Antibiotics are among the most important drugs against infectious diseases caused by bacteria. Antimicrobial resistance is a defence mechanism of bacteria against the antibiotic agents. The bacteria are able to inactivate an antibiotic by removing it with their cell-internal transport system before it develops its effect. A change in the cell wall prevents antibiotics from reaching the interior of the bacteria. Another strategy is the formation of enzymes that break down the antibiotic active substances and render them harmless. The bacteria often store the resistance genes in an annular piece of DNA outside their chromosome – on a plasmid. These plasmids can be easily exchanged between bacteria so that they quickly pass on their antimicrobial resistance. In this way, antibiotics gradually become ineffective.
The best-known resistant pathogens are methicillin-resistant Staphylococcus aureus (MRSA乐动体育滚球) and vancomycin-resistant enterococci (VRE).