Effect of microbial-derived and acid based feed additives on the antibiotic resistome in broilers

Use of antibiotics results in the emergence of antibiotic resistance, which is a cause of global concern for human and animal health. The extent to which antibiotic resistance is associated with the use of chemical and biological agents used for the expressed purpose to control, deter, inhibit or kill harmful microorganisms is poorly understood, according to FAO, 2018. Three studies conducted in Thailand, USA and Austria evaluate the effect of antibiotics, probiotics and an acid-based feed additive on the prevalence of antibiotic-resistant bacterial population in broilers.

Study Thailand: Shotgun metagenomics was used to evaluate the effect of an antibiotic compound as well as a microbial derived product on the broiler caecal microbiota (microbiome), virulence factor abundance (virulome) as well as the antibiotic resistance genes (resistome). Taxonomical analysis revealed the positive influence of the product on the chicken gut microbiota, indicated by significantly increasing the abundance of the healthy microbiota, such as short chain fatty acid (SCFA) producing bacteria and by reducing the population of potentially pathogenic microorganisms (Escherichia coli, Salmonella enterica, Campylobacter jejuni, Eimeria spp., etc. This resulted in a significantly lower abundance of bacterial antibiotic resistance genes and virulence factors in the caecal microbiome of the chickens.

Study USA: The aim of this study was to evaluate the effect of a microbial derived product tested in the study in Thailand, an organic acid-based feed additive and ampicillin on the prevalence of antibiotic resistant E. coli in the ceca of broilers. Administration of ampicillin in broilers for five days led to a significant increase in the abundance of E. coli strains resistant to ampicillin, amoxicillin-clavulanic acid, cefoxitin, and ceftriaxone. The effects of the microbial derived and acid-based feed supplementation on the prevalence of resistant E. coli are demonstrated by the significantly lower ceftriaxone minimal inhibitory concentration (MIC) values for this group than for the antibiotic group. Additionally, the group received microbial derived product exhibited lower MIC values than the ampicillin group.

Study Austria: The aim of this study was to evaluate the effect of an acids-based feed additive, as well as fluoroquinolone antibiotics, on the prevalence of antibiotic resistant E. coli. Treatment of broilers with enrofloxacin significanlty increased the number of E. coli resistant to ciprofloxacin, streptomycin, sulfamethoxazole and tetracycline; it also decreased the number of E. coli resistant to cefotaxime and extended spectrum beta-lactamase-(ESBL) producing E. coli in the ceca of broilers. The supplementation of feed with organic acids based product did not contribute to an increase of antibiotic resistant E. coli. The oposite was observed: significant decrease in E. coli resistant to ampicillin and tetracycline compared to the control and antibiotic group. The reason for such a decrease needs to be investigated further. In summary, the findings from this experiment provided more evidence on the potential of microbial derived and organic acid-based feed additives as safe antibiotics’ alternative in poultry farming.

Keywords: resistance, antibiotics, probiotics, acidifiers, microbials.

Abstract presented at the 3rd International Symposium on Alternatives to Antibiotics 2019.