**3. Implications: impact on consumers' health and economy**

Residual amounts of antimicrobials, antibiotics or their toxic metabolites found in meat, organs or other products such as milk and egg of food producing animals after slaughtering is called veterinary drug residues [32]. Consumption of such food products poses a major health risk due to the failure of treatment following the development of resistant microorganisms [33]. Various impacts of antimicrobial residues on human health are reported below.

#### **3.1 Impact on consumers' health**

### *3.1.1 Drug resistance*

The possibility of propagating resistant bacteria through the food chain in treated animals was noticed as early as 1969 by Swan, who reported the development of vancomycin resistance to *Enterococci* in avoparcin fed animals. Animal feeds containing antibiotics, have been reported to result in antimicrobial resistance, leading to failure of medical treatment both in animals and humans. Situations whereby drugs are completely ineffective have also been reported to be a possibility [34]. Giving the established fact of an animal to human microbial resistance transfer [35], resistant micro-organism can gain entrance, directly through contact, into

*Veterinary Drug Residues in Meat and Meat Products: Occurrence, Detection and Implications DOI: http://dx.doi.org/10.5772/intechopen.83616*

humans or indirectly via animal products and by-products (e.g. milk, egg, etc.). The findings of [36] in a study conducted in Taiwan from slaughtered pigs revealed the rate of antimicrobial resistance to salmonella for these drugs; tetracycline (88.2%), gentamycin (82.7%), chloramphenicol (54.3%), amoxicillin (34.6%), nalidixic acid (30.7%), ampicillin (26.8%), kanamycin (18.1%), cephalothin (7.1%), nitrofurantoin (6.3%), ciprofloxacin (0.8%) [36]. Failure of antimicrobial therapy due to resistant strain is a future concern [13].

#### *3.1.2 Allergy or hypersensitivity reactions*

Allergy or immune-mediated response to a chemical agent (e.g. drug) can develop in a sensitized patient. Such allergic reactions are usually mediated by IgE and could be elicited following administration of drugs or macromolecules such as protein, lipids and carbohydrates. Dayan [37] affirmed that human population estimate of about 4–11% are believed to be allergic to penicillin. Such class of humans consuming meat products having penicillin residues is at risk of developing allergy which can manifest as a skin rash or even severe anaphylaxis [35]. Thong and Tan [38] reported that IgE-mediated allergic anaphylaxis is linked to penicillin and other anesthetic drugs following their administration during perioperative periods. Mild rash to severe toxidermia are some of the skin reactions following human exposure to sulfonamide [39]. However, such adverse reaction was not a direct effect of consuming animal products containing relative trace amounts of sulfonamides. Studies have also shown that damages done to hepatic liver cells can be traced to allergic response to macrolide antibiotics (e.g. erythromycin, clarithromycin) [40].

#### *3.1.3 Carcinogenic effect*

The term carcinogenic refers to any substance or an agent capable of altering the genetic makeup of an organism so that they multiply and become rancorous while carcinogen refers to any substance that promotes carcinogenesis, the formation of cancer or having carcinogenic activity. Carcinogenic residues functions by covalently binding intracellular components including DNA, RNA, proteins, glycogen, phospholipids and glutathione [49]. The ban of Diethylstilbestrol (DES), an hormone-like compound used for food producing animals, was as a result its strong carcinogenic effect [27]. According to the International Agency for Research on cancer (IARC), evidence abounds to suggest that metronidazole is carcinogenic in animal, but insufficient to do so in humans [41].

#### *3.1.4 Disruptions of normal intestinal flora*

Intestinal microflora plays an important role in human physiology. They establish control and prevent the colonization of pathogenic bacteria in the gastrointestinal tract [42]. However, studies have shown that antimicrobials administered for therapeutic purposes can potentially alter or change the ecological composition of the intestinal flora [43, 44]. Degree of change however, depends on the dosage of the antimicrobial drug, route of administration, its bioavailability, metabolism, exposure length to the drug and distribution in the body including excretion route [45]. Disruption of intestinal flora has been reported due to the use of broadspectrum antibiotics. Commonly used drugs like streptomycin, tylosin, metronidazole, nitroimidazole and vancomycin are commonly implicated in human in the diagnosis of gastrointestinal disorders [46].

