoa responsible for malaria?

Answer 34

1. P. falciparum 2. P. Ovale 3. P. vivax 4. P. malariae

Question 35

Which mosquito is responsible for malaria?

Answer 35

Female ANOPHELES mosquito

Question 36

What is the pathology of malaria?

Answer 36

1. Anaemia 2. Cytokine release 3. Widespread organ damage due to impaired microcirculation

Question 37

What are the clinical features of malaria?

Answer 37

1. Incubation period = 10-21 days 2. Chills & sweats 3. Myalgia (muscle pain) 4. Fatigue 5. N,D&V

Question 38

What is the life cycle of malaria?

Answer 38

Mosquito > sporozoites > human blood > liver > merozoites > RBC > gametocytes > mosquito