This study compares genetic diversities of E. coli O157:H7 and Salmonella isolated during finishing in feedlot steers fed with direct-fed microbial (DFM; Lactobacillus acidophilus; BT1386) versus those not fed DFM. E. coli O157:H7 and Salmonella were isolated and subjected to pulsed-field gel electrophoresis (PFGE) to address genetic variation of the bacteria using both groups. One hundred and ninety four E. coli O157:H7 plus fifty eight Salmonella archive isolated were used in the study. Based on this study, low on-farm diversity was evident although varied genotypes of E. coli O157:H7 and Salmonella existed among the steer population. Additionally, although DFM had an effect in the reduction of E. coli O157:H7 shedding but not Salmonella, feeding DFM to cattle as a pre-harvest intervention strategy may not have any influence on the genetic diversity of the bacteria studied. Thus a detailed study is needed over an extended period and also between farms of different feedlots in order to establish the significance of DFM on E. coli O157:H7 and Salmonella genetic diversity.
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