ASTM G22-76(1996)

Standard Practice for Determining Resistance of Plastics to Bacteria (Withdrawn 2002)

SCOPE
1.1 This practice covers two procedures, A and B, for determining the effect of bacteria on the properties of plastics in the form of molded and fabricated articles, tubes, rods, sheets, and film materials. Procedure B provides a more extensive contact between the test bacteria and the specimens than does Procedure A. Changes in optical, mechanical, and electrical properties may be determined by the applicable ASTM methods.  
1.2 The values stated in SI units are to be regarded as the standard.

General Information

• Status: Historical
• Publication Date: 09-Jun-1996
• ICS: 83.080.01 - Plastics in general
• Technical Committee: G03 - Weathering and Durability
• Drafting Committee: G03.04 - Biological Deterioration

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: G 22 – 76 (Reapproved 1996)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
Determining Resistance of Plastics to Bacteria
This standard is issued under the fixed designation G 22; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope growth of bacteria. It is generally the other components, such
as plasticizers, lubricants, stabilizers, and colorants that are
1.1 This practice covers two procedures, A and B, for
responsible for bacterial attack on plastic materials. It is
determining the effect of bacteria on the properties of plastics
important to establish the resistance of plastics to microbial
in the form of molded and fabricated articles, tubes, rods,
attack when plastics are used under conditions of high tem-
sheets, and film materials. Procedure B provides a more
perature and humidity favorable for such attack.
extensive contact between the test bacteria and the specimens
4.2 The effects to be expected are:
than does Procedure A. Changes in optical, mechanical, and
4.2.1 Surface attack, discoloration, and loss of transmission
electrical properties may be determined by the applicable
(optical).
ASTM methods.
4.2.2 Removal of susceptible plasticizers, modifiers, and
1.2 The values stated in SI units are to be regarded as the
lubricants, resulting in increased modulus (stiffness), changes
standard.
in weight, dimensions, and other physical properties, and
2. Referenced Documents
deterioration of electrical properties such as insulation resis-
tance, dielectric constant, power factor, and dielectric strength.
2.1 ASTM Standards:
4.3 Often the changes in electrical properties are due prin-
D 618 Practice for Conditioning Plastics and Electrical
cipally to surface growth and associated moisture, and to pH
Insulating Materials for Testing
changes caused by products of bacterial metabolism. Other
G 21 Practice for Determining Resistance of Synthetic
effects include preferential growths caused by nonuniform
Polymeric Materials to Fungi
dispersion of plasticizers, lubricants, and other processing
3. Summary of Practice
additives. Pronounced physical changes may be observed on
products in film form or as coatings where the ratio of surface
3.1 The procedure described herein consists of the follow-
to volume is high, and where nutrient materials such as
ing steps:
plasticizers and lubricants continue to diffuse to the surface as
3.1.1 Selection of suitable specimens for determination of
they are utilized by the organisms.
pertinent properties,
4.4 Since attack by organisms involves a large element of
3.1.2 Inoculation of specimens with suitable organisms,
change due to local accelerations and inhibitions, the order of
3.1.3 Exposure of inoculated specimens under conditions
reproducibility may be rather low. To assure that estimates of
favorable to growth,
behavior are not too optimistic, the greatest observed degree of
3.1.4 Examination and rating for visual growth, and
deterioration should be reported.
3.1.5 Removal, sterilization, and evaluation of specimens.
4.5 Conditioning of specimens such as exposure to leach-
NOTE 1—Since the procedure involves handling and working with
ing, weathering, heat treatment, etc., may have significant
bacteria that may be capable of infecting man, it is essential that personnel
effects on the resistance of plastics to bacteria. Determination
