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CRITERIA FOR THE SELECTION OF GERMICIDES Laboratory Section WITH the emergence of antibiotic resistant bacteria, the use of chemi-cal germicides has received renewed at-

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Criteria for the Selection of Germicides

CRITERIA FOR THE SELECTION OF GERMICIDES Laboratory Section WITH the emergence of antibiotic resistant bacteria, the use of chemi-cal germicides has received renewed at-

CRITERIA FOR THE SELECTION OF GERMICIDES

Laboratory Section

WITH the emergence of antibiotic for comprehensive background informa-
resistant bacteria, the use of chemi-
tion and bibliography too extensive for
cal germicides has received renewed at- inclusion in this report.

tention. The selection of such agents for Some germicidal agents are combined
particular uses, however, presents diffi- with detergents and marketed as deter-
cult problems because both laboratory gent-disinfectants or detergent-sanitizers.
methods and field evaluation procedures Such products, involving both physical
removal and chemical destruction of the
are necessary to measure results to be microbiological flora, should be con-
expected and actually obtained. The sidered from both points of view by the
selection of effective agents has been user. It makes little difference if micro-
complicated further by overenthusiastic
claims of sales and advertising staffs organisms are removed from the en-
and by the scarcity of qualified person- vironment while still viable or if they
nel sufficiently interested and informed are left in the environment in a non-
to evaluate the multitudinous products viable condition. Products must be
showered upon the market.
judged separately for their ability to
The Committee on Antimicrobial suppress viable organisms and for their
Agents (Disinfectants) is responsible for
proposing to the Laboratory Section ability as cleaning agents. It should be
procedures and criteria which the Ameri- remembered that although the use of a
can Public Health Association can recom- disinfectant is usually more efficient after
mend to manufacturers, users, and sani- the cleaning procedure has been com-
tation control agencies as the basis for pleted, certain advantages, such as sav-
compounding, selecting, and evaluating ing in labor costs, may accrue if a
germicidal products. This report out- product provides both cleansing and
lines the viewpoints and objectives of the antimicrobial action.
committee in approaching its responsi-
bilities. In particular, it sets forth The word disinfectant or other words
criteria for screening germicides and denoting germicidal action should not
evaluating their performance in use. be confused with the words deodorant
or deodorizer as is sometimes done on
The name of the committee includes labels and in advertising since the term
the word "Antimicrobial" which implies disinfectant involves the killing of micro-
all types of agents antagonistic to micro- organisms while the other terms involve
organisms. This report and the initial the removal of odors by cleaning or by
activities of the committee will be limited masking objectionable odors with a
to chemicals marketed in liquid, gaseous, highly scented material. However, the
soluble solid, spray, and pressurized use of a germicidal agent to destroy
spray form. These agents are known by putrefactive organisms may often be the
a number of terms including disinfectant, most effective means of controlling
odors.
sanitizer, antiseptic, germicide, bacteri-
cide, fungicide, virucide, sporicide, and The purchaser must know the use
similar words which include the suffix which he intends to make of the product,
-cide. These terms are defined in the as no one material can be equally effec-
literature' to which the reader is referred tive against all microorganisms in all
situations. A product to be used in the

