A Meta-analysis of the association of Lactobacillus acidophilus NP51 administration with Escherichia coli O157 in feces and on hides of feedlot cattle.

Inclusion of the direct-fed microbial (DFM) Lactobacillus acidophilus NP51 (L. acidophilus NP51), in feedlot rations has been associated with decreased burden of Escherichia coli O157:H7 (E. coli O157) in feces and on hides of cattle. The objectives of this meta-analysis were to a) assemble available data from studies that have evaluated an association of L. acidophilus NP51 with E. coli O157; b) reanalyze the data using harmonized statistical models; and c) perform a meta-analysis to produce a summary effect measure and evaluate between study variance. Pen-level fecal and hide prevalence data were gathered from 15 trials that administered L. acidophilus NP51 at 109 CFU/animal/day, 107 CFU/ animal/day, or both. Fecal and hide data were available for 15 and 8 studies, respectively. Data were analyzed to produce study-level relative risk estimates (and their 95% confidence intervals) using generalized linear mixed models. The inverse of study-level variance was used to weight each observation and study-to-study variance was assessed. Outcomes of interest include post-exposure measure of effect, terminal measure of effect, and a dose response. Summary measures of effect from the meta-analysis revealed that E. coli O157 was 42 and 33% less likely to be recovered from feces and hides, respectively, of harvest-ready cattle receiving L. acidophilus NP51 at 109 CFU/animal/day compared to control animals. Fecal E. coli O157 prevalence averaged over time was reduced by 42 and 45% among cohorts receiving high and low doses, respectively. Furthermore, supplementation of L. acidophilus NP51 was associated with a 1.1 log10 CFU/g and 0.26 log10 CFU/g reduction of E. coli O157 concentration in positive fecal samples from cattle receiving high and low doses, respectively.