INTRODUCTION:

Around 6 billion people consume milk and milk products worldwide; most of them live in developing countries. Animal husbandry practices are extensively increased due to the extended demand of milk.

The use of veterinary drugs is a vital part of animal husbandry practices to treat various diseases in farm animals. Quality of milk, milk technological properties, quality of dairy products and human health issues are the factors related to antimicrobial residues found in milk. Food Safety and Standards Act, 2006 states residues of veterinary drug as “the parent compounds or their metabolites or both in any edible portion of any animal product and include residues of associated impurities of the veterinary drugs concerned”. Presence of antibiotic residues in milk and dairy products is considered as illegitimate.^1,2,3

Fungicidal agents, organophosphates, chlorinated pesticides, antimicrobials, hormones, detergents and disinfectants, dioxins, nitrites, poly chlorinated, herbicidal agents, antihelminthetic drugs, poly brominated biphenyles, mycotoxins, heavy metals and somatotropin hormone are some examples of chemical residues that contaminate milk. Tetracycline, betalactams, sulphonamides, macrolides and amino glycosides are the source of antibiotics residues. Antibiotics above the normal residue levels in milk and milk products is labelled as unfit for human use. Antibiotics are compounds with low to medium molecular weight that exhibiting a variety of chemical and biological properties. For prophylactic and chemotherapeutic purposes many antibiotics are used to enhance the growth and feed efficiency.⁴Majority of the countries in the world has gotten impressive consideration about the safe and effective use of antibiotic in animal production. After a long period of treatment with antibiotic, residues would be present in the milk if not following the withholding period. After the period of treatment the minimum withhold period of milk is 7 days.⁵ Development of microbial drug resistance and the spread of resistant bacteria are the contributing factors for antibiotic residues in milk and milk products.⁶ Around the world antibiotic residues in milk and dairy products are nowadays an issue, associated with public health concerns that include antibiotic resistance, hypersensitivity reactions, toxicity, carcinogenicity and teratogenicity. Therefore, exact detection of low levels of antibiotic residues in milk is vital for the dairy industry and farmers to ensure that the contaminated milk from individual cows are not dispatched to the bulk tank.⁷

World Health Organization (WHO) and the Food Agriculture Organization (FAO) have set standards for acceptable daily intake and maximum residue limits in foods to safeguard human health.⁸ Various countries imposed a regulatory limit for antibiotic residues and other chemical residues in milk and dairy products.^9,10However, in our state they have not taken any initiatives to limit the antibiotic residue in the milk and other variants edible products. No control programs to ensure the safety of the milk has not been established in the Indian livestock industry. In order to protect the health of the consumers strong enactments must be implemented at all levels in India livestock industry about the antimicrobial residues and chemical residue limits in milk and other animal consumable products. By this review it came to understand about the impact on developing public health issues by the consumption of antibiotic residue based milk and milk products.

Case reports about antibiotic residues:

In South Africa, some of the researchers found in their studies that the milk and meat got contaminated due to the antibiotic contents transferred from tetracyclines and pencillin group of antibiotics. The study showed greater concentrations of tetracycline residues in slaughtered beef cattle and residues of organochlorine pesticides in human and cow's milk, highlighting the importance of the antibiotic residue issue in Ethiopia.²⁸

The world population's antibiotic intake risen by 36 percent in the year 2010 and is associated with the appearance of drug-resistant bacteria. 76 percent of this total is due primarily to nations called as BRICS (Brazil, Russia, India, China, and South Africa). Major cause of this rise is due to ingestion of animals or their food derivatives contaminated with antibiotics.²⁹

A study was carried out to detect antibiotic residues and evaluate the microbial load of cattle milk samples gathered from six collection centres of distinct consumers in India. Residues of antibiotics were discovered in 28 samples with a detection rate of 23.3 percent. The study results indicate that from the point of view of microbial load, the milk produced and distributed in the study area can be considered to be of fair quality. Since the existence of antibiotic residues could pose a risk to human health, awareness of the use of antibiotics and adherence to the withdrawal period should be raised.³⁰

In a study conducted in Turkey, a total of 240 milk samples per month collected from various markets analyzed in terms of streptomycin, penicillin, gentamicin, tetracycline and neomycin by using TLC. The concentrations found in pasteurized samples were exceeding maximum residue limits in milks accepted among European Countries. The proportion of antibiotic residue contamination was identified as 1.25%, according to the complete amount of samples analyzed.³¹

A research in Iran found that pasteurized milk provided in the studied town is highly contaminated owing to elevated antibiotic use. To avoid the harmful effects, a standard limit must be set for the correct level of antibiotic residue in milk.³²

