It is recommended that the B. coli group be considered as including all
non-spore-forming bacilli which ferment lactose with gas formation and
grow aërobically on standard solid media.
The formation of 10 per cent. or more of gas in a standard lactose broth
fermentation tube within 24 hours at 37° C. is presumptive evidence of
the presence of members of the B. coli group, since the majority of the
bacteria which give such a reaction belong to this group.
The appearance of aërobic lactose-splitting colonies on
lactose-litmus-agar or Endo’s medium plates made from a lactose broth
fermentation tube in which gas has formed confirms to a considerable
extent the presumption that gas-formation in the fermentation tube was
due to the presence of members of the B. coli group.
To complete the demonstration of the presence of B. coli as above
defined, it is necessary to show that one or more of these aërobic plate
colonies consists of non-spore-forming bacilli which, when inoculated
into a lactose broth fermentation tube, form gas.
It is recommended that the standard tests for the B. coli group be
either (A) the _Presumptive_, (B) the _Partially Confirmed_, or (C) the
_Completed_ test as hereafter defined, each test being applicable under
the circumstances specified.