Why are some E. coli colonies more purple and others more dark navy blue?
A 4. The reason for this is that there are thousands of different strains of E. coli found in the environment, and some produce more of the one enzyme and less of the other. So if a lot of the Red Gal enzyme and only a small amount of the X-gluc enzyme is produced by a strain, the color will be more purple (and will commonly have a pink halo surrounding it), while if less Red Gal enzyme and more X-gluc enzyme is produced the colonies will be dark blue (and will commonly have no noticeable pink halo). Therefore, any colony that looks blue or purple is E. coli because that indicates that both enzymes are produced. Teal green colonies are technically not coliforms, but are likely closely related organisms like Proteus or Salmonella or an unusual form of E. coli. The only way to determine the identity of these is to run further biochemical tests, which should be done by a qualified technician or lab. Q 5. How can I tell if a colony is really only pink and therefore a coliform, if there is