#### *3.1.5 Mutagenic effect*

Mutagens are chemicals or substances with potentials to cause mutations in a DNA molecule thereby altering the genetic makeup of a cell or organism. Studies have shown alkalizing agents and analogous of DNA bases are mutagenic. There is a growing fear of a possible drug-related gene mutagen or chromosome breakage among human population [47, 48].

#### *3.1.6 Teratogenic effect*

Congenital malformation of the foetus during pregnancy as a result of toxic metabolites of drugs or chemical agents has been reported [47]. Such drugs or teratogens alter the structural and functional integrity of the developing embryo/ foetus during the critical phase of gestation. Studies have shown that benzimidazole (an anthelmintics) is not only mutagenic but also has teratogenic activities and is highly toxic to embryo when ingested at early stages of conception or pregnancy [49, 50].

#### **3.2 Impact on global economy**

Antimicrobials' usage in livestock either at sub-therapeutic or therapeutic dosage and its attendant residues in food animals have become a global issue and concern. The growing awareness about the potential risk of diseases such as cancer and also the distortion of body's functional and system integrity (i.e. endocrine, nervous, reproductive and immune system) [51], resulting from the consumption of such 'compromised' food of animal origin, have reduced consumers' confidence and the resultant adverse impact on global economy. Additionally, the maximum residual limits (MRLs) set by Codex Alimentarius Commission (Codex) for veterinary drug residues as an international food safety standards are however not generally accepted by the committee of nations [52]. The limitation of Codex and World Trade Organization (WTO) to enforce adoption of MRLs [53], has resulted in differences in food safety standards across countries and nations. Such differences usually end as trade disputes [54] leading to a gradual decline in meat and meat products exported.

## **4. Detection: mode of examination and equipment or methodologies**

Studies are replete with developments of antimicrobial resistance from food producing animals after consumption. There is also a general upsurge in form of sensitization on the need to minimize exposure to antibiotic residues in food [55, 56]. Antimicrobial residues in meat and meat products are the results of non-compliance of withdrawal periods, antibiotics overdosing and the continuous use of antibiotics banned for treatment of economic animals [57, 58]. Giving the foregoing above, specific legislation has been set to protect consumers from exposures to potentially harmful residues of veterinary medicines, pesticides and environmental contaminants in food of animal origin. Maximum residual limits (MRLs) have been set for veterinary medicines, pesticides and environmental contaminants (European Regulation (EC) No 470/2009). The Regulation not only seeks to identify but also demand quantitative assessment of antibiotic residues.

Control of antibiotic residues in food of animal origin follows two basic steps: Firstly, the animal product is screened qualitatively or quantitatively. In qualitative

#### *Veterinary Drug Residues in Meat and Meat Products: Occurrence, Detection and Implications DOI: http://dx.doi.org/10.5772/intechopen.83616*

assessment, the presence of an antimicrobial residue is detected here and it's usually reported as either positive or negative. Identification and quantification of a particular residue is done using the quantitative screening method and it is also reported as a concentration of the residue. If results are positive, a confirmatory procedure is usually followed for specific antibiotics with the aid of a more sensitive physic-chemical method.

#### **4.1 Microbial screening method**

Though its use dates back as early as 1964 and was adopted initially to monitor the dairy industry with a view to preventing problems in the fermentative dairy industry, it has now been extended as a regulatory residue screening method in slaughter animals even till date. The microbial inhibition assay can cover an entire antibiotic spectrum under one test.

The microbial inhibition assay adopts either the tube test or the plate test. The tube test makes use of a tube, vial or an ampule containing a growth medium inoculated with (spores of) a sensitive test bacterium, supplemented with a pH or redox indicator. At the appropriate conditions of temperature and pH, there is a color from the acid produced by the growing bacteria. Absence or delay of the color change is indicative of the presence of an antimicrobial residue and is usually a commonly used routine in the milk industry [59, 60]. It has however been used for analysis of other matrices [61, 62]. In the plate test, the test sample is spread on the layer of the plate containing inoculated nutrient agar. Presence of an antimicrobial residue is detected by the formation of an opaque layer by the growing bacterial, thus yielding a clear growth-inhibited area around the sample. This method is commonly used in Europe for screening of antibiotics residues in slaughter animals [63, 64].