1054 VOL. 51, NO. 7, A.J.P.H.

CRITERIA FOR THE SELECTION OF GERMICIDES

laundry might require different prop- 1. Screening Phase
erties from one suitable for the disinfec-
tion of water, the sanitization of food The manufacturer may furnish all
equipment, or the decontamination of air the information necessary in the screen-
ducts and filters. In any case, the in-g phase on the label of the container
product with the widest spectrum of anti- and amplified in supporting literature.
microbial effectiveness would offer the The following information, partially out-
greatest safety, other factors being equal. lined in the literature,2 should be in-
cluded:
Since each product offered on the
market as a germicide is affected in use A. Identification of product
by various factors, including human B. Registration infonnation
error, time of contact, condition and C. Directions for use
nature of surface, humidity, concentra- D. Proof of germicidal potency
tion, dirt, organic matter, temperature, E. Major pathogens not subject to product
pH, mineral content of the water, and so
forth, its selection and ultimate applica- action
tion should be under the supervision of a F. Information on safety
technically trained and competent indi- G. Use characteristics
vidual. The responsible person should
be a part of or closely allied to the pro- A. Identification of Product
fessional staff and should receive the
active support of management. The Distinctive Brand Name Since many
good products are known by brand
rather common practice of leaving the names rather than by chemical composi-
selection of germicidal materials to jani- tions, such usage has definite sales value
and serves conveniently to identify a
torial workers or purchasing agents product. Multiple use of a brand name
should be eliminated. This responsibility for different products intended for sani-
in the hands of a competent person tation purposes, for example detergent
would minimize the effect of extravagant and disinfectant, without clear differ-
sales appeal to persons unqualified to entiation causes unnecessary confusion
evaluate the many factors involved in among purchasers. Likewise, changes in
the selection and use of a germicidal composition of products sold under es-
product. tablished brand names may be mislead-
ing.
After a prospective user has de-
termined precisely what is to be accom- Identification of Type of Product-
plished by the use of a germicide, he Descriptive words indicating the pri-
mary use for which the product is recom-
must select an appropriate product. The mended should appear in a conspicuous
selection resolves itself into two phases: place on the label. Since no one ma-
first, the preliminary screening phase terial can serve all sanitation purposes,
based upon information available to him the manufacturer should clearly state on
from the manufacturer or other reliable the label that the product is a disin-
fectant, a sanitizer. a detergent-disin-
sources and possibly upon tests per- fectant, a deodorizer, or other category.
formed under his supervision; and
second, the performance evaluation phase If the product is primarily a general
encompassing procedures and standards hospital disinfectant, such uses as de-
by which he may measure and monitor tergency, deodorization, or antisepsis
effectiveness under use conditions. These should be mentioned only in a clear and
criteria are equally applicable by the appropriate manner and not confused
manufacturer who wishes to formulate with the primary use.
an acceptable germicide.
Name and Address of Manufacturer-

The mutual advantages of the appear-
ance of the name and address of the

JULY. 1961 I 055

manufacturer on the label appear occur in that use situation. Notable
obvious since the prospective customer contraindications to use, such as water
can scarcely be expected to have con- hardness or excessive organic matter,
fidence in a product with which the should also be included.
manufacturer does not identify himself.
D. Proof of Germicidal Potency
Listing of Ingredients by Chemical
Composition and Percentage Composi- The label or supporting printed ma-
tion-Only when the quantitative chemi- terial should state clearly the basis upon
cal composition, including both active which germicidal claims are made.
and inert ingredients, is available can
an intelligent assessment be made of Usually such information will include
the product's effectiveness, safety, and the results of germicidal tests which in-
response to various conditions of use. dicate the conditions under which
selected organisms will be destroyed by
B. Registration Information the product when tested in the labora-
tory. Since germicides are seldom
Although germicides entered in inter- called upon to kill pathogenic organisms
state commerce must be registered with unprotected by organic matter and in
the U. S. Department of Agriculture pure cultures, additional factors may be
under the provisions of the Federal In- introduced to simulate conditions of use.
secticide, Fungicide and Rodenticide
Act, products may be compounded Laboratory tests are available which
within some states to meet bid specifi- can be used as screening procedures to
cations without sufficient time or evalua- eliminate materials or products that
tion to be registered or, for that matter, show little or no promise as practical
even to have a label printed for inspec- germicides. It is a generally accepted
tion. Such registration fixes responsi- premise that materials which do not
bility under the act for any claims made destroy organisms in the laboratory will
on the label or in supporting printed ma- not efficiently do so under the severe
terial. The purchaser may demand proof conditions of use.
of registration but this fact and the sig-
nificance of registration are not always Because destruction of microorganisms
known to personnel selecting the product. is the required effect, it is necessary to
The committee recommends that the show that the action of a compound at its
Federal Insecticide, Fungicide and Ro- recommended concentration is bacterici-
denticide Act be amended to require a dal rather than merely bacteriostatic.
statement on the label of the registration This has been attempted with more or
status with the U. S. Department of Agri- less success by dilution or the addition
culture and that this information and the of neutralizing substances to the test
registration number be prerequisites to organisms after exposure. This com-
consideration for purchase. mittee proposes that formulations which
are primarily bacteriostatic in recom-
C. Directions for Use mended use dilutions not be considered
as germicides.
Clearly understandable directions for
making and applying the recommended The tests used routinely by govern-
use dilutions should be a conspicuous mental control agencies and published
part of the label. The dilution recom- in the Official Methods of Analysis of the
mended for the purpose for which the Association of Official Agricultural
germicide is sold should be effective Chemists3 do not appear in literature
against the spectrum of pathogenic which is readily available to medical and
microorganisms usually expected to sanitary personnel. Tests published in
the current edition include the follow-

ing:

