IC1 eL

Question 1

Possible source of normal flora

Answer 1

• Maternal genital tract
• Skin
• Mouth and pharynx
• Air-borne organisms
• Environment & food

Question 2

Normal sterile sites

Answer 2

• CNS
• CVS
• Lower respiratory tract
• Bone, Joint
• Genitourinary tract, except urethra & vagina

Question 3

Common pathogens for bacterial meningitis

Answer 3

• Streptococcus pneumoniae
• Neisseria meningitidis
• Haemophilus influenzae
• Streptococcus agalactiae
• Listeria monocytogenes

Question 4

Common pathogens for sinusitis

Answer 4

• Streptococcus pneumoniae
• Haemophilus influenzae

Question 5

Common pathogens for otitis media

Answer 5

• Streptococcus pneumoniae

Question 6

Common pathogens for community-acquired pneumonia

Answer 6

• Streptococcus pneumoniae
• Haemophilus influenzae
• Staphylococcus aureus

Question 7

3 categories of community-acquired pneumonia

Answer 7

• Community acquired
• Atypical
• Tuberculosis

Question 8

Common pathogens for sexually transmitted diseases

Answer 8

• Chlamydia trachomatis
• Neisseria gonorrhoea
• Treponema pallidum
• Ureaplasma urealyticum
• Haemophilus ducreyi

Question 9

Common pathogens for Upper resp tract infection

Answer 9

• Streptococcus pyogenes
• Haemophilus influenzae

Question 10

Common pathogens for urinary tract infection

Answer 10

• E. coli
• other Enterobacteriaceae
• Staph. saprophyticus
• Pseudomonas aeruginosa

Question 11

6 types of lab diagnostics

Answer 11

1. Microscopy e.g. gram stain, acid-fast
2. Culture e.g. broth/ agar/ growth condition
3. Biochemistry e.g. specific nutrients/ enzymes
4. Serologic/ immunologic diagnostics e.g. to detect antigen/ antibodies
5. Molecular/ nucleic acid-based diagnostics e.g. PCR
6. Mass spectrometry

Question 12

Usual timeline from specimen collection to identification, culture and susceptibility results

Answer 12

Day 1: Gram stain
Day 2-3: Culture bacteria
Day 3-4: Identify bacteria & AST

Question 13

Macroscopic appearance for Pseudomonas aeruginosa

Answer 13

blue-green colonies, grape-like odour

Question 14

Macroscopic appearance for Staphylococcus aureus

Answer 14

golden colonies

Question 15

What is MacConkey’s Agar used for?

Answer 15

To isolate gram negative enteric bacteria and differentiates lactose fermenting and non-lactose fermenting gram negative bacteria.

Question 16

Colour for lactose vs non-lactose fermenting colonies

Answer 16

Lactose: Pink
Non-lactose: Colourless

Question 17

Examples of lactose fermenting colonies

Answer 17

• E.coli
• Enterobacter spp.
• Klebsiella spp.

Question 18

Which streptococcus causes complete haemolysis?

Answer 18

beta-haemolytic streptococcus

Question 19

Which streptococcus causes partial haemolysis?

Answer 19

alpha-haemolytic streptococcus

Question 20

Which streptococcus causes no haemolysis?

Answer 20

gamma-haemolytic streptococcus

Question 21

Example of gram positive cocci in clusters

Answer 21

Staphylococcus spp

Question 22

Example of Gram positive diplococcus

Answer 22

Streptococcus pneumoniae

Question 23

Example of Gram positive cocci in chains

Answer 23

Streptococcus

Question 24

Example of Gram negative rod

Answer 24

E. coli

Question 25

Colour for gram-negative and gram-positive

Answer 25

Gram-positive: Purple Gram-negative: Pink

Question 26

Key steps in gram stain

Answer 26

1. Fixation 2. Crystal violet 3. Iodine treatment 4. Decolourisation 5. Colour stain with Safranin

Question 27

Examples of non-fermenters

Answer 27

Pseudomonas aeruginosa, Acinetobacter baumanii

Question 28

What do fermenters mean?

Answer 28

refers to ability to ferment sugar/carbohydrate

Question 29

Which bacteria would test catalase +ve?

Answer 29

Staphylococcus

Question 30

How to differentiate btw S. aureus and S. epidermidis?

Answer 30

Coagulase test. - Coagulase +ve staphylococcus (S. aureus) - Coagulase –ve staphylococcus (S. epidermidis)

Question 31

Observation for a coagulase -ve test

Answer 31

Bacteria remain dispersed and no clumping

Question 31

How to differentiate btw P. aeruginosa and E. coli?

Answer 31

Oxidase test. Oxidase +ve GNR (eg P. aeruginosa) Vs Oxidase -ve GNR (eg E. coli)

Question 32

Observation for oxidase +ve result

Answer 32

Purple colour appears

Question 32

Principles of Minimum inhibitory concentration (MIC)

Answer 32

The lowest concentration of an antimicrobial that prevents visible growth of an organism

Question 33

How is MIC determined?

Answer 33

Carry out agar e.g. E-test/ broth dilution test

Question 34

Another method for AST apart from MIC

Answer 34

Kirby-Bauer disk diffusion method

Question 35

How is the Kirby-Bauer disk diffusion method carried out?

Answer 35

- organism is streaked onto the agar - Antibiotics are added to the plate - incubate - zone of inhibition observed is used to determine susceptibility Diameter of zone of inhibition corresponds/ correlates with antimicrobial activity

Question 36

What are breakpoints?

Answer 36

Critical concentrations which predict susceptibility/resistance (interpretive criteria for S,I,R)

Question 37

MIC > breakpoint -> S/ I/ R?

Answer 37

R

Question 38

MICs of different drugs against a particular organism are not directly comparable (Y/N)

Answer 38

Y

Question 39

Lowest MIC on a AST report indicate the best treatment option. (Y/N)

Answer 39

not necessarily