Antimicrobial Effectiveness Testing

Antimicrobial preservatives are substances added to some pharmaceutical and personal care products to protect them from microbial growth or from microorganisms that are introduced inadvertently during or after the manufacturing process. Common types of preservatives are parabens, propionates, phenoxyethanol, imidazolidinyl urea and methylisothiazolinone. Due to the toxic nature of these substances, the concentration of the preservative must be shown to be both effective against microorganisms and below a level that is toxic to human beings.

In a standard Antimicrobial Effectiveness Test according to USP <51> the product to be tested is divided and inoculated separately with five microorganisms: Escherichia coli (a gram negative fermentor), Pseudomonas aeruginosa (a gram negative non-fermentor), Staphylococcus aureus (a gram positive cocci), Candida Albicans (a yeast), and A. brasiliensis (a mold). The inoculum level is targeted to have between 105 and 106 colony forming units per ml or gram of the product in Categories 1, 2 and 3, and between 103 and 104 colony forming units per ml of the product in Category 4.

At intervals of 7, 14, and 28 days, the product is sampled and the target organism enumerated. For each category of product, there is an unique criteria for the log reduction in microorganisms necessary for the antimicrobial agent in the product to be considered effective.

Deibel Laboratories has a strong history of successful Antimicrobial Effectiveness testing, for all categories of product. We can also inoculate the product with other microorganisms or in house isolates of organisms recovered from a client’s environmental monitoring program. In fact, challenging a product with strains of bacteria which exist in niche environments in the manufacturing facility would be considered advantageous to fully ascertain the products ability to withstand any contamination during the blending and filling process. In house isolates are notoriously more resistant to antimicrobial substances and may be able to survive when other ATCC versions of the standard USP recommended organisms above would be controlled.