AN APPROACH TO THE STUDY OF INTERACTIVE PHENOMENA AMONG MICROORGANISMS INDIGENOUS TO MAN

The importance of interactions between species in the mixed microbic populations in nature is recognized, but the subject is poorly unclerstoo(l. The need for studies in this field has been noted byAppleton (1940), AW'oodls (1947), and Lucas (1949). Some of the manifest difficulties that beset an adequate approach to it are mentioned by Topley and Fielden (1922) and Annear and Hayes (1950). Such an approach might be facilitated by means of a rapidl screening method, sufficiently sensitive an(l plreferably at least roughly quantitative, wN-hich lwould permit (lisclosure and preliminary classification of interactive phenomena among a wide range of microbic species. This report (lescribes a method which seems to meet these criteria andl presents data thus far obtained by its use. The problem in hand may be (lelimited in terms of interactions of imicroorganisms as a phase of microbic ecology, with special reference to human hygiene. The micioorganisms of most imme(liate interest are in consequence those indigenous to man, as they interact with one another and with pathogens and transient saprophytes. Our approach tlhus excludes phenomena in soil and sewage and differs from studies whose primary purpose is the discovery of useful antibiotic substances. A moderately extensive literature bearing on aspects of this problem need not be reviewed here in detail. To save space, references are given onlyr to earlv and recent papers. AMost studies have been concerned with inhibitory effects and have (lealt mainly with the search for possible therapeutic agents or a particulai (lisease, e.g., diphtheria. Included are (a) a group of ieports on antibiotic substances produced by lactic streptococci and acting upon other streptococci, pneumococci, staphylococci, the diphtheria bacillus, and other organisms (Ox1 Aided by a grant fronm the John anid Mlary R. Markle Founi(lation. ford, 1944; Hirsch and 'heater, 1951); (b) the so-called colicines, produced by strains of Escherichia coli and acting upon other strains of the same species oI upon other enteric bacteria (Gratia, 1925; Blackford et al., 1952); (c) both inhibitory and stimulatory effects produced by certain micrococci or staphylococci in relation to the diphtheria bacillus, streptococci, enteric pathogens, and other bacteria (Dujardin-Beaumetz, 1932; Halbert et al., 1953); and (d) inhibitory effects produced by pneumococci, greening streptococci, and occasionally bv hemolytic streptococci and lactobacilli mainly against Corynebacteriurn diphtheriae and certain staphylococci ('McLeod and Gordon, 1922; W'heater et al., 1952). The last mentioned group of phenomena has been attributed to hydrogen peroxi(le prOduced by the inhibitor species and is thought to encompass the analogous inhibitory properties found in whole saliva by Dold and Wreignmann (1934) and many latei workers. In addition two repoorts deal with effects l)roduced by E. coli, but evi(lentlv distinct from colicines: one bv AWtiedling (1945) on an inactivator of growtth of Penicilliumi notatum distinct from penicillinase; and another by Paine (1952) on a relatioinship between E. coli and Candida krusei. Among examples of coop)erative or plrobiotic microbial associations may be mentioned the classical satellitism of Hemophilns influenzae bv Micrococcuis aureus (Grassberger, 1897), and various fermentation effects described as "synergism" (Holman and -Meekison, 1926) or "svmbiosis" (Castellani, 1926) such as the production of gas from mannite by a mixture of Protenis nmorganii and Shigella dysenteriae Flexner. The foregoing probably constitutes a very incomplete listing of either antibiotic oI Pirobiotic effects relevant to the indigenous microorganisms. The passing mentioni accordecd by Exvans et al. (1950) to inhibitioin of Propionibacteriuini acnes by anaerobic micrococci suggests the