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Use of MRSD medium and the hydrophobic grid membrane filter technique to differentiate between pediococci and

R A Holley1, G E Millard

  • 1Food Research Centre, Agriculture Canada Ottawa, Ontario.

International Journal of Food Microbiology
|October 1, 1988
PubMed

Insights

A modified MRS medium (MRSD) allows for the differentiation and enumeration of pediococci and lactobacilli in meat starter cultures. This method accurately identifies these bacteria in fermented sausages, improving starter culture performance documentation.

Area of Science:

  • Microbiology
  • Food Science
  • Analytical Chemistry

Background:

  • MRS medium is commonly used for lactic acid bacteria but lacks specificity for differentiating pediococci and lactobacilli.
  • Accurate enumeration and differentiation of these bacteria are crucial for monitoring starter culture performance in fermented meat production.

Purpose of the Study:

  • To develop a modified MRS medium (MRSD) for the selective differentiation and enumeration of pediococci and lactobacilli.
  • To validate the MRSD medium's efficacy in analyzing starter cultures and fermented dry sausages.

Main Methods:

  • MRS medium was modified with L-arginine-HCl, phenol red, polymyxin B sulfate, reduced glucose, and increased Mn2+.
  • The hydrophobic grid membrane filter (HGMF) system was combined with Fast Green FCF dye and adjusted pH 5.5 for differential plating.
  • Post-growth staining with bromocresol purple differentiated blue colonies (Pediococcus) from green colonies (Lactobacilli) after anaerobic incubation.

Main Results:

  • The MRSD medium successfully differentiated Pediococcus (blue) from Lactobacillus (green) colonies.
  • Analysis of 7 Pediococcus strains, 16 Lactobacillus strains, and 18 commercial starter cultures showed accurate enumeration without interference from other genera.
  • The method was effective in starter cultures and fermented dry sausages, demonstrating reliable starter culture performance documentation.

Conclusions:

  • The developed MRSD medium provides a reliable method for differentiating and enumerating pediococci and lactobacilli in food matrices.
  • This technique enhances the ability to assess starter culture viability and performance in fermented meat products.
  • MRSD medium offers improved specificity compared to standard MRS for analyzing complex microbial communities in fermented foods.

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