The genomes of Escherichia coli growing in doxycycline and drug-free media over 21 days.

Bacteria exhibit a 'growth-death' trade-off whereby slower growth results in slower population decline. Given that bacteriostatic antibiotics slow down bacterial growth, they could mediate this trade-off. However, due to the design of antibiotic susceptibility tests, death phases are never quantified and so the impact of antibiotics on longevity is unknown. We sought conditions under which antibiotics may benefit bacterial longevity by growing Escherichia coli in a treatment-growth-death protocol over 28 days in which there was a single exposure to ribosome-targeting antibiotics (doxycycline and erythromycin) and non-ribosome targeting antibiotics (penicillin and rifampicin). Both ribosome-targeting drugs were found to increase population densities and longevity, and there are multiple mechanisms that contribute towards these benefits, such as the scavenging of ROS by doxycycline and changes to carbon metabolism. However, the drug must interact with the ribosome to mediate these benefits as they are absent in a strain with a ribosome protection resistance mechanism. Ribosome protection, therefore, is beneficial in nutrient-rich conditions due to protection from the antibiotic, but is detrimental as nutrients are exhausted.