They can easily spread genes among colonies and reproduce as quickly as every 20 minutes. One cell can become a million in a short time, so that strains adapted to surviving new challenges can quickly evolve. From a human standpoint, this means that some species of bacteria are able to evolve quickly enough to evade our defenses and thus cause disease. Antibiotic drugs and vaccines have been our most powerful weapons to date against bacteria, but neither is completely effective. As a result, bacterial infections that are resistant to one or more antibiotics are rapidly becoming commonplace.
Vaccines are another powerful way to control both bacterial and viral infections.
Vaccines work by stimulating the human immune system to eliminate incoming pathogens before they have an opportunity to establish infection. However, many bacteria are able to hide from the immune system by camouflage or repeatedly changing the molecules on their surface. These organisms have been notoriously difficult foes in the battle to develop effective vaccines. Key Concepts Bacteria differ from viruses. Although most bacteria are not harmful to humans, some species have developed ways to evade host defenses and cause disease.