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Medical Microbiology > 6 Laboratory Diagnosis > Flashcards

6 Laboratory Diagnosis Flashcards

1
Q

Two-way communication

A 
Specimens and completed forms arrive 
Register the specimen 
Microscopy 
Culture 
Antibiotic sensitivity testing
Final report
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2
Q

what is methods of bacterial diagnosis - serology used for

A

> for antigens e.g. latex agglutination

> for antibodies

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3
Q

molecular methods of bacterial diagnosis examples

A

PCR, sequencing

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4
Q

MALDI-TOF MS -bacterial diagnosis

A

matrix-assisted laser desorption/ionisation-time of flight mass spectrometry

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5
Q

Gastrointestinal infection types

A

bacterial
viral
parasites

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6
Q

bacterial GI infection examples

A

Campylobacter spp.

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7
Q

viral GI infection examples

A

rotavirus

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8
Q

parasites GI infection examples

A

Cryptosporidium sp.

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9
Q

GI specimens

A

Liquid stool samples (aim for 3 specimens – especially for ova/cysts/parasites ‘OCP’) NOT vomit

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10
Q

GI examination of stool sample

A
  • macroscopic appearance
  • microscopy for ova, cysts and parasites
  • EIA
  • PCR
  • selective culture
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11
Q

macroscopic appearance GI examination

A

formed or not formed, blood-stained, ‘rice-water’

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12
Q

microscopy GI examination

A

with concentration-spun through filter to remove faecal matter

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13
Q

EIA GI examination

A

Clostridium difficile toxins
viruses (adenovirus and rotavirus)
ELISA for norovirus

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14
Q

PCR GI examination

A

Clostridium diffiicle toxin gene

norovirus

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15
Q

selective culture GI examination

A

for specific bacterial pathogens, stool contains mostly commensal bacteria – detecting pathogen is difficult

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16
Q

what is the enzyme immunoassay for toxin like

A

fast
highly specific
BUT poor sensitivity

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17
Q

what plates are used in the examination of stool samples – selective culture and enrichment
- Salmonella / Shigella

A

Desoxycholate-citrate (DCA)
OR
Xylose-lysine-desoxycholate (XLD) agar

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18
Q

Salmonella / Shigella examination of stool sample what is used

A

> selective and indicator

> prior enrichment using Selenite broth

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19
Q

what is usually used for shigella

A

DCA as relatively low selectively

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20
Q

how are shigella and salmonella colonies usually identified in stool examination

A

using slide agglutination and biochemical tests

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21
Q

what plates are used in examination of stool samples – selective culture and enrichment - Campylobacter

A

agar containing vancomycin, polymyxin B and trimethoprim

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22
Q

how are the campylobacter colonies identified in stool sample examination

A

colonies identified by oxidase test and Gram film appearance

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23
Q

what plate is used in examination of stool samples – selective culture and enrichment - Vibrio cholerae

A

thiosulphate-citrate-bile-salt-sucrose (TCBS) agar

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24
Q

what is Vibrio cholerae enriched in for stool sample examination

A

alkaline peptone water

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25
Q

effect of Vibrio cholerae on TCBS

A

ferments the sucrose and makes yellow colonies

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26
Q

what plate is used in the examination of stool samples – selective culture and enrichment - Yersinia spp.

A

CIN agar

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27
Q

what is the typical appearance of yersinia spp.

