Interpretive Summary

Alternatives to conventional antibiotics: novel ideas, successes and failures

Norman J. Stern; Poultry Micro. Safety Research Unit; USDA-ARS, Athens, GA

Antibiotics are currently used to control animal disease and to enhance animal production. These two issues are of enormous economic concern. Antibiotic resistance in both veterinary and medically relevant bacteria is a serious concern. Most knowledgeable individuals advocate the prudent use of antibiotics. However, the general public desires drastic reductions in the application of antibiotics in animal husbandry. Consequently, alternatives need be sought.

One alternative to conventional use of antibiotics include application of enhanced biosecurity measures. This approach has been successfully used by the animal industries to reduce mortality and diminish disease transmission among neonatal offspring. The enhanced hygienic measures applied to poultry breeding and hatcheries has resulted in increased hatch rates and reduced disease. However, the practice of food animal production farming in North America (and for most of the world) has not become a bastion of low bacteriological exposure, nor is this likely to occur in the near future.

The Nurmi concept (competitive exclusion) has been successfully applied to both poultry and swine production to control Salmonella presence. The principle demonstrates that selected non-disease-causing commensal organisms can either crowd-out or prevent such pathogens from colonizing the animals. However, this effective and safe approach has, thus far, met with resistance from the Regulatory Agency because of inconsistencies in product content. Additionally, the efficacy of such a product has proven inconsistent in controlling Campylobacter spp. colonization in chickens.

Application of cytokines in combination with defined probiotic Lactobacillus spp. may provide enhance production among farm animals. In one large-scale experiment with piglets, the rate of mortality of the treated animals was halved. In that experiment 4.6% of the treated piglets had diarrhea while 13.4% of the untreated animals had diarrhea. In another experiment with poultry, mortality was dramatically reduced among the treated animals. Clearly, far more work is needed to bring this technology into the realm of possibility. Perhaps as much effort will be needed to educate the public and bring public opinion to accept such treatments of farm animals.

Isolates antagonistic to Campylobacter jejuni using in-vitro tests have been discovered. Spore-forming Bacillus and Paenibacillus spp. were isolated from poultry production environments. Secretions from broth cultures of these were purified through ammonium sulfate precipitation and further purified by gel-filtration and ion-exchange chromatography. The purified materials were shown to create zones of inhibition surrounding the material. The protein nature of these materials were rendered inactive upon exposure to protease enzymes but were stable after exposure to lysozyme, lipase or 100^oC for 15 min. Molecular weights, isoelectric points, and amino acid sequences were determined for each of these bacteriocins. One selected bacteriocin was encapsulated and distributed in chicken feed. In 15 trials, chickens were colonized by Campylobacter jejuni, and 3-days before termination treated birds were given the bacteriocin. Colonization was reduced 5 to 8 logs/gm of feces of treated vs. control birds.

Contact: Norman J. Stern, USDA-ARS, 950 College Station Road, Athens, GA 30605, nstern@saa.ars.usda.gov