Preservative Efficacy Testing (antimicrobial Effectiveness Test)

Antimicrobial preservatives are substances added to products to protect them from microbiological growth or from microorganisms that are introduced inadvertently during or subsequent to the manufacturing process. In the case of products packaged in multiple-dose containers, antimicrobial preservatives are added to inhibit the growth of microorganisms that may be introduced from repeatedly withdrawing individual use doses.

Upon determination that a product has been properly neutralized and has very low levels of contamination (< 10 cfu/gram), the user can conduct a Preservative Efficacy Test (PET), sometimes referred to as the Antimicrobial Efficacy Tests. This test is required for all cosmetic and personal care products in the United States and follows the guidelines set forth by USP 51.  Briefly put, the product must be challenged within individual containers, each going through this process separately using one of the five required organisms, which include ATCC established strains of E. coli, S. aureus, P. auruginosa, C. albicans, and A. brasiliensis. The PET assay measures the reduction of a high inoculum (106-107 cfu/g) in the presence of a product containing preservative over 28 days, which also tests the ability of the preservative to prevent a rebound of an organism (re-growth).

The BioLumix Alternative

The procedure utilized allows for an easy estimate of the initial inoculum with a single ready-to-use vial that can replace multiple plates. After the product interaction with inoculated product the system automatically calculates if the appropriate reduction in numbers of organisms was achieved.


The BioLumix system offers the advantage of generation of a one-time standard curve (calibration curve) for the inoculum of each specific organism.  For example, a Calibration Curve is generated for pure culture Staphylococcus aureus ATCC 6538 in the Figure 1.  The inoculum is merely added to a test TAC vial and the corresponding Detection Time is matched to the Calibration Curve.  It is not necessary to complete serial dilutions in tubes followed by plating for colony counts.

Each product is inoculated with a single organism or a pool of organisms. At the sampling intervals (i.e., 7, 14, 28 days) 0.1 ml of the 1:10 dilution of the sample is added to vial.  The BioLumix DT is automatically transferred to log cfu/g from the calibrations curves residing in the software built-into the Instrument.

Upon completion of the PET tests using the BioLumix instrument, a certificate of analysis with a succinct report of the microbiological properties of each product is generated for use at your convenience. This equates to proactive detection of contaminated products, and helps to ensure that minimal resources are spent on production and subsequent recall of said products if they are found to be contaminated.

The system is fully automated (automated data archiving, data maintenance in databases, and automated report generation).  It is paperless, increasing efficiency and saving on disposables, time and space, and best of all the system is immune against product interference.


  • Labor reduction by 75-80% of the labor required for the Petri dish method
  • Less disposable used
  • Faster time to results
  • Good correlation with current methodology

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