A

typical colonial appearance ‘bull’s eye’ = Y. enterocolitica or pseudotuberculosis

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28
Q

Urinary tract infection

common in

A

women and children

29
Q

effect of recurring UTI in children

A

recurrent infections in children may cause renal damage

30
Q

UTI symptoms

A

dysuria, frequency, urgency

31
Q

common organisms for UTI infection

A

Staphylococci

Candida albicans

32
Q

UTI samples

A
  • midstream urine (MSU
  • ‘clean-catch’
  • suprapubic aspirate (SPA)
  • catheter urine (CSU)
  • nephrostomy/ureteric urine
33
Q

midstream urine (MSU) UTI sample

A

needs to be carefully taken to avoid contamination, >10^5 organisms/ml (semi-quantitative culture) is significant

34
Q

‘clean-catch’ or ‘bag’ urine UTI sample

A

young children, contamination is a problem

35
Q

suprapubic aspirate (SPA) UTI sample

A

sterile, any growth is usually significant

36
Q

catheter urine (CSU) UTI sample

A

often colonised with bacteria

37
Q

nephrostomy/ureteric urine UTI sample

A

any growth from fresh sample usually significant

38
Q

UTI examination - dipstick used for

A

blood, nitrite, leukocyte esterase

39
Q

UTI examination - manual microscopy

A

RBC and WBC using inverted microscope – SPA, nephrostomy, urostomy

40
Q

what does > 10/mm3 RBC in manual microscopy urine examination mean

A

Haemitura

41
Q

Urine examination tests

A

semi-quantitative culture

antibiotic sensitive tests

42
Q

what agar is used in urine

A

using CLED agar or Chromogenic media

43
Q

what does urine examination differentiate

A

common urinary pathogens to family/genus level

44
Q

what does a pure culture indicate in a urine examination

A

infection

45
Q

what does mixed growth in a urine examination indicate

A

contamination

46
Q

types of respiratory tract infection

A
  • upper respiratory tract infection (URTI)

- lower respiratory tract infection (LRTI)

47
Q

upper respiratory tract infection (URTI) diseases

A

sinusitis

pharyngitis

48
Q

lower respiratory tract infection (LRTI) diseases

A

bronchitis

pneumonia

49
Q

what is LRTI usually

A

bacterial

50
Q

Diagnosis of respiratory tract infection: specimens

A
  • throat swab
  • sputum (NOT saliva)
  • tracheal aspirate
  • bronchoalveolar lavage (BAL)
  • nasopharyngeal aspirate (NPA)
  • pernasal swab
  • urine
  • acute and convalescent serum
51
Q

where should a throat swab for RTI be taken from

A

pharnyx

52
Q

when may sputum specimen be taken

A

may be obtained after chest physiotherapy

53
Q

what is bronchoalveolar lavage (BAL) like

A

> invasive, but ‘optimum’ specimen

54
Q

what is urine sample for - detect what

A

Legionella and pneumococcal antigen detection

55
Q

what is urine sample detection like

A

rapid and specific

56
Q

what does acute and convalescent serum detect

A

pathogen-specific antibodies

57
Q

what is acute and convalescent serum like

A

slow

58
Q

sputum microscopy - Examination of respiratory samples

A

> gram stain: pus cells, organisms

> auramine/Ziehl-Neelsen (ZN) stain for Mycobacteria

59
Q

culture - Examination of respiratory samples what is the sample like

A

liquefied and diluted (reduces growth of mouth organisms)

60
Q

Microscopy for TB - what stain is used

A

auramine staining (UV microscopy)

61
Q

what stain in TB microscopyis used to confirm the auramine positive samples

A

ZN stain

62
Q

what is Microscopy for TB like

A

sensitive but not very specific

63
Q

what must happen to TB culture

A

specimen decontaminated (e.g. using sodium hydroxide)

64
Q

what agar is TB culture grown on

A

solid agar slopes (Lowenstein-Jenson media)

65
Q

how is liquid culture of TB used

A

liquid culture using Mycobacteria Growth Indicator Tube (MGIT

66
Q

Immunofluorescence

A

using organism-specific monoclonal antibodies linked to a fluorescent dye

67
Q

what does > 10/mm3 WBC in manual microscopy urine examination mean

A

Infection

68
Q

what does > 10/mm3 Epithelial cells in manual microscopy urine examination mean

A

Contaminated

Medical Microbiology (13 decks)

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