Figure 1.
Study of the effect of time, pH and rpoS deletion on Escherichia coli BJ4 inactivation by (+)-limonene.
Log10 of survival counts of Escherichia coli BJ4 (wild type: □) and BJ4L1 (ΔrpoS: ) after 10 min, 6 h and 24 h with 200 µL/L of (+)-limonene in citrate-phosphate buffer of pH 4.0 (A) or 7.0 (B) at 20° C. Cells were recovered in TSAYE. Discontinuous line indicates initial cell concentration (3·107 CFU/mL). Arrow indicates survival counts under detection limit. Error bars indicate standard error.
Table 1.
Influence of previous sub-lethal heat, cold and acid treatments on Escherichia coli BJ4 resistance to (+)-limonene.
Figure 2.
Study of sub-lethal injury caused by (+)-limonene on Escherichia coli BJ4 determined using selective plating technique.
Log10 of survival counts of Escherichia coli BJ4 after 6 h with 200 µL/L of (+)-limonene in citrate-phosphate buffer of pH 4.0 or 7.0 at 20° C. Cells were recovered in TSAYE (□), TSAYE-SC (sodium chloride: vertical stripes) or TSAYE-BS (bile salts: horizontal stripes). Discontinuous line indicates initial cell concentration (3·107 CFU/mL). Error bars indicate standard error.
Figure 3.
Correlation between permeabilized and inactivated Escherichia coli BJ4 cells.
Correlation between the percentage of inactivated Escherichia coli BJ4 and the percentage of cells stained with propidium iodide (permeabilized cells) after different treatment times (10 min, 25 min, 1 h, 6 h, 24 h) with 200 µL/L of (+)-limonene (initial cell concentration: 3·107 CFU/mL) at pH 4.0 (•) or 7.0 (▪).
Figure 4.
ATR-IRMS spectra of (+)-limonene treated Escherichia coli BJ4 cells.
Typical raw spectra (A, D) and soft independent modeling class analogy (SIMCA) of class projections (B, E) and discriminating power (C, F) of non-treated and (+)-limonene treated (200 µL/L) Escherichia coli BJ4 (initial concentration: 3·107 CFU/mL) at pH 4.0 (A, B, C) or 7.0 (D, E, F) of transformed attenuated total reflectance infrared micro spectroscopy (ATR-IRMS) spectra. Black and gray lines and symbols represent non-treated (+)-limonene treated cells, respectively. Spectra were obtained from three independent samples.
Figure 5.
Effect of increased outer membrane permeability on Escherichia coli MC4100 resistance to (+)-limonene.
Survival curves of Escherichia coli MC4100 (•) and its defective mutant ΔlptD4213 (▪) after exposure to 200 µL/L of (+)-limonene in citrate-phosphate buffer of pH 4.0 (A) and pH 7.0 (B). Cells were recovered in TSAYE (•, ▪) and TSAYE-SC (sodium chloride: ○, □). Arrows indicate survival counts under detection limit. Error bars indicate standard error.
Figure 6.
Inactivation of Escherichia coli O157:H7 by combined processes of heat and Pulsed Electric Treatments with (+)-limonene.
Log10 of survival counts of Escherichia coli O157:H7 after lethal heat treatments (54° C for 10 min) (A) or Pulsed Electric Fields treatments (30 kV/cm and 25 pulses) (B) in absence (□) or presence of 200 µL/L of (+)-limonene (▪) and recovery onto TSAYE. Cells after heat and PEF treatments without (+)-limonene were also recovered onto TSAYE-SC (sodium chloride: vertical stripes) or TSAYE-BS (bile salts: horizontal stripes). Discontinuous line indicates initial cell concentration (3·107 CFU/mL). Arrows indicate survival counts under detection limit. Error bars indicate standard error.