The first one because there are many types of bacteria that are harmful and helpful For instance some types of bacteria have side effects likr pneumonia (Streptococcus pneumoniae), meningitis (Haemophilus influenzae), strep throat (Group A Streptococcus), food poisoning (Escherichia coli and Salmonella), and a variety of other infections.
Some good types of bacteria are Lactobacillus Acidophilus. Dairy products like yogurt are prepared by exposing milk to lactobacillus acidophilus bacteria. there are Streptomyces and Rhizobium that are also good for the human body. I hope I have answered your question.
Emigration means an animal leaves its home because the habitat is no longer ideal for them, and they need to find a more suitable environment. Animals that immigrate or emigrate do not return to the land they left.
