Prophylactic use of antibiotics

Published:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

CHAPTER 2

LITERATURE REVIEW

2.1 GenoMar Supreme TilapiaTM

GST (Plate 2.1) is a fast-growing strain that developed from genetically improved farmed tilapia (GIFT), starting in 1990. This strain is transformed from GIFT by adopt the DNA parentage identification system to carry out the conventional selective breeding process instead of involving any transformation of genetic information. (Acosta and Gupta 2010). Dissimilar with the physical tags that used in traditional selective breeding, this system allows the assessment of a set of complete data regarding fish genealogy, stages in reproduction cycle and genetic gains in each generation. As a result, substandard inbreeding is avoided effectively as the potential parents can be identified individually before selected to breed. Generally, genetic gains has been amplified with the prerequisite of retaining diversity by using optimal contributions selection method, and thus the most appropriate mating candidates has been schemed by utilizing automate software (GenoMar).

The name of GST is originated from a private company in Norway named GenoMar ASA, one of the world’s leading aquaculture biotechnology companies, who made an agreement with GIFT Foundation for collaboration to modify the GIFT strain to better strain (WorldFish). This superior strain has been proven to have tremendous growth performance which excel 60% to 70% than any commercial strain available in market (GenoMar). According to Zimmermann and Natividad (2004), 3rd generation of GST was reported significance higher weight gain and survival rate than 1st generation of GST. GST acclaimed to reach marketable size two times faster than normal undeveloped tilapia strains as the succession of each generation revealed more than 15% of growth enhancement and 35% of genetic gains from previous generation (GenoMar, cited in Acosta and Gupta 2010).

2.2 Prophylactic use of antibiotics

Antibiotics are often incorporated into animals feed or directly feeding orally to infected animals for the purpose of reducing disease mortality rates. By virtue of prevention, application of antibiotics on apparent healthy animals with no disease symptoms is termed as prophylactic use of antibiotics (Phillips et al. 2004). This is a prevalent practice that used in animal farming to minimize economic damages due to disease outbreak (Ng and Koh 2011). In fact, antibiotics used extensively in terrestrial animals nearly half century because of the overwhelming result obtained from growth stimulant and antimicrobial effect (Jacela et al. 2012). After introducing antibiotics into farmed animals, alteration of gut microflora ecology of targeted species occurs. Pathogens are prohibited from colonizing inside the intestine of host animals and thus, animal’s immune system is fortified (Swick 2011). This conditions are owing to the interruptions of metabolic reactions in pathogenic bacteria and consequently weakened and ceased the bacterial cell (Ferket 2004). As a result, more nutrients are available for the host animals because lesser gut flora to compete food with the host animals (Swick 1996). The earlier studies of Visek (1978) and Swick (1996) indicated that shorter or lighter intestine tract and higher nutrient intake rates has been observed in animals fed subtherapeutic amount of antibiotics diets. This circumstances are achieved by alleviate requirement of metabolism in leaner epithelium gastrointestinal tract and hence, sufficient energy is accessible for growth utility (Ferket 2004). Despite enhancement on growth rate, high feed utilization in livestock and aquatic animals fed with antibiotics diets is also declared. (Lückstädt 2008). From the view of economic prospect, both total productivity and profitability has been maximized in the consequences of shorten culture period required to harvest marketable size animals and lower feed conversion ratio (FCR). (Ferket 2004).

Nevertheless, farmed animals welfare, humans as well as the environment will be affected as a result of antibiotics usage. For instance, the aquatic animals will accumulate antibiotics in their bodies and hence, causes potential hazard to human health (Nawaz, cited in Ng et al. 2009). Furthermore, the bacteria which develop resistance to certain antibiotics have the probability to obtain other antibiotics resistance due to the similar resistance mechanism may effect on different antibiotics which called cross-resistance (Holmström et al. 2003). Other animals or humans are more susceptible to ailments on account of the strong antibiotic resistances that build up in bacteria of farmed animals (Hernandez-Serrano, cited in Ng et al. 2009). Environmental crisis crop up when leakage of antibiotics from the feed pellets that are not eaten by farmed species is subsequently introduce into aquatic environment (Inglis 20-22 May 1996). As a result, bioaccumulation of poisonous antibiotics in water bodies and sediments deteriorates the water quality and thus, aquatic plants and animals are at stake (Holmström et al. 2003). Hence, a total ban on antibiotics has been imposed by Europe Union in 2006 to avoid those negative consequences (Ferket 2004; Lückstädt and Kuhlmann 2011). Owing to the safety affair, researchers are currently investigating on various potential alternative feed additives to substitute the application of antibiotics in aquafeed industry (Lückstädt and Kuhlmann 2011; Swick 2011).

