Assesses ability of bacteria to penetrate through dressings using S. marcescens as the challenge organism (very small and highly motile so provides a harder challenge). Other organisms such as MRSA and E. coli can be used in the test.

Samples must be provided sterile so contaminants do not outgrow the test organism.

Wet-wet testing is suitable for dressings which have a film. Called wet-wet as the dressing has broth on both sides of the equipment. Wet-wet testing is the most challenging of the 3 types of bacterial barrier testing.

Wet-dry involves placing droplets of culture in broth (“wet”) on the back of a dressing which has been placed face down on an agar plate (“dry”). If the bacteria are able to pass through the dressing it fails the test.

Dry-dry (rarely used) involves growing the test organism on an agar plate in a cross then clamping the dressing between that and a sterile agar plate. The results will be the same as for wet-dry.