What is minimal germicidal concentration of a preservative?

Abdullah

This is MIC and minimal germicidal concentration of formalin.

 MIC means minimum concentration at which microbes can't grow. what does minimal germicidal concentration mean?

PhilGeis

Minimal /lowest concentration, in context of the test ,that rendered all cells nonviable.  No growth after agent was removed - neutralized.

Abdullah

PhilGeis said:

Minimal /lowest concentration, in context of the test ,that rendered all cells nonviable.  No growth after agent was removed - neutralized.

@PhilGeis am i understanding it correct? Both MIC and minimal germicidal concentration is lowest concentration that stops the growth of organisms. So what is the difference? 

PhilGeis

MIC - the cells are alive but are not growing.  If you removed those cells from exposure to formaldehyde and put them in medium without the formaldehyde, they would grow.
Minimal Germicidal concentration.  Those cells are dead.  If you put them in medium without formaldehyde, they would not grow.

Abdullah

PhilGeis said:

MIC - the cells are alive but are not growing.  If you removed those cells from exposure to formaldehyde and put them in medium without the formaldehyde, they would grow.
Minimal Germicidal concentration.  Those cells are dead.  If you put them in medium without formaldehyde, they would not grow.

@PhilGeis so if the MIC is 125 ppm formaldehyde to prevent growth of a bacteria, shouldn't it be more than 125ppm not less to be able to kill that bacteria? 

Chart is from the book: cosmetic Microbiology: a practical approach

PhilGeis

Right - does seem confusing.couternintuitive.  These were different tests and one has to take published data as they are.
Didn't inlcude that and other specific testing data in 3rd ed. for that reasoin.

Abdullah

PhilGeis said:

Right - does seem confusing.couternintuitive.  These were different tests and one has to take published data as they are.
Didn't inlcude that and other specific testing data in 3rd ed. for that reasoin.

Thanks 

On type of tests, one is serial dilution test and another is suspension test. any comments on them that what do they mean here and what is the difference? 

Mayday

Was the serial dilution test performed on agar plates but the suspension test performed in vials? I see the microbe concentration was equalized to 10 cfu/ml.

If on culture plates, could the medium be providing some level of structural protection from the formaldehyde? Like how HPMC/MC/CMC can reduce effectiveness of Phenoxyethanol by shielding (particularly over 0.5%). Or PEG-4000 and methylparaben.

PhilGeis

I haven't notes from the 2006 book.   Agree with Abdullah, does look odd.

Mayday - this does speak to the necessity of testing in product context and the limited significance of supplier data.   That's why it's not in 3rd ed that just includes target levels.