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Model examination of selective media for isolation of Listeria strains
1Laboratory of Veterinary and Food Investigation Institute, Budapest, Hungary.
Abstract:
During the Tenth International Symposium on Listeriosis (Pécs, Hungary, 1988) the Working Party on Culture Media of IUMS-ICFMH suggested comparative examination of nine enrichment broths and nine solid selective media. On the basis of this proposal the following media were studied: LiCl-phenylethanol-moxalactam agar (LPM), polymyxin-acriflavine-LiCl-ceftazidime-aesculin-mannitol agar (PALCAM) No. 1 (home made) and No. 2 (Merck), acriflavine-ceftazidime agar (AC), Oxford agar, tripaflavine-nalidixic acid serum agar (TNSA) and Forray's agar. The study was performed as described in "Testing methods for use in quality assurance of culture media". Oxford agar proved to be the best medium. LPM, AC and Forray's agars were somewhat more inhibitory than Oxford medium. In productivity TNSA and PALCAM media were weakest but the latter one was more selective. When 43 sausage samples were enriched in UVM broths and subcultured on the above mentioned media the number of positive samples was the same on Oxford, LPM, AC and TNSA agars but it was lower on PALCAM agar No. 1. When 103 milk samples were subcultured on TNSA and PALCAM agar No. 2, the number of positive samples was the same.
Insights
Oxford agar was the most effective selective medium for Listeria isolation. Other media like LPM, AC, and Forray's agar showed higher inhibition, while TNSA and PALCAM had lower productivity but better selectivity.
Area of Science:
- Microbiology
- Food Safety
- Diagnostic Microbiology
Background:
- The International Union of Microbiological Societies (IUMS) Working Party on Culture Media proposed a comparative study of selective media for Listeria.
- Accurate detection of Listeria is crucial for public health and food safety.
Purpose of the Study:
- To evaluate the performance of nine solid selective media for Listeria isolation.
- To identify the most effective culture medium for Listeria detection in food samples.
Main Methods:
- Comparative analysis of LiCl-phenylethanol-moxalactam (LPM) agar, polymyxin-acriflavine-LiCl-ceftazidime-aesculin-mannitol (PALCAM) agar (Nos. 1 and 2), acriflavine-ceftazidime (AC) agar, Oxford agar, tripaflavine-nalidixic acid serum (TNSA) agar, and Forray's agar.
- Media were tested according to standardized quality assurance methods.
- Food samples (sausage and milk) were analyzed after enrichment in UVM broth.
Main Results:
- Oxford agar demonstrated the best overall performance for Listeria isolation.
- LPM, AC, and Forray's agars exhibited higher inhibitory properties compared to Oxford agar.
- TNSA and PALCAM media showed the lowest productivity, though PALCAM was more selective.
- Positive Listeria detection rates were consistent across Oxford, LPM, AC, and TNSA agars for sausage samples.
- PALCAM agar No. 1 yielded fewer positive results for sausage samples.
- TNSA and PALCAM agar No. 2 showed comparable results for milk samples.
Conclusions:
- Oxford agar is recommended as the superior selective medium for Listeria isolation.
- The choice of selective medium can impact Listeria detection rates, particularly in different food matrices.
- Further validation of PALCAM agar performance is warranted.