ASTM D3870-91
(Practice)Standard Practice for Establishing Performance Characteristics for Colony Counting Methods in Microbiology (Withdrawn 2000)
Standard Practice for Establishing Performance Characteristics for Colony Counting Methods in Microbiology (Withdrawn 2000)
SCOPE
1.1 This practice deals with the performance characteristics of enumeration methods for microorganisms of health and sanitary significance. The performance characteristics cover membrane filter, pour plate, and spread-plate colony counting techniques. A performance characteristic is a quantitative, experimentally determined value that is used to assess the suitability of an analytical method for a given purpose. The performance characteristics dealt with here are specificity, including selectivity, recovery, upper counting range, and precision and lower counting range.
1.2 The purpose of establishing performance characteristics is to provide a set of uniform properties to describe bacterial enumeration techniques and selective media.
1.3 This standard does not purport to address the safety problems, 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
Relations
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NOTICE: This standard has either been superseded and replaced by a new version or discontinued.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: D 3870 – 91
Standard Practice for
Establishing Performance Characteristics for Colony
Counting Methods in Microbiology
This standard is issued under the fixed designation D 3870; 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 3.1.5 specificity—the ability of a method to select and
distinguish the microorganism under consideration from all
1.1 This practice deals with the performance characteristics
others in the same environment.
of enumeration methods for microorganisms of health and
3.1.6 upper limit of counting range—that point above which
sanitary significance. The performance characteristics cover
the reliability of the colony count on a single plate or
membrane filter, pour plate, and spread-plate colony counting
membrane from a specified volume is affected by uncontrol-
techniques. A performance characteristic is a quantitative,
lable factors.
experimentally determined value that is used to assess the
3.2 Definitions—For definitions of other terms used in this
suitability of an analytical method for a given purpose. The
practice, refer to Terminology D 1129.
performance characteristics dealt with here are specificity,
including selectivity, recovery, upper counting range, and
4. Significance and Use
precision and lower counting range.
4.1 Data on the performance characteristics are required to
1.2 The purpose of establishing performance characteristics
describe the acceptability of microbiological counting methods
is to provide a set of uniform properties to describe bacterial
to the user.
enumeration techniques and selective media.
4.2 Such data are used to determine the applicability of
1.3 This standard does not purport to address the safety
counting methods for research, monitoring, and regulatory
problems, if any, associated with its use. It is the responsibility
purposes in order to assure uniformity and comparability of
of the user of this standard to establish appropriate safety and
method results.
health practices and determine the applicability of regulatory
4.3 Living microorganisms are inherently more variable in
limitations prior to use.
numbers and in responses to test conditions, than chemical
2. Referenced Documents analytes. Hence, there is a need to establish criteria to assure
that different microbiological methods are evaluated and char-
2.1 ASTM Standards:
acterized against a standard set of performance characteristics.
D 1129 Terminology Relating to Water
These are herein established.
3. Terminology
5. Statistical Procedures
3.1 Definitions of Terms Specific to This Standard:
5.1 Specificity and Selectivity:
3.1.1 lower limit of counting range—that count below
5.1.1 Specificity is evaluated by selecting a representative
which the anticipated error becomes unacceptably large in
number of target and nontarget colonies recovered from
relation to the count itself.
various aquatic environments. Multiple dilutions of a water
3.1.2 precision—the degree of agreement of repeated mea-
sample are plated or filtered in triplicate from a sample or
surements of the same sample. The usual index of precision is
sample dilution that will provide noncrowded colonies. Incu-
the standard deviation.
bate as directed. Examine all the colonies from no less than
3.1.3 recovery—the degree of agreement between the den-
two plates or filters. Each plate must contain at least 30
sity of microorganisms obtained with a test method and the
presumptive target organisms. Perform sufficient biochemical
density obtained with an acceptable reference method.
tests on each colony to identify it as the target organism.
3.1.4 selectivity—the ability of a method to encourage
Designate as false positives all colonies that do not verify as
growth of the target organism while retarding development on
target types. Similarly, designate as undetected target all
nontarget organisms. In this way, overcrowding problems can
presumptive nontarget colonies that verify as target types.
be minimized.
5.1.2 The results of specificity testing are expressed as two
individual terms; the error introduced by false positive colonies
This practice is under the jurisdiction of ASTM Committee D-19 on Water and
and the error resulting from undetected target colonies. Calcu-
is the direct responsibility of Subcommittee D19.24 on Water Microbiology.
late the first term by dividing the number of false positive
Current edition approved June 15, 1991. Published October 1991. Originally
e1
published as D 3870 – 79. Last previous edition D 3870 – 79(1984) .
target colonies by the total presumptive target colony count. If
Annual Book of ASTM Standards, Vol 11.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 3870
TABLE 1 Results from Example 2 TABLE 2 Results from Example 4
Test Medium Reference medium LC HC LC HC LC HC
A A
Count Count
8to48 12to64 21to98
0h 24 h 0 h 24h 9to44 14to67 21to100
9to48 14to70 21to102
A
Strain 1 101 97 101 93
10 to 50 14 to 72 22 to 100
Strain 2 99 95 105 103
10 to 51 14 to 72 23 to 96
Strain 3 101 98 97 109
11 to 50 15 to 70 23 to 95
Strain 4 110 100 105 100
11 to 52 17 to 80 24 to 97
Strain 5 100 98 100 95
A
11 to 53 17 to 82 26 to 95
Average recovery 102 98 102 100
A
11 to 53 17 to 83 28 to 97
A A
Mean of 5 counts from replicate plates. 11 to 55 19 to 85 28 to 100
A
Calculations: 12 to 55 19 to 90 28 to 99
A
test medium count
12 to 57 19 to 92 28 to 101
Recovery ~0h!5 3 100 A
reference medium count 12 to 58 19 to 93 30 to 103
A
102~100! 12 to 58 20 to 95 32 to 106
5 5 100 %
A
12 to 58 20 to 95 36 to 110
12 to 60 20 to 96
98~100!
Recovery ~24 h!5 5 98 %
12 to 63 20 to 98
A
The μ-test values are greater than 1.96 and therefore the expected (5 3 LC)
and observed (HC) counts are not members of the same distribution of means. The
upper limit of the counting range for this technique would be 95 colonies.
there are no false positive colonies, this term will equal zero.
replicates at each dilution. Repeat this procedure with five or
Calculate the second term by dividing the number of undetec-
more strains of the target organism.
ted target co
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.