Another research carried out in Kerala, India, found that the use of veterinary drugs in livestock producing food has the capacity to produce residues in products obtained from livestock and poses a health hazard to the customer. The most evident reason for unacceptable residues, including the use of overdose and long-acting drugs, may be due to inability to maintain to the withdrawal period. Terms of withdrawal should be strictly observed and guidelines on antimicrobial residue boundaries should be strictly implemented to make the animal products safe for human consumption.³³

Antibiotics used in dairy animals:

Antibiotics are used for both therapeutic and prophylactic purposes in modern dairy farms. Antibiotic classes such as tetracyclines, sulfonamides, fluoroquinolones, macrolides, lincosamides, aminoglycosides, beta-lactams, cephalosporins etc are mainly administered in food-producing animals, which may led to presence of their residues in milk.¹¹ About 90% of all antibiotics used in farm animals and poultry are reported to be administered at subtherapeutic concentrations. About 70% of this is for the purpose of disease prevention and 30% are for growth promotion. When comparing developing countries with developed one risk of antibiotic residue in the milk is higher in developing countries. This is due to the lack of availability for detection and regulatory firm that control the antibiotic residues level in foods in the form of maximum residue limits (MRL).¹² Antibiotics and other drugs are mainly used to provide the animal health, control and treat the aliments and to increase the production. The most common and economically important widespread disease in cattle is called as mastitis. The most prevalent treatment to control mastitis in dairy cattle involves intramammary infusion of antibiotics.

The failure to observe prescribed withdrawal times is the major reason to of presence of drug residues. Withdrawal time is defined as the time required for the residue of toxicological product to reach safe concentration in terms of tolerance. However, the extra label use of antibiotics, primarily dosages that deviate from drug manufacturer’s recommendations, falls under the major reason for occurrence of antibiotic residues in milk after the end of the withholding period in India. The negligence regarding withholding periods of milk and improper use of veterinary drugs leads to the presence of residues of these drugs or their metabolites. Antibiotic usage as preservatives and as growth promoter has also been reported. Education on correct use of antibiotics is important to be particularly lacking amongst dispensers and prescribers of antibiotics.^13,14

Antibiotics as growth promoter:

Nowadays, the antibiotics are used to increase growth especially in broilers and fatteners. By destroying harmful bacteria and partitioning proteins to muscle accretion by suppressing monokines, they can generate enhanced growth rate due to thinning of mucous membrane of the intestine, enabling better absorption, changing gut motility to improve assimilation, generating favourable circumstances for beneficial microbes in the intestine of animals. Antibiotics also promote development by reducing the degree of immune system activity, reducing nutrient waste and reducing the development of toxins. Only young growing animals and poultry in most instances are sensitive to antibiotic mediated growth development.

Antibiotics in therapeutics:

In all instances of pyrexia, inflammation, injuries and viral diseases, indiscriminate use of antibiotics has extensive residual impacts on edible tissues. It is justified to use antibiotics only under particular circumstances because the roll of microbial agents is primarily to kill the rapidly dividing invading cells that invade.

Antibiotics in prophylaxis:

In order to avoid possible infection, animals and poultry receive sub therapeutic concentrations of antibiotics. However, antibiotics are particular to their spectrum of activity only in the active multiplying phase of bacteria. But it’s not going to provide overall protection. Antibiotic prophylaxis is only required in certain instances such as dry cow treatment and surgical processes.

Miscellaneous use of antibiotics:

During the processing and storage of milk and milk products, antimicrobials are used either directly or indirectly. During processing, storage and transportation, direct contamination of milk can happen from air and water. Indirect contamination can occur through feed given to animals. Man will be the final consumer of these residues of antibiotic. There are some causes of various use, such as lack of knowledge, absence of extension activities, insufficient manufacturer literature, absence of safe medicines, and exploitation of more manufacturing and animal benefit. The extra label use of chloramphenicol, furazolidone, nitrofurazone, sulphonamide drugs, and flouroquinolones in lactating animals are prohibited by FDA.

