You cannot prevent bacteria from entering your body. They enter constantly, every time you use a toothbrush, rub your eyes, eat a bite of food, breathe in a cougher's aerosolized droplets, etc.
In reality, having the right kind of bacteria colonizing our oronasopharynx, our skin, our GI tract, etc. prevents many pathogenic bacteria from getting a foothold in our bodies. That is the theory (and the emerging science) behind prebiotics and probiotics (which is different than saying commercial probiotics are recommended).
How we can give good immunity power to our kids?
Our microbiomes (the make-up of the various communities of bacteria living on and inside of us) are influenced heavily by the families we are raised in, the area in which we live, etc. But we do have some influence over them. We should not be afraid of harmless bacteria.
“I think we are coming around to the view that most microbes are indeed beneficial,” says Rob Knight of the University of Colorado Boulder. “Instead of declaring war, we need to think in the context of ecosystems that make up our bodies. Figuring out how to encourage good microbes while eliminating the bad will be of increasing importance.”
Without going into too much detail (you can search the internet for useful advice), some things are being recommended to promote a healthy microbiome (applying common sense is always important, of course), such as:
- eat more plants and less highly-processed foods: vegetables and leafy greens promote a healthier microbiome.
- keep a pet: families that have an indoor dog tend to have fewer allergies and certain other illnesses.
- visit a farm (an organic dairy farm with perhaps a petting zoo).
- avoid unnecessary antibiotics; don't self-prescribe antibiotics (for example, don't save the last few pills from a prescription of antibiotics to take "next time you come down with a bug").
- know the difference between viruses (they do not respond to antibiotics) and bacteria. Don't ask your doctor for antibiotics when you are told you have a virus.
- avoid unnecessary 'industrial strength' household cleaners (mild detergents and elbow grease are frequently good enough. You don't need a germ-free home; it won't ever happen anyway).
- tend a small garden.
- get your proper immunizations. Some are for protection against harmful bacteria.
In general**, do what doctors have been advocating for decades: eat healthily, get outside, exercise, etc. and wash your hands often with soap and water. And don't worry too much about fighting normal bacteria.
** Obviously, if you have special circumstances, follow your doctor's recommendations.
Your Changing Microbiome <- Easy-to-understand introduction
The Human Microbiome <- Introduction to wide range of topics regarding microbiomes
Change Your Microbiome, Change Yourself <- Interesting reading
Research Shows How Household Dogs Protect Against Asthma, Infection
The farm effect