48 



BACTERIA IN WATER 



nitroso-indol) does not appear at once, the culture may be incubated for a biief 

 period. 



Reduction of nitrate. — B. coli is a vigorous denitrifying organism. In twenty- 

 four hours at 37° C. the reduction of nitrates to nitrites is well mai-ked. (Bouillon 

 5 per cent., KNOg O'l per cent, water 94 '9 per cent). 



Aerobic or facultative anaerobic. 



Vitality and powers of resistance, not considerable, but more than the typhoid 

 bacillus. 



The following table of comparative features of B. coli and B. typhosus is a 

 provisional scheme of some of the diiferences between a typical B. coli and a 

 typical typhoid bacillus. As is pointed out elsewhere, the Coli group is large and 

 its characteristics vary according to origin, race, cultivation, and many other 

 conditions. In some ways the table is misleading, as it is exceptional to find a 

 bacillus which gives all these features, but the table is inserted for reference, 

 because in a general way it states the broad diiferences between the types : — 



Comparative Features of B. coli and B. typhosus 



B. typhosus. 

 Morphology — Bacillus of unequal lengths ; 



some filaments. 

 Flagella — Long, wavy, spiral, numerous 



(9 to 18) ; movement very active. 



On gelatine and agar — Angular, irregular, 



slightly raised colonies ; slow growth ; 



medium remains clear. 

 In gelatine — In ordinary gelatine and in 



lactose gelatine no gas is produced (at 



20° C). No liquefaction. 

 Milk — Not curdled by the bacillus (at 



37° C). No acid production. 

 Indol — In bouillon and Witte's peptone 



water, no production of indol. 

 Bouillon containing 0"3 per cent. Phenol, 



or Formalin (1 : 7000) — No growth. 

 Lactose — bouillon at 37° C. — No gas pro- 

 duction. 

 Neutral-red glucose-agar — No change. 

 Glucose or lactose media, shake cultures— 



No gas production. 

 Potato — An "invisible gi-owth " if the 



potato is acid in reaction. 

 25 per cent, gelatine at ZT C. — Strongly 



and uniformly turbid (Klein). No 



pellicle. 

 Elsner^s iodised potato-gelatine — Slow 



growth ; small transparent colonies. 

 Proskauer and Oapaldi's Medium, No. 1 



— No growth ; no change in reaction. 

 WidaVs reaction — Bacilli became motion- 

 less and agglutinated when suspended 

 in blood serum from a typhoid patient. 



(S«« Appendix.) 

 M'Conkey's lactose agar — Surface colonies 



transparent ; medium clear. 

 Vitality in water or sewage — B. typhosus 

 soon ceases to multiply and more or 

 less readily dies. 

 Pfeiffer's inoculation test with antirtyphoid 

 serum — Negative result. 



B. coli. 

 Bacillus shorter and thicker: 



filaments 



Shorter, stiffer, few (average 3), move- 

 ment less active, and sometimes almost 

 absent. 



Colonies with even margin, homogenous, 

 much larger and quicker growth, 

 medium becomes turbid or coloured. 



Under the same circumstances abundant 

 gas is produced. No liquefaction. 



Milk is curdled, within 24 to 48 hours at 



37° C. Abundant acid production. 

 Indol is present as a rule. 



Grows well and uniformly throughout 



medium. 

 Gas production occurs. 



Marked green fluorescence. 

 Marked gas production. 



Thick, yellowish-white growth, later be- 

 coming brown in colour. 



Gelatine remains clear within 48 hours, 

 but a thick pellicle forms on the 

 surface. 



Rapid growth ; large brown colonies. 



Growth ; acid reaction. 



B. coli remains motile and not aggluti- 

 nated. 



Surface colonies white with yellow 



centre ; haze on medium. 

 B. coli retains vitality and power of 



self-multiplication. 



Positive result, variable symptoms ac- 

 cording to virulence of bacillus. 



