Bacteria are always useful is this true?
NO! bacteria causes a host of diseases, among them pneumonia, typhoid, tuberculosis, and the notorious flesh eating bacteria is certainly not useful.
Bacteria are of immense importance for very existence of human race. Vise verse is also true for many species of bacteria. You can not survive without bacteria in your colon. List of uses of bacteria is too long to mention. Even disease causing bacteria are also probably useful for LONG TERM existence of human being.
antibiotics are useful against bacteria because they help to kill off the nasty bacteria or they can also stop the bacteria from reproducing - so the illness doesn't get worse. this then gives your body time to make antibodies which will eventually distroy the bacteria. after this, you won't get the disease again because you are immune to it.
very useful. we have 100 trillion cells in our body, but only about ten trillion are ours. the other is bacteria. In the digestive tract are bacteria, which aid in digestion, compete with possibly virulent bacteria that are inhaled on a daily basis, synthesize vitamins, convert dietary fiber, and degrade toxins.