coli (Figure 7). With amino acid supplementation, sizes of the ZOI reduced for MAPK inhibitor both the wild type and the ΔarcA mutant E. coli, and the difference in the sizes of the ZOI between wild type and ΔarcA mutant E. coli diminished with amino acid supplementation (Figure 7). We tested single amino acids and combinations of various amino acids, and none of the combinations tested was
able to complement the susceptibility of the ΔarcA mutant E. coli as the total amino acids (data not shown). Figure 7 Amino acid complementation increased the resistance of E. coli to H 2 O 2 and reduced the difference in H 2 O 2 resistance between the wild type and ΔarcA mutant E. coli. Resistance of wild type (diamond) and the ΔarcA mutant E. coli (square) to H2O2 was assayed by the ability to grow in the presence of H2O2 and more resistant bacteria show a smaller diameter of inhibition. Various volumes of 20 mM amino acid solution was spread onto each M9 minimal medium plate containing approximately 1 × 106 c.f.u. wild type or ΔarcA mutant E. coli and a paper disc of 1/4″” with 10 μl of 30% H2O2 was
added to the center of each plate. Zone of inhibition Selleckchem Vorinostat was measured after overnight Selleck Brigatinib incubation and plotted against the volume of amino acid supplementation. At least three experiments were performed, and results from a representative experiment performed in triplicates are shown. Error bars indicate standard deviation and sometimes fall within the data label..
Antibiotic that inhibits protein synthesis increased susceptibility of E. coli to H2O2 To test if protein synthesis is important for bacterial survival and if protein synthesis inhibition is detrimental to bacteria under reactive oxygen stress, we assayed the resistance of E. coli to H2O2 in the presence of chloramphenicol, an antibiotic that inhibits peptide bond formation and hence protein synthesis. Without H2O2 or antibiotic, wild type E. coli grew approximately 2log10 during 6 hours of incubation (Figure 8, left half, open bar). Hydrogen peroxide was bactericidal and the bacterial concentration decreased for over 1log10 (Figure 8, left half, this website diagonally-hatched bar). Supplementation of chloramphenicol alone prohibited bacterial proliferation and the bacterial concentration decreased slightly (Figure 8, left half, vertically-hatched bar). Incubation in the presence of both H2O2 and chloramphenicol was more detrimental to E. coli than either H2O2 or chloramphenicol alone, and the bacterial concentration decreased by nearly 4log10 (Figure 8, left half, cross-hatched bar). This indicates that chloramphenicol enhanced the bactericidal activity of H2O2. To determine if this enhanced bactericidal activity is due to the bacteriostatic activity of chloramphenicol, we tested the effect of ampicillin, an antibiotic that inhibits the bacterial cell wall synthesis, in the same assay.