Microbes are often identified using biochemical tests that detect specific enzymes of metabolic pathways. e. coli typically ferments lactose, whereas shigella does not. if a pure culture of each bacterium was placed in a tube containing lactose as the only food source, and a chemical indicator changed color after a ph change, what would the tubes look like after the bacteria were incubated?

a. both tubes would show the evidence of lactose fermentation by turning alkaline.
b. the tube with e. coli would indicate a ph change, and the shigella tube would indicate no change.
c. neither tube will show any change.
d. both tubes would show the evidence of lactose fermentation by turning acidic and changing the ph indicator.