RcsB-Deficient Escherichia coli K-12 Do Not Exhibit Decreased Intrinsic Resistance Towards Antibiotics That Target the Cell Wall

Understanding intrinsic antibiotic resistance is crucial in face of the many challenges arising in therapeutic antibiotic use. The protein RcsB in the regulator of capsule synthesis pathway has been suggested to be a key player in intrinsic resistance in Escherichia coli towards antibiotics that target cell wall synthesis. We compared the resistance of RcsB knockout strains versus wild type strains of Escherichia coli towards various antibiotics using minimum inhibitory concentration assays. Contrary to our expectations, no difference in antibiotic resistance was observed between the two strains, including towards penicillin. We further validated these results with plate assays and disk-diffusion assays. Additionally, we began preliminary investigation into why the RcsB knockout strain did not exhibit previously observed penicillin susceptibility. Through additional minimum inhibitory concentration assays, we determined that neither differing growth phases nor varying inoculum concentration explained our results. Other factors such as biofilm formation or compensatory signaling through alternative pathways may have
contributed to resistance in the RcsB knockout strain instead.