Diagnosis Of Infectious Diseases

Question 1

Give examples of artificial media

Answer 1

Solid agar media
Liquid culture media
Tissue culture

Question 2

For pathogens, how are they categorised?

Answer 2

Hazardous groups 1-4

Question 3

What hazard group do S. aureus, Strep. pyogenes and Vibrio cholerae belong to?

Answer 3

Hazard group 2

Question 4

What hazard group do Bacillus anthracis, Hepatitis B virus, Mycobacterium tuberculosis, Salmonella typhi and West Nile Virus belong to?

Answer 4

Hazard group 3

Question 5

What does Mycobacterium tuberculosis stand for?

Answer 5

TB

Question 6

What is another name for Salmonella typhi?

Answer 6

Typhoid fever

Question 7

What is another name for West Nile Virus?

Answer 7

Encephalitis

Question 8

What hazard group do Ebola virus, Dengue virus, Haemorrhagic viruses and Variola virus belong to?

Answer 8

Hazard group 4

Question 9

What is another name for Variola virus?

Answer 9

Small pox

Question 10

What are the different types of artificial media used for?

Answer 10

Used to classify pathogens

Question 11

What does Mycobacterium leprae cause?

Answer 11

Leprosy

Question 12

How can you directly diagnose a sample from a patient?

Answer 12

Culture microbe from a specimen

Question 13

How can you indirectly diagnose a sample from a patient?

Answer 13

Find evidence of an antibody response in a patient’s serum

Question 14

What 6 things are important in taking a specimen?

Answer 14

• Pre treatment
• Appropriate site
• Enough material
• Appropriate container
• Rapid transport
• Transport medium

Question 15

What 7 types of specimens are there?

Answer 15

• Swabs
• Urine
• Faeces
• Sputum
• CSF
• Blood (culture)
• Blood (serum)

Question 16

When should you collect specimens?

Answer 16

• before antibiotics
• depends on disease e.g. malaria take sample at spiking fever - parasites into blood
• serology - second sample 2 weeks later to look for antibody titres

Question 17

What information needs to be given with the sample?

Answer 17

• type of specimen/site
• date and time of collection
• date of onset of illness
• age/gender
• details of illness/history

Question 18

What difference is there in infected urine and CSF?

Answer 18

cloudy

Question 19

What difference might there be in sputum?

Answer 19

pus in sputum

Question 20

What general bacteriology diagnostic tests are there?

Answer 20

• microscopy
• culture
• identification
• antimicrobial susceptibility testing

Question 21

What 7 kinds of non-cultural techniques/microscopy are there?

Answer 21

• wet preps
• gram stain
• acid fast stain
• fluorescent antibody stains
• phase contrast microscopy
• dark field microscopy
• inverted microscopy

Question 22

What colour is the acid fast stain of sputum?

Answer 22

pink

Question 23

Acid fast stain - what is a good pathogen that stains?

Answer 23

TB

Question 24

Examples of pathogens that are stained: dark field microscopy of spirochaetes

Answer 24

lyme disease

syphillis

Question 25

Examples of pathogens that are stained: phase contrast

Answer 25

yeast

Question 26

Examples of pathogens that are stained: inverted microscope

Answer 26

tissue culture

Question 27

What other non-cultural techniques are there?

Answer 27

- serology | - molecular methods - gene probes

Question 28

What is serology?

Answer 28

look for an antibody response to the organism over a couple of weeks

Question 29

What different serology techniques are there?

Answer 29

- agglutination (plate/slide) - immunofluorescence - complement fixation - ELISA

Question 30

What can an agglutination plate be used to diagnose?

Answer 30

Flu

Question 31

How does ELISA work?

Answer 31

Colour change - makes it easier to identify - use plate reader

Question 32

When would you use PCR?

Answer 32

- determining outbreaks - quick result e.g. TB - probe for toxin e.g. cholera toxin in faeces

Question 33

When is TB PCR used?

Answer 33

- developed counties - to look for drug resistant strains - result within hours

Question 34

What is the downside to TB PCR?

Answer 34

expensive

Question 35

What types of non-selective media are there?

Answer 35

- blood agar - chocolate agar - liquid media, as in blood cultures

Question 36

What typically grows on chocolate agar?