Maximum residue limits:

A number of national and international organizations are involved in the development of control mechanisms for the drugs used in animal production. Individual countries may follow different guidelines. These mechanisms include control of the distribution, use, determination of safe residue levels and residue detection technologies to be employed. On the international level these organizations include the Codex Alimentarius Commission, whose guidelines are set by the Codex Committee on Residues of Veterinary Drugs in Food (CCRVDF) based on the scientific advice of the Joint WHO/FAO Expert Committee on Food Additives (JECFA). Other international groups include the European Agency for the Evaluation of Medicinal Products (EMEA), Office International des Epizooties (OlE) and Consultation Mondiale de l'Industrie de la Sante Animale (COMISA). Many countries have specialist groups involved such as the Food and Drug Administration in the United States, the Bureau of Veterinary Drugs in Canada and the Veterinary Products Committee of the Ministry of Agriculture, Fisheries and Foods in the United Kingdom.¹⁵ Limits have been established for drug residues in foods in the form of tolerances or maximum residue limits (MRLs). It should be noted that the term tolerance is used in the United States while MRL is used in Canada and the European Union, but the two terms are synonymous.¹⁶ The word MRL may be characterized as the maximum concentration of marker residue resulting from the use of a veterinary drug expressed as new weight components like parts per million (ppm) or parts per billion (ppb) legally allowed or acknowledged as acceptable in or on food. The MRL of a compound is based on the acceptable daily intake (ADI). The ADI is a rough estimate of the quantity of a veterinary drug given on a body weight basis that can be ingested daily by a person without significant toxicological health danger throughout a lifetime and can be regarded the safety standard for that compound. The following procedures are used for the establishment of MRLs and withdrawal periods in Canada by the Bureau of Veterinary Drugs, Human Safety Division.¹⁷

Calculation of the ADI of a veterinary drug:

The ADI is determined by the no observable effect level (NOEL) r the dosage level (mg/kg or ppm) at which no adverse effects are observed as established by animal bioassay toxicological studies using the most sensitive testing methods available in the most sensitive animal species (e.g., teratogenicity, carcinogenicity, mutagenicity or immunopathological effects). The ADI is obtained by dividing the NOEL by a safety factor (SF) which varies from 100 to 1000 depending on the use of the drug in question and the amount and degree of toxicity data presented by the manufacturer.

ADI (mg/kg/day) = NOEL

Table 1: Maximum Residues Limit (MRL) of antibiotic in mil as per Codex Alimentarius commission

S. No.	Name of Antibiotics	Maximum Residual Limit (μg/kg)
1	Benzyl penicillin	4
2	Ampicillin	4
3	Amoxycillin	4
4	Oxacillin	30
5	Cloxacillin	30
6	Dicloxacillin	30
7	Tetracycline	100
8	Oxytetracycline	100
9	Chlortetracycline	100
10	Dihydrostreptomycine	200
11	Gentamycine	200
12	Sulphonamides	100
13	Ceftiofur	100

Techniques used for drug residue detection and analysis

- ELISA

- HPLC

- Liquid chromatography

- Gas chromatography

- Paper chromatography

Pathological effects due to antibiotic residues in food

- Antibiotic resistant bacteria transfer to the human.

- Immunopathological effects

- Bone marrow toxicity by Chloramphenicol

- Autoimmunity

- Reproductive disorders

- Hepatotoxicity

- Carcinogenicity by Sulphamethazine, Oxytetracycline, Furazolidone

- Mutagenicity

- Nephropathy by Gentamicin

- Allergy by Penicillin

Harmful consequences of antibiotic residues:

The presence of antibiotic residues in milk and milk products can lead to consumer health hazards. Problems related to antimicrobial residues in milk include the risk of allergic reactions and occurrence of antibiotic resistant bacteria, the risk of foetal teratogenicity, developing teeth hypoplasia, bone marrow aplasia, chronic insidious consumption leading to increased risk of cancer and abnormality of body’s reproductive, immune, endocrine and nervous system. The major problem concerning dietary exposure of antibiotic residues is due to advent of pathogen resistant antibiotic strains, which complicating the therapy for both human and animal diseases. Due to pasteurization or drying, penicillin is not inactivated by levels as low as 0.03 IUmL^-1.¹⁸ Penicillins have low toxicity; the most prevalent adverse effects of hypersensitivity reactions, particularly skin rashes. Gastrointestinal disturbances may also sometimes occur, including diarrhoea, nausea and vomiting.¹⁹ In addition, nitrofurans can respond to produce nitrosamines with nitrite (carcinogenic), tetracycline can produce bacterial resistance; oxytetracycline induces antibiotic resistance in the form of coli microorganisms present in the human intestine in particular. The development of resistant bacteria in humans and the transfer of genes of antibiotic resistance (R-factor) from non-pathogenic bacteria to other bacteria or human pathogens leading to extensive resistance.^7,20,18

