Antimicrobial Efficacy Testing ASTM E2180

Scope:

ASTM E2180 test standard is used to quantitatively test the antimicrobial effectiveness of incorporated agents in flat hydrophobic or polymeric materials. Other microorganisms like yeast and fungal conidia can be also determined using this test. To determine the antimicrobial activity, proper contact of microbial to the surface of antimicrobial is essential. It is difficult to spread the micro-organisms on hydrophobic surfaces like polymers. The ASTM E2180 test overcomes this obstacle by incorporating the test inoculum into an agar slurry that provides good contact of microorganisms with antimicrobial-treated hydrophobic surfaces.

Test Procedure:

A thin layer of the microorganisms inoculated agar slurry is used for the ASTM E2180 test. This agar slurry provides full contact between the polymeric or hydrophobic surfaces and the bacterial cultures. Then, the inoculated agar slurry is spread onto the test samples, and minimum triplicate samples are used for the untreated control material. The designated incubation time period is 24 hours. Then, surviving micro-organisms are recovered by eluting the inoculated agar slurry via the test substrate into neutralizing broth. After that, dilution series are made and then plated, followed by an incubation period of 48 hours at a specified temperature. Then, the agar plates are removed from the incubator, and bacterial colonies from each dilution series are computed and noted. To calculate the percent reduction of bacteria, a comparison of the treated vs. untreated samples is made. In some cases, the exposure periods might be increased to 96 hours if there are more resistant micro-organisms. Usually, Pseudomonas aeruginosa or Klebsiella pneumoniae and Staphylococcus aureus are used for the test. Other microorganisms such as yeast or fungi can also be used for the test using the same procedure.

Sample size:

The samples are 8 10 inches pieces. The squared samples of  3.03.0 inches are for the treated and control test materials. An untreated control sample is also necessary for the test. 

Data:

The results of the test are expressed by the relation;

For log expression: geometric mean = (Log R1 +Log R2+Log R3)/3

where;

R = number of microorganisms recovered from the incubation period untreated or incubation period treated samples.

The percent expression is given by;

R(%)=Nu-Na Nu 100

where;

Nu= the antilog of the geometric mean of micro-organisms recovered from each incubation period (untreated samples)
Na= the antilog of the geometric mean of micro-organisms recovered from each incubation period (treated samples)