Food Protection Trends

Abstracts - July 2003

Listeria monocytogenes Incidence and Distribution on a Selective/ Differential Plating Medium in Listeria-Positive Environmental Samples from Ready-to-Eat Food Facilities

A Novel Intervention for the Reduction of Bacteria on Beef Carcasses

Listeria monocytogenes Incidence and Distribution on a Selective/ Differential Plating Medium in Listeria-Positive Environmental Samples from Ready-to-Eat Food Facilities

William Lionberg, Lawrence Restaino,* Elon W. Frampton, Vaughn Lewis, andMegan Liedtke

R & F Laboratories, 245 West Roosevelt Road, Building 3, Unit 16, West Chicago, Illinois, 60185, USA

SUMMARY
One thousand sixty-three environmental samples (sponges) from 9 meat, dairy, fish and bakery ready-to-eat food processing facilities were analyzed for Listeria. The ratios and distribution of Listeria monocytogenes to non-L. monocytogenes were determined by use of the chromogenic L. monocytogenes plating medium (LMPM). LMPM differentiates among the Listeria spp. by detecting phosphatidylinositol-specific phospholipase C activity specific for Listeria monocytogenes/L. ivanovii. L. monocytogenes and L. ivanovii form turquoise colonies, whereas all other Listeria spp. produce white colonies with a blue tinge.  L. monocytogenes confirmatory medium and acid production from rhamnose were used to rapidly differentiate L. monocytogenes from L. ivanovii, and all 136 turquoise colonies tested were identified as L. monocytogenes. Two hundred six samples were identified as Listeria-positive. On LMPM-positive plates, the ratios of L. monocytogenes to non-L. monocytogenes spp. were arranged into 5 categories on the basis of colony color.  In the two distribution extremes, 34% of the Listeria-positive LMPM plates contained 100% non-L. monocytogenes Listeria and 23.3% contained 100% L. monocytogenes colonies, accounting for 57.3% of the total positive samples. Eighteen percent of the Listeria-positive LMPM plates contained a majority (> 75%) of white (non-L. monocytogenes Listeria spp.) and < 25% turquoise (L. monocytogenes) colonies,  and on half these plates there were 10 or fewer turquoise colonies. Of the remaining distributions, Listeria-positive LMPM plates containing a majority of turquoise colonies (> 75%, compared with < 25% white Listeria spp. colonies) and plates with approximate equal proportions of Listeria turquoise to white constituted 15.5 and 9.2% of the total positive samples, respectively. Thus, a selective/differential plating medium capable of differentiating L. monocytogenes/L. ivanovii from varying concentrations of other Listeria spp. is a useful tool when L. monocytogenes is a minority component of the total Listeria present.

A Novel Intervention for the Reduction of Bacteria on Beef Carcasses

Joellen M. Feirtag-1* and Michael M. Pullen-2

1-Department of Food Science and Nutrition, College of Agricultural, Food and Environmental Science
2-Department of Clinical and Population Sciences, College of Veterinary Medicine

University of Minnesota, St. Paul, MN  55108, USA

ABSTRACT
The Rinse & Chill™ Technology developed by MPSC, Inc., St. Paul, Minnesota involves the vascular transfer of a chilled solution of sugars and salts through the cardiovascular system.  The solution removes most of the residual blood as it circulates throughout the carcass and drains.  Rinse & Chill™  Technology is a process that ensures a consistent reduction in pH and internal temperature by vascular transfer of a chilled solution into the arterial/venous system and has been demonstrated to reduce significantly the number of microorganisms, particularly coliforms and generic Escherichia coli. Data collected from two separate commercial beef slaughtering facilities demonstrated reductions of a 40.3% (n=180; P = 0.039) and 41.2% (n = 100; P = 0.009)  for aerobic microorganisms on rinsed carcasses, compared to controls.  More importantly, the two commercial facilities demonstrated reductions of 99.3% (n = 180; P = 0.125) and 67.8% (n = 100; P = 0.002) in coliforms on the rinsed carcasses versus the controls. One of the facilities also demonstrated an 83.7% (n = 100; P = 0.0008) reduction in generic E. coli on the rinsed carcasses versus the controls.  This study demonstrates that the Rinse & Chill™ Technology provides a novel intervention for improving microbial control of contamination on bovine carcasses.