A sIMPLIFIED METHOD FOR DETERMINING THE APPROXIMATE BACTERIOSTATIC POTENCY OF CHEMICALS* By ARTHUR •R. C^DE, Ph.D. Research oea3oratories, Givaudan-Delawanna, Inc., Delawanna, THE l'OX30SE or this pres- entation is threefold: (a) to pre- sent a general outline of the phe- nomena of bacteriostasis as it is understood and' employed at the present time (b) to show where and how bacteriostasis is applied in a practical way and (c) to show how its relative effectiveness, as exhibited by different chemicals, is determined. DEFINITIONS In order that it may be more clear as to what we are talking about, and especially because the terminology as used in the literature is somewhat confusing, we are pre- senting here definitions of some of the terms as we shall employ them. First, we will endeavor to make a clear distinction between the terms germicidal action, antisepsis, and bacteriostasis. These words have become used to designate situations which overlap considerably. For example, many so-called bacterio- static conditions are not truly * Presented at the May 20, 1949, Meeting, New York CitY. 39'1- "static" ones, but rather situations in which the functions assumed to be static are merely retarded in their speed of activity such that the end result is the same as though they were truly static. Likewise, the word antiseptic has become so badly misused as to mean almost anything, covering the whole range from truly bacteriostatic action down to truly germicidal efforts should be made to discontinue its use for defining purposes other than for its original meaning. Literally it means "against sepsis" and, therefore, describes a situation wherein putrefaction (or other forms of decomposition) of the substrate has been prevented. It will be noted that antisepsis refers to a con- dition in the substrate (i.e., outside of the bacterial cell) brought about by certain activities of the cell whereas, germicidal and bacterio- static conditions are situations within the cell itself. It is thus pos- sible to have bacteria present and growing in a substrate (e.g., a cos- metic cream), yet at the same time to have an antiseptic situation exist,

the proper chemical is present, in correct amount, to stop the •ccurrence of the untoward redc- ons from being brought about. In other words, it is possible to have an "antiseptic cream" which, at the same time, might not be "germ- free." :. • According to its derivation, a ß germicide kills the bacterial cell, thereby putting it in a condition of •o activity, with no recovery pos- :sible. A bacteriostatic substance inhibits certain cell functions so that there is little or no activity, with •)?!:? recovery possible under proper con- !?!?!!:ditions. Usually these qualifying i.!/2•:i::" i: ,, ,, . . i •%:.:• terms refer to growth (either m :i•i)ii:::i•::isize or reproduction), but as used :•i!?i!today they also include other met- ? ::.abolic processes, i.e., a product • which stops the enzyme formation of 5(? a certain cell so that no harmful 'i• 3:)i': effects are produced in the substrate :i!i}?.:is considered a bacteriostatic one, ?!ii:?' whether or not the cell can repro- '? duce. i'::'}: i: i Location or the Activity The Cell The Substrate germicide kills the cell. An antiseptic prevents sepsls. Stops all metabolism. May consist No recovery possible. or any one "pseudobacteriostatic" or combi- substance inhibits nations of (slows up) cell grow th, these as well as other met- others. abolic processes. bacteriostatic substance inhibi ts (s tops) growth. Stops most all cell me- tabolism. ' Recovery possible. Actually one should consider bac- teriostasis to include cnly that DETERMINING BACTERIOSTATIC POTENCY OF CHEMICALS 395 condition in .which the bacterial cell is entirely "static." Such a situation occurs when a. cell goes into a spore formation, wherein a thick membrane is formed around the cell or its nucleus, and, although it metabolizes to a small extent within the spore (just as an animal would do when it hibernates), it is truly "static" as far as "growth" is concerned, as well as to its effects upon the substrate. As usually employed, the term bacteriostasis refers, for the most part, to conditions that are not truly "static," but rather which are merely retarded in their speed of action such that the net result, as far as producing harmful or unde- sirable effects upon the substrate, or on a host, are the same as though the cell was truly "static." However, in these latter situations which should really be called "pseudo-' bacteriostasis," there exists a state of equilibrium which can be dis- turbed by a neutralizing process. Thus, the bacteria in question can "recover from death" and start growing normally again. This is not possible for a germicidal situa- tion. As a result a bacteriostatic con- dition, in its broad sense, may be brought about by (a) producing a truly static set-up, as in a spore formation (curve 2) (b) increasing the killing time of the organism (curve3b) (c) increasing the lag- phase of the bacteria so that the time that it requires to adjust itself to the chemical is prolonged (curve 3a). In each of the three cases the