1056 VOL. 51, NO. 7. A.J.P.H.

CRITERIA FOR THE SELECTION OF GERMICIDES

Phenol Coefficient-Official the testing of antiseptics. More recently
Use Dilution Method-Official this modification was found to be im-
Available Chlorine Germicidal Equivalent portant in testing disinfectants, since
certain chemicals are more effective
Concentration-Official
Sporicidal Test Official against the Gram-negative organisms
Fungicidal Test-Official than against Gram-positive cocci and vice
Germicidal and Detergent Sanitizers Test-
versa.
Official (Chambers)
Later, it was found that the use dilu-
It should be pointed out that the pub- tions of some products derived from
lished recommendation of methods by their phenol coefficient data were less
recognized professional organizations effective than anticipated. The AOAC
confers upon them at least a quasi-legal "Use Dilution Test" using dried cultures
status. The suggestion is therefore made of Salmonella choleraesuis on stainless
that the above mentioned tests, along steel cylinders was devised in an attempt
with other procedures of use in the to elminiate misleading results. S. aureus
evaluation of germicides, be brought is also used as a test organism to simu-
together and published by this commit- late conditions encountered in hospitals
tee in a form more generally available or where pyogenic cocci are present.
to public health workers.
The phenol coefficient test has been
If comparable and meaningful results adapted to tests with the pathogenic
on germicidal agents are to be available, molds and published as an AOAC
it is necessary that the selected tests be method. It has also been modified for
followed exactly. Since there is no single testing against Mycobacterium tuber-
test which will indicate the efficiency of culosis.
all products against all organisms, ap-
propriate tests must be selected to fit the Many tests have been devised to evalu-
situation at hand. Under no circum- ate the probable action of products on
stances, however, should the evaluating floors and other surfaces. Each method
agency accept as proof of efficiency tests gives valuable information but each has
or modifications of tests selected only for failed to achieve the status of a "stand-
the favorable results obtained with a ard test" largely because of the many
given procedure. The committee would variables involved in actual disinfection.
welcome suggestions regarding the se-
lection of the combination of tests which Tests have been devised for special
will give most usable results for the purposes. The sporicidal test devised
effort expended. for the evaluation of products proposed
for use in the chemical sterilization of
The laboratory procedure most widely instruments has been published as an
used and which has attained nearest to AOAC method. The Chambers modifi-
"standard test" status for liquid products cation of the Weber and Black test has
is the phenol coefficient test. The test attained considerable acceptance for use
affords a rapid and easy method for de- in evaluating sanitizers to be used in
termining whether a water soluble prepa- connection with surfaces which come
ration possesses bactericidal effect or is
completely devoid of such properties. into contact with foods. This test also
This test was devised originally to com- has value in the laboratory screening of
pare the activity of an unknown material liquid germicidal agents generally.
with that of phenol against Salmonella
typhosa and arrive at a use dilution with Because of limited testing of chemi-
a wide margin of safety. An early modi- cals as virucides and the great differ-
fication was the substitution of Staphylo- ences among viruses and between viruses
coccus aureus as the test organism for and bacteria, the best that can be said
about a product is that it destroys a
given virus or a number of viruses under

