Low sub-minimal inhibitory concentrations of antibiotics generate new types of resistance

Antibiotic resistance is a major threat to modern medicine. Routes of transmission of resistant bacteria are complex and include spread between humans, between humans and animals, between animals and to humans and animals via the environment. Recent findings have shown that resistant bacteria can be selectively enriched even at antibiotic concentrations several hundred-fold lower than previously expected, such as those found in sewage water. In addition, these low concentrations can select for high level resistant bacteria with very low fitness cost in contrast to resistant bacteria selected at high concentrations such as during antibiotic treatment of patients. This calls for action to determine what concentrations and combinations of antibiotics that can be considered safe in waste water and ensure proper measures to reduce the antropogenic contamination with antibiotics.