AOAC Germicidal Spray Test (GST)

Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) and Health Canada accept data based on AOAC International’s Germicidal Spray Products Test (GSPT) method for product registration. The test organisms required in this semi-quantitative method are Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella enterica.
Glass slides (Fig 1) are used as representative hard, nonporous surfaces after contamination with the test organism and the inocula dried. The carriers are then exposed for a predetermined contact time to a spray of the test formulation. At the end of the contact time, each carrier is separately placed in a tube with a recovery broth containing a suitable neutralizer. After incubation, the broth tubes are examined for turbidity to indicate bacterial growth, and the formulation is declared as having passed or failed the test in accordance with the criteria of the target regulatory agency.
The main steps in this method are summarized in the flowchart below.
For product registration, three production lots of each test formulation are required to be tested against each one of the organisms.
GSPT is a semi-quantitative test with the following limitations:
– Prone yield variable result due to operator- and technique-sensitivity.
– Inoculum drying conditions insufficiently described and this may impact on the level of viable organisms on the carriers.
Ratio between the contaminated area on the carrier surface and volume of the test volume may not be reflective of field conditions.
– Unsuitable for testing virucidal activity.
– The surface of the glass carriers may be too smooth to represent many environmental surfaces.
– No wiping action is included.