Bacteria, viruses and protozoans are tiny microorganisms that exist virtually everywhere on Earth and are essential to life. The only places devoid of bacteria are the ones that have been manually sterilized by humans. While you cannot see bacteria with the naked eye, they are visible under a microscope. Carpets are one part of the home that's particularly likely to harbor potentially harmful bacteria, but careful cleaning can help reduce bacteria levels in your carpets and other areas.