Recovery and Growth Potential of Listeria monocytogenes in Temperature Abused Milkshakes Prepared from Naturally Contaminated Ice Cream Linked to a Listeriosis Outbreak.

Yi Chen,Anna Wooten,Dumitru Macarisin,Thomas S Hammack,Anna Laasri,Ishani Sheth,Minji Hur,Emma Allard

doi:10.3389/fmicb.2016.00764

Abstract

The recovery and growth potential of Listeria monocytogenes was evaluated in three flavors of milkshakes (vanilla, strawberry, and chocolate) that were prepared from naturally contaminated ice cream linked to a listeriosis outbreak in the U.S. in 2015, and were subsequently held at room temperature for 14 h. The average lag phase duration of L. monocytogenes was 9.05 h; the average generation time was 1.67 h; and the average population level increase per sample at 14 h was 1.14 log CFU/g. Milkshake flavors did not significantly affect these parameters. The average lag phase duration of L. monocytogenes in milkshakes with initial contamination levels ≤ 3 CFU/g (9.50 h) was significantly longer (P < 0.01) than that with initial contamination levels > 3 CFU/g (8.60 h). The results highlight the value of using samples that are contaminated with very low levels of L. monocytogenes for recovery and growth evaluations. The behavior of L. monocytogenes populations in milkshakes prepared from naturally contaminated ice cream linked to the listeriosis outbreak should be taken into account when performing risk based analysis using this outbreak as a case study.

Highlights

In March 2015, a listeriosis outbreak was reported from a hospital involving five highly susceptible elderly patients who were hospitalized for other medical conditions prior to exposure to Listeria monocytogenes (Centers for Disease Control and Prevention, 2015)
This is the first report of the recovery and growth potential of L. monocytogenes in milkshakes prepared with ice cream products that were naturally contaminated with very low levels of bacteria and produced from a production line that was implicated in a listeriosis outbreak
The lag phase duration and generation time of L. monocytogenes determined in the present study contributed to a better understanding of the behavior of L. monocytogenes in the temperature abused milkshake prepared with naturally contaminated ice cream

Summary

Introduction

In March 2015, a listeriosis outbreak (outbreak I) was reported from a hospital (hospital X) involving five highly susceptible elderly patients who were hospitalized for other medical conditions prior to exposure to Listeria monocytogenes (Centers for Disease Control and Prevention, 2015). Recovery and Growth of L. monocytogenes in Milkshake ice cream scoops that were produced in production line A (Centers for Disease Control and Prevention, 2015; Karl Klontz, personal communication). Chen (2015) enumerated the levels of L. monocytogenes in 2,320 individually wrapped scoops of ice cream produced in production line A. The levels of L. monocytogenes in individual scoops were below 20 and 50 most probable number (MPN)/g in 92.3 and 98.4% of tested scoops, respectively; and they were homogeneously low among different production dates with a geometric mean concentration of 0.15 to 7.1 MPN/g (Chen, 2015)

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