Antibacterial efficacy of nisin, bacteriophage P100 and sodium lactate against Listeria monocytogenes in ready-to-eat sliced pork ham

ABSTRACT The effectiveness of bacteriophage P100, nisin and sodium lactate, individually and in combination, in inhibiting Listeria monocytogenes in ready-to-eat pork ham slices was assessed. The antimicrobials were applied to the surfaces of ready-to-eat pork ham slices, which were inoculated with a mixture of L. monocytogenes. Among the individual antimicrobial treatments, bacteriophage P100 was the most effective, decreasing L. monocytogenes to undetectable levels at zero and 72 h post-infection. Sodium lactate was the least effective treatment. Treatment with nisin at zero h significantly reduced initial cell density (p < 0.05). However, this pattern was not observed at 72 h of storage. A significant difference (p < 0.05) existed between the results of separate bacteriophage and nisin treatments after refrigerated storage, but not immediately upon inoculation of the bacteria. The results showed that the use of bacteriophage P100 is the method of choice for the control of bacteria.

Control of Listeria monocytogenes growth in soft cheeses by bacteriophage P100

The purpose of this study was to determine the effect of bacteriophage P100 on strains of Listeria monocytogenes in artificially inoculated soft cheeses. A mix of L. monocytogenes 1/2a and Scott A was inoculated in Minas Frescal and Coalho cheeses (approximately 10(5) cfu/g) with the bacteriophage added thereafter (8.3 x 10(7) PFU/g). Samples were analyzed immediately, and then stored at 10 ºC for seven days. At time zero, 30 min post-infection, the bacteriophage P100 reduced L. monocytogenes counts by 2.3 log units in Minas Frescal cheese and by 2.1 log units in Coalho cheese, compared to controls without bacteriophage. However, in samples stored under refrigeration for seven days, the bacteriophage P100 was only weakly antilisterial, with the lowest decimal reduction (DR) for the cheeses: 1.0 log unit for Minas Frescal and 0.8 log units for Coalho cheese. The treatment produced a statistically significant decrease in the counts of viable cells (p < 0.05) and in all assays performed, we observed an increase of approximately one log cycle in the number of viable cells of L. monocytogenes in the samples under refrigeration for seven days. Moreover, a smaller effect of phages was observed. These results, along with other published data, indicate that the effectiveness of the phage treatment depends on the initial concentration of L. monocytogenes, and that a high concentration of phages per unit area is required to ensure sustained inactivation of target pathogens on food surfaces.

Efecto de agregado de ácidos y temperatura sobre el desarrollo de listeria monocytogenes / Acids aggregated effect and temperature over listeria monocytogenes development

Listeria monocytogenes es un microorganismos patógeno asociado a enfermedades de origen alimentario que puede crecer y sobrevivir a temperaturas de refrigeración y a pH bajos. Se analiza el efecto de pH 3.0-6.5 dado por diferentes concentraciones de acidulantes (ac. cítrico, ac. láctico, y ac ascórbico) y de la temperatura de refrigeración (4 y 10ºC sobre el desarrollo y supervivencia de listeria monocytogenes en caldo de cultivo triptona soya y extracto de levadura. Se observó disminución de velocidad de desarrollo de l. monocytogenes al disminución la temperatura. El ácido cítrico resultó tener acción antimicrobiana más efectiva manteniendo los recuentos en fase de latencia a baja concentración. El ácido ascórbico fue el menos efectivo ya que la acción bactericida. Se observó a concentraciones muy altas, este junto con el ac. láctico presentaron un efecto inicial en el recuento de microorganismos. La información obtenida fue sintetizada mediante el índice de inhibición (II) y el efecto inhibitiorio (EI).