trained in microbiology perform the portion of the procedure involving
of these effects is not covered in this document.
handling of bacterial organisms and inoculated specimens.
5. Apparatus
4. Significance and Use
5.1 Glassware—Glass vessels are suitable for holding
4.1 The resin portion of plastic materials is usually resistant
specimens when laid flat. Depending on the size of the
to bacteria, in that it does not serve as a carbon source for the
specimens, the following are suggested:
5.1.1 For specimens up to 75 mm (3 in.) in diameter,
150-mm (6-in.) covered petri dishes.
This practice is under the jurisdiction of ASTM Committee G-3 on Durability
5.1.2 For 75-mm (3-in.) and larger specimens, such as
of Nonmetallic Materials and is the direct responsibility of Subcommittee G03.04
on Biological Deterioration.
tensile and stiffness strips, large petri dishes, trays of borosili-
Current edition approved Nov. 26, 1976. Published January 1977. Originally
cate glass; or baking dishes covered with squares of window
published as G 22 – 67 T. Last previous edition G 22 – 67 T.
2 glass or other suitable covering.
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 06.01. 5.2 Incubator—Incubating equipment for all test methods
G22
shall maintain a temperature of 35 to 37°C (95 to 99°F) and a sterilized media shall be allowed to cool and gel in a slanted
relative humidity of not less than 85 %. Automatic recording of position to afford an appropriate surface on which the bacteria
wet and dry bulb temperature is recommended. may be cultured.
6.4.3 The inoculum shall be prepared from not less than two
6. Reagents and Materials
successive transfers in nutrient broth. To prepare nutrient
6.1 Purity of Reagents —Reagent grade chemicals shall be
broth dissolve 0.3 % beef extract and 0.5 % peptone in distilled
used in all tests. Unless otherwise indicated, it is intended that
water and dispense in suitable test tubes or flasks. Plug and
all reagents shall conform to the specifications of the Commit-
autoclave at 103 kPa (15 psi) steam pressure at 121°C. Transfer
tee on Analytical Reagents of the American Chemical Society,
the bacteria with a flame-sterilized needle from the nutrient
where such specifications are available. Other grades may be
agar slant to nutrient broth. Incubate for 24 h. Transfer this
used, provided it is first ascertained that the reagent is of
broth culture to the sterile nutrient broth medium and culture as
sufficiently high purity to permit its use without lessening the
before. Centrifuge the broth culture. Decant the broth and
accuracy of the determination.
resuspend the bacteria cells in sterile normal saline solution
6.2 Purity of Water—Unless otherwise indicated, references
(0.8 % NaCl). Centrifuge, decant the saline solution, and
to water shall be understood to mean distilled water.
resuspend the bacteria cells in fresh normal saline. Determine
6.3 Nutrient-Salts Agar —This is a carbon-free culture
the bacterial cell concentration.
medium used in Practice G 21. Although intended for the
6.4.4 The concentration of the bacterial cells may be esti-
cultivation of fungi, nutrient-salts agar will support growth of
mated turbidimetrically using a photoelectric colorimeter. The
the test bacteria when carbon requirements are supplied by
turbidimetric standard is obtained by concurrent plate counts
susceptible plastic materials. Prepare this medium by dissolv-
and turbidimetric measurements of a serially diluted bacterial
ing in 1 L of water the designated amounts of the following
cell suspension. Reference to a calibration curve of cell count
reagents:
versus absorption will give a measure of concentration. The
Potassium dihydrogen orthophosphate (KH PO ) 0.7 g
2 4
cell count need be done only once to establish the calibration
Potassium monohydrogen orthophosphate (K HPO ) 0.7 g
2 4
curve.
Magnesium sulfate (MgSO ·7H O) 0.7 g
4 2
Ammonium nitrate (NH NO ) 1.0 g 6.5 Viability Control—Streak onto sterile nutrient agar
4 3
Sodium chloride (NaCl) 0.005 g
poured into a sterile petri dish a loop-full of the bacterial
Ferrous sulfate (FeSO ·7H O) 0.002 g
4 2
suspension at the start and end of the bacterial in
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