Emerging Infectious Diseases

Sigma S (ss) controls the synthesis of resistance proteins in stationary pathogenic bacteria [(e.g., Escherichia coli (UPEC)]. Deletion of the rpoS gene rendered E. coli more sensitive to bactericidal antibiotics (BAs): gentamicin, nnorfloxacin and ampicillin. Proteomic analysis implicated a weakened antioxidant defense (AD). Use of the psfiA genetic reporter, 3-(p hydroxyphenyl) fluorescein (HPF) dye, and Amplex Red showed that BAs generated more oxidative stress (OS) in the mutant. Co-administration of the antioxidant N-acetyl cysteine (NAC) and treatment under anaerobic conditions decreased drug lethality of the mutant, further indicating AD involvement. The greater OS in this strain results from impaired capacity to quench endogenous ROS, e.g., respiration linked electron leakage. Infection by UPEC in mice showed that AD was important for UPEC antibiotic reistance also in vivo. Disruption of AD by eliminating quencher proteins, or those of pentose phosphate pathway (which provides NADPH for quenching oxygen radicals) also generated greater OS and killing by BAs. Thus, BAs kill stationary-phase bacteria also by generating OS, and targeting AD can therefore enhance their efficacy. Using bioinformatics, small molecule compounds were identified towards this end, and initial results have given promising results. In space flights, astronauts often suffer from UPEC infection. The EcAMSat mission, using a highly sophisticated microfluidic system showed that UPEC missing ss had increased sensitivity to gentamicin also in space. We have also developed method for determining resistance at single cell level. Together, these results promise to provide powerful means to combat bacterial antibiotic resistance.