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Updated: Aug 18, 2026
Aseptic Laboratory Techniques: Plating Methods
Published on: May 11, 2012
Comparison of seven plating media for enumeration of Listeria spp
M J Loessner1, R H Bell, J M Jay
1Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202.
Abstract:
The suitability of seven media for the enumeration of Listeria spp. was evaluated at 30 degrees C for 48 h. The media tested were (i) the original McBride Listeria agar formulation (with glycine); (ii) modified McBride agar containing glycine anhydride; (iii) LiCl-phenylethanol-moxalactam (LPM) agar; (iv) acriflavine-ceftazidime agar; (v) Rodriguez isolation agar (RISA); (vi) modified Vogel-Johnson (MVJ) agar; (vii) cyclohexanedione-nalidixic acid-phenylethanol agar; and tryptose agar as control. A total of 66 organisms were used including 11 Listeria monocytogenes strains and 5 other Listeria spp. For L. monocytogenes strains only, all media performed highly similarly. Of the other Listeria spp., only two grew on MVJ agar and three each grew on LPM and RISA. Only LPM agar inhibited the 50 non-listeriae, including five yeasts, while MVJ agar inhibited all but one yeast. The McBride Listeria agar formulation that contained glycine anhydride was less selective than the original. When pure cultures of 10 bacteria (including one L. monocytogenes strain) were combined and plated on four media, L. monocytogenes colonies were easiest to enumerate on MVJ agar, followed by LPM and RISA. These media ranked in the same order when plated with homogenates of various foods to which was added L. monocytogenes Scott A, but LPM agar was the best overall since Scott A was inhibited by MVJ. Upon microscopic examination of listerial colonies from the plating media, atypical cell morphology was noted with cells being about twofold in size on LPM, MVJ, and acriflavine-ceftazidime agars. Overall, LPM agar was the most suitable of the media tested even though it was inhibitory to Listeria grayi and Listeria murrayi.
Insights
This study evaluated seven Listeria spp. enumeration media. LiCl-phenylethanol-moxalactam (LPM) agar demonstrated the best overall suitability for Listeria monocytogenes enumeration, despite some inhibition of other Listeria species.
Area of Science:
- Microbiology
- Food Safety
- Bacteriology
Background:
- Accurate enumeration of Listeria species is crucial for food safety.
- Several selective agars exist for Listeria detection, but their efficacy varies.
- Optimizing culture media is essential for reliable microbial analysis.
Purpose of the Study:
- To evaluate the suitability of seven different agar media for enumerating Listeria spp.
- To compare the performance of various selective media against Listeria monocytogenes and other Listeria species.
- To identify the most effective medium for Listeria enumeration in food samples.
Main Methods:
- Seven selective media (McBride, modified McBride, LPM, acriflavine-ceftazidime, RISA, MVJ, cyclohexanedione-nalidixic acid-phenylethanol) and tryptose agar were tested.
- Media were incubated at 30°C for 48 hours with 11 Listeria monocytogenes strains and 5 other Listeria spp.
- Performance was assessed based on growth, selectivity against non-listeriae, and enumeration accuracy in pure cultures and food homogenates.
Main Results:
- All tested media performed similarly for Listeria monocytogenes enumeration.
- LiCl-phenylethanol-moxalactam (LPM) agar showed the best selectivity, inhibiting 50 non-listeriae strains.
- Modified Vogel-Johnson (MVJ) agar inhibited most non-listeriae but also restricted growth of other Listeria spp.; LPM agar was superior for overall Listeria enumeration in food matrices.
- Atypical Listeria morphology was observed on LPM, MVJ, and acriflavine-ceftazidime agars.
Conclusions:
- LiCl-phenylethanol-moxalactam (LPM) agar is the most suitable medium for enumerating Listeria spp., particularly Listeria monocytogenes, in food safety applications.
- While effective, LPM agar can inhibit certain Listeria species like Listeria grayi and Listeria murrayi.
- Further research may be needed to optimize media for comprehensive Listeria detection without compromising selectivity or morphology.
