Differences in growth and antibiotic susceptibility in Escherichia coli stringent response mutants are conferred in minimal nutritional conditions irrespective of amino acid limitation.

09/09/2018

Massimo Cau, Aidan Goodall, Leo Liu, Nicole Liu​

Volume 22
Fall 2017 / Winter 2018

SUMMARY The rise of antibiotic resistance crisis is a critical challenge facing healthcare providers around the world. To combat this phenomenon, we must understand underlying cellular processes that contribute to antibiotic resistance, such as the stringent response. The stringent response is a bacterial stress triggered signal transduction pathway that leads to global reprogramming at transcriptional and translational levels. The primary mediator of the stringent response is guanosine tetraphosphate (ppGpp), an alarmone that indirectly regulates essential processes for survival including amino acid biosynthesis, translational assembly and stress-associated proteins in response to environmental stimuli. In Escherichia coli, ppGpp levels are controlled by two proteins, RelA and SpoT. In this study, we characterized the growth and antibiotic susceptibility of single and double mutants of RelA and SpoT, to provide a future basis for characterization of the stringent response-controlled genes that mediate antibiotic resistance. A relA/spoT double mutant strain exhibited reduced growth compared to the wild type strain in M63B1 minimal medium with defined amino acid concentrations but not in Mueller-Hinton broth supplemented with excess valine. All strains displayed reduced overall growth in minimal medium. Minimum inhibitory concentrations of antibiotics were determined in Mueller-Hinton broth and M63B1 minimal medium with defined amino acid concentrations. Under the conditions tested, the stringent response mutants showed up to a 2-fold increase in antibiotic susceptibility. Further work is required to develop a robust strategy for activating the stringent response in future studies.