2.3 Organic acids (OA)

Volatile short chain fatty acids or carboxylic acids are the common names of OA. Possession of carboxyl group (–COOH) as functional group has make these acids structure easily differentiates from other compounds. Mono or double salts are yields when combine with minerals such as calcium, sodium and magnesium (Ng and Koh 2011). OA and its salts both have been used as preservatives either in food or feed additives since long time ago (Kochannek 2011). In consideration of OA only partially dissociate (ions are not discharge completely) in aqueous solutions, hence they are regarded as weak acids (Cherrington et al. 1991). A proton (hydroxonium ion) and an anion (conjugate base) are the products of dissociation of organic acids in aqueous solutions. The equation below manifests the reaction where HA represents organic acids, A- is the conjugate base and H3O+ is hydroxonium ion.

HA + H2O ↔ A- + H3O+

According to Cherrington et al. (1991), acid dissociate constant (Ka) or in its logarithmic constant (pKa) can be used to verify the intensity of an acid. Ka is a ratio which independent of the acid concentration and it can be represented by the equilibrium equation [H+][A-]/[HA]. Meanwhile, pKa can be calculated by using logarithms as pKa = –log10 Ka. The pKa value is inversely proportional to the acidity. The pH or the proportions of free undissociate acid molecules can be acquired by using Henderson-Hasselbalch equation where pH = pKa + log [A-]/[Ha] (Lambert and Stratford 1999).

At room temperature, OA with low molecular weight are exists in liquid state (Cherrington et al. 1991). These acids dissolved in water more readily. However, the solubility in water declines as the number of carbon in the acids increased (Cherrington et al. 1991). The physical and chemical characteristics of various OA are demonstrated in the Table 2.1. OA in liquid state are more difficult to handle as its volatile properties if compared to solid state (Mroz 2005). Nevertheless, recent innovation of MOAB which protected the liquid OA into a matrix has addresses this problem (Mroz 2005).

Table 2.1 List of organic acids with its chemical and physical characteristics (adapted from Mroz 2005)

Name

Mol. Formula

Mol.wt (g/mol)

pKa value

Physical form

Odour

CR[1]

Formic

CH2O2

46.03

3.75

Liquid

Pungent

+++

Acetic

C2H4O2

60.05

4.76

Liquid

Pungent

+++

Propionic

C3H6O2

74.08

4.88

Oily liquid

Pungent

++

Butyric

C4H8O2

88.12

4.82

Oily liquid

Rancid

+

Lactic

C3H6O3

90.08

3.86

Liquid

Sour milk

+

Sorbic

C6H8O2

112.1

4.76

Solid

Mildy acrid

+

Fumaric

C4H4O4

116.1

3.02, 4.38

Solid

Odourless

0 to +

Malic

C4H6O5

134.1

3.46, 5.10

Solid

Apple

+

Citric

C6H8O7

192.1

3.1, 4.8, 6.4

Solid

Odourless

0 to ++

CR= corrosiveness rate: high (+++), medium (++), low (+), negligible (0)

2.3.1 Mechanisms of action of OA against miroorganisms

Each type of OA acquires peculiar capability to combat bacteria. However, OA and its salts with the ability to fight against microbes are usually short chain acids with 1 to 7 carbons (Dibner and Buttin 2002). Hence, generation of synergistic and constructive pathogens inhibition reactions is normally accomplished by virtue of OAB. (Huyghebaert, cited in Dibner and Buttin 2002). Nevertheless, contradictory argument appears as Kochannek (2011) claimed that OA do not possessed synergistic effect as no supportive report clarify on it. Investigation from Waldroup et al. (1995) also reported that if compared to single formic acid and single lactic acid, broilers fed with blend of these two acids yielded inconsistent results on growth performance and FCR.

