3. Factors associated with antimicrobial resistance in animals

Since the discovery of the first antibiotic, penicillin, by Alexander Fleming, there has been a tremendous use of antibiotics in farm animals. In animals, antibiotics have been used as growth promoters as prophylaxis as well as metaphylaxis. Both approaches involve the administration of antibiotics in animals either by injection or through feed/water.

The primary goal of antibiotics was to treat the infectious diseases in animals and, thereby, improve the overall health of animals and humans. However, an unexpected thing observed in chickens during the 1940s was that antibiotic use may also cause an increase in the growth rate in animals. This finding has led to their use as growth promoters. Antibiotics have been used as growth promoters for decades. This aspect is of tremendous controversy since the beginning. The practice employs the use of antibiotics at subtherapeutic levels, with the main purpose to control the enteric and respiratory diseases in farm animals associated with poor management. The exact mechanism by which antibiotic may enhance the growth rate in animals is yet unknown precisely; however, it is postulated that antibiotics may increase the animal growth rate by either one of the following mechanisms:

countries have banned the use of the latest antibiotics as growth promoters in animals (to be intended for human use only in order to minimize the chances for development of antimi-

Emergence of Antimicrobial Resistance, Causes, Molecular Mechanisms, and Prevention Strategies…

http://dx.doi.org/10.5772/intechopen.79757

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There are some exceptions in this aspect of development of the resistance in microbial communities against antimicrobial use as AGPs. The typical example is the use of ionophores which are mainly used to reduce the incidence of coccidiosis as well as improve the microbial communities in rumen (favor the microbial communities toward Gram-positive bacteria). Furthermore, latest studies have also shown that the use of the AGPs may contribute toward the disturbance of normal microflora in animals, thereby greatly affecting the immune system

4. Molecular mechanisms of the resistance against major antimicrobial

against different antibiotics, they can be broadly classified as follows.

4.1. Degradation of the antibacterial drug by the bacterial enzymes

ansferases, acetyl transferases and the adenyl transferases [11, 12].

4.2. Reduced permeability to a drug by bacteria

hinders the entry of the majority of drugs [13].

4.3. Increased efflux of the drug

Although, till now, different types of the resistance mechanisms have been reported in bacteria

Several bacterial beta lactamases can degrade the beta lactam antibiotics. Beta lactamases do it so by degrading the beta lactam ring of the antibiotics. Also, some antibiotics can be degraded by the addition of the specific group, e.g., chloramphenicol molecule possesses hydroxyl group that can be easily acetylated by the incorporation of acetyl-CoA, a reaction that is catalyzed by acetyl transferases. Moreover, aminoglycosides can also be easily degraded by the addition of phosphate, acetyl-CoA, and adenylyl group, and these additions are carried out by the phosphotr-

For example, most of the Gram negatives contain extremely small-sized porin in their outer membrane, and this imparts a major permeability barrier to a large number of antibiotics to cross that barrier. In similar manner, Mycobacterium also offers a major permeability barrier to most of the antibiotics as they contain a thick layer of the mycolic acid, and this waxy material

Several bacterial species possess the efflux pumps that actively pump out the drug by bacterial cells. Such pumps effectively reduce the bactericidal concentration of a particular antibiotic drug, and they have been actively implicated in the emergence of resistance against a myriad of the antibiotics particularly against tetracyclines, aminoglycosides, and sulfonamides. The

crobial resistance) [5, 6].

of the animals [7–10].

drugs


Currently, China, the USA, and Brazil are the leading countries of antibiotic utilization in animals. Approximately, 40 antibiotics have been approved for animals in the USA, out of which more than 30 are currently being used in humans. Majority of antibiotic use in animals falls in either one of the three uses:

#### 3.1. For the treatment of infectious diseases in animals (therapeutic use)

Therapeutic treatment usually involves the treatment of either single or whole herd/flock with specific doses of specific antimicrobial drugs. One typical care should be kept in mind in this aspect is that each animal should receive the complete dose of antibiotics and the antibiotic treatment should be continued for at least 72–120 h. But there may be problems in this aspect of antibiotic use as the diseased animal has greatly reduced appetite, and this thing may lead to the reduced intake of the specific antibacterial drug. This may lead to the potential problem of developing the resistance in microbial communities against these antibiotics [4].

#### 3.2. For the prevention of a variety of infections in animals (prophylactic use)

Traditionally many antibiotics were being used in the feed lot and dairy cattle to prevent against a variety of diseases. However, this practice is discouraged.

#### 3.3. The use of antibiotics as growth promoters

Although the use of antibiotics in animals has greatly contributed in increasing the production in farm animals, however, their use as growth promoter was an issue of great controversy as this practice has greatly enhanced the development of resistance in a variety of microbial species not only in animals but also in humans. Therefore, nowadays, several

countries have banned the use of the latest antibiotics as growth promoters in animals (to be intended for human use only in order to minimize the chances for development of antimicrobial resistance) [5, 6].

There are some exceptions in this aspect of development of the resistance in microbial communities against antimicrobial use as AGPs. The typical example is the use of ionophores which are mainly used to reduce the incidence of coccidiosis as well as improve the microbial communities in rumen (favor the microbial communities toward Gram-positive bacteria). Furthermore, latest studies have also shown that the use of the AGPs may contribute toward the disturbance of normal microflora in animals, thereby greatly affecting the immune system of the animals [7–10].
