6 Laboratory Diagnosis Flashcards
Two-way communication
Specimens and completed forms arrive Register the specimen Microscopy Culture Antibiotic sensitivity testing Final report
what is methods of bacterial diagnosis - serology used for
> for antigens e.g. latex agglutination
> for antibodies
molecular methods of bacterial diagnosis examples
PCR, sequencing
MALDI-TOF MS -bacterial diagnosis
matrix-assisted laser desorption/ionisation-time of flight mass spectrometry
Gastrointestinal infection types
bacterial
viral
parasites
bacterial GI infection examples
Campylobacter spp.
viral GI infection examples
rotavirus
parasites GI infection examples
Cryptosporidium sp.
GI specimens
Liquid stool samples (aim for 3 specimens – especially for ova/cysts/parasites ‘OCP’) NOT vomit
GI examination of stool sample
- macroscopic appearance
- microscopy for ova, cysts and parasites
- EIA
- PCR
- selective culture
macroscopic appearance GI examination
formed or not formed, blood-stained, ‘rice-water’
microscopy GI examination
with concentration-spun through filter to remove faecal matter
EIA GI examination
Clostridium difficile toxins
viruses (adenovirus and rotavirus)
ELISA for norovirus
PCR GI examination
Clostridium diffiicle toxin gene
norovirus
selective culture GI examination
for specific bacterial pathogens, stool contains mostly commensal bacteria – detecting pathogen is difficult
what is the enzyme immunoassay for toxin like
fast
highly specific
BUT poor sensitivity
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
Salmonella / Shigella examination of stool sample what is used
> selective and indicator
> prior enrichment using Selenite broth
what is usually used for shigella
DCA as relatively low selectively
how are shigella and salmonella colonies usually identified in stool examination
using slide agglutination and biochemical tests
what plates are used in examination of stool samples – selective culture and enrichment - Campylobacter
agar containing vancomycin, polymyxin B and trimethoprim
how are the campylobacter colonies identified in stool sample examination
colonies identified by oxidase test and Gram film appearance
what plate is used in examination of stool samples – selective culture and enrichment - Vibrio cholerae
thiosulphate-citrate-bile-salt-sucrose (TCBS) agar
what is Vibrio cholerae enriched in for stool sample examination
alkaline peptone water
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
