Evaluation of NP51 Feed Additive in a Research Feedlot Facility and Its Effectiveness in Reducing Shiga Toxin-producing Escherichia coli (STEC) in Cattle Feces

Introduction: Due to harmful and sometimes deadly effects to consumers, Shiga toxin-producing Escherichia coli (STEC) are a growing threat to public health.  Various beef products are associated with STEC illnesses and cattle harbor these pathogens in their gastrointestinal tract.  When fed, selected strains of Lactobacillus acidophilus (NP51) are proven to reduce the presence of some pathogens, including E. coli O157:H7, in the digestive track of cattle; thus, this intervention warrants investigation into the control of non-O157 STECs.

Purpose: Evaluate the effectiveness of Lactobacillus acidophilus (NP51) at a rate of 10⁹/head/day as a feed additive in cattle rations to reduce STEC in fecal samples. 

Methods: One hundred and twelve head of cattle were separated into twenty-eight pens and fed either a treatment (NP51) or control feed ration.  Fecal samples were collected from cattle and evaluated for the presence of Escherichia coli O26, O45, O103, O111, O121, O145 and O157:H7 by enriching ten grams of fecal sample in ninety ml of gram negative broth.  Enrichments were then screened for the non-O157 STEC serogroups using the Dupont Qualicon BAX^®system and O157:H7 immunomagnetic bead were used to plate enrichments on R&F E. coli O157:H7 agar to test for O156.

Results: A 60% (P < 0.10) reduction in overall STEC prevalence was observed among cattle fed NP51 in comparison to control cattle.  Similarly, cattle fed NP51 demonstrated reduced prevalence rates of 20%, 15%, 15% and 8% for serogroups O26, O45, O121 and O103, respectively.  Conversely, an increase in prevalence was observed for serogroups O111 and O145 among cattle fed NP51. 

Significance: These data indicate a significant reduction in most STEC fecal populations among cattle fed the pre-harvest intervention Lactobacillus acidophilus NP51 at 10⁹/head/day.  Decreasing STEC in cattle before harvest is an important step to improving food safety and this study demonstrates the efficacy of NP51 as a pre-harvest intervention.