ASTM D7818-12

Standard Test Method for Enumeration of Proteolytic Bacteria in Fresh (Uncured) Hides and Skins

SIGNIFICANCE AND USE
4.1 This test method enumerates proteolytic bacteria. Proteolytic bacteria have been known to cause damage to hides and skins.
SCOPE
1.1 This test method covers the enumeration of bacteria that can hydrolyze protein/collagen in fresh (uncured) hides and skins. This test method is applicable to uncured hides and skins.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Aug-2012
• ICS: 07.100.99 - Other standards related to microbiology
• Technical Committee: D31 - Leather
• Drafting Committee: D31.02 - Wet Blue

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7818 − 12
StandardTest Method for
Enumeration of Proteolytic Bacteria in Fresh (Uncured)
Hides and Skins
This standard is issued under the fixed designation D7818; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
4.1 This test method enumerates proteolytic bacteria. Pro-
1.1 Thistestmethodcoverstheenumerationofbacteriathat
teolytic bacteria have been known to cause damage to hides
can hydrolyze protein/collagen in fresh (uncured) hides and
and skins.
skins. This test method is applicable to uncured hides and
skins.
5. Apparatus
1.2 The values stated in SI units are to be regarded as
5.1 Incubator, 35 6 1°C.
standard. No other units of measurement are included in this
standard.
5.2 Colony counter—(not mandatory, but highly recom-
mended).
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 5.3 Sterile pipets.
responsibility of the user of this standard to establish appro-
5.4 Bent glass rods, sterile.
priate safety and health practices and determine the applica-
5.5 Stomacher, for mixing initial dilution. (If stomacher is
bility of regulatory limitations prior to use.
unavailable, hand-mix.)
2. Referenced Documents
5.6 Balance.
2.1 ASTM Standards: 5.7 Sterile petri dishes.
D6715Practice for Sampling and Preparation of Fresh or
5.8 Autoclave (sterilizer). (Check the effectiveness of ster-
Salt-Preserved (Cured) Hides and Skins for Chemical and
ilizationweekly.Forexample,placesporesuspensionsorstrips
Physical Tests
of Bacillus stearothermophilus(commerciallyavailable)inside
E691Practice for Conducting an Interlaboratory Study to
glassware for a full autoclave cycle. Follow manufacturer’s
Determine the Precision of a Test Method
directions for sterilization of specific media.)
E177Practice for Use of the Terms Precision and Bias in
5.9 Stomacher bags, or sterile, sealable quart plastic bag
ASTM Test Methods
(e.g. food storage type, sterile bag).
3. Summary of Test Method 5.10 Cutting tool, sterile (e.g. scalpel blade and forcep, as
needed for cutting fresh hides and skins).
3.1 Samples of uncured hides and skins are serially diluted
5.11 Vortex mixer, for mixing dilution tubes (optional).
and plated on agar containing casein from skim milk. The
plates are incubated under aerobic conditions at 35°C for 48 h.
5.12 pH meter.
After incubation, to determine bacteria that can hydrolyze
5.13 Waterbath, 45 6 1°C.
protein(proteolytic),theplatesarefloodedwithdiluteacidand
the colonies showing a halo are counted.
5.14 Autoclave thermometer.
6. Reagents and Materials
This test method is under the jurisdiction ofASTM Committee D31 on Leather
6.1 5 % acetic acid.
and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
Current edition approved Sept. 1, 2012. Published October 2012. DOI: 10.1520/ 6.2 Butterfield’s Phosphate Stock Solution: Dissolve 34 g
D7818-12
KH PO (Potassium Phosphate monobasic) in 500 mL DI
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
water.Adjust the pH to 7.2 6 0.1 with 1N – 6N NaOH. Bring
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
volume to 1 L with DI water. Sterilize for 15 min at 121°C.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. NOTE 1—Typical autoclave setting is 120–124°C. (See 5.8.)
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7818 − 12
6.3 Butterfield’s Phosphate Diluent (BPD):Take1.25mLof 9.3 Prepare a 10 % powdered skim milk mixture by adding
Butterfield’s Phosphate Stock solution (6.2) and bring to 1 L 10gpowderedskimmilkto100mLDIwater,thenstirringthe
with DI water. Dispense into 1 L bottles and 9 mL dilution mixture to dissolve it. Autoclave the mixture for 15 min at
