i am working on gram positive isolates for the identification and isolation of Strep.pneumoniae. so at first i perform the catalase test to exclude staph but after a while i noticed that nearly all of my isolates are catalase positive! so i have some doubts about the accuracy of my proceedure i put one drop of Hydrogen peroxide on a slide then take one colony from the surface of the culture media" blood agar " and emulsify it in the solution. Will the culture media affect the results of the test? should i emulsify the colony in saline or distilled water before mixing with hydrogen peroxide?
Hi Rakhi, Catalase test is standard and should not be affected by the blood agar, however whats the concentration of your hydrogen peroxide, for catalase test you can not just use hydrogen peroxide, for catalase test you hzve to use 3% hydrogen peroxide
You should avoid picking blood agar while taking the Strep. pneumoniae colonies, as mention by Niklas. To id S.pneumoniae can easily identify by seen the type heamolysis on Blood agar (alpha hemolysis), colony appearances (typical type with volcano shape), sensitivity toward Optochin and Co-trimoxazole, bile solubility, PYR and bile esculin.
If you work with pneumococci you shoud avoid to let them longer then 48h at 37°C in CO2. If you want them alive you can let them at room-temperature (20°C)for more than 48 hours in CO2. The problem is the autolysis, it starts in the middle of the colony. Maybe only the staphylococci survived..... I agree with all other answers
Nice greetings from lower austria
Heidelinde Schranz
As it has been mentioned above by the eminent researchers, you should be careful in picking up the tiny colonies of S. pneumoniae from blood agar 2 perform catalase test as you could have false positive results if you took blood with the colony as it contains catalase enzyme. So you should try to pick only the top of the colony. Another precaution while performing catalase test is to pick your colonies with a wooden stick and not the nickel chrome loop as this could also give a false positive result.
Carryout optochin disc test to confirm the identity of Streptococcus pneumoniae. Also, avoid picking some part of the blood agar when picking the bacterial colonies. Use fresh culture of the bacterium as old culture tends to give false-positive results. Finally, ascertain the quality control of your hydrogen peroxide. The above suggestions by other researchers are worth considering also.
Probably the answers might have solved your problem, to carry out different tests for different bacteria you may see guidelines and methods in the book available at the link, it is free to download.
Book Labtop for Microbiology Laboratory
thank you niklas thilo you are right bile solubility is also authentic method.
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