Variations of B. atrophaeus
The ATCC (American Type Culture Collection) recommends B. atrophaeus no. 9372 for monitoring sterilization processes.
Depending on the media growth B. atrophaeus ATCC 9372 may occur in 2 variations (= colours):
· Var. niger: Creme beige or black
· Var. globigii: orange or black
It has been found out that B. atrophaeus var. niger turns into B. atrophaeus var. globigii. The black variation is achieved under specific culture conditions of var. niger or of var. globigii. All 3 colours are suitable for monitoring sterilization processes.
The orange version commonly known as globigii is produced by taking orange dissociated selected germs and growing them under specific conditions. However, in time they turn back to the creme beige version, known as var. niger version.
Therefore it does not make sense to differentiate between the two variations when used for monitoring of sterilization processes. The only important criterion for a given strain is D-value and population – nothing else.
We know that in a lot of procedures, old standards and pharmacopeias a specific strain selection is required. This requirement has been established due to the (wrong) belief that a certain strain has a certain resistance. This is not correct. We are even able to manipulate the resistance of identically the same strains by a factor of 5 to 10.
The resistance of a biological indicator is determined by:
lg population x D-value = FBIO-value
Only this FBIO-value is the characteristic for the total resistance. Therefore the colour (= variation) of B. atrophaeus is without any significance for monitoring the sterilization process.