JULY, 1961 1 057

defined conditions. Consequently, no chemicals differ in mode and site of
general conclusions can be drawn as to action, extent of absorption, and period
the virucidal effectiveness of most of retention in the body, safe levels are
products from the testing which has usually determined by expert evaluation
been done against bacteria or the lim- of toxicological studies on individual
ited testing against viruses. products, rather than by compliance with
general criteria. Information of the fol-
Improved tests for "self-disinfecting" lowing types is required for such evalua-
surfaces may serve to rule out as ineffec- tive studies.
tive many products for which extrava-
gant claims have been made. Because Irritancy and Allergenic Responses-
of the recent appearance of many In addition to any evidence available
products with germicidal claims dis- from prior human experience with a par-
pensed in spray or pressurized spray ticular chemical, the minimum concen-
form, work is needed to evaluate them. tration causing irritation on the skin of
Tests for evaluating the killing effect of closely clipped adult albino rabbits is
gases in closed spaces have been quite determined and efforts are made to sensi-
successful. tize guinea pigs. Even infrequent in-
stances of severe skin irritation or al-
E. Major Pathogens Not Subject to lergic responses in man, resulting from
Product Action recommended use dilutions of a germi-
cide, may warrant discontinuing its use.
Since some germicidal compounds are In the case of new products, anaphylaxis
effective against most microorganisms in the guinea pig or skin irritation in the
but not against certain groups, any rabbit greater than that shown by a 1
major pathogens not killed under the
recommended use concentrations should per cent aqueous solution of Liquor
be listed. Cresolis Saponatus NF IX may be used
to screen out objectionable compounds.
F. Information on Safety
Acute Toxicity-It is necessary to de-
By their very nature concentrated termine the oral LD50 (single dose kill-
germicides are potentially toxic, but the ing 50 per cent of animals) for several
character and extent of toxicity vary species, such as mice, rats, and guinea
widely with different compounds. Safe pigs. When the germicide consists of a
use of these products depends upon a mixture of substances, the entire mixture
knowledge of their ingredients and upon should be tested. An LD50 of less than
an understanding of their pharmacologi- 5,000 milligrams per kilogram of body
cal properties. Where germicidal treat- weight indicates that the compound may
ments leave residues with which man be hazardous if consumed accidentally
may come in contact, they must be re- in large amounts. Intravenous injections
moved by rinsing, vaporization, or other of animals may also be used to study
methods unless it can be demonstrated mechanism and site of action associated
that they cause no adverse effects on with acute toxicity.
man of an acute or chronic nature.
Where foods entering interstate com- Subacute and Chronic Toxicity-Two
merce are involved, germicidal residues types of tests are generally used for the
may constitute adulteration within the study of chronic toxicity. One consists
meaning of the Federal Food, Drug and of feeding groups of rats and dogs for
Cosmetic Act. In the interest of safety from 30 to 90 days at levels up to the
for both the sanitation employee and the highest tolerable concentration. The
public, germicides should be evaluated other involves feeding groups of rats,
with respect to irritancy, acute toxicity, dogs, and/or monkeys for from one to
and chronic toxicity. Because germicidal two years at levels chosen on the basis of

1 058 VOL. 51, NO. 7. A.J.P.H.

CRITERIA FOR THE SELECTION OF GERMICIDES

the first test. Typically, chronic toxicity Odor-The diluted solution should
tests are designed to provide the follow- have no odor or one acceptable under
ing feeding regimens: (a) control, re- conditions of use.
ceiving no product; (b) a level showing
no effect in the 30-90 day test; (c) 100 Effect on Surfaces-Continued use of
times the concentration expected to be germicide according to directions should
encountered under practical conditions; not decrease conductivity of flooring, or
(d) a higher "intermediate" level; and damage surfaces of metals, ceramics,
(e) the maximum concentration toler- plastics, flooring, or other objects to
ated. Multiple observations are made on which it may be applied.
these animals which require expert
evaluation. If the biochemical tests, I. Performance Evaluation Phase
weight measurements, and other observa-
tions fall into a recognizable pattern In many localities, the use of germi-
characteristic of well known compounds, cidal agents in connection with water
the determination of safe tolerances may purification and food sanitation is regu-
be relatively straightforward; but when lated by ordinances and codes requiring
evidence of carcinogenicity, reproduc- that cleaned and sanitized surfaces be
tive impairment, or other complex phe- monitored bacteriologically. Also, much
nomena are encountered, the problem help in determining the life of a solution,
may become extremely difficult. Prefer- and thus its value, may be furnished by
ence in the selection of germicides is a practical chemical field test which will
usually given to compounds showing the indicate the concentration of the active
least tendency to induce chronic ab- ingredient present. Satisfactory field
normalities. tests are available for some types of
germicides and should, if possible, be
G. Use Characteristics provided for all new products.

