Question

E. coli, Enterobacter aerogenes, Salmonella typhi, and Proteus vulgaris are all able to metabolize glucose. Why are they all not able to metabolize lactose and sucrose?

Answer 1

these microorganisms do not have enzymes that are needed for cleavage of
lactose and sucrose (disaccharides) to glucose and
fructose (monosaccharides). These enzymes are called invertase and
lactase.

Microorganisms can do nothing with lactose and sucrose without
these enzymes.