Measurement of Antibacterial Activity of Textile Materials Using the Parallel Streak Method

The AATCC 147 method, commonly known as the Parallel Streak method, is designed to qualitatively evaluate the antibacterial activiry of diffusable antimicrobial agents on treated textile materials. In other words, it tests the ability of the treated textile to inhibit the growth of microorganisms, to be Bacteriostatic. This method allows you to roughly estimate the activity and efficacy against different concentrations of the microorganisms. 


Summary of the AATCC 147 Test
  • The test microorganism is prepared, usually by growth in a liquid culture medium. Per the method, two representative microorganisms are specified, S. aureus and K. pneumoniae
    • Depending on the Study Sponsors testing objectives and products end goals, Microchem Laboratory can modify the test method to better fit your testing objectives, as mentioned in the method. This includes testing against more clinically and product relevant microorganisms.
  • Prior to initiating the test, sterilized molten growth agar is poured into sterile petri dishes and allowed to solidify completely before inoculating.
  • The suspension of test microorganism is then standardized by dilution in sterile distilled water.
  • Using a sterile inoculating loop, one loopfull of the diluted inoculum suspension is used to streak 5 consecutive streaks, spaced evenly apart, without refilling the loop, onto the solidified growth agar.  This allows for 5 parallel streaks varying in concentration.
  • Samples, which have been cut to be rectangular in shape and measuring 25 x 50 mm, as recommended by the method, are evenly placed across the five parallel streaks.
  • A parallel untreated test sample is also cut and tested alonside Treated Test Samples.
  • Gentle pressure is placed on the samples onto the agar in order to ensure contact of the entire test sample and the inoculated agar.
  • Treated and Untreated (Control) Samples, on the inoculated agar agar, are then incubated at the microorganism specific temperature and incubation period, to ensure optimal growth. 
  • All microbiological assays run at Microchem Laboratory are performed with the necessary parallel controls to provide adequate comparisons at both the start of the test as well as after the contact time.
  • Post incubation, the plates are removed from the incubator and and measurements on either side of the samples, if present, are averaged and a method specified formula is used to calculated its the Zone of Inhibition. 

Strengths of the AATCC 147 Test
  • The method is relatively quick easy to perform.
  • The method offeres a quick and easy alternative to the more involved AATCC 100, making it a great screening tool.
  • The method is useful for testing against both Gram Positive and Gram Negative Microorganisms.
  • Due to its simplicity, it is very reproducible.
  • The method provides estimates of efficacy against different concentrations of microorganim, therfore providing a increased degree of sentivity. 
  • With the inclusion of a laundering step, prior to testing samples, the method allows for evaluation of resiual efficacy.
  • The method offers options as to what microorganisms to test against, depending on the study sponsors testing objectives and products end use. 

Weaknesses of the AATCC 147 Test
  • The method is not quantitative, and therfore only provides qualitative data.
  • The method does not include a "pass/fail" criterion for the calculated levels of antimicrobial activity observed in test samples.
  • The method is not suitable for test substances with technologies that are non-diffusable. 

The AATCC 147 is a fast, qualitative means to measure the ability of an antimicrobial textile to inhibit the growth of microorganisms.

Microchem Laboratory was built around antimicrobial innovation and antimicrobial research and development. If your company is interested in textiles for their ability to inhibit the growth of microorganisms, the AATCC 147 may be a great place to start.

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An EPA and FDA GLP-compliant testing organization staffed by skilled, experienced microbiologists and chemists.  Microchem can help speed your project to completion.

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