tubes. Sterilize for 15 min at 121°C. (See Note 1.) 121°C. (See Note 1.)
6.4 Standard plate count agar containing 100 mL of 10 %
9.4 Cooltheagar(9.2)to45 61°C,thenadd100mLofthe
powdered skim milk solution per litre of agar. sterile10%powderedskimmilkmixture(9.3)perlitreofagar.
NOTE 2—Do not allow agar to solidify prior to pouring (9.5).
6.5 Alcohol (for flame sterilizing), e.g. 70 % Isopropyl
9.5 Pour the sterile agar into petri dishes. Replace the cover
alcohol.
and swirl to evenly distribute the agar. Allow to solidify at
6.6 Bent glass rod (“hockey-stick”).
roomtemperatureonaflatsurface.Whensolid,invertthepetri
6.7 Powdered skim milk.
dishes, with the cover on the bottom, leaving a slight opening
to allow the plates to dry for ⁄2 h.
6.8 Distilled or deionized water.
6.9 Bacillus stearothermophilus spore suspensions or strips
10. Procedure
(commercially available), or equivalent.
10.1 Using a sterile scalpel, aseptically weigh a 20 6 0.1 g
6.10 1N – 6N NaOH.
specimen in a sterile bag. Include both flesh and hair side.
7. Hazards
10.2 Add 180 g of BPD (6.3) diluent into the same sterile
7.1 Allreagentsandchemicalsshouldbehandledwithcare. bag (10.1). Stomach or hand-massage for 1 min.This provides
a 1:10 dilution.
Before using any chemical, read and follow all safety precau-
tions and instructions on the manufacturer’s label or MSDS
10.3 Prepare the following sample dilutions using 9mL
(Material Safety Data Sheet). -2 -3 -4 -5 -6 -7
dilution tubes (BPD): 10 ,10 ,10 ,10 ,10 , and 10 (see
Fig. 1).
8. Sampling
10.3.1 Control Blank—In 10.9, incubate one of the petri
8.1 The specimen shall be sampled in accordance with
dishes prepared in 9.5 as-is, with the sample plates.
-2 -1
Practice D6715, and placed in sterile containers.
Example:Toobtaina10 dilution,mixthe10 dilutionand
-1
pipet 1mL of that 10 dilution intoa9mL dilution tube.
9. Preparation of Standard Plate Count Agar
NOTE 3—When transferring the aliquots between the tubes, the analyst
9.1 Prepare the standard plate count agar per manufacturer
must use a different pipet or pipet tip for each transfer.
label directions.
10.4 Pipet an appropriate portion (0.1mL or 0.2mL), of the
-2
9.2 Autoclave the prepared agar for 15 min at 121°C. (See 10 dilutionandplacetheliquidinthemiddleofadried,skim
Note 1.) milk agar plate.
FIG. 1 Plating
D7818 − 12
10.5 Flame sterilize a bent glass rod, or obtain a sterile, 10.11 Record each plate’s dilution and count on the work-
autoclaved bent glass rod. sheet. This initial count is the aerobic plate count (A).
10.12 For the same plate(s) counted in 10.10, flood the
10.6 Using the glass rod, spread the liquid evenly on the
plate(s) with 5 % acetic acid.
agar surface.
NOTE 6—Use enough of the 5 % acetic acid to fully cover the surface
10.7 Replace the cover and allow the plate to dry at room
of the plate.
temperature.
10.13 Pour off the acetic acid and immediately count only
10.8 Repeat steps 10.4 – 10.7 for each dilution.
those colonies completely surrounded by a semi-clear zone.
10.9 Invert all plates and incubate at 35 6 1°C for 48 6 3
NOTE7—Proteolytic Colonies—Donotcountallthecoloniesinsidethe
zone,onlycountthecoloniesthatcause/affecttheshapeofthezone.When
h.
identifying the semi-clear zone(s) it is sometimes helpful to pick up the
10.10 Following incubation, count only those plates that
plateandchangetheangleofviewslightlytodetermineifitisatruecircle
have 25–250 colonies.
orifithasanotherprotruberanceoffit’sedge.[Forweaksemi-clearzones,
it is helpful to rotate the plate in the light to be sure about the clearing].
NOTE4—Ifaplateshows confluent growth(i.e.bacterialgrowthcovers
the entire plate, making it impossible to determine the existence of Look for a circle of clearing around a centrally located colony. If the
discretecolonies),recordthatplate’scountasTNTC–“TooNumerousTo clearing is an elongated shape such as in the bottom right quadrant of Fig.
Count”). See Figs. 2 and 3 for diagrams of a countable plate and a TNTC 5(“5:30”position),breaktheclearedzoneintoseparatecirclesofclearing
plate, respectively. (circles can be of varying sizes) and count the colonies located in the
NOTE 5—Count all the distinct colonies on the plate. If there are centersofeachofthecircles.Whentherearemultiplecol
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