New method of isolating Salmonellae from milk.

Area of Science:

• Food Microbiology
• Bacteriology
• Dairy Science

Background:

• Accurate detection of Salmonella in liquid milk is crucial for public health and food safety.
• Traditional methods for Salmonella isolation may have limitations in sensitivity and efficiency.
• The North procedure is a recognized method for Salmonella recovery, but its sensitivity in liquid milk warrants further investigation.

Purpose of the Study:

• To compare the sensitivity of a cotton gauze swab method with the revised North procedure for isolating Salmonella from liquid milk.
• To evaluate the effect of different incubation temperatures on the efficacy of the swab method for Salmonella recovery.
• To assess the robustness of the swab method in detecting low levels of Salmonella contamination and its persistence after washing.

Main Methods:

• Liquid milk samples were artificially contaminated with known levels of Salmonella.
• Salmonella isolation was performed using a cotton gauze swab method and the revised North procedure.
• Swab cultures were incubated at different temperatures (37°C and 43°C).
• Media used for isolation included Bismuth Sulfite Agar and Brilliant Green Sulfadiazine Agar.

Main Results:

• The cotton gauze swab method demonstrated higher sensitivity in isolating Salmonella from liquid milk compared to the North procedure.
• Incubation at 43°C significantly enhanced the sensitivity of the swab method, allowing detection of Salmonella at levels as low as one per liter.
• Swabs exposed to milk with 100 Salmonella per liter remained positive even after a 2-hour wash in non-contaminated milk.
• Both Bismuth Sulfite Agar and Brilliant Green Sulfadiazine Agar were equally effective, with combined use yielding maximal Salmonella isolations.

Conclusions:

• The cotton gauze swab method, particularly when incubated at 43°C, offers a more sensitive approach for detecting Salmonella in liquid milk.
• This elevated temperature incubation is effective for identifying low-level Salmonella contamination.
• The swab method's resilience to washing suggests its reliability in challenging sample matrices.
• Using both Bismuth Sulfite Agar and Brilliant Green Sulfadiazine Agar optimizes Salmonella recovery from broth cultures.