Despite their beneficial use, embryotoxicity, teratogenicity and other adverse effects in a variety of animal species induced by benzimidazoles or their metabolites.²¹Consequently, significant attention has been paid to the risk to human health resulting from consumed food of animal origin such as milk, cheese and butter. In certain products of animal origin, including meat and milk, the European Union has set maximum residue limits (MRLs), but not for other dairy products.²²The need for more intensive residue controls is growing with several studies indicating that benzimidazoles are not degraded after microwave and oven baking, storage at -18°C for three to eight months and after cooking.²³ The incidence of chemical residues in lactating cow's milk is a matter of public health concern, as dairy products are commonly taken by babies, children and adults. Therefore, the presence of antibiotic residues in milk is a key problem for food safety.^24,25

Public health aspect:

Antibiotic residues in milk are a major problem for public health as milk is commonly consumed throughout the world by children, youth and adults. Antibacterial residues may pose hazards to human pharmacology, toxicology, microbiology, and immunopathology. Acute and chronic adverse effects of antibiotics residues are transfer of antibiotic resistant bacteria to the human, autoimmunity, carcinogenicity due to sulphamethazine and oxytetracycline, mutagenicity, nephropathy due to gentamicin, hepatotoxicity, reproductive disorders, chloramphenicol induced bone marrow toxicity, allergy reactions due to penicillin. These hazards can be classified as direct-short-term hazards and indirect-long-term hazards in up to two types, depending on the duration of residue exposure and the timing of health effects. Direct health risks include the health impacts triggered by the excretion of the drug in milk, as an instance of which the beta-lactam group of antibiotics, irrespective of their low milk concentration, triggers an allergic hypersensitive reaction in the sensitized person instantly after consumption, while chronic toxic impacts with extended exposure to small concentrations of antibiotics include carcinogenicity, teratogenicity, reproductive effects, development of antibiotic resistance bacteria in treated animals and destruction of normal human flora in the gut. Chronic OTC exposure includes changes in blood such as leucocytosis, atypical lymphocytes, lung congestion, granulocyte toxic granulation, and purpura thrombocytopenia, and brown teeth discoloration. Antibacterial agents such as tetracyclines, nitrofurans, and sulfonamides are used in cattle feed as feed additives that can excrete in milk and are sometimes linked with human toxicology.^26,27

Antibiotic residues prevention:

· The first step in residue avoidance is to raise awareness of the issue by training veterinary staff, organisations, and literatures and government agencies to people and organisations.

· Rapid screening methods for antibiotic residue assessment and immediate grading and prohibition of more than MRL containing foods.

· Milk aid processing to inactivate antibiotics. Refrigeration leads penicillin to disappear. Most antibiotics will lose activity in pasteurization.

· The use of activated charcoal, resin and UV radiation also contributes to the inactivation of antibiotics.

· Irrational use of antibiotics should be prevented in the field of veterinary practice.

· Simple and economic field test development to identify drug residue in consumable animal goods.

· To promote Ethno-veterinary procedures.

· Wide tracking and periodic surveillance of microbial residue in edible products and milk by nation.

Solution to tackle with antibiotic residues:

Governments are responsible for regulating consumer protection against occurrence of chemicals in food. To address the threat of antimicrobial residues in animal-derived foods such as dairy, meat and their products, a number of global organisations such as the Codex Alimenterius Commission (CAC), the European Economic Community (EEC), the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) are engaged in controlling drug use in animal-derived products. These organisations have suggested maximum residue levels (MRLs) for livestock products based on periodic monitoring, control and surveillance programs to minimize the risk to human health for this purpose. It is illegal to detect antibiotic residue levels in milk supplies that are greater than the MRLs, which should be controlled to prevent this public health hazard. People should guarantee rigorous adherence to the drug withdrawal period prescribed. It is vital to establish legislative norms and excellent management methods that decrease the risk of antibiotic residues in the dairy supply for human food safety.²⁷

CONCLUSION:

Once antibiotics are given to the animal body; their products contain antibiotic residues in elevated or low levels. However, it relies primarily on the duration of antibiotic administration. The withdrawal time of various drugs should therefore be strictly observed and milk should not be used for human consumption during this period. Antibiotic use as a growth promoter should be strictly forbidden and should be used in appropriate doses and for proper time whenever used for therapeutic purposes. Thus, we can minimize the harmful impacts of antibiotic residues by following adequate scientific guidelines and precautions. Therefore, Strict national legislation passed on livestock sector to avoid unnecessary use of chemicals, avoid using antibiotics in the veterinary field without a veterinarian’s prescription and educate dairy owners on drug withdrawal period of treated animals, national chemical residues control and monitoring program should be design to set standards on the use of chemicals (antimicrobials, insecticides, pesticides, etc.).

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Received on 16.11.2019 Modified on 23.12.2019

Res. J. Pharmacology and Pharmacodynamics.2020; 12(1):15-20.

DOI: 10.5958/2321-5836.2020.00004.X