Question

how many types of bacteria are present in a digestive tract ?

Answer 1

 E. coli, Clostridium bacteria,Fusobacteria,Eubacteria,Bifidobacteria ,Peptostreptococcus, Ruminococcus and Peptococcus.

Answer 2

there are many types of bacteria present in our body 
1)most of them cause many diseases to humans
2)some bacterias are useful

some of  bacterias are

E. coli,
Clostridium bacteria,
Lactobacillus
Bifidobacteria
Fusobacteria
Bacillus cereus
Eubacteria
Bifidobacteria
Peptostreptococcus
Listeria monocytogenes