title: Comparative evaluation of direct plating and most probable number for enumeration of low levels of Listeria monocytogenes in naturally contaminated ice cream products.
abstract: A precise and accurate method for enumeration of low level of Listeria monocytogenes in foods is critical to a variety of studies. In this study, paired comparison of most probable number (MPN) and direct plating enumeration of L. monocytogenes was conducted on a total of 1730 outbreak-associated ice cream samples that were naturally contaminated with low level of L. monocytogenes. MPN was performed on all 1730 samples. Direct plating was performed on all samples using the RAPID'L.mono (RLM) agar (1600 samples) and agar Listeria Ottaviani and Agosti (ALOA; 130 samples). Probabilistic analysis with Bayesian inference model was used to compare paired direct plating and MPN estimates of L. monocytogenes in ice cream samples because assumptions implicit in ordinary least squares (OLS) linear regression analyses were not met for such a comparison. The probabilistic analysis revealed good agreement between the MPN and direct plating estimates, and this agreement showed that the MPN schemes and direct plating schemes using ALOA or RLM evaluated in the present study were suitable for enumerating low levels of L. monocytogenes in these ice cream samples. The statistical analysis further revealed that OLS linear regression analyses of direct plating and MPN data did introduce bias that incorrectly characterized systematic differences between estimates from the two methods.
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA. Electronic address: yi.chen@fda.hhs.gov.
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Office of Analytics and Outreach, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Régis
authors.initials: R
authors.lastname: Pouillot
authors.affiliation: Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
authors.forename: Laurel
authors.initials: L
authors.lastname: S Burall
authors.affiliation: Office of Analytics and Outreach, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Errol A
authors.initials: EA
authors.lastname: Strain
authors.affiliation: Office of Analytics and Outreach, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Jane M
authors.initials: JM
authors.lastname: Van Doren
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Antonio J
authors.initials: AJ
authors.lastname: De Jesus
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Laasri
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Laila
authors.initials: L
authors.lastname: Ali
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Aparna
authors.initials: A
authors.lastname: Tatavarthy
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Guodong
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Lijun
authors.initials: L
authors.lastname: Hu
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: James
authors.initials: J
authors.lastname: Day
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Ishani
authors.initials: I
authors.lastname: Sheth
authors.affiliation: Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
authors.forename: Jihun
authors.initials: J
authors.lastname: Kang
authors.affiliation: Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
authors.forename: Surasri
authors.initials: S
authors.lastname: Sahu
authors.affiliation: Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
authors.forename: Devayani
authors.initials: D
authors.lastname: Srinivasan
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Eric W
authors.initials: EW
authors.lastname: Brown
authors.affiliation: Office of the Center Director, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Mickey
authors.initials: M
authors.lastname: Parish
authors.affiliation: Office of the Center Director, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Zink
authors.affiliation: Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, Food and Drug Administration, Laurel, MD 20708, USA.
authors.forename: Atin R
authors.initials: AR
authors.lastname: Datta
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Hammack
authors.affiliation: Office of Regulatory Science, Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD 20740, USA.
authors.forename: Dumitru
authors.initials: D
authors.lastname: Macarisin
mesh_terms: D000362:Agar; D000465:Algorithms; D001499:Bayes Theorem; D015169:Colony Count, Microbial / Q000379:methods*; D003470:Culture Media; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D007054:Ice Cream / Q000382:microbiology*; D016018:Least-Squares Analysis; D057230:Limit of Detection; D008089:Listeria monocytogenes / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction; D011336:Probability; D015203:Reproducibility of Results
chemical_list: D003470:Culture Media; D000362:Agar
keywords: Direct plating; Ice cream; Most probable number