In general, harmful effects of antibiotics drug/hormone residues in milk, meat, egg, poultry or fish may be drug resistance, hyper sensitivity, reduced reproductive performance, gastric, respiratory, neurological disease, growth inhibition heart disease, cancer.
The addition of antibiotics in meat, milk and eggs must not be permitted. However, if use of antibiotic is necessary (e.g. for the treatment of disease), a withholding period must be followed to avoid residual toxicity. The WHO recommended that an antibiotic exceeding 100 ppm must be given only under the guidance of a Veterinarian and it must be discontinued for sufficient time prior to slaughter.
(a) Drug resistance:
The heavily exposed (due to consumption of foods from antibiotic treated animals) human beings have a higher incidence of antibiotic- resistant organism than the general population. This leads to problem in therapy.
(b) Hyper sensitivity:
Antibiotics such as penicillin and streptomycin are commonly and neomycin less externally used as feed additives or in chemotherapy. These produce hypersensitivity or allergic reaction in human beings. Streptomycin above the level of 0.2, 1 and 0.5 ppm in milk, meat and eggs and neomycin above the level of 0.15, 0.5 and 0.2 ppm respectively produce allergic reaction in human beings.
Tetracycline:
It is widely used antibiotic as feed additive or in therapeutic. The tetracyclines are absorbed from the gastro intestinal tract and bind in teeth and skeletal structures (calcium rich parts of body) and inhibit their growth. The teeth may discolored and hypoplasia of deciduous and permanent teeth are seen.
A level of 5-7 ppm of tetracycline is found to be toxic in human beings. The tetracycline is excreted through milk after intravenous injection and intrauterine therapy. The oral therapy of tetracyline shows its residue in tissues such as fat, heart, kidney, liver and muscle.
Use of long acting tetrtacylines such as doxycycline and minocycline in food producing animals may be limited because of persistant drug residues. Doxycycline persists in milk much longer than oxy-tetracyline after i. m. injection. The withdrawal period before slaughter should be 5-12 days. The tolerance limit is 0.-25 ppm.
Chloramphenicol:
The use of chloramphenicol is contraindicated as feed additives or in chemotherapy in food animals. No residue in edible tissues are permitted by the FDA. In human beings chloraphenicol causes aplastic anemia and granulocytopenia. It also affects liver and nerve cells resulting hepatitis and optic neuritis and called as “gray syndrome” in new born infant.
Penicillin:
It produces allergic reaction in human beings after consumption of milk containing penicillin. It is most commonly used antibiotics for the treatment of bovine mastitis. Milk may be contaminated with intramammary infusion. The treated cow should not be slaughtered for meat purpose within 3-4 days. Penicillin (50 g/900 kg feed) used as feed additives does not show any residue in liver, muscle, fat and kidney.
Cloxacillin:
It is commonly used for the treatment of bovine mastitis as intramammary infusion and milk get contaminated. In cattle Cloxacillin residue in milk is found for 48 hours after intramammary infusion. A tolerance of 0.01 ppm has been established.
Di-hydro-streptomycin:
This drug is commonly used with penicillin as intrauterine infusion in dairy cattle during and after insemination. The discard time for milk is 36 hours for such treated animals. In food animals this drug should not be used as its residue is found in muscle tissue following intramuscular injection.
Neomycin:
Neomycin residue is found in kidney for 90 days after treatment of animal. The FDA has recommended a tolerance level of neomycin for milk and edible tissue as 0.1 ppm and 1 ppm respectively.
Sulfonamides:
Sulfonamides are excreted in milk following administration. After intrauterine infusion the residue can be detected in milk and blood at-least for 48 hours. Tissue residue has been seen in poultry, sheep, swine and cattle after administration of a number of sulfonamides. In USA the withdrawal period of sulfamethazine is 15 days in swine before slaughter. A tolerance level for sulfamethazine has been established at 0.1 ppm in the edible tissue of swine and 0.01 ppm in milk.
Gentamycin:
In milking animals the gentamycin residue is detected in milk for 16 hours after i/m injection. Following i/m use of this antibiotic residue persists in kidney tissue. In USA the treatment of piglets, turkeys and day-old chicks with gentamycin is not recommended if these are used for meat production.
Gentamycin sulfate residue have been determined in ducks, pigeon and quail in liver and kidney. The pre-slaughter withdrawal period in turkey has been recommended as 63 days. The tolerance level in edible tissue is 0.1 ppm.
Nicin:
It contains nicotinic acid which is used as a colour preservative and vitamin additives in formation of meat and vegetable products. It causes sudden cutaneous vasodilation. The symptoms occur within an hour after ingestion of contaminated food. Intense flushing of skin, warm feeling, itching and abdominal discomfort are common symptoms.
Other Chemical Additives in Food:
Monosodium glutamate (MSG):
This is commonly used food additives for intensifying flavour. The poisoning with this chemical is also known as “Chinese Restaurant Syndrome”. One teaspoonful of MSG in empty stomach is sufficient to cause toxicity in man. Women are more susceptible than men.
Symptoms occur within few minutes to 1/2 hour and manifested as numbness, pressure, tingling sensations in scalp, back of neck, sides of face, jaw, arms, legs ; dizziness, blurred vision, restlessness, headache and nausea. The duration of illness is usually 2 to 7 hours. The most common food involved are Chinese Restaurant foods. The use of MSG in baby food is contraindicated.
Nitrate and Nitrite:
It is commonly used as curing agent in most of the processed meat products. It is also used as colour developer as well as to check the growth of nitrate reducing bacteria in meat and meat products. The nitrate reducing bacteria in meat reduces nitrate into nitrite and forms nitrosamines which are carcinogenic in nature.
Secondly it interferes with oxygen-carrying capacity of red blood cells. Symptoms occur within 1-2 hours like nausea, vomiting, cyanosis, rapid breathing, fall in blood pressure, headache, dyspnea, trembling, convulsions and loss of consciousness. The M.F.P.O. of India prescribed the level of nitrate and nitrite in processed food and these should not be more than 500 ppm and 200 ppm respectively.
Warfarin:
It is a rodenticide used for the control of rodents in field and at home. Basically it is an anticoagulant which acts by inhibition of por-thrombin formation and capillary damage. Any food accidently contaminated with this rodenticide and eaten over a period of several days lead to toxicity.
The symptoms are seen after 7-10 days of consumption of contaminated food. Back and abdominal pain, vomiting, nose bleeding, bleeding of gums, massive bruises, extensive blood loss and shock may be seen. Vitamin K therapy must be adopted to counter act the effect of warfarin poisoning.