Chemical Properties-The product The committee recommends that every
must not lose its germicidal potency by available effort be made to evaluate the
chemical reaction with substances in the germicide in actual use. Any reduction
water with which it is to be diluted in in microbiological flora obviously will be
use. Any adverse effect of salts and pH a combination of technics including the
must be known and allowance made, if germicidal procedures instituted. If the
necessary, either by changing to a value of the germicide is to be known, it
product not so affected or by increasing must, therefore, be evaluated separately.
the concentration of the product at hand.
To test satisfactorily the value of a
Also, the effect of organic material germicide in use, the treated areas must
must be considered. A product may be be evaluated bacteriologically (1) before
useful as a sanitizer on clean surfaces use of the candidate germicide is begun
but entirely unsatisfactory on a floor but after all other known related vari-
where considerable organic matter is ables such as air, masks, human activity,
present. and so forth, have been standardized;
and (2) after the disinfectant has been
Solubility-When mixed with tap put into use.

water according to directions, the The use of a germicidal agent is based
product should produce satisfactory solu- on the premise that soap and water
tions or emulsions. cleanliness either does not go far enough
or is too difficult to apply effectively.
Stability-The product as purchased Unless the effect of the germicide is de-
should maintain its germicidal properties termined and monitored, its incorpora-
undiminished after storage for at least tion into a housekeeping program may
one year.

JULY, 1961 1 059

be useless because of the unjustified ex- sanitation is important. This evaluation
penditure and the false sense of security resolves itself into two phases involving
which is engendered. Information ob- the following considerations:
tained by bacteriological monitoring will
also determine the frequency with which I. Screening Phase
the agent must be applied. A residual
germicide having active germicidal prop- A. Identification of product
erties over periods of days or weeks 1. Distinctive brand name
would be highly desirable. Such a 2. Identification of type of product
germicide however must come in contact 3. Name and address of manufacturer
with organisms. This is possible only in 4. Listing of ingredients by percentage
areas of medium to high humidity-a chemical composition
condition not always present-or by use
of volatile agents-a condition not com- B. Registration information
patible with extended residual action. C. Directions for use
Thus, claims for extended residual action D. Proof of germicidal potency
by a germicide should be checked most E. Major pathogens not subject to product
thoroughly.
action
Similar to the accepted significance of F. Information on safety
numbers of bacteria on surfaces in con- G. Use characteristics
tact with food and water as indications
of good sanitary practice would be stand- 2. Performance Evaluation Phase
ards for the bacteriological cleanliness
of surfaces and air in various hospital The evaluation of the performance of a
areas. Some such standards have been germicide should include bacteriological moni-
proposed, but they cannot be accepted toring of surfaces and spaces involved with
until a relationship can be established final selection of a usable germicide based
between the number of bacteria in the upon satisfactory performance under condi-
environment and the resultant infection tions of actual use.
rate. Until such standards can be estab-
lished and validated, a reduction in total The committee further recommends
and in pathogenic bacteria to levels sig- that germicidal tests and use perform-
nificantly lower than would be the case ance evaluation procedures be assembled
without its use is a logical justification in a form more readily available to
for the use of a germicide. For those health workers as well as to manufactur-
situations in which a comprehensive ers of germicidal products.
study is not feasible, a program based
upon the results of other studies with a REFERENCES
given germicidal agent by competent in-
vestigators would be second best. 1. Reddish, George F. Antiseptics, Disinfectants, Fungi-
cides, and Chemical and Physical Sterilization (2nd
Summary ed.). Philadelphia, Pa.: Lea & Febiger, 1957.

This committee strongly recommends 2. Klarmann, Emil G. Suggested Specifications for a
careful selection of germicidal agents in General Purpose Hospital Disinfectant. Am. J. Hos-
institutions or other establishments where pital Pharm. 15:795-801, 1958.

3. Association of Official Agricultural Chemists. Official
Methods of Analysis (9th ed.). Washington, D. C.:

AOAC, 1960.

NICHOLAS D. DUFFETT, Ph.D., F.A.P.H.A.,
Chairman, Committee on Antimicrobial
Agents (Disinfectants). (Director, Public
Health Laboratories, Health Division, St.
Louis Department of Health and Hospitals,
St. Louis, Mo.)

FRANK B. ENGLEY, JR., Ph.D., F.A.P.H.A.
LAWRENCE B. HALL, M.E.
FLOYD W. HARTMANN, Sc.D., F.A.P.H.A.
KEITH H. LEWIS, Ph.D.

This report of the Committee on Antimicrobial Agents (Disinfectants) was
presented before the Laboratory Section of the American Public Health Associa-
tion, at the Eighty-Eighth Annual Meeting in San Francisco, Calif., November

2, 1960.

1060 VOL. 51, NO. 7. A.J.P.H.


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