preliminary identification of bacteria

Simple tests for preliminary identification of non fastidious bacteria on Endo agar with biochemical slope.

Notice two main groups: lactose positive and lactose negative bacteria.

Hydrogen sulfide positive strains of E.coli are not common among human isolates.

Some strains of E.coli (lactose delayed E.coli) can look exactly the same as Shigella sonnei in the picture (see also here). S.sonnei is less metabolically active and ferments glucose without gas production.

Cultivation 24 hours, 37°C in an aerobic atmosphere.