Twenty-four-hour direct presumptive enumeration of Listeria monocytogenes in food and environmental samples using the ISO-GRID method with LM-137 agar.
A new culture medium, LM-137 agar, was developed for use with the ISO-GRID hydrophobic grid membrane filter system for direct presumptive enumeration of Listeria monocytogenes in 24 h. The method was validated against three-replicate, three-dilution most probable number procedures based on enrichment methods specified by the U.S. Department of Agriculture, the Association of Official Analytical Chemists International and the U.S. Food and Drug Administration. The study encompassed meats, dairy products, egg, produce, seafood, and environmental samples. The ISO-GRID filter method produced significantly higher recovery of L. monocytogenes from fermented sausage, hot dogs, pasteurized and raw milk, raw shrimp, and environmental swab samples (P < 0.05). The reference methods yielded significantly higher counts from frozen raw pork and cole slaw (P < 0.05). Confirmation rates of presumptive positive isolates from the filter method ranged from a low of 92% (frozen raw pork) to 100% (most other products). Neither the recovery efficiency nor the confirmation rate were affected by the presence of competing aerobic flora.
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QA Life Sciences, Inc., San Diego, California 92121, USA. bugsy@qalife.com
Lerner
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D000332:Aerobiosis; D000818:Animals; D015169:Colony Count, Microbial / Q000379:methods*; D003470:Culture Media; D003611:Dairy Products / Q000382:microbiology; D004783:Environmental Microbiology; D005374:Filtration / Q000379:methods; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000254:growth & development* / Q000302:isolation & purification; D008461:Meat Products / Q000382:microbiology; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D003470:Culture Media