6 Laboratory Diagnosis Flashcards by Yasmin Yau

Two-way communication

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

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what is methods of bacterial diagnosis - serology used for

> for antigens e.g. latex agglutination

> for antibodies

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molecular methods of bacterial diagnosis examples

PCR, sequencing

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MALDI-TOF MS -bacterial diagnosis

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

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Gastrointestinal infection types

bacterial
viral
parasites

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bacterial GI infection examples

Campylobacter spp.

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viral GI infection examples

rotavirus

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parasites GI infection examples

Cryptosporidium sp.

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GI specimens

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

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GI examination of stool sample

macroscopic appearance
microscopy for ova, cysts and parasites
EIA
PCR
selective culture

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macroscopic appearance GI examination

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

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microscopy GI examination

with concentration-spun through filter to remove faecal matter

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EIA GI examination

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

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PCR GI examination

Clostridium diffiicle toxin gene

norovirus

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selective culture GI examination

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

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what is the enzyme immunoassay for toxin like

fast
highly specific
BUT poor sensitivity

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

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

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Salmonella / Shigella examination of stool sample what is used

> selective and indicator

> prior enrichment using Selenite broth

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what is usually used for shigella

DCA as relatively low selectively

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how are shigella and salmonella colonies usually identified in stool examination

using slide agglutination and biochemical tests

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

agar containing vancomycin, polymyxin B and trimethoprim

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how are the campylobacter colonies identified in stool sample examination

colonies identified by oxidase test and Gram film appearance

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

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

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what is Vibrio cholerae enriched in for stool sample examination

alkaline peptone water

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effect of Vibrio cholerae on TCBS

ferments the sucrose and makes yellow colonies

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

CIN agar

what is the typical appearance of yersinia spp.

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

Urinary tract infection | common in

women and children

effect of recurring UTI in children

recurrent infections in children may cause renal damage

UTI symptoms

dysuria, frequency, urgency

common organisms for UTI infection

Staphylococci | Candida albicans

UTI samples

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

midstream urine (MSU) UTI sample

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

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

young children, contamination is a problem

suprapubic aspirate (SPA) UTI sample

sterile, any growth is usually significant

catheter urine (CSU) UTI sample

often colonised with bacteria

nephrostomy/ureteric urine UTI sample

any growth from fresh sample usually significant

UTI examination - dipstick used for

blood, nitrite, leukocyte esterase

UTI examination - manual microscopy

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

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

Haemitura

Urine examination tests

semi-quantitative culture | antibiotic sensitive tests

what agar is used in urine

using CLED agar or Chromogenic media

what does urine examination differentiate

common urinary pathogens to family/genus level

what does a pure culture indicate in a urine examination

infection

what does mixed growth in a urine examination indicate

contamination

types of respiratory tract infection

- upper respiratory tract infection (URTI) | - lower respiratory tract infection (LRTI)

upper respiratory tract infection (URTI) diseases

sinusitis | pharyngitis

lower respiratory tract infection (LRTI) diseases

bronchitis | pneumonia

what is LRTI usually

bacterial

Diagnosis of respiratory tract infection: specimens

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

where should a throat swab for RTI be taken from

pharnyx

when may sputum specimen be taken

may be obtained after chest physiotherapy

what is bronchoalveolar lavage (BAL) like

> invasive, but ‘optimum’ specimen

what is urine sample for - detect what

Legionella and pneumococcal antigen detection

what is urine sample detection like

rapid and specific

what does acute and convalescent serum detect

pathogen-specific antibodies

what is acute and convalescent serum like

slow

sputum microscopy - Examination of respiratory samples

> gram stain: pus cells, organisms | > auramine/Ziehl-Neelsen (ZN) stain for Mycobacteria

culture - Examination of respiratory samples what is the sample like

liquefied and diluted (reduces growth of mouth organisms)

Microscopy for TB - what stain is used

auramine staining (UV microscopy)

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

ZN stain

what is Microscopy for TB like

sensitive but not very specific

what must happen to TB culture

specimen decontaminated (e.g. using sodium hydroxide)

what agar is TB culture grown on

solid agar slopes (Lowenstein-Jenson media)

how is liquid culture of TB used

liquid culture using Mycobacteria Growth Indicator Tube (MGIT

Immunofluorescence

using organism-specific monoclonal antibodies linked to a fluorescent dye

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

Infection

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

Contaminated