The source of lactose is cow's milk.
Probably because that is where the gram negative bacteria have found a food source. Lactose is not the perfered diet, but it works and they are most likely there because they can tolerate the environment, and survive (on lactose) when their #1 food source is not available.
There are different types of food that are a good source of hydrogen. This mostly includes sugars like lactose, fructose and sucrose among others.
Lactose is also called "milk sugar" because it comes from milk. Think LACTose, like in lactate, lactation, etc.
It means that the organism can use Lactose as an energy source
Food manufacturing and processing is the predominant industry of the Philippines.
Bacteria preferentially utilize lactose as a carbon source.
It means that the organism can use Lactose as an energy source
The genes that produce the enzymes needed to break down lactose are not expressed.
Sucrose, Lactose, Maltose
milk
lactulose is manufactured by enzymatic isomerization of lactose.
the lacZ gene encodes b-galactosidase, a key enzyme in lactose metabolism. Which lactose is present in the cell, the cell expresses lacZ and metabolizes lactose. source (Matseringbiology.com and campbell biology)