ASTM G22-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G22 − 23
Standard Practice for
Determining Resistance of Plastics to Bacteria
This standard is issued under the fixed designation G22; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 Selection of suitable specimens for determination of
pertinent properties,
1.1 This practice covers two procedures, A and B, for
3.1.2 Inoculation of specimens with suitable organisms,
determining the effect of bacteria on the properties of plastics
3.1.3 Exposure of inoculated specimens under conditions
in the form of molded and fabricated articles, tubes, rods,
favorable to growth,
sheets, and film materials. Procedure B provides a more
3.1.4 Examination and rating for visual growth, and
extensive contact between the test bacteria and the specimens
3.1.5 Removal, sterilization, and evaluation of specimens.
than does Procedure A. Changes in optical, mechanical, and
electrical properties may be determined by the applicable
NOTE 1—Since the procedure involves handling and working with
bacteria that may be capable of infecting man, it is essential that personnel
ASTM methods.
trained in microbiology perform the portion of the procedure involving
1.2 The values stated in SI units are to be regarded as the
handling of bacterial organisms and inoculated specimens.
standard.
4. Significance and Use
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4.1 The resin portion of plastic materials is usually resistant
responsibility of the user of this standard to establish appro-
to bacteria, in that it does not serve as a carbon source for the
priate safety, health, and environmental practices and deter-
growth of bacteria. It is generally the other components, such
mine the applicability of regulatory limitations prior to use.
as plasticizers, lubricants, stabilizers, and colorants that are
1.4 This international standard was developed in accor-
responsible for bacterial attack on plastic materials. It is
dance with internationally recognized principles on standard-
important to establish the resistance of plastics to microbial
ization established in the Decision on Principles for the
attack when plastics are used under conditions of high tem-
Development of International Standards, Guides and Recom-
perature and humidity favorable for such attack.
mendations issued by the World Trade Organization Technical
4.2 The effects to be expected are:
Barriers to Trade (TBT) Committee.
4.2.1 Surface attack, discoloration, and loss of transmission
(optical).
2. Referenced Documents
4.2.2 Removal of susceptible plasticizers, modifiers, and
2.1 ASTM Standards:
lubricants, resulting in increased modulus (stiffness), changes
D618 Practice for Conditioning Plastics for Testing
in weight, dimensions, and other physical properties, and
G21 Practice for Determining Resistance of Synthetic Poly-
deterioration of electrical properties such as insulation
meric Materials to Fungi
resistance, dielectric constant, power factor, and dielectric
strength.
3. Summary of Practice
4.3 Often the changes in electrical properties are due prin-
3.1 The procedure described herein consists of the follow-
cipally to surface growth and associated moisture, and to pH
ing steps:
changes caused by products of bacterial metabolism. Other
effects include preferential growths caused by nonuniform
dispersion of plasticizers, lubricants, and other processing
This practice is under the jurisdiction of ASTM Committee G03 on Weathering
additives. Pronounced physical changes may be observed on
and Durability and is the direct responsibility of Subcommittee G03.04 on
products in film form or as coatings where the ratio of surface
Biological Deterioration.
Current edition approved Feb. 1, 2023. Published February 2023. Originally
to volume is high, and where nutrient materials such as
approved in 1976. Last previous edition approved in 1996 as G22 – 76 (1996) which
plasticizers and lubricants continue to diffuse to the surface as
was withdrawn January 2002 and reinstated in February 2023. DOI: 10.1520/
they are utilized by the organisms.
G0022-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.4 Since attack by organisms involves a large element of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
change due to local accelerations and inhibitions, the order of
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. reproducibility may be rather low. To assure that estimates of
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G22 − 23
NOTE 2—Nutrient-salts agar readily supports growth of fungi which
behavior are not too optimistic, the greatest observed degree of
may be present on the test specimens. Fungal contamination can be
deterioration should be reported.
controlled by either (1) the addition of 0.15 % cycloheximide to
4.5 Conditioning of specimens such as exposure to
nutrient-salts agar or (2) sterilization of the specimens by some suitable
means such as exposure to ethylene oxide.
leaching, weathering, heat treatment, etc., may have significant
effects on the resistance of plastics to bacteria. Determination
6.4 Bacterial Cell Suspension:
of these effects is not covered in this document.
6.4.1 The following test organism shall be used, or a
suitable bacterium as agreed upon among parties concerned:
5. Apparatus
6 7
Pseudomonas aeruginosa ATCC 13388, MYCO B1468.
5.1 Glassware—Glass vessels are suitable for holding speci-
6.4.2 Cultures of the organism shall be maintained on slants
mens when laid flat. Depending on the size of the specimens,
of nutrient agar. To prepare nutrient agar slants suspend 0.3 %
the following are suggested:
beef extract, 0.5 % peptone, and 1.5 % agar in distilled water
5.1.1 For specimens up to 75 mm (3 in.) in diameter,
and heat until dissolved. Tube, plug, and autoclave for 15 min
150 mm (6 in.) covered petri dishes.
at 103 kPa (15 psi) steam pressure at 121 °C. The tubed and
5.1.2 For 75 mm (3 in.) and larger specimens, such as
sterilized media shall be allowed to cool and gel in a slanted
tensile and stiffness strips, large petri dishes, trays of borosili-
position to afford an appropriate surface on which the bacteria
cate glass; or baking dishes covered with squares of window
may be cultured.
glass or other suitable covering.
6.4.3 The inoculum shall be prepared from not less than two
successive transfers in nutrient broth. To prepare nutrient
5.2 Incubator—Incubating equipment for all test methods
broth dissolve 0.3 % beef extract and 0.5 % peptone in distilled
shall maintain a temperature of 35 °C to 37 °C (95 °F to 99 °F)
water and dispense in suitable test tubes or flasks. Plug and
and a relative humidity of not less than 85 %. Automatic
autoclave at 103 kPa (15 psi) steam pressure at 121 °C.
recording of wet and dry bulb temperature is recommended.
Transfer the bacteria with a flame-sterilized needle from the
6. Reagents and Materials
nutrient agar slant to nutrient broth. Incubate for 24 h. Transfer
this broth culture to the sterile nutrient broth medium and
6.1 Purity of Reagents—Reagent grade chemicals shall be
culture as before. Centrifuge the broth culture. Decant the broth
used in all tests. Unless otherwise indicated, it is intended that
and resuspend the bacteria cells in sterile normal saline
all reagents shall conform to the specifications of the Commit-
solution (0.8 % NaCl). Centrifuge, decant the saline solution,
tee on Analytical Reagents of the American Chemical Society,
and resuspend the bacteria cells in fresh normal saline. Deter-
where such specifications are available. Other grades may be
mine the bacterial cell concentration.
used, provided it is first ascertained that the reagent is of
6.4.4 The concentration of the bacterial cells may be esti-
sufficiently high purity to permit its use without lessening the
mated turbidimetrically using a photoelectric colorimeter. The
accuracy of the determination.
turbidimetric standard is obtained by concurrent plate counts
6.2 Purity of Water—Unless otherwise indicated, references
and turbidimetric measurements of a serially diluted bacterial
to water shall be understood to mean distilled water.
cell
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