Related Experiment Video
Updated: Jun 20, 2026
12:50
Measuring Bacterial Load and Immune Responses in Mice Infected with Listeria monocytogenes
Published on: August 9, 2011
Inhibition of Listeria monocytogenes in cooked ham by virulent bacteriophages and protective cultures
Applied and Environmental Microbiology
|September 1, 2009
Abstract:
Protective cultures can be used successfully as an additional hurdle together with phages to reduce growth of Listeria monocytogenes on sliced cooked ham. Addition of phages resulted in a rapid 10-fold reduction of L. monocytogenes. After 14 to 28 days of storage, a 100-fold reduction was observed in samples with phages and protective culture compared to results for samples with phages alone.
Insights
Protective cultures and phages effectively reduce Listeria monocytogenes in cooked ham. Combining these methods significantly enhances bacterial reduction during storage.
Area of Science:
- Food microbiology
- Bacteriology
- Food safety
Background:
- Listeria monocytogenes is a significant foodborne pathogen.
- Contamination of ready-to-eat meats like cooked ham poses a public health risk.
- Traditional preservation methods may not always be sufficient to control Listeria.
Purpose of the Study:
- To evaluate the efficacy of protective cultures as an additional hurdle against Listeria monocytogenes.
- To assess the combined effect of protective cultures and bacteriophages in reducing Listeria monocytogenes.
- To determine the impact of this combined approach on Listeria monocytogenes during storage of cooked ham.
Main Methods:
- Application of bacteriophages to sliced cooked ham inoculated with Listeria monocytogenes.
- Co-application of bacteriophages and protective cultures to sliced cooked ham.
- Enumeration of Listeria monocytogenes populations over a 28-day storage period.
- Comparison of bacterial reduction in samples treated with phages alone versus phages plus protective cultures.
Main Results:
- Bacteriophage addition rapidly reduced Listeria monocytogenes by 10-fold.
- Samples treated with both phages and protective cultures showed a 100-fold greater reduction compared to phages alone after 14-28 days.
- Protective cultures enhanced the antimicrobial effect of bacteriophages.
Conclusions:
- Protective cultures serve as a valuable additional hurdle when used with phages.
- The combination of phages and protective cultures offers a synergistic approach to control Listeria monocytogenes in cooked ham.
- This strategy improves the microbiological safety of processed meat products.
Related Concept Videos
01:26Methods of Controlling Food Spoilage
Food spoilage is caused by microbial growth or by chemical and physical changes, all of which affect the taste, texture, and safety of food.Temperature-Based PreservationRefrigeration at 0–4 °C slows microbial growth and enzyme activity, making it ideal for short-term storage. However, certain spoilage organisms—such as psychrotrophs like Listeria monocytogenes—can still proliferate at these temperatures. Freezing below -18 °C further slows biological processes by forming ice crystals, which...
01:28Pasteurization and Food Preservation
Pasteurization is a widely employed thermal processing technique designed to enhance the safety and shelf life of perishable food and beverages. By subjecting products to specific high temperatures for controlled durations, this method effectively inactivates pathogenic microorganisms and spoilage enzymes without significantly compromising sensory qualities. The technique has been pivotal in food safety management, especially for consumables susceptible to microbial contamination such as milk,...
01:27Principles of Food Preservation
Food spoilage results from microbial growth, enzymatic activity, and environmental factors that gradually degrade the sensory, nutritional, and safety qualities of food. Preservation techniques aim to slow or halt these processes to extend shelf life and maintain product quality.A key concept in food microbiology is the microbial growth curve, which includes four phases: lag, exponential (log), stationary, and death. During the lag phase, bacteria adjust to their environment without significant...
01:23Physical Methods for Controlling Microbial Growth: Temperature
Heat is a widely used method to control microbial growth by targeting and denaturing cellular proteins, thereby killing or inactivating microbes. This method's effectiveness is quantified using parameters such as the thermal death point (TDP), thermal death time (TDT), and decimal reduction time (D value). TDP represents the lowest temperature at which all microorganisms in a liquid suspension are eliminated within 10 minutes, whereas TDT is the time necessary to achieve sterilization at a...
00:43Lysogenic Cycle of Bacteriophages
In contrast to the lytic cycle, phages infecting bacteria via the lysogenic cycle do not immediately kill their host cell. Instead, they combine their genome with the host genome, allowing the bacteria to replicate the phage DNA along with the bacterial genome. The incorporated copy of the phage genome is called the prophage. Some prophages can re-activate and enter the lytic cycle. This often occurs in response to a perturbation, such as DNA damage, but can also transpire in the absence of...
01:28Regulation of Bacterial Virulence
Pathogenic bacteria employ a range of regulatory mechanisms to modulate the expression of virulence genes in response to environmental and host-derived signals. These mechanisms ensure that virulence factors are expressed only under favorable conditions, thereby optimizing infection and survival strategies.Mechanisms of Virulence RegulationKey regulatory strategies include:Two-Component Systems: These consist of a membrane-bound sensor kinase and a cytoplasmic response regulator. Environmental...