Antimicrobial resistance (AMR) is of concern in public health.  Use of preventive antibiotics during livestock finishing, and particularly in confined cattle feeding systems (i.e., feedlots) to help prevent formation of liver abscesses, is common.  Such treatments, as opposed to treatments for clinical animal illnesses, are generally provided to animals in feed or water over the duration of finishing.  And, AMR prevalence is thought to be affected by time that a dose is applied as it is likely that “horizontal transfer” of microbial genetics among a community occurs over longer periods of treatment that permanently modify composition of the microbiome.  Liver abscesses are thought to result from transmission of certain rumen organisms that are generally the target of preventive antimicrobial treatments, and are seemingly more prevalent when livestock are fed high-concentrate diets.  So, time and horizontal transfer are enemies of technologies like Tylosin.  In our studies, we have demonstrated that very few AMR genes are truly transmitted to society via beef supply chain.  However, other studies have demonstrated that AMR genes can be pooled in the environment.  Our labs have attempted to displace need for longer-term antimicrobials applied in feed or water by modifying the rumen microbiome.  Using rumen-derived fluids from fistulated (cannulated) steers, we have set up ‘simulated rumens’ in a lab.  We then ‘feed’ the simulated rumens the compounds or combinations of compounds of interest.  As the simulated rumens digest the feed and supplemental compounds, we use mass spectrometry technology to measure types and abundance of volatiles produced.  Such mass spec data provide indices of the impact that compounds can have on ruminate growth efficiency.  Likewise, as digestion progresses, we collect liquid samples from the simulated rumen tubes and evaluate whether or not the composition of the microbiome is modified in a meaningful manner using 16S genetic sequencing techniques.  These measures can indicate whether or not a significant adjustment in the microbiome is expected that could lead to reductions in liver abscess prevalence.  Lastly, we use the gene editing tool of CRISPR-Cas9 (i.e., Clustered Regularly Interspaced Short Palindromic Repeats in conjunction with the CRISPR-associated protein endonuclease enzyme system) to selectively kill organisms for which we can design a CRISPR guide RNA that marks specific target genes of interest.<br/>

Opportunities to displace the need for antimicrobials in production

2019 Spring National Meeting

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