Penicillin, first described by Fleming in 1929 and clinically used since 1941, is a β-lactam antibiotic produced by Penicillium species, effective against various bacterial infections. The document details its classifications into natural, penicillinase-resistant, aminopenicillins, and extended spectrum penicillins, along with their indications for treating specific infections. It also covers the mechanism of action, chemical structure, biosynthesis, and production methods of penicillin, highlighting advancements in yield over time.

1. PENICILLIN
PRAKSH DHAKAL
Public Health Microbiology
Tribhuvan University

2. INTRODUCTION :
 First described by Fleming in 1929.
 Isolated by Florey and Chain in 1940 from
Penicillium notatum.
 The first clinical application of penicillin was in
1941.
 Penicillins are produced by Penicillium and
Aspergillus species.
 Penicillins belongs to the group of antibiotics called
β-lactams which also include
cephalosporin,carbapenems,monbactams.
 They are labile in acid and may be inactivated by
splitting the β-lactam ring with β-lactamases.

3.  Currently the group of penicllins includes more than 20
antibiotics which are divided into several categories.
1. Natural Penicillins :
( Penicllin G, Procaine, Penicillin G, Penicillin V,
Benzathine) The natural penicillins were the first
antibiotics introduced in clinical practice. Natural
antibiotics are active against gram-positive bacteria
such as Streptococcus spp, Staphylococcus spp.,
Bacillus spp., in less degree against Enterococcus spp.
L.monocytogenes, E.rhusiopathiae and corynebacteria
(including C.diphtheriae), the most of anaerobic bacteria
(Peptostreptococcus spp., Clostridium spp.) are highly
sensitive to natural penicillins. Natural penicillins are
highly effective against spirochetes (Treponema,
Borrelia, Leptospira).

4.  2 . Penicillinase-Resistant Penicillins :
(Cloxacillin, Dicloxacillin, Methicillin, Nafcillin,
Oxacillin). Methicillin was the first member of this
group, followed by oxacillin, nafcillin, cloxacillin
and dicloxacillin. Currently Oxacillin is the most
widespread among penicillinase-resistant
penicillins and is actively used for the treatment of
infections caused by staphylococci including
PRSA.

5.  3.Aminopenicillins (Ampicillin, Amoxicillin,
Bacampicillin). Aminopenicillins were the first
penicillins discovered to be active against gram-
negative bacteria (such as E. coli and H.
influenzae). Aminopenicillins are acid-resistant and
that is why are administered orally. Aminopenicillins
possess a broader spectrum of antibacterial activity
against some strains such as E.coli, Shigella spp.,
Salmonella spp. and P.mirabilis, which are
characterized by low levels of production of
chromosomal β-lactamase. Aminopenicillins are
susceptible to hydrolysis by β -lactamses and that
is why are usually come in combination with β -
lactamse inhibitors.

6.  4.Extended Spectrum Penicillins (sometimes
called anti-pseudomonal penicillins). Extended
spectrum penicillins include both alpha-
carboxypenicillins (carbenicillin and ticarcillin) and
acylaminopenicillins (piperacillin, azlocillin, and
mezlocillin). These antibiotics possess similar
spectrum of antibacterial activity as aminopenicillins
but with additional bactericidal activity against the
majority of gram negative microorganisms such as
Pseudomonas aeruginosa. Along with
aminopenicillins, extended spectrum penicillins are
inactivated by beta-lactamase. These drugs can be
used in monotherapy of infectious diseases or in
combination with aminoglycosides.

7.  Penicillins indication
The indications for penicillins vary depending on penicillins
group. Natural penicillins are used in:
 Infections caused by S.pyogenes, and their consequences:
 tonsilopharyngitis
 scarlet fever
 erysipelas
 year-round rheumatism prevention.
 Infections caused by S.pneumoniae:
 community-acquired pneumonia
 meningitis
 sepsis
 Infections caused by other streptococci:
 Infective endocarditis (in combination with gentamicin or
streptomycin);
 Meningococcal infections (meningitis)
 Syphilis
 Leptospirosis
 Tick-borne borreliosis (Lyme disease)
 Gangrenous emphysema
 Actinomycosis

8.  Penicillinase-Resistant Penicillins and namely
oxacillin is used in:
Staphylococcal infections of different localizations
and susceptible to oxacillin
Infections of skin, soft tissue, bone and joints
Pneumonia
Infectious endocarditis
Meningitis
Sepsis

