Crl and RpoS May Not Be Involved in Cross Protection against Tetracycline in Escherichia coli in Response to Heat Stress

RpoS is the general regulator of stress response in Escherichia coli and is up-regulated under environmental stress conditions such as heat stress, low pH and starvation. Upon primary stress, E. coli develops increased resistance against a secondary unrelated stressor such as antibiotics. This phenomenon is termed cross protection. Crl, a transcription regulator, is involved during primary stress by working in concert with RpoS; however, it has yet to be investigated whether Crl is necessary during cross protection. In this study, the role of RpoS and Crl were investigated by subjecting wild-type (WT) E. coli strain BW25113, ΔrpoS strain JW5437-1, and Δcrl strain JW0230-1 to different durations of heat stress at 45°C. Following heat stress, resistance against tetracycline was determined using the minimum inhibitory concentration (MIC) assay. We could not detect an increase in tetracycline resistance following heat shock in the WT strain. In addition, the results of the MIC showed no difference in tetracycline resistance between the WT and knockout strains after increasing heat stress. This suggests that Crl and RpoS may not be involved in cross protection against tetracycline in response to prolonged primary heat stress.