Water Activity Leves Required to Support Microbial Growth Microorganism Type

Water Activity (aw) (Typical Values)





Pseudomonas aeruginosa Bacteria (Gram-negative 0.97

rod)





Bacil us cereus Bacteria (Gram-positive, 0.95

spore forming) Clostridium botulinum Bacteria (Gram-positive, 0.95

spore forming anaerobe) Escherichia coli Bacteria (Gram-negative 0.95

rod)





Salmonel a spp.

Bacteria (Gram-negative 0.95

rod)





Bacil us subtilis Bacteria (Gram-positive, 0.90

spore forming) Saccharomyces cerevisiae Yeast

0.90





Staphylococcus aerus Bacteria (Gram-positive 0.86

coccus)





Aspergillus niger Filamentous fungus 0.77





Zygosaccharomyces rouxii Osmophilic yeast 0.62





Xeromyces bisporus Xerophilic filamentous 0.61

fungus





0.50

No microbial proliferation below this level





USP-Proposed Microbial Limit Testing Strategies Product

Typical Potential Testing

Testing

Type

aw

Contamina Recommended in Recommended in nts

USP <1111> USP <1112> Based on a





Nasal liquid

0.99

Gram-

TAM and TYMC; absence TAM and TYMC; absence inhalant

negative rods of S.aureus and P.

of S.aureus and P.

aeruginosa

aeruginosa





Topical cream 0.97

Gram-positive TAM and TYMC; absence TAM and TYMC; absence bacteria

of S.aureus and P.

of S.aureus and P.

aeruginosa

aeruginosa





Oral liquid

0.90

Gram-positive TAM and TYMC; absence TAM and TYMC

bacteria and

of S.aureus and P.

fungi

aeruginosa





Oral suspension 0.87

Fungi

TAM and TYMC, absence Reduced testing of E.coli





Topical

0.55

None

TAM and TYMC; absence Reduced testing ointment

of S.aureus and P.

aeruginosa





Compressed

0.36

None

TAM and TYMC, absence Reduced testing tablets

of E.coli





Vaginal

0.30

None

TAM and TYMC; absence Reduced testing suppusitories of S.aureus, P.

aeruginosa and C.albicans





Liquid-Filled 0.30

None

TAM and TYMC, absence Reduced testing oral Capsules of E.coli