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[Isolation of Staphylococcus aureus by the Baird Parker method from powdered milk]
M Sánchez Mendoza1, E Fernández Rendón, L Mota de la Garza
1Departamento de Microbiología de la Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D.F., México.
Abstract:
There are many media recommended for the isolation of Staphylococcus aureus from foods, but only with some media one can obtain a good growth started with stressed cells. The Baird Parker (BP) medium is considered the best choice to recover stressed cells, however, it is not as good a medium to isolate Staphylococcus aureus from powder milk. Therefore, it is important to count with alternative media to enhance the chance for Staphylococcus aureus to grow from dehydrated products. Thirty-one powder milk samples contaminated with Staphylococcus aureus were analysed by Baird Parker method, employing four culture media: Baird Parker (BP), Baird Parker + tween + MgCl2 (BPTM), Pork plasma with bovine fibrinogen agar (PPF) and Salt Milk agar (SL). Staphylococcus aureus was isolated in SL, 38.7%; in BP, 3.2%; in BPTM, 6.4%; and PPF, 0%.
Insights
Salt Milk agar effectively isolates Staphylococcus aureus from stressed, dehydrated milk powder. This alternative medium shows higher recovery rates than traditional Baird Parker methods for specific food safety applications.
Area of Science:
- Microbiology
- Food Safety
- Bacteriology
Background:
- Isolation of Staphylococcus aureus from food requires specific culture media, especially for stressed or dehydrated samples.
- Baird Parker (BP) medium is effective for stressed cells but suboptimal for isolating Staphylococcus aureus from powder milk.
Purpose of the Study:
- To evaluate alternative culture media for enhanced isolation of Staphylococcus aureus from powder milk.
- To compare the efficacy of Salt Milk agar (SL), Baird Parker (BP), Baird Parker + tween + MgCl2 (BPTM), and Pork plasma with bovine fibrinogen agar (PPF) for Staphylococcus aureus recovery.
Main Methods:
- Thirty-one powder milk samples were artificially contaminated with Staphylococcus aureus.
- Samples were analyzed using the Baird Parker method with four different culture media: BP, BPTM, PPF, and SL.
Main Results:
- Staphylococcus aureus isolation rates varied significantly across media.
- Salt Milk agar (SL) demonstrated the highest isolation rate at 38.7%.
- Baird Parker (BP) yielded 3.2%, Baird Parker + tween + MgCl2 (BPTM) yielded 6.4%, and Pork plasma with bovine fibrinogen agar (PPF) yielded 0%.
Conclusions:
- Salt Milk agar (SL) is a superior medium for isolating Staphylococcus aureus from dehydrated products like powder milk.
- Alternative media are crucial for improving the detection of Staphylococcus aureus in challenging food matrices.