Differentiation nf Certain Genera of Gram Negative Bacteria 501 



TABLE 1 

 Summary of Tests used in Determinative Scheme 



Medium Observation 



Nutrient agar Colony appearance 



Gram stain 



Morphology 



Oxidase test (37) 



Antibiotic and 0/129 sensitivity tests (45) 

 Nutrient broth Motility 



Morphology 

 King's media Diffusible fluorescent pigments 



detected under U.V. light 

 Paton's medium Ditto 



+ 2 keto-gluconic acid 

 Hugh and Leifson's medium Dissimilation of carbohydrates 



Nutrient agar -|- 30% Pigment production in Flavobacterixim 



skim milk sp. 



Nutrient agar slope Flagella stain (Casare-Gils) 



mimication ) . For the detection of iiitra-cellular pigments, as in 

 the fla\'obacteria, a nutrient agar, incorporating 30 per cent skim 

 milk, has been found to be most useful. In tlie motile cultures 

 the type of flagellation is determined by a modified Cesare-Gils 

 (42) flagella stain or by electron microscopy. Most of the above 

 tests are carried out at 20C and only occasionally at 37C. 



On the basis of the above tests, the broad groupings given 

 in Table 2 are obtained. These groupings are, of course, strictly 

 applicable only to microorganisms from marine environments. 

 We have, howe\'er, tested this differential scheme against many 

 strains isolated by other workers from widely differing en\'iron- 

 ments and it is clear that while tlie great majority of these can be 

 classified by our scheme, some important exceptions occin\ 



As will be seen from Table 2, an important differentiating 

 test for the motile rods is that of Kovacs' - the oxidase test. In 

 our experience it is invaluable in differentiating the Enterobac- 

 teraceae (oxidase -ve) from the Pseudomonadaceae (oxidase + 

 ve). This contention has recently been supported by Ewing and 

 Johnson (15) who examined a total of 1301 cultures, 1222 of 

 which were Enterobacteraceae with representatives of all the 

 recognised genera and the remainder consisting of members of 

 the Pseudomonadeceae (and including Flavobacter, Xantho- 



