Method for in vitro determination of bacterial filtration efficiency (BFE)

B.1 General

WARNING — Staphylococcus aureus is a pathogen. The relevant national provisions by law and hygienic instructions when dealing with pathogens shall be complied with.

B.2 Principle

A specimen of the mask material is clamped between a six-stage cascade impactor and an aerosol chamber. An aerosol of Staphylococcus aureus is introduced into the aerosol chamber and drawn through the mask material and the impactor under vacuum. The bacterial filtration efficiency (BFE) of the mask is given by the number of colony forming units passing through the medical face mask material expressed as a percentage of the number of colony forming units present in the challenge aerosol. For test apparatus see Figure B.3.

B.3 Reagents and materials

B.3.1 General

B.3.2 and B.3.3 describe commercially available solutions of tryptic soy agar and tryptic soy broth.

Other variants may be suitable.

B.3.2 Tryptic soy agar

Formula/litre

Enzymatic digest of casein 15 g

Enzymatic digest of soybean meal 5 g

Sodium chloride 5 g

Agar 15 g

Final pH 7,3 ± 0,2 at 25 ℃

B.3.3 Tryptic soy broth

Formula/litre

Enzymatic digest of casein 17 g

Enzymatic digest of soybean meal 3 g

Sodium chloride 5 g

Dipotassium phosphate 2,5 g

Dextrose 2,5 g

Final pH 7,3 ± 0,2 at 25 ℃

B.3.4 Peptone water

Formula/litre

Peptone 10 g

Sodium chloride 5 g

Final pH 7,2 ± 0,2 at 25 ℃

B.3.5 Culture of Staphylococcus aureus ATCC 6538, growing on tryptic soy agar slants.