#### **4.2 Immunological technique**

The immunological techniques work on the principle of antigen-antibody interactions and it is usually very specific and helps in detecting residues from in food producing animals. The enzyme-linked immunosorbent assay (ELISA) is commonly used and detection of antimicrobials is based an enzyme-labeled reagents. ELISA has proven very useful for residual screening in meat especially for tylosin and tetracycline [65, 66]. ELISA's antigen-quantification could take different forms like the direct and indirect sandwich ELISA. Sandwich ELISA works on the principle of recognizing specific antigens that share similar epitopes with other antigens. The indirect sandwich ELISA has the advantage of being highly specific and sensitive. Radioimmunoassay measures the radioactivity of immunological complex using a counter [67].

#### **4.3 Chromatographic method**

Liquid chromatography is also useful in the qualitative and quantitative screening of multi-residues in food animals, though its use has rapidly decreased during the last decade [68]. The high-performance liquid chromatography (HPLC) relies on pumps to pass a pressurized liquid solvent containing the sample mixture through a column filled with a solid adsorbent material. Each component in the sample interacts slightly differently with the adsorbent material, causing different flow rates for the different components and leading to the separation of the components as they flow out the column. It has been applied for the detection of antimicrobials in meat, fish and internal organs [69, 70].

Laboratories' use of HPLC has grown very rapidly and has the capacity to analyze multiple residues in a sample within a short time. Also, the equipment is fully automated (injection, elution, washing of column, detection) and controlled with the aid of a computer. Hence, it can be used as a screening technique [68].

Coupling of HPLC with mass spectrometry (MS-MS) has resulted in substantial reduction of analysis time for confirmation in presumed positive samples after initial screening. Such a combination could effectively be used simultaneously for screening and confirmation [71, 72].

#### **4.4 Biosensors**

This is a recent and modern approach for detecting veterinary residues in meat and dairy products while ensuring their quality and safety. It has applications for high throughputs within biotechnology. The instrument is made up of biological recognition element (bioreceptor), which recognizes the target antimicrobial residue and a signal transduction element (transducer) which converts the recognition event into a measurable signal [73]. It is usually in close contact and connected to data acquisition and processing systems [74]. The instrument is rapid, highly selective, inexpensive, simple and can be handled by an unskilled personnel [75]. The type of bioreceptor or transducer used forms the basis for classifying biosensors. A bioreceptor can be an organic molecular species (e.g. an antibody, enzyme, protein, or nucleic acid) or a living biological system (e.g. cells, tissues or whole organisms) using biochemical recognition mechanism [76]. Enzymatic biosensors are commonly used for the analysis of herbicides contaminants. Kiran and kale [77] reported an enzyme biosensor that was developed to detect penicillin. However, fewer applications for antibiotic residues and food contaminants have been reported. Cellular biosensors employed for the detection of antibiotic residues such as tetracyclines [78, 79], beta-lactam antibiotics [80, 81]; quinolones [80], chloramphenicol and quinolones [82] have proven to be very effective and fast in detecting of multiple residues simultaneously, within a very short period of time. In transducer-biosensor, common and popular varieties developed for antibiotic residues detection in food producing animals include the mass-based, optical and electrochemical.

## **5. Possible solution for eliminating antimicrobial residues in meat and meat products**

#### **5.1 Promotion of disease resistant livestock breeds**

Development and breeding of disease resistant livestock breeds could be a panacea to reduce the use of antimicrobial drugs, antimicrobial residue and antimicrobial resistance in meat and meat products. Some indigenous breeds of cattle, goats and sheep are either tolerant or resistant to specific diseases and parasites, and are also able to withstand very harsh environmental conditions [83]. Evidence has shown that indigenous breeds such as N'Dama cattle, Red Maasai sheep, Meishan pigs, Lohman Brown chickens, Mandarah chickens and Nguni goat are more resistant to ticks (various species) diseases [84], *Haemonchus contortus* [85] *Sarcocystis miescheriana* [86], *Ascaridia galli* [87], Newcastle disease virus/infectious bursal disease [88] and heart water disease [89], respectively than other breeds. According to Zekarias et al. [90] difference in disease resistance among individuals and breeds are based on immunological system and its interaction with physiological and environmental factors. Alhaji et al. [4] found in their study that antimicrobials are rarely used in local bird flocks, making them likely organic and safe from