The strength to depress microorganisms is only possessed by undissociated OA molecules (Cherrington et al. 1991; Lambert and Stratford 1999). Lambert and Stratford (1999) declared that OA do not wipe out the microbial population but instead, they prevent the growth and proliferation of microbes. From their studies, suppression by OA can be achieved by its lipophilic properties. These properties enable the penetration of OA molecules to the plasma membrane of pathogenic bacteria. OA is drives to dissociate and release both protons (hydrogen ions) and anion (conjugate base) upon the arrival at cytoplasm which has higher pH value. Cherrington et al. (1991) reviewed that both protons and anions are playing their parts in depress the proliferation of microbes. The high concentration of hydrogen ions causes the pH of cytoplasm to decline and thus, creates an unfavorable environment for the enzyme to carry out metabolic reactions (Lambert and Stratford 1999). This situation stimulates the bacterial cell spent energy to discharge the protons out from the cytoplasm through H+-ATPase pump for the purpose of bringing back the original pH in cytoplasm (Theobald and Lückstädt 2011). On the contrary, anions cannot expel out and therefore remains in the cytoplasm. As a result, the metabolic pathway in respiration, glycolysis as well as active transport is obstructed due to the accumulation of anions. (Lambert and Stratford 1999; Theobald and Lückstädt 2011). The bacterial cell becomes unable to sustain its life consequently as it cannot undergo metabolism to synthesize nutrients and energy. Illustration of this mechanism is clearly demonstrated as the Figure 2.2.

antimicrobial

Figure 2.2 Penetration of OA into the microbial membrane and dissociation occur in the cytoplasm. The protons are able to discharge out by H+-ATPase pump whereas the anions are remains in the cytoplasm. (adapted from Lambert and Stratford 1999)

2.3.2 Effects of OA on gastrointestinal tract

The positive impacts of OA on gastrointestinal tract generally can be categorized into two which are improved digestibility and antimicrobial behavior. Incorporation of OA into the feed creates more acidic environment in the stomach. Concentration of hydrochloric acid is decreased when the cultured animals ingested feed with high protein content (Lückstädt 2008). Consequently, the pepsin activation is affected as low pH is the optimal pH for pepsinogen convert to pepsin (Tung and Pettigrew 2006; Theobald and Lückstädt 2011) . Therefore, OA play a role as stimulant for protein hydrolysis (Mroz, cited in Lückstädt 2008) which in turn activates pepsin and other enzymes to secrete for improved protein digestion (Eidelsburger, cited in Lückstädt 2008; Theobald and Lückstädt 2011). One of the great benefits that OA surpass antibiotics is the pancreatic enzyme secretion (Dibner and Buttin 2002). According to Kluge, cited in Lückstädt (2008), the OA enhance nutrient digestibility and nitrogen retention as the pH of duodenum is decrease. Apart from this, villus height, surface area and crypt depth in colon and jejunum is showing increment after the application of n-butyric acids as reviewed in Frankel, cited in Dibner and Buttin (2002). This means, multiplication of gastrointestinal cell which trigger by OA has imposed an improvement on the nutrient absorption (Dibner and Buttin 2002).

Under the condition of pH value below 5, the growth of Gram-negative bacteria for instance, E.coli and Salmonellae is stunted (Lückstädt 2008). The proliferation of bacteria is inhibited by the lipophilic nature of organic acids. Penetration of OA into the membrane of bacterial cell allows them to dissociate when entering the cytoplasm in order to bring down the pH. As a result, the bacteria ceased as they cannot undergoes metabolism or enzymatic chemical reactions to supply energy for them. This phenomena has been proven by several studies which indicates the microbial population in stomach and duodenum is diminished after ingesting the feed that added OA (Kirchgessner, cited in Lückstädt 2008). In addition, declination of microbial loads in jejunum increases the nutrient availabilities for host as it lower the chances for microflora to compete with it. Besides, the reduced population of microbiota enables more amino acids available for host to absorb as the deamination of amino acids from microbes is eliminated (Dibner and Buttin 2002). Studies from Eckel et al., cited in Dibner and Buttin (2002) indicated that 1.25% formic acid feed successfully lowered the amount of ammonia in gastrointestinal tract of weaned piglets. This is able to clarify that the ammonia content in wastes of farmed animals is decreased as well as the nitrogen digestibility is improved by feeding them with OA incorporated feeds. However, different parts of intestinal tract received different response of antimicrobial effect of OA (Tung and Pettigrew 2006). For example, Lactobacillus is tended to decrease its population in the intestine whereas E.coli population is reduced greatly in colon after introducing OA.

