Microbiology Laboratory Turkey

Mikrobiyoloji Ile Ilgili Tüm Konuların Kısa ve Öz Anlatımları. Microbiology Lab Information.

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MicroLab

5 Kasım 2018 Pazartesi

OPTOCHIN TEST

OPTOCHIN TEST 

Susceptibility to optochin (ethylhydrocupreine hydrochloride) is a simple and reliable method of differentiating Streptococcus pneumoniae from other alpha-haemolytic Streptococci.


TEST PRINCIPLE
The optochin test detects an organisms susceptibility to the chemical optochin ethylhydrocupreine hydrochloride). The chemical tests the fragility of the bacterial cell membrane and causes Streptococcus pneumoniae to lyse due to changes in surface tension.
The optochin test is widely used in the form of filter paper discs, impregnated with ethylhydrocupreine hydrochloride which are applied directly to inoculated plates before incubation.

REAGENTS AND EQUIPMENT
Filter paper discs impregnated with 5µg of ethylhydrocupreine hydrochloride
Bacteriological straight wire/loop (preferably nichrome) or disposable alternative

Quality Control Organisms
Positive control: Streptococcus pneumoniae 
Negative control: Streptococcus viridans 


METHOD/PROCEDURE AND RESULTS
Pure colony
  • Streak a blood plate with the organism to be tested
  • Place an optochin disc in the centre of the inoculum
  • Incubate at 35-37o C for 18-24h in 5% CO2
  • Examine for zones of inhibition 

Specimen

  1. Streak the specimen onto a blood plate
  2. Place an optochin disc on the edge of the primary inoculum
  3. Incubate at 35-37oC for 18-24h in 5% CO2
  4. Examine for zones of inhibition 


Positive result 
Zone of inhibition of ≥5mm radius from  the edge of the disc eg test  organism is S. pneumoniae
Negative result 
No zone of inhibition, or a zone <5mm  radius from the edge of the  disc eg test organism is not  S. pneumoniae.


PRECAUTIONS/LIMITATIONS OF PROCEDURE
Some “viridans” streptococci may produce a small zone of inhibition. Equivocal results should be confirmed using the bile solubility test or by the use of a commercial kit.
False-negatives may be reported if cultures are incubated in high concentrations of CO2. 
Occasional strains of optochin resistant S. pneumoniae have been reported.

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