9.  Aminopenicillins are indicated for the treatment of:
Infections of upper and lower respiratory system including
sinusitis, aggravation of chronic bronchitis, pneumonia
Urinary tract infections: cystitis, pyelonephritis
Meningitis caused by H.influenzae and L.monocytogenes
Endocarditis
Intestinal infections caused by Shigella and Salmonella
(ampicillin)
Eradication of H.pylori in patients with stomach and
duodenal ulcers
Prophylaxisof endocarditis
Intraabdominal infections
Skin and soft tissue infections

10.  Carboxypenicillins are usually indicated for the
treatment of:
Nosocomial infections caused by sensitive strains
P.aeruginosa. Carboxypenicillins must be used only in
combination with other antibacterial preparations
(aminoglycosides, fluorquinolones). Ticarcillin in
combination with clavulonate is indicated in:
Lower respiratory tract infections
Urinary tract infections
Intraabdominal infections
Sepsis
Infections of skin, soft tissue, bones and joints

11. ACTION MECHANISM :
 All β -lactam antibiotics exert bactericidal action
which is associated with inhibition of bacterial cell
wall production. Their target is penicillin-depending
bacterial proteins which fulfill a function of enzymes
on the final stage of peptidoglycan synthesis-
biopolymer and the main component of bacterial
cell wall. Suppressing of peptidoglycan synthesis
leads to consecutive bacterial lysis. Some of
penicillin antibiotic exert bacteriostatic effect in low
doses which may or may not control the infection

13. CHEMICAL STRUCTURE :
 The basic structure of penicillin is 6-
aminopenicillanic acid(6-APA), consisting of a
thiazolidine ring with a condensed B-lactam ring.

14. BIOSYNTHESIS AND REGULATION :
 B-lactam –thiazolidine ring of penicillin is
constructed from L-cysteine and L-valine.
 Biosynethesis occurs in a non ribosomal process by
means of a dipeptide composed of L-alpha-
aminoadipic acid ( L-alpha –AAA) and L-cysteine or
a breakdown product of cystathionine.
 Then subsequently , L valine is connected via an
epimerization reaction resulting in the formation of
the tripeptide delta –(L –alpha-aminoadipyl)-
cysteniyl –D-valine.

15.  The first product of the cyclization of the tripeptide
which can be isolated is isopenicillin N, but the
biochemical reactions leading to this intermediate
are not understood.
 Benzylpenicillin is produced in the exchange of L-
alpha-AAA with activated phenylacetic acid.
 Penicllin biosynthesis is affected by phosphate
concentration and also shows a distinct catabolite
repression by glucose, in addition to regulation by
concentration of ammonium ion, the latter by an
unexpalined mechanism.

17. STRAIN DEVELOPMENT :
 The pencillin production of Fleming’s isolate was
about 2 international units/ml ; today’s process yield a
penicillin titer of about 85,000 units/ml .
 This is an increase from 0.0012 g/l to about 50 g/l .

18. PRODUCTION METHOD :
 Penicllin G and V are produced using submerged
process in 40,000 to 200,000 liter fermenters
 Due to difficulties with O2 supply ,larger tanks
cannot be employed.
 It is a aerobic process with a volumetric oxygen
absorption rate of 0.4-0.5 mM/l-min.
 The inoculum is started using lyophilized spores.
 Spore concentration ( optimal 5x103/ml ) and pellet
formation are crucial for the subsqent yield.
 For optimal penicillin formation ,pellets must be
grow not as compact balls , but in loose form.

19.  The growth phase is of 40 hrs duration cwith a
doubling time of 6 hrs, during which time the
greatest part of the cell mass is formed.
 Oxygen supply should be maintained.
 After growth phase penicillin production phase
occurs. In this phase growth is sharply reduced,
 By feeding with various culture medium
components , the production phase can be
extended to 120-180 hrs.
 The medium varies according to strain used and
usually consists of corn steep liquor ( 4-5 % by dry
wt) which may be replaced by other nitrogen
sources, in addition soy meal, yeast extract or
whey; a carbon source and buffers.

20.  PH is kept constant at 6.5.
 Phenyl acetic acid or pehnoxyacetic acid is fed
continuously as precursor.
 About 65 % of the metabolized carbon source is
used for maintenance energy, 25% for growth and
only 10 % for penicillin production.
 Yield increase of 25 % is reported by adding
glucose and acetic acid.
 Pencillin is excreted into the medium and less than
1% remains mycelium bound.

21.  After separation of mycelium, product recovery is
accomplished by means of a two stage continuous
countercurrent extraction of the fermenter broth
with amyl or butyl acetate at 0-3Oc and PH 2.3-3.0 .
The yield is around 90 %.

22. 
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