Table 1.
Minimum inhibitory concentration (MIC) range of biocides for microorganisms tested in nutrient rich and synthetic wastewater media (105 CFU/mL inoculum).
Fig 1.
Comparison of pH and cell density dependent killing efficacy of HSP, H2O2, and NaOCl Killing efficacy of biocides (20 ppm) at pH 7.0 on 106 E. coli (A), at pH 8.5 on 106 E.coli (B), and at pH 7.0 on 103 E. coli (C) as measured by total CFU/mL over 300 min (A,B) or 60 min (C).
H2O2 is much slower at killing bacteria at pH 7.0 than either HSP or HOCl2 (A). Raising the pH to 8.5 increases the 100% kill times of NaOCl to equal to or greater than that of HSP (B). At lower cell densities HOCl2 reaches 100% killing in 15–30 minutes while both HSP and H2O2 show slower killing kinetics (C).
Fig 2.
Comparison of the effect of neutralization of biocide on killing of E.coli at high and low cell densities.
Killing efficacies of HSP or H2O2 (20 ppm) was measured at high (A, C) or low (B, D) cell densities with and without neutralization of biocide by addition of 20 ppm catalase. Killing rates at high cell densities by HSP or H2O2 are not influenced by neutralization (A, C), whereas at low cell densities bacteria exposed to HSP, but not neutralized, are killed significantly more quickly than those neutralized (B). This effect is not seen with H2O2 at the low cell densities (D).
Table 2.
Effect of mono and divalent salt concentrations on the killing efficacy of 20 ppm HSP or H2O2 against 106 CFU/mL E. coli K12 at pH 7.
Fig 3.
Comparison of HSP, HSP-silver and silver nitrate on the metabolism and cell viability of a P. aeruginosa biofilm in a continuous flow apparatus.
Stable, established biofilms of P. aeruginosa monocultures were exposed to the indicated concentrations of HSP, HSP-silver or silver nitrate for 2 hrs and CO2 generated was monitored and plotted as the maximum reduction relative to the untreated biofilm pre biocide exposure (A). While silver nitrate and HSP-silver had negligible effects on metabolism, HSP treatment of the biofilm significantly inhibited metabolism. (B) and (C) show the viability of planktonic cells released from the biofilm measure by total viable count (B) or by enumerating live and dead bacteria via epifluorescence microscopy using the BacLight Bacterial Viability Kit (C). Treatment with HSP shows a dose dependent effect on cell viability at more significant levels than either HSP-silver or silver nitrate. Stars indicate HSP treatments statistically significantly different from silver treatments (P ≤0.05) Bars are included where HSP treatment is significantly different from only one type of silver treatment.