Nisin is one of the most effective natural antibacterials chanced upon by man and it was originally isolated in 1928 becoming a popular food preservative extensively used by the food industry. Nisin belongs to the broad group of antibiotics commonly known as Lantibiotics because they contain the unique special amino acid Lanthionine. There are about 30 members in Lantibiotics group, the most famous being Nisin A. Some of the other well known members of this group include mersacidin, actagardin, subtilin and epidermin. Nisin itself has variants designated as Nisin Types A, Z, F, Q derived from the bacteria Lactococci lactis while types U and U2 are obtained from Streptococci species. Generally Lanthionine antibiotics are effective against Gram positive bacterial pathogenes but in combination with the chelation agent, EDTA they can be equally effective against Gram negative bacteria also.
Nisin is a unique short chain poly cyclic peptide containing 34 amino acids and it can boast of some special uncommon amino acids like lanthionine, methyl lanthionine, didehydro alanine and didehydro amino butyric acid. The variants of Nisin differ basically in terms of the number of amino acids contained in the polypeptide varying between 24 and 34 amino acid moieties per molecule. Their excellent solubility in water, proven safety for humans and high effectiveness at low concentrations make them ideal for preservation of many foods. More important they are digested in the GI like any other peptides and proteins leaving no traces that can cause problem. Added to this it has high resistance against acidic environment and commonly encounterd processing temperatures. It is used in a variety of foods that include milk and milk products, meat and derived products, poultry meat, fish products, canned foods, fruit juices, plant proteins, fast food preparations and health care products. Unlike conventional chemical preservatives, Nisin action is independent of pH and there for are excellently suited for extending the life of many traditional food products of India.
Lantionine antibiotics are classified under two broad groups, A and B based on their mode of action against pathogens. Type A antibiotics containing flexible polypeptides cause pores or holes on the cell wall of the contaminating bacteria causing the cell content to leak out leading to their eventual death and Nisin & Epidermin are important members belonging to this type. In contrast Type B products inhibit some of the vital enzymes required for survival and growth of the pathogenic bacteria and prominent ones include Mersacidin and Actagardin. Generally a concentration of 1-25 ppm would be sufficient to get 100% kill of the infection. With an ADI value of 0.13 mg per kg body weight, Nisin is considered safe as the use dosage rarely exceeds 2-3 mg per serving. An international unit (IU) of Nisin is the dose required to inhibit one cell of Streptococcus agalatiae in 1 ml broth and a standard Nisin preparation should have 900 IU per mg. Recent toxicological evidence using nisin preparations containing low Sodium Chloride, usually used for adjusting the potency has further raised the ADI values several fold confirming the innocuous nature of this preservative.
Attempts are being made to increase the potency of Nisin as a broad spectrum antibiotics against major disease vectors through genetic engineering techniques and possibly such efforts may succeed eventually. Bioengineered Nisin, still in an experimental stage, is reported to be effective against difficult to eradicate bacteria such as MRSA, Vancomycin resistant Enterococci VRE, Listeria etc. The antibacterial characteristics of Nisin A, Z, F and Q which are more effective some bacterial species and those of Nisin U and U2 against others are combined through gene transfer to evolve new Nisin variant for use against a wide range of bacteria. It is a question of time before world comes to recognize the potential of Nisin antibiotics for ensuring safety of most of the foods which are facing serious infection problems from many pathogenic bacteria forcing the industry to recall tainted products from the market and incur heavy financial set back.
Food industry world over is going through a difficult period because of increasing cost of processing and higher expectation of the consumer regarding lower prices, better quality and absolute safety. Energy inputs required to get products with impeccable safety credentials are very high while over heated food products tend to lose its quality in terms of taste, texture and flavor. A priority goal for the industry is cutting down on energy cost in day to day operations and Nisin can achieve significant energy saving because of its synergistic effect with temperature calling for lower heating schedule to obtain complete sterilization. Same is true while using chemical preservatives which are under critical scanner regarding their safety and use of Nisin in conjunction with chemical preservatives at lower levels can achieve same results. One of the advantages of Lanthionine antibiotics is that they are never used to fight infectious diseases in man and there fore the much feared antibiotic resistance is a non-issue.
While all look rosy there can be hiccups for using Nisin as a universal preservative because, being a peptide there can be a few who may develop allergy against this preservative. Though there are no major allergic episode so far, presence of milk proteins in Nisin preparation derived from milk substrate can pose problems to consumers vulnerable to lactose allergy. How ever there is technology to produce Nisin using plant derived materials as substrate for fermentation and this problem is unlikely to pose any major challenge to this unique preservative in the near future.