2.3.3 Effects of OA on feed

To prevent spoilage, inclusion of OA in commercial feeds manufacture has protrated history (Theobald and Lückstädt 2011). The feeds are susceptible to microorganisms contamination especially in hot and humid (more than 14% humidity) condition (Lückstädt 2008). According to Sava (2011), high humidity in the environment will promote the proliferate and growth of eukaryotes and prokaryotes. The speedy proliferation will produce water and heat which causing the quality of feeds to deteriorate in three stages. At first, the feeds started to form lumps following by the disintegration of carbohydrate and proteins. As a result, the nutritional value of these feeds is damaged. Eventually, this condition elicits the production of mycotoxins due to the multiplication of microorganisms in the third stage. These toxic substances weakened the immune system of cultured animals by attacking the internal organs which can cause stunted growth rate or fatality (Muschen and Frank, cited in Sava 2011). Therefore, OA for instance, sorbic and propionic acid have been used to maintain the feed quality by lowering the feed pH and thus, prevent the colonization of microbes and fungi (Dibner and Buttin 2002). In fact, OA are able to fight against microorganisms via obstruction of pyruvate decarboxylase enzyme in the energy generation cycle (Sava 2011). Therefore, the chances for cultured animals to ingest the pathogenic microorganisms are reduced (Lückstädt 2008). In short, OA ensure the good quality of feeds and helps sustain the health status of farmed animals. Table 2.2 manifested the strength of different OA at minimum concentration to combat the behavior of microorganisms.

Table 2.2 The minimum inhibition concentration of different acids (%) (adapted from Coelho, cited in Sava 2011)

Types of microoragnism

Formic acid

Acetic acid

Propionic acid

Sorbic acid

Butyric acid

Benzoic acid

Aspergillus flavus

0.50

0.50

0.25

0.45

0.45

0.50

Cladosporium sp

0.50

0.50

0.25

0.50

0.65

0.50

Staphylococcus aureus

0.12

0.25

0.25

0.75

0.95

0.85

Escherichia coli

0.10

0.50

0.50

0.75

0.85

0.70

Candida albicans

0.25

1.00

0.50

0.20

0.40

0.50

Apart from this, the buffering capacity of the feeds can be decreased by the strength of OA to ensure the optimum acidic environment is provides to the intestine especially the foregut. This is owing to foregut is playing a crucial role to manipulate the microbes inhabitation and secrete digestive enzyme. For instance, the digestibility of ileal amino acid is enhanced nearly 10% after reducing the buffering capacity as reviewed in Blank et al., cited in Dibner and Buttin (2002)

2.3.4 Effects of OA on metabolism

Prevention of microbial growth is not only the solely benefits of OA, but it can served as the sources of carbon and energy (Cherrington et al. 1991). OA aids in energy production in metabolic reactions such as ATP production in Krebs Cycle (Lückstädt 2008). This can be achieved by short-chain OA which usually have high gross energy level as shown in Table 2.3. The efficiency of energy production enhanced because only passive diffusion is needed for the assimilation of OA into intestinal epithelia to harvest energy in metabolism (Lückstädt 2008).

Table 2.3 The gross energy content of organic acids and its salts that used in aquafeeds adapted from Freitag, cited in Lückstädt (2008)

Organic acid

Solubility in water

Gross energy (kcal/kg)

Formic

Very good

1385

Acetic

Very good

3535

Propionic

Very good

4968

Lactic

Good

3607

Citric

Good

2460

Calcium formate

Low

931

Sodium formate

Very good

931

Calcium propoinate

Good

3965

Calcium lactate

Low

2436

2.3.5 OAB with microencapsulation technology

The entire gastrointestinal tract inhabited by microbial population. However, most of the undissociated organic acids cannot reach far to the hind gut where the most abundance of microbes exists (Mroz, cited in Tung and Pettigrew 2006). The recent technology of microencapsulation which coated the OA in matrix allows the it to be released gradually along the gastrointestinal tract instead of dissociate mostly once they entered the gastrointestinal tract (Piva et al. 2007). Von Felde and Rudat, cited in Mroz (2005) claimed that microencapsulation can even manipulate the OA releasing site along the gastrointestinal tract as well as the rate of dissociation. Piva et al. (2007) also reported that the concentration of sorbic acids and vanillin along the gastrointestinal tract was higher in the pigs which fed with MOAB than normal OAB without protective capsules. Their studies also indicated that the pigs fed with dietary treatment of OAB without encapsulation yielded lower concentration of sorbic acids along the gut as it dissociate completely after exit from the stomach. On the contrary, the MOAB dietary treatment enabled the sorbic acids release gradually along the gastrointestinal tract and hence, antimicrobial effect of organic acids reached extensively in the entire gut.


[1]

Writing Services

Essay Writing
Service

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing
Service

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision
Service

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.