Did you know we are at war? The enemy: pathogenic bacteria.
Humanity and our livestock are engaged in a constant arms race against disease-causing bacteria. We are at a distinct disadvantage though. The enemy outnumber us billions to one and adapt at an alarming rate.
We scored a major win roughly 70 years ago with the discovery of antibiotics; our greatest weapon to date. However, the enemy has been developing resistance ever since, meaning we need to stock our arsenal in this biological war with new and different weapons.
Seriously speaking, the efficacy of antibiotics is a growing public health concern around the world. Who or what is to blame for drug-resistant bacteria is hotly contested, but the actions of many countries are not.
Nations around the world have outlawed certain uses of antibiotics to preserve their efficacy in human medicine. Several countries, including the U.S., have banned the use of medically-important antibiotics for growth promotion purposes in livestock. As reported last week, the World Health Organization recommended countries ban the use of all antibiotics for this purpose, and ban the use of medically-important antibiotics in livestock for any purpose.
Because of these bans, and the likelihood of more in the future, research into antibiotic alternatives has been ramping up. There are many possibilities, but they all come with pros and cons. In many cases, existing research is thin and inconclusive, or effects have only been tested in labs rather than in practical settings. But if antibiotics are going to be a tool of the past for food production, alternates need to be pursued.
Below is a list of eight different antibiotic alternatives being explored for use in livestock:
Phytochemicals
These are plant-derived compounds that may have antibiotic- or growth-promoting properties. Some of the greatest interest is in compounds from alliums (garlic, onion), thyme, oregano, hot peppers, cloves, juniper berries, dill, and cinnamon. Different compounds have different effects, but most are being investigated for antimicrobial properties that may have potential rumen health benefits.
Pros: Extensive familiarity in human culinary and medicinal use, wide variety of sources to exploit that are readily available, relatively low cost, unlikely to cause negative residues in meat
Cons: Mechanism poorly understood, extreme variability of results based on how the sourced plant was grown and processed, inconclusive results in existing studies, some dosages may negatively affect meat flavor
Bacteriophages
Some viruses prey on specific bacterium; these are called bacteriophages or simply “phages.” These viruses can be used to combat specific bacterial infections much in the way parasitic wasps can be used to prey on harmful flies.
Pros: Some phages can be quite effective at destroying their target bacteria, phages adapt with their prey bacterium
Cons: Phages are strain-specific so they would not work widely, infections would need to be accurately identified to choose the right phage, the animal immune system would attack them as viruses, they could aid in horizontal gene transfer across different bacteria, phages are very temperature-sensitive, phages can release toxins from the bacteria they kill, phage therapies are very time-sensitive
Antimicrobial Peptides
Peptides are short-chain amino acids that act as a defense mechanism in some bacteria against other specific bacteria. These can be isolated and cultivated for use apart from their host bacteria. In using antimicrobial peptides, we can effectively steal bacteria’s weapons against each other and use them ourselves.
Pros: Some antimicrobial peptides have been used for decades such as bacitracin zinc, do not leave residues in meat, do not pollute the environment
Cons: Can be expensive to produce, some types are potentially toxic to human and animal cells, only narrowly effective against certain bacteria
Pre- and Probiotics
Fighting fire with fire. Pre- and probiotics are using microorganisms to fight other microorganisms. But rather than directly fighting bad bacteria, the purpose of pre- and probiotics are intended to outcompete bad bacteria and help an animal’s gut health improve, thereby giving them more tools to better fight off an infection if or when it happens.
Pros: Probiotics have been used for decades in livestock, existing infrastructure, known to human medicine, no residues, resistance development almost completely impossible
Cons: Production and standards are poorly organized at this point, some research suggests lack of prebiotic efficacy in cattle, storage and viable usage can be problematic in a commercial setting
Vaccines
Like vaccines against viruses, vaccines against bacteria work by presenting an animal’s body with a weakened or killed example of a bacteria. The animal’s immune system then can fight the weakened bacteria and create antibodies to be ready if an actual infection strikes. Some antibacterial vaccines already exist in the cattle industry, like the Bangs vaccine against the Brucella abortus bacterium.
Pros: Proven efficacy in commercial settings in some cases, existing infrastructure and knowledge base on the production and administration of vaccines
Cons: Injections require additional animal handling and stress, many vaccines are strain-specific, vaccines must be given before infection occurs and enough time must pass for the animal’s immune system to respond
Feed Enzymes
Enzymes are molecules that make things happen in the body on a chemical level. Targeted enzymes can be added to livestock feed to theoretically help the animal’s body accomplish some biochemical task better. For example, certain enzymes can help break down cellulose. This is thought to both give the animal’s metabolism access to more useful nutrients while at the same time robbing harmful bacteria of those otherwise inaccessible nutrients.
Pros: No residues, very low likelihood of triggering resistance
Cons: Not effective in ruminants since the rumen inactivates most consumed enzymes, results widely varied in other species, can be expensive to produce, unclear production standards
Egg Yolk Antibodies
Chickens are infected with the causative agents for diseases that don’t affect them. The hen’s body produces antibodies without getting sick. These antibodies are concentrated in the egg yolk. The egg yolk can then be fed to the target livestock or antibodies can be isolated from the egg yolk, giving the target livestock the benefit of the antibodies without the risk.
Pros: Egg production is relatively cheap and easy, egg yolk-based feedstuffs do not result in residues and can be incorporated into mammalian feeds, no undesirable side effects
Cons: Widely inconsistent results in feed trials
Clay and Rare Elements
Different kinds of clay, minerals, and rare earth elements (lanthanoids from the periodic table) have chemical compounds that are thought to bind with the cell membranes of harmful bacteria. The effect is to render the bacteria less toxic to effectively harmless. Though these have been used as livestock feed additives for centuries in some traditions, the mechanism is not well understood.
Pros: Poor absorption reduces the likelihood of residues, little to no bacterial resistance pressure, long tradition of use as livestock feed supplement
Cons: Wildly varied efficacy results in studies, mechanism not understood, inconsistent results in feed trials, safety data lacking or inconclusive — Kerry Halladay, WLJ editor