Answer 36

- more 'fastidious' pathogens | e. g. Neisseria, Haemophilus - usually incubated in CO2

Question 37

How are organisms grown in liquid media?

Answer 37

- one anaerobic - one aerobic - one subcultured

Question 38

What is selective media?

Answer 38

Contain substances which inhibit the natural flora or select for certain organisms

Question 39

Is Maconkey selective or non-selective?

Answer 39

Selective

Question 40

What does Maconkey contain?

Answer 40

Bile salts and lactose

Question 41

Why does Maconkey contain bile salts and lactose?

Answer 41

Select for gut organisms

Question 42

What sites is Maconkey selective for?

Answer 42

abdominal wounds

Question 43

What specimens is XLD agar selective for?

Answer 43

faeces

Question 44

Is XLD selective or non-selective

Answer 44

selective

Question 45

what does XLD contain?

Answer 45

xylose, lysine and deocycholate

Question 46

How do you grow genital specimens?

Answer 46

grow on chocolate with antibiotics to select for particular organism

Question 47

if the organism grown on maconkey ferments lactose, what colour does the agar change?

Answer 47

red

Question 48

if the organism grown on maconkey does not ferment lactose, what colour does the agar change?

Answer 48

pinky

Question 49

what is an example of an organism that maconkey is selective for, and ferments lactose?

Answer 49

e.coli

Question 50

what does maconkey differentiate between?

Answer 50

lactose fermenters and non-lactose fermenters

Question 51

what colour is shigella on XLD?

Answer 51

pink

Question 52

what colour is salmonella on HEK?

Answer 52

blue

Question 53

what final ID tests are there?

Answer 53

API (biochemical) | agglutination e.g. staph ID or strep grouping

Question 54

coagulase test - is staph aureus positive or negative?

Answer 54

positive

Question 55

coagulase test - is staph epidermidis positive or negative

Answer 55

negative

Question 56

if the suspected pathogen is a staph, what media should be used?

Answer 56

mannitol salt

Question 57

if the suspected pathogen comes from an abdominal wound swab, what media should be used?

Answer 57

maconkey

Question 58

if the suspected pathogen comes from a skin sample, what media should be used?

Answer 58

mannitol salt?

Question 59

if mannitol salt turns yellow, what is it likely to be?

Answer 59

staph aureus

Question 60

if mannitol salt turns pink, what is it likely to be?

Answer 60

staph epidermidis, but this is probably not the pathogen

Question 61

2 examples of anaerobes

Answer 61

clostridium perfringens | bacteroides fragilis

Question 62

for urine specimens, what does a dipstick measure?

Answer 62

sugar in urine

Question 63

why do a microscopy-cell count of a urine sample?

Answer 63

count white blood cells for a sign of infection

Question 64

if the dipstick is positive for nitrates and proteins, what should you do?

Answer 64

culture the sample

Question 65

how can you identify bacteria?

Answer 65

- size - colour - shape - biochemical tests - antibiotic sensitivity to aid ID

Question 66

would you gram stain a faeces sample? why?

Answer 66

no - too many organisms

Question 67

what is the problem with gram staining e.coli and salmonella?

Answer 67

they look the same!

Question 68

what tests do you do on faeces samples?

Answer 68

- culture | - microscopy for parasites

Question 69

what media should you use for faeces samples? what should they contain?

Answer 69

need bile salts - XLD - HE - maconkey isn't very selective

Question 70

for a sputum sample, what tests should you do?

Answer 70

- microscopy - culture look at the microscopic appearance - does it contain pus or is it just saliva?

Question 71

if you are looking for TB in a sputum sample, what tests should you request?

Answer 71

specialist agar | separate TB request

Question 72

when collecting a CSF sample, how should you collect it and what should you do with it?

Answer 72

3 separate tubes tubes 1 and 2 to cytology 3 to microbiology - less chance of contamination

Question 73

when you suspect meningitis in a patient, what tests should you do?

Answer 73

microscopy gram stain culture to check antibiotics

Question 74

what tests do you do after culturing the organism?

Answer 74

- identification - need a pure culture - biochemical tests (APIs), lactose fermentation - antigen/antibody tests (usually latex beads that clump together - molecular methods - DNA fingerprinting etc

Question 75

how can you test viruses?

Answer 75

- electron microscopy - immunofluorescence microscopy - culture in tissue culture - growth in eggs