Introductory Chapter: Antibiotics and Probiotics in Animal Food – Impact and Regulation

1. Introduction

In farm animals, use of antibiotics is very common since decades to control, treat, and prevent infections. The first antibiotic, i.e., penicillin, was discovered by Alexander Fleming in 1928 when he was working on Staphylococcus bacteria. Interestingly, some traces of tetracycline antibiotic were recognized in the guts of ancient mummies and skeletons from ancient Nubians (350–550 AD) showing that antibiotics were actually discovered by the peoples of old world [1]. Since discovery, penicillin was recognized as a marvel drug as it saved billions of human and animal lives. In the Second World War, penicillin was heavily used to treat troops that led to the start of antibiotic resistance due to emergence of resistant bacteria [2]. After world war, Thomas Jukes, a British-American biologist, revealed that in-feed antibiotics in poultry may help to improve performance of birds. This study makes a revolution in commercial farming and many antibiotics such as tetracycline, bacitracin, penicillin, etc., were adopted to use as growth promoters by adding a sub-therapeutic level in the feed [3]. Today, the annual business of antibiotic industry is about 25 billion USD [2].

It has been estimated that from 1961 to 2014, global meat consumption raised from 24 to 43 kg per capita. This happens due to industrialized farming practices that primarily use antibiotics to increase yields, control diseases, reduce labor costs, and contain economic risks for producers [3]. As a net result, antimicrobial resistance (AMR) is increasing day by day, and currently, it is a global threat that is recognized as a “ticking time bomb” by the researchers. Because, it is estimated that dissemination frequency of AMR and its environmental reservoirs may create the superbugs in the near future [4].

The history of probiotics is as old as the use of fermented foods in human diet. The word probiotic was first used by the Lilley and Stillwell in 1965. They adopted this term from a Greek word that means “for life.” Since beginning, the word probiotic was adopted to express the microbial products (secretion) that have effect on the growth of other microorganisms. In 1974, Parker used and redefined it as “organisms and their substances which effects intestinal balance.” Later in 1989, Fuller made some modifications in the definition and defined it as “live microorganisms that beneficially affects intestinal microbial balance” [5]. Currently, probiotics are used in humans, animals, poultry, and fish farming to optimize the gut health and to reduce the chances of disease occurrence. These are well-known alterative of antibiotic growth promoters [6].

2. Merits and demerits of antibiotics and probiotics use

There are plenty of evidences that clearly established that use of antimicrobials in farm animals for therapeutic and/or growth promotion causes the creation of antibiotic-resistant bacteria in the environment that ultimately deteriorate the therapeutic options in human medicine [7, 8, 9]. About, 7 million deaths in hospitals have been estimated due to antibiotic-resistant infection [10]. Antibiotics that are used in food-producing animals such as poultry led to transfer of resistant bacteria to human beings via animal food. In the human gut, these bacteria may further transfer resistant genes into the non-pathogenic commensal flora [11]. It is estimated that the antibiotics used in poultry are not completely metabolized in body tissues that accumulate in meat [12] and also excreted into the environment via poultry droppings [13]. The global consumption of antibiotics is around 100,000–200,000 tons per year. Among this about 46.1% use is for animals alone (with majority of use in commercial poultry). The summary of commonly used antibiotics in poultry industry is presented in Table 1.

Antibiotic name	Class	Use in poultry*
Enrofloxacin, Sarafloxacin	Quinolones	Infections cure
Neomycin, Gentamicin	Aminoglycosides	Infections cure
Tylosin , Erythromycin	Macrolides	Infections cure
Penicillin	ß-Lactams	Infections cure, AGP
Lincomycin	Lincosamides	Infections cure, AGP
Bacitracin	Polypeptides	AGP
Monensin, bambermycin, semduramicin, salinomycin	Ionophores	AGP
Chlortetracycline, oxytetracycline, tetracycline	Tetracyclines	Infections cure

Table 1.

Summary of commonly used antibiotics in poultry.

*

AGP: Antibiotic growth promoter

Adopted from Ref. [13].

When poultry droppings used as manure in agriculture fields, then these antimicrobials enter into the soil ecosystem and made significant alterations in the soil contagious communities [14]. Moreover, crops/vegetables cultivated in such fields when consumed by humans transmit antimicrobial-resistant genes to them [10, 15].

In 1981, the American Council for Agricultural Science and Technology published a report on the use of antibiotics in feed animals [16]. Though the report did not provide any data that use of antibiotics in animals causes the emergence of resistant microorganisms that may produce drug-resistant infections in human beings; however, it started a debate on the use of antibiotics in food animals [17]. In the last decade of the twentieth century, several countries such as Sweden, Denmark, Namibia, and European Union Commission banned the use of antibiotics in food-producing animals and directed to adopted suitable alternative approaches to get optimal animal production [6].

By the start of the twenty-first century, pharmacists and nutritionists are trying to develop some alternatives to maintain or enhance farm animals’ performance and well-being. Many substitutes were tested experimentally using in vivo and vitro approaches for their effectiveness in both animals and humans. Among those tested alternatives, one is probiotics [18, 19].

Probiotics could be defined as the live microorganisms that have useful effects on the host health when fed in suitable amount [20]. These were recognized as one of the best replacements due to their multiple useful aspects for both for humans and animals [21]. Probiotic can be used to decrease the dangerous bacteria and to increase the growth and production of animals by improving gut function [22]. Probiotics have also been recommended in mice for treatment of antibiotics-induced dysbiosis [23] and in humans [24]. Probiotics include the microorganisms of various species such as bacteria, yeast, and fungi. Some probiotics of bacterial origin (namely Lactobacillus, Bifidobacterium, Streptococcus, and Bacillus subtilis) also have antimicrobial effects against many pathogenic microbes such as Staphylococcus aureus, E. coli, Salmonella typhimurium, and Clostridium perfringens, etc. However, correct dose and proper selection of probiotics strains are important to get maximum health effects [25, 26].

3. Future perspective of antibiotics and probiotics use

It has been estimated that true survival and well-being of human being are hidden in chemical-free organic food production that is only possible via the use of good substitutes of synthetic growth promoters such as medicinal plants, prebiotics, probiotics, etc. [27]. Because the use of antibiotics in food-producing animals causes the creation of resistant microorganisms that disseminate to human beings via the food items (milk, meat, eggs, etc.), animal movements, food handlers and by other indirect mechanical means. Available data show that probiotics are good and feasible alternative of synthetic growth promoters to use in food-producing animals. These are known for their positive effects on GIT health. They protect the gut from pathogenic bacteria by producing selective antimicrobial substances and reducing toxin production and also enhance the digestion by stimulation of digestive enzyme synthesis. Probiotics help to restore gut mucosa, upregulate the intestinal motility, improve mucous production, and modulate the host innate immunity by stimulation of Th1 and Th2 immune components. Probiotics create cross-feeding between various bacterial strains of intestinal ecosystem and also reduce the blood cholesterol level via bile salt hydrolase action [28]. Keeping in view the available studies, probiotics could be used in the feed of animals to enhance their growth potential in combination of good animal husbandry practices. There is need of further studies concerning their mechanism of action, mode of delivery and to improve their in vivo efficacy.