The bactericidal activity of β-lactam antibiotics is increased by metabolizable sugar species

Here, the influence of metabolizable sugars on the susceptibility of Escherichia coli to beta-lactam antibiotics was investigated. Notably, monitoring growth and survival of mono- and combination-treated planktonic cultures showed a 1000- to 10 000-fold higher antibacterial efficacy of carbenicillin and cefuroxime in the presence of certain sugars, whereas other metabolites had no effect on beta-lactam sensitivity. This effect was unrelated to changes in growth rate. Light microscopy and flow cytometry profiling revealed that bacterial filaments, formed due to beta-lactam-mediated inhibition of cell division, rapidly appeared upon beta-lactam mono-treatment and remained stable for up to 18 h. The presence of metabolizable sugars in the medium did not change the rate of filamentation, but led to lysis of the filaments within a few hours. No lysis occurred in E. coli mutants unable to metabolize the sugars, thus establishing sugar metabolism as an important factor influencing the bactericidal outcome of beta-lactam treatment. Interestingly, the effect of sugar on beta-lactam susceptibility was suppressed in a strain unable to synthesize the nutrient stress alarmone (p)ppGpp. Here, to the best of our knowledge, we demonstrate for the first time a specific and significant increase in beta-lactam sensitivity due to sugar metabolism in planktonic, exponentially growing bacteria, unrelated to general nutrient availability or growth rate. Understanding the mechanisms underlying the nutritional influences on antibiotic sensitivity is likely to reveal new proteins or pathways that can be targeted by novel compounds, adding to the list of pharmacodynamic adjuvants that increase the efficiency and lifespan of conventional antibiotics.