*Veterinary Drug Residues in Meat and Meat Products: Occurrence, Detection and Implications DOI: http://dx.doi.org/10.5772/intechopen.83616*

antimicrobial residues and resistance. However, most of the indigenous breed are less productive than some imported or exotic breeds and so do not meet producer's needs. It is known in most cases that exotic breeds are easily susceptible diseases and because of this, it is essential to develop breed that are genetically resistant to diseases (either by cross breeding local and exotic animal together), although they may be costly and impossible to achieve in the absence of useful levels of resistance [91]. Selective breeding and management interventions could be a technically feasible approach to manage diseases in livestock.

#### **5.2 Promotion of** *in vitro* **cultured meat**

Another means to reduce antimicrobial residues in meat and meat products is by embracing the production and development of *in vitro* cultured meat when it is commercially available. Basically cultured meat is produced from embryonic stem cells or adult stem cells without slaughtering the animal [92]. It involves culturing of animal muscle cells in a controlled environment (i.e. in a medium that contains nutrients and energy sources required for the division and differentiation of the cells into muscle cells that form into tissue) [93, 94]. The development of cultured meat is projected to compliment conventional meat production and diminish the increasing problems associated with meat including health claims (food-borne illnesses, antimicrobial residues, antimicrobial resistance and animal welfare) [94–97]. The production of in vitro culture meat will require the use of fewer livestock to feed the consumers thereby reducing mass production of livestock when commercially available [98]. This in turn will drastically reduce the usage of antimicrobial drugs in prevention and treatment of livestock infection caused by *Salmonella, E. coli, Campylobacter* and so on. Since meat sold today is raised on factory farms, where animals are fed antimicrobial drugs to keep them disease-free [98], production of *in vitro* cultured meat could be a better option.

#### **5.3 Promotion of ethno-veterinary practices as alternative to veterinary drugs**

The role of ethno-veterinary practices in reducing of antibiotic residue and antimicrobial resistance in livestock production is enormous as they are regarded safe and efficacious [99]. They play a significant role in maintaining or restoring animal health in several regions of the world especially in areas where livestock is a main source of income for rural peoples [100]. Ethno-veterinary medicines is often obtained from herbal plants. Recently, there is a greater interest in uses of plants (herbal) due to their accessibility, availability, affordability, efficacy and ease of preparation [100]. Traditional ethno-veterinary medicines have been identified for treatments of small ruminants against ecto- and endo-parasites, gastro-intestinal diseases, viral and bacterial diseases, wounds, sprains and bruises [101]. Furthermore the use of ethno veterinary practices for the treatment of fowl pox in turkey [102], bronchitis [103], hepatotoxicity [104] and foot and mouth disease [104] in ruminants has been established. According to Ranganathan [99], the ethno-veterinary medicine can be advocated to combat issues related to antimicrobial resistance and also minimize the possibility of residues in meat products. Report has shown that the prevalence of antimicrobial resistance was 10–20% lower where antibiotic use was restricted compared to those where it was not [1].

#### **5.4 Other measures for solution**

According to Vishnuraj et al. [6], other measures that could be adopted to reduce antimicrobial residues in meat and meat products include (1) reduction of antimicrobial usage in livestock production (as many developed countries have banned its usage as growth promoters), (2) enforcement of appropriate withdrawal periods of antimicrobial drugs application by government authorities or regulatory bodies before livestock slaughter (3) creation of mass awareness on implication of antimicrobial drugs residues in meat and meat products among consumers, and individual farmer, (4) livestock producer should be educated on farm management, hygiene practices and antimicrobial usages in order to prevent occurrence of antimicrobial residues in meat production and lastly (5) rapid screening methods should be developed for detecting and segregating samples contains above antimicrobial residues before the food products get to consumers. More so, establishment of framework to proper monitoring of drug usage and surveillance of antimicrobial resistance would be of great advantage [105].
