Antibiotic Resistance in Livestock: Why the failure?

Antibiotic Resistance Occurrence in Livestock

Antibiotic resistance in livestock presents an increasing global concern for the agriculture sector. The very microbes that cause infections and disease are becoming resistant to antimicrobial drugs because of overuse, misuse and counterfeiting. The more these drugs are abused, the greater the likelihood that microbes will become resistant, thereby placing livestock and livelihoods at risk.

Bacteria are constantly evolving and this enables them to efficiently adapt to new environments. Antibiotic resistant is the ability of a bacterium to grow in the presence of a chemical (antibiotic) that would normally kill it or limit its growth. At the same time the antibiotic is working effectively against the non-resistant or sensitive strains of the same bacterium at the same location. That is, the antibiotic medication favours the resistant bacteria and these will ultimately dominate the scene often monopolizing it and displacing their sensitive counterparts. Antimicrobial resistance makes it harder to eliminate an infection from the body which, in effect, means the antibiotic becomes less effective. As a result, some infectious diseases are now more difficult to treat than they were just a few decades ago. As more microbes become resistant to antimicrobials, the protective value of these medicines is reduced. Overuse and misuse of antimicrobial medicines are among the factors that have contributed to the development of drug-resistant microbes.

Antibiotic Resistance:How it Occurs in Livestock

How does bacteria resistance arise in the first place? All genetic material occasionally and spontaneously randomly mutates. On many occasions this is of no consequence but very rarely it will throw up a genetic change of consequence to the bacterium such as the conferring of antibiotic resistance, enhancing virulence or, as probably occurred with Salmonella enteritidis in poultry, making it more invasive. Mutation is a relatively rare event but it appears to occur more frequently in bacteria because of their relatively short generation gap. Mutation occurs when the bacteria are replicating and one mutation occurs every100, 000,000 replications.

In simple terms in any population of bacteria, there are likely to be some resistant ones. When the animal is treated with an antibiotic many bacteria, including those causing the disease (pathogenic bacteria) and good bacteria which protect the body from infection are killed. This leaves the door open for antibiotic resistant bacteria to grow and multiply and become the dominant bacteria and take over. If the antibiotic resistant bacteria are pathogenic, the antibiotic will not kill them and the animal succumbs to the disease. Bacteria are transmitted from animals to man by the consumption of products derived from animals, by close or direct contact with animals or through the environment.

There are four ways by which bacteria exhibit resistance to bacteria. These are:

Drug inactivation or modification.

Alteration of the target site on/in the bacterium for the antibiotic.

Alteration of a metabolic pathway in the bacterium.

Reduced antibiotic accumulation in the bacterium.
Sometimes a bacterium can survive antibiotic treatment and multiply because it is intrinsically resistant. A good example of this can be seen when an antibiotic, such as penicillin that prevents cell-wall building, cannot control a bacterium that does not even build a cell wall (Gram negative bacteria). This is known as intrinsic resistance. Bacteria are also able to acquire resistance. This occurs when a bacterium changes in such a way that it is protected from the effects of a particular antibiotic.

Such resistance can be gained in one of two ways – through a new genetic change that helps the bacterium survive or by getting DNA (genetic material) from another bacterium that is already resistant. This is acquired resistance.
To guard against antimicrobial resistance and as part of overall efforts to reduce hunger, FAO helps countries develop and promote
Good hygiene practices to control the spread of resistance through food.
Efficient animal husbandry services for healthier, more productive animals.
Guidelines for prudent use of antimicrobials in aquaculture.
Good animal health and management practices including improved biosecurity and use of vaccines instead of antimicrobial drugs.
Policies and capacities for responsible antimicrobial use.
Health management approaches that recognise the links between animals, humans and ecosystems.


Prudent use of antimicrobials in livestock and aquaculture is essential in light of the increased demand for animal proteins by a rapidly growing world population. Intensifying production means additional challenges in disease management and even higher potential for increased antimicrobial resistance. Antibiotic resistance in livestock can be tackled by minimizing the contact between the bacterial population in our animals and these other bacterial populations. This may be possible in modern housed intensive farming but it is also virtual impossibility in outdoor or free range production. It can also be tackled by working closely with veterinarians, farmers, feed and food producers and food safety professionals, to support best animal health and production practices which underpin the prudent use of antimicrobials.

Read the previous post on Antibiotic Resistance

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Understanding the Basics of Antibiotic Resistance: International Hatchery Practice Vol.30.3

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