THE COLI-AEROQENES GROUP 665 



belonged to the indole-negative coli group, only 10 did so. The value of the 

 method has now been amply confirmed (see Mackenzie and Hilton-Sergeant 1938, 

 Dodgson 1938, Bardsley 1938a, Clegg and Sherwood 1939, Perry 1939, Eaven, 

 Peden and Wright 1940, Ferramola 1940, Clegg 1941, Sherwood and Clegg 1942, 

 Batty-Smith 19426, Stuart et al. 1942). Two discordant reports on the value of 

 the test have appeared. Kaghavachari and Iyer (1939a) found that about 50 per 

 cent, of aerogenes-like strains in Madras waters, and Boizot (1941) about 10 per cent, 

 in Singapore waters, were able to produce gas in MacConkey broth at 44° C. 

 Possibly this may be due to a higher optimal temperature for growth of aerogenes 

 strains in the tropics than in temperate climates. With this reservation, however, 

 we may say that the 44° C. MacConkey test appears to be of greater value 

 than any other single test in picking. out typical faecal coli strains. 



There can, weHhink, be no doubt that the primary division of the lactose fer- 

 menters must be made on the basis of the gas ratio, methyl red, Voges-Proskauer, 

 and citrate tests. By this means we obtain a primary classification into coli, inter- 

 mediate,. and aerogenes groups. The secondary division is more difficult. From 

 an ecological standpoint, we believe that the indole, 44° C. MacConkey, and gelatin 

 liquefaction tests afford the most satisfactory grouping, but from a systematist's 

 point of view there is much to be said in favour of classification on sugar reactions. 

 Taking the first method of grouping, we may note that about 93 per cent, of strains 

 from human and animal faeces produce indole, and that about 95 per cent, give 

 a positive 44° C. MacConkey reaction. On the other hand, indole-negative and 

 44° C. MacConkey negative faecal strains are uncommon. A positive indole test 

 given by a citrate-negative strain, or a positive 44° C. MacConkey test given by 

 any strain, is therefore strongly suggestive of its faecal origin. Though both 

 intermediate, aerogenes and cloacce strains are often present in mammalian faeces 

 in small numbers (Cruickshank and Cruickshank 1931, Parr 1939), the balance 

 of evidence strongly suggests that in this country, and in the United States (see 

 Griffin and Stuart 1940), these organisms are primarily of non-faecal origin. Their 

 main habitat is still in doubt, but they are found most often in soil, grains, grasses, 

 food-stuffs, and decaying vegetation. The classification reached by this method 

 is of special value in the interpretation of water analysis tests and is depicted in 

 Chapter 92. 



With regard to the second method of grouping, the test substances that have been 

 accorded special prominence are saccharose, dulcitol and salicin, the value of the last being 

 emphasized by Kligler (1914a, 6) and by Levine (1917). Winslow, Kligler and Rothberg 

 (1919), in their excellent review of the classification of the whole coli-typhoid group, 

 conclude that the types set out in Table 41 inider their appropriate names are the only 

 ones which are sufficiently well estabhshed to merit separate consideration. 



It will be noted that, although the reactions in dulcitol and adonitol are included in the 

 table, the species are adequately defined by the reactions in saccharose and salicin, together 

 with the presence or absence of motihty. It will also be noted that Bad. coscoroba diEFers 

 from Bad. coli communius in being non-motile, Bad. immobile from Bact. coli commune 

 in the same way, and Bad. griinthal from Bad. acidi-ladici only in being motile. 

 Winslow and his colleagues express the view that the presence or absence of motiUty, 

 taken alone, does not justify specific differentiation ; and they suggest the recognition 

 of four species. Bad. neapolitanum, Bad. coli communius. Bad. coli commune, and Bad. 

 acidi-ladici, regarding the coscoroba, immobile, and griinthal types as varieties of the 

 corresponding species. This appears to us a wise and conservative view. We should, 

 ourselves, prefer to narrow the limits still further, regarding Bad. coli as a single species, 

 and placing the neapolitanum, communius, commune and acidi-ladici types as varieties. 



