Combined effect of stringent or relaxed response, temperature and rom function on the replication of pUC plasmids in Escherichia coli.

The combined antimicrobial effects of hop resins with sodium hexametaphosphate, glycerol monocaprate, and lysozyme were investigated aiming to make an effective agent against Escherichia coli. When they are used separately, the antimicrobial activity against E. coli was minimal. However, the combination of hop resins with sodium hexametaphosphate exhibited strong antimicrobial activity against E. coli, but no effect was found in combinations of hop resins with the other agents. The activity was strongest when the combination was added at the beginning of growth of the bacteria, resulting in a prolonged lag phase. However, when the antimicrobials were added during the log phase, growth was depressed considerably. By addition of these materials, cell components with absorbance near 260 nm were leaked out. This possibly may have resulted from damage to the cell membranes of the bacteria. The combined effect was also detected in model food systems such as mashed potatos. The use of hop resins and sodium hexametaphosphate in combination may thus be useful for controlling E. coli.

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Combined effect of betaine and trehalose on osmotic tolerance of Escherichia coli in mineral salts medium

Biotechnology Letters ◽

10.1007/s10529-006-9226-0 ◽

2006 ◽

Vol 29 (2) ◽

pp. 213-217 ◽

Cited By ~ 21

Author(s):

E. N. Miller ◽

L. O. Ingram

Keyword(s):

Escherichia Coli ◽

Combined Effect ◽

Mineral Salts ◽

Osmotic Tolerance

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Efficacy of Selected Acidulants in Pureed Green Beans Inoculated with Pathogens (Escherichia coli O157:H7 and Listeria monocytogenes)

Journal of Food Protection ◽

10.4315/0362-028x-69.8.1865 ◽

2006 ◽

Vol 69 (8) ◽

pp. 1865-1869 ◽

Cited By ~ 6

Author(s):

AAKASH KHURANA ◽

GEORGE B. AWUAH ◽

BRADLEY TAYLOR ◽

ELENA ENACHE

Keyword(s):

Escherichia Coli ◽

Acetic Acid ◽

Listeria Monocytogenes ◽

Titratable Acidity ◽

Combined Effect ◽

Escherichia Coli O157 ◽

Green Beans ◽

E Coli ◽

Acid Ph ◽

D Values

Studies were conducted to evaluate the combined effect of selected acidulants (acetic, citric, malic, and phosphoric acid) and heat on foodborne pathogens (Escherichia coli O157:H7 and Listeria monocytogenes) in pureed green beans. To establish a consistent reference point for comparison, the molar concentrations of the acids remained constant while the acid-to-puree ratio, titratable acidity, and undissociated acid were either measured or calculated for a target acidified green beans at a pH of 3.8, 4.2, and 4.6. The D-values at 149°F were used as the criteria for acid efficacy. Generally, acetic acid (puree, pH 3.8 and 4.2) represented the most effective acid with comparatively low D-values irrespective of the target microorganism. A 10-s heating at 149°F inactivated approximately 106 CFU/ml of E. coli O157:H7 in pureed beans at pH 3.8. The efficacy of acetic acid is likely related to the elevated percent titratable acidity, undissociated acid, and acid-to-puree ratio. The effectiveness (which in this study represents the combined effect of acid and heat) of the remaining acids (citric, malic, and phosphoric) at puree pH values of 3.8 and 4.2 were statistically insignificant (α = 0.05). Surprisingly, acetic acid (puree, pH 4.6) appeared to be the least effective as compared to the other acids tested (citric, malic, and phosphoric) especially on E. coli O157:H7 cells, while L. monocytogenes had a similar resistance to all acids at puree pH 4.6. With the exception of citric acid (pH 3.8), acetic acid (pH 4.6), and malic acid (pH 3.8 and 4.6), which were statistically insignificant (P > 0.05), the D-values for L. monocytogenes were statistically different (P ≤ 0.05) and higher than the D-values for E. coli under similar experimental conditions. A conservative process recommendation (referred to as the “safe harbor” process) was found sufficient and applicable to pureed green beans for the pH range studied.

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Combined Effect of Nisin and Pulsed Electric Fields on the Inactivation of Escherichia coli

Journal of Food Protection ◽

10.4315/0362-028x-63.6.741 ◽

2000 ◽

Vol 63 (6) ◽

pp. 741-746 ◽

Cited By ~ 52

Author(s):

MAURICIO R. TEREBIZNIK ◽

ROSA J. JAGUS ◽

PATRICIA CERRUTTI ◽

MARTA S. DE HUERGO ◽

ANA M. R. PILOSOF

Keyword(s):

Escherichia Coli ◽

Protective Effect ◽

Electric Fields ◽

High Voltage ◽

Combined Treatment ◽

Action Spectrum ◽

Pulsed Electric Fields ◽

Combined Effect ◽

Bacterial Cells ◽

Doehlert Design

The Doehlert design was applied in order to investigate the combined effect of nisin and high voltage pulsed electric fields (PEF) on the inactivation of Escherichia coli in simulated milk ultrafiltrate media. Nisin alone was totally inactivated by PEF, but in the presence of bacterial cells a protective effect was observed. However, the effectiveness of nisin was still decreased when bacterial cells were subjected to the combined treatment. In spite of this phenomenon, an almost additive response emerged as a consequence of the combined treatment. A 4-log cycle reduction may be accomplished with around 1,000 IU/ml (7.15 μM) of nisin and three pulses of 11.25 kV/cm or 500 IU/ml for five pulses of the same intensity. The observed efficacy arising from the combination of both treatments suggests the possibility of using PEF for improving the action spectrum of natural antimicrobials.

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