DEFINITION OF SOME TERMS 159 



Definition of Some Terms. 



The terminology of antibacterial effects produced by all kinds of compounds 

 is confused. The failure of an inoculum of bacteria to grow after exposure to 

 a given compound is referred to sometimes as a bacteriostatic effect, sometimes 

 as a bactericidal effect. The agent producing this effect may be called variously 

 an antiseptic, a bacteriostatic, a bacterial antagonizer, an inhibitor or a suppressor 

 of growth, and so forth. Agents which protect the bacterium from the anti- 

 bacterial action may be referred to as a deviating substance, an antagonizer, a 

 reversing substance, or an inhibiting substance. 



To speak formally, the term bacteriostasis should be applied only to those 

 cases in which there is no change in the count of viable bacteria during exposure 

 to a bacteriostatic substance. But a bacterium whose reproduction is held up 

 by some agent may die of starvation, or what we loosely call senescence, so that 

 in a bacterial population exposed to a bacteriostatic agent, the number of viable 

 organisms will gradually decrease. This being so, the distinction between a bacterio- 

 static and a bactericidal effect rests to a large extent on the rapidity of bacterial 

 death ; the slower the death rate, and the more it deviates from the rapidly initiated 

 unimolecular reaction characteristic of antiseptic action, the more bacteriostatic 

 and less bactericidal is the effect. In many cases the distinction may be clearly 

 drawn, even between the effect of a high and a low concentration of one substance ; 

 in other cases, the distinction is difficult to make and, when made, may be 

 invaUd. 



With regard to the terms for antibacterial agents and substances that protect 

 bacteria from them, we propose to adopt generally the names suggested by Henry 

 (1943) for these substances in the sulphonamide group. Substances that diminish 

 the growth of bacteria will be referred to throughout the chapter as inhibitors, 

 and substances that reverse the effect of these inhibitors as antagonizer s. 



The In Vitro action of Sulphonamide drugs on Bacteria. 



We are in this chapter concerned with the direct antibacterial action of the 

 sulphonamides. Their action in the body is discussed in Chapter 54. It is neces- 

 sary to anticipate the discussion only in one respect, namely to adopt the gener- 

 ally accepted hypothesis that their in vivo therapeutic effects are referable entirely 

 to the damage they inflict on the infecting bacteria. The damage is qualitatively 

 the same as that which occurs in vitro. It often appears to be quantitatively 

 different ; but this is to be expected, since the disappearance of living bacteria 

 from the tissues is conditioned firstly by the inhibitory action of the drug, and 

 secondly by the natural defence mechanisms that come into play against the 

 already damaged bacteria. The antibacterial effect of a sulphonamide in vitro can 

 be demonstrated quite simply. If small measured inocula of a sulphonamide- 

 susceptible streptococcus are added to a nutrient fluid containing the sulphonamide 

 drug, the increase in population with incubation of the culture is very small com- 

 pared with that of a control culture containing no drug. 



For example, at pH 7-6 in horse digest broth, a concentration of 1 part in 40,000 

 inhibited the growth of an inoculum of Sir. pyogenes. Concentrations above 1 in 100 

 were bactericidal in that the inoculum itself was killed (Oag 1939). Low concentrations 

 are apparently bactericidal with prolonged action, but the effect appears to be due more 

 to a starvation of the organisms than to a direct kUhng. Thus Neter (1941) found that 

 hseraolytic streptococci died as quickly in a non-nutrient medium as they did in a nutrient 

 medium containing 1 per cent, sulphanilamide. 



