One milliliter of culture containing a five-strain mixture of Escherichia coli O157:H7 (similar to 10(10) CFU) was inoculated on a 100-cm(2) area marked on unscarred cutting boards. Following inoculation, the boards w...
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One milliliter of culture containing a five-strain mixture of Escherichia coli O157:H7 (similar to 10(10) CFU) was inoculated on a 100-cm(2) area marked on unscarred cutting boards. Following inoculation, the boards were air-dried under a laminar flow hood for 1 h, immersed in 2 liters of electrolyzed oxidizing water or sterile deionized water at 23 degrees C or 35 degrees C for 10 or 20 min;45 degrees C for 5 or 10 min;or 55 degrees C for 5 min. After each temperature-time combination, the surviving population of the pathogen on cutting boards and in soaking water was determined. Soaking of inoculated cutting boards in electrolyzed oxidizing water reduced E. coli O157:H7 populations by greater than or equal to 5.0 log CFU/100 cm(2) on cutting boards. However, immersion of cutting boards in deionized water decreased the pathogen count only by 1.0 to 1.5 log CFU/100 cm(2). Treatment of cutting boards inoculated with Listeria monocytogenes in electrolyzed oxidizing water at selected temperature-time combinations (23 degrees C for 20 min, 35 degrees C for 10 min, and 45 degrees C for 10 min) substantially reduced the populations of L. monocytogenes in comparison to the counts recovered from the boards immersed in deionized water. E coli O157:H7 and L. monocytogenes were not detected in electrolyzed oxidizing water after soaking treatment, whereas the pathogens survived in the deionized water used for soaking the cutting boards. This study revealed that immersion of kitchen cutting boards in electrolyzed oxidizing water could be used as an effective method for inactivating foodborne pathogens on smooth, plastic cutting boards.
D-values (decimal reduction times) and z-values (increase in temperature required for a 1-log change in D-value) for Listeria monocytogenes Scott A were determined in liquid whole egg with nisin (0 or 10 mu g ml(-1)) ...
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D-values (decimal reduction times) and z-values (increase in temperature required for a 1-log change in D-value) for Listeria monocytogenes Scott A were determined in liquid whole egg with nisin (0 or 10 mu g ml(-1)) and NaCl (0 or 10%) by a submerged glass ampoule procedure. Samples were plated onto nonselective agar at appropriate intervals, and D-values were determined using a modified biphasic logistic equation. Addition of NaCl increased D-values at all temperatures tested. The addition of nisin to unsalted liquid whole egg resulted in a rapid 4-log reduction in viable counts within the first hour. Nisin significantly (P less than or equal to 0.05) decreased D-values at lower (<58 degrees C) temperatures in both unsalted and salted liquid whole egg but had little effect on the D-values at current minimum U.S, and Canadian pasteurization temperatures (60 degrees C without NaCl;63 degrees C with NaCl). However, when nisin was added 2 h prior to heat treatment, D-values were significantly (P less than or equal to 0.05) reduced at these temperatures. Inhibitory levels of nisin were detected in the liquid whole egg postpasteurization. Nisin could have a favorable impact on the control of L. monocytogenes in pasteurized liquid egg products.
The aim of this study was to examine the physicochemical surface properties and the ability to adhere to stainless steel of three strains of Listeria monocytogenes after different cultivation procedures. To this end, ...
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The aim of this study was to examine the physicochemical surface properties and the ability to adhere to stainless steel of three strains of Listeria monocytogenes after different cultivation procedures. To this end, bacteria were cultivated at 37 degrees C after storage at two frequently used temperatures (4 degrees C or -80 degrees C) and were then transferred into the liquid medium (trypticase soy broth supplemented with 6 g liter(-1) of yeast extract, pH 7.3) between one and four times. In addition, the influence of supplementing the growth medium with lactic acid was explored, this organic acid being representative of both the dairy and cured meat industries. The hydrophobic/hydrophilic and electron-acceptor/electron-donor characteristics of the strains were evaluated by the microbial adhesion to solvents method. Using this technique, we recorded an increase in the hydrophobic properties of one strain stored at 4 degrees C, with an increasing number of transfers in the media (P < 0.05), Another plant-isolated strain appeared more hydrophobic and stuck better to stainless steel when cells were stored at 4 degrees C rather than at -80 degrees C. Preculturing L. monocytogenes in a lactic acid-supplemented medium increased the affinity of microbial cells to solvents and the bacterial attachment to stainless steel (P < 0.05).
Listeria monocytogenes inhibition by Carnobacterium strains and crude bacteriocins on sterile and commercial vacuum-packed cold-smoked salmon stored at 4 degrees C and 8 degrees C was investigated. Carnobacterium pisc...
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Listeria monocytogenes inhibition by Carnobacterium strains and crude bacteriocins on sterile and commercial vacuum-packed cold-smoked salmon stored at 4 degrees C and 8 degrees C was investigated. Carnobacterium piscicola V1 was bactericidal against L. monocytogenes at the two temperatures, whereas Carnobacterium divergens V41 presented a bacteriostatic effect. C. piscicola SF668 delayed L. monocytogenes growth at 8 degrees C and had a bacteriostatic effect at 4 degrees C. Listeria growth was not affected by a non-bacteriocin-producing C. piscicola. Crude extracts of piscicocins were bactericidal at 4 degrees C and 8 degrees C. Listeria growth was delayed by divercin V41 at 8 degrees C and was inhibited at 4 degrees C. Nisin delayed Listeria growth at 8 degrees C and was bacteriostatic at 4 degrees C. The present study demonstrates that L. monocytogenes growth could be prevented on vacuum-packed cold-smoked salmon by Carnobacterium and associated bacteriocins at chilled temperatures. Moreover, no product spoilage could be observed with the use of such bacteriocin-producing strains as demonstrated by good sensorial analyses and low biogenic amine production.
L. monocytogenes infections are most common in newborn infants and persons with impaired defense mechanisms. Although there are reports of successful treatment with ampicillin alone, there is uncertainty as to what re...
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L. monocytogenes infections are most common in newborn infants and persons with impaired defense mechanisms. Although there are reports of successful treatment with ampicillin alone, there is uncertainty as to what regimen constitutes the most effective therapy. The in vitro synergism between ampicillin and gentamicin against L. monocytogenes was studied. Seven L. monocytogenes strains isolated from blood or CSF of infants and 3 control strains obtained from the Center for Disease Control were tested. Minimal inhibitory concentrations of ampicillin and gentamicin were determined in Todd-Hewitt broth with an inoculum of 105 organisms/ml. Killing curves were determined for ampicillin (6 .mu.g/ml), gentamicin (0.5 .mu.g/ml) and the combination of ampicillin (6 .mu.g/ml) plus gentamicin (0.5 .mu.g/ml). Incubation of approximately 107 organisms/ml with these concentrations of ampicillin and gentamicin caused no significant reduction in the viable bacterial population in 24 h. The combination was bactericidal in all 7 strains isolated from patients and 1 control strain. The ultimate test of the superiority of this combination to ampicillin alone probably must come from clinical studies. The synergistic and bactericidal effects of ampicillin with gentamicin may be desirable in treatment of newborns and patients with underlying disease.
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