Penicillin is a broad spectrum antibiotic. Penicillin is first obtained from the mould, Penicillium notatum (Figure 6.8).
Penicillium chrysogenum is a high yielding strain, used for the commercial production of penicillin. This strain is highly unstable, so the spore suspensions are maintained in a dormant state to prevent contamination. Most penicillin form filamentous broth and hence is difficult to mix and it hinders oxygen transfer due to their high viscosity. This is avoided by using bubble columns air lift reactors which agitates the medium providing even oxygen distribution.
Penicillin has a basic structure 6-amino penicillanic acid 6-(APA). It consists of a thiazolidine ring with a condensed β-lactum ring. It carries a variable side chain in position 6. Natural penicillins are produced in a fermentation process without adding any side chain precursors. If a side chain precursor is added to the broth, desired penicillin is produced and it is called bio-synthetic penicillin.
Semi synthetic penicillin is one in which, both fermentation and chemical approach are used to produce useful pencillins. It can be taken orally and active against gram negative bacteria. (eg) Amphicilin. Nowadays, semi synthetic pencillins makeup the bulk of the penicillin market.
In later (1939) using (Flemings’ work) Howard Florey and Ernst Chain managed to purify penicillin in a powdered form. In 1941, they successfully treated a human. In 1943, they produced penicillin on a large scale. This helped immensely to treat causalities during the 2nd World War ww1 that had bacterial inflations due to their wounds.
The main objective of producing semi synthetic penicillin is to generate compounds with improved properties. (eg) acid stability, Resistance to enzymic degradation, broader spectrum of activity. Here side chain is removed to form (6 - APA) via immobilization in a column of penicillin acylase. Penicilln is converted to (6-APA) and phenyl acetic. Then it is chemically to acylated produce Semi Synthetic Pencillin.New kinds of synthetic penicillin can also be produced which are readily absorbed by the intestine compared to natural penicillin. Example: Phenithicilin.
The initial strain of Penicillium chrysogenum (NRRL, 1951) was low yielding strain and so it is was treated with mutagenic agents such as X-rays, UV right and some other repeated methods to get a high yielding strain Q-176.
Penicillin production is done by one of the following.
1. Surface culture
2. Submerged fermentation process
To inoculate fermentation medium one of the following methods can be employed.
1. Using dry spores to seed the fermentation medium.
2. Making suspension along with non toxic wetting agent like Sodium lauryl sulphate and inoculating germinated organism
3. Using pellet inocula obtained by the germination of spores
The lyophilized spores (or) spores in well sporulated frozen agar slant are suspended in water or in a dilute solution of a nontoxic wetting agent.
(1:10,000 sodium lauryl sulphonate)
Spores are then added to a bottles containing wheat bran solution It is incubated for 5-7 days at 24°C for heavy sporulation
The resulting spores are then transferred to production tank
The micro organism in the inoculumtank is checked for contamination.
The production tanks are inoculatedwith a mycelial growth
Production medium contains following medium components.
Carbon source as Lactose, Nitrogen source as Ammonium sulphate, Acetate or Lactate (Corn steep liquor is the cheap and easy source of nitrogen)
Mineral sources as K, P (Potassium di hydrogen phosphate), Mg, S (Magnesium sulphate), Zn, Cu(Copper sulphate) (Corn steep liquor supply some of these minerals)
Precursor (Example: phenyl acetic acid)is added to the medium
Antifoam agent (Example: corn orsoybean oil) is added before sterilization
The sufficient aeration and agitation is given and are incubated at 25°C to 26°C for 3 to 5 days at PH range of 7 to 7.5
Process of penicillin production occurs in three phases
First phase: Growth of mycelium occurs in this phase where the yield of antibiotic is low. The pH increases due to the release of NH3.
Second phase: In this phase, intense synthesis of penicillin occurs due to rapid consumption of Lactose and Ammonium nitrogen. The mycelial mass increases and the pH remain unchanged (Figure 6.9).
Third phase: In this phase, the concentration of antibiotics decreases in the medium. Autolysis of mycelium starts, liberating Ammonia leading to slight rise in pH.
After penicillin fermentation, the brothis filtered on rotary vacuum filte
Mycelium is separated
To the broth sulphuric acid or phosphoric acid is added
Penicillin is converted into anionic form
It is extracted in counter current solvent extractor, by using organic solvent, amyl acetate, methyl isobutyl ketone)
It is then back extracted with water from the organic solvent by adding potassium or sodium hydroxide
Shifts between water and solvent aid in the purification of penicillin
The resulting sodium or potassium penicillin is then crystallized
Then it is washed, dried and used for commercial purpose