How do you find the D and F value for Biological indicator,
in the autoclave?
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Answer Posted / mohit bibra
THE AUTOCLAVE USED FOR THE STERLISATION METHODS IS SET AT
TEMPERATURE OF 121.1◦C.
1)TO FIND THE F VALUE(WHICH REPRESENTS A MEASURE OF THE
CAPACITY OF A HEAT PROCESS TO REDUCE THE NUMBER OF SPORES
OR VEGETATIVE CELLS OF A GIVEN ORGANISM PER CONTAINER)OF AN
BIOLOGICAL INDICATOR THE NUMBER OF THE CELLS IN THE INITIAL
POPULATION BEFORE KEEPING IN THE AUTOCLAVE AND THE NUMBER
OF THE CELLS IN THE FINAL POPULATION AFTER TAKING OUT OF
THE AUTOCLAVE ARE COUNTED USING A HEMATOCYTOMETER AND THE F
VALUE IS CALCULATED BY THE FORMULA
F0 = Dr (log a − log b),
2)TO CALCLATE THE D VALUE(WHICH REPRESENTS THE TIME
REQUIRED TO KILL THE 90% OF THE POPULATION)THE ININTIAL
NUMBER OF THE CELLS AND THE FINAL NUMBER OF THE CELLS ARE
COUNTED AS STATED ABOVE AND THEN A SEMI-LOGARITHMIC GRAPH
BETWEEN THE NUMBER OF THE CELLS(ON THE Y-AXIS LOGARTHMIC
SCCALE)AND TIME(ALONG THE X-AXIS ON NORMAL SCALE)IS
PLOTED.THE POINT AT WHICH THE 90% OF THE POPULATION DIES
NOTE THAT TEMPERATURE FRROM THE GRAPH WHICH REPRESENS THE D-
VALUE.
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