Chair of Medical biology, Microbiology,
Virology, and Immunology
Antibiotics, classificaions
and mechanism of action.
The main principles of
rational antibiotic therapy
of diseases.
By As. Prof. O.Pokryshko
Lectures schedule
1. History of antibiotics discovery.
2. Classification of antibiotics.
3. Examination of bacterial susceptibility to
antibiotics.
4. The main principles of rational antibiotic
therapy of diseases.
5. Complication of antibioticotherapy.
- Diarrheal diseases - 4 billions cases,
- Malaria - 500 mln,
- acute infection of respiratory tract - 395 mln,
- sexual transmitted diseases - 330 mln,
- measles - 42 mln,
- whooping cough - 40 mln
- tuberculosis – 1,9 bln of infected persons,
9 mln of new cases of diseases
- AIDS – 50 mln cases, 6 mln people died
- SARS, hemorrhagic fever
Modern chemotherapy has been dated
to the work of Paul Ehrlich (Germany)
Ehrlich postulated that it would be
possible to find chemicals that
were selectively toxic for parasites
but not toxic to humans.
He introduced the concept of chemotherapy
dealing with the treatment of diseases with
chemicals. This idea has been called the
"magic bullet" concept.
The first antibiotic, Penicillin
G, was discovered in 1929
by Alexander Fleming.
1940s: Penicillin was
tested clinically and mass
produced.
A. Fleming
He observed that Penicillium fungus made an
antibiotic, penicillin, that killed S. aureus.
Figure 1.5
In 1944 Waksman isolated
streptomycin and subsequently
found agents such as
chloramphenicol, tetracyclines,
and erythromycin in soil
samples.
S. Waksman
In 1939 Florey and colleagues at Oxford University again
isolated penicillin
G. Florey
E. Chainy
Antibiotics are chemical substances
produced by microorganisms (such as
bacteria, fungi, actinomyces) or other
organisms which suppress the growth
of other microorganisms and eventually
destroy them.
Some antibiotics have been produced
by chemical synthesis or semisynthetically from natural substances.
The term “antibiotics” proposed in
1942 S. Waksman
It means: anti – against, bios - life
Microbial antagonism
is the basis of
modern
use
of
antibiotics
L. Pasteur
Peculiarities of antibiotics
- high level of biological activity
- high election specificity
Activity of antibiotics is
evaluated in International Unit
Classification of antibiotics
according to their origin
1. Antibiotics from fungi:
Penicillins (Penicillium notatum,
P.chryzogenum),
Cephalosporins (Cephalosporium
salmosynnematum),
Griseofulvinum (P. griseofulvum, P. patulum, P.
nigricans),
Fusidin (Fusidium coccineum),
2. Antibiotics from Actinomyces:
Aminoglicosides: Streptomycin (Streptomyces
griseus), neomycin (S. fradiae), kanamycin (S.
kanamyseticus), tobramycin (S. tenebrarius),
gentamycin (Micromonospora purpurea), sisomicin
(Micromonospora inyoensis);
Tetracyclines: chlortetracycline (S.
aureofaciens), oxytetracycline (S. rimosus);
Chloramphenicol (S. venezuelae);
Macrolides: oleandomycin, (S. antibioticus),
erythromycin (S. erythreus),
2. Antibiotics from Actinomyces:
Linkomycin (S. lincolniensis); е) Rifampicin
(S. mediterranei);
Polyenes: nystatin (S. noursei), levorin (S.
levorys Krass), amphotericin B (S. nodosus);
Inhibitors of beta-lactamases: klavulanic
acid (S. clavuligerus),
Carbapenem (S. olivaceus),
Thienamycin (S. cattleya).
3. Antibiotics from bacteria:
Bacillus: polymyxin (B. polymyxa),
licheniformin (B. licheniformis), gramicidin С
(B. brevis), subtilin (B. subtilis);
Pseudomonas: piocianin (P. aeruginosa),
sorbistin (P. sorbistini),
other bacteria: monobactams
(Chromobacterium violaceum), nisin
(Streptococcus lactis), prodigiosin (Serratia
marcescens), coliformin (E. coli), streptosin,
diplococcin (Streptococcus spp.), azomycin,
nocardamin (Nocardia)
4. Antibiotics from plants
Chorellin (Chlorella vulgaris);
Arenarin (Helichrysum arenarium);
Gordecin (barley);
Chinin (cinchona tree);
Alicin (garlic, Allium sativum);
Raphanin (radish, Raphanus sativum);
Phaseolin (haricot bean, Phaseolus vulgaris).
5. Antibiotics from animal tissues:
interferons (spleen, macrophages, tissue
cells),
lysozyme (most body fluid, salive, eggs);
erythrin (red cells, liver);
ecmolin (fish)
Classification of antibiotics according
to the spectrum of biological action
1. Antibacterial:
А. Narrow spectrum of action which are active against
gram-positive bacteria: а) natural Penicillins; b) semisynthetic Penicillins (methicillin, oxacillin);
c)
Cephalosporins;
d) Lincomycin; е) Macrolodes.
Б. Broad spectrum of action
а) semi-synthetic
Penicillins (Ampicillin, Amoxicillin); b) Cephalocporins
of
ІІ-IV
generation;
c)
Tetracyclines;
d)
Chloramphenocol;
e) Aminoglycosides; f)
Polymixins; g) Fluoride quinolones
Classification of antibiotics according to
the spectrum of biological action
2. Antifungal (amphotericin).
3. Antiviral (amantadin, vidarabin).
4. Antiprotozoal (emethin, chinin).
5. Antineoplastic (bleomycin, mitomycin C,
actinomycines).
Spectrum of Activity
Relates to the number of microbes that are
susceptible to the action of the drug
–Narrow (limited number) / Broad (wide)
• Penicillin G is a narrow spectrum drug as it is
only effective against gram-positive microbe
• Tetracyclines are effective against gram-positive
and gram-negative microbes (Broad)
Note: Never confusion these terms with potency
levels of the drugs or efficacy (ie. Narrow are weak,
Broad are strong)
Classification of antibiotics according to
the spectrum of action
Bacteriostatic􀂅
Reversible inhibition of growth
When the antibiotic is removed, almost all of
the bacteria can replicate
Bactericidal􀂅
Irreversible inhibition of growth
When the antibiotic is removed, almost none of
the bacteria (10-7to 10-3) can replicate
Bactericidal agents are more effective, but bacteriostatic agents can be
extremely beneficial since they permit the normal defenses of the host to
destroy the microorganisms.
Mechanism of Action:
1. Inhibition of Cell Wall Synthesis
2. Disruption of Cell Membrane
3. Inhibition of Protein Synthesis
4. Interference with Metabolic
Processes
NB:
Bactericidal
Bacteriostatic
Inhibition of Cell Wall Synthesis
Most bacteria possess a cell wall to protect
from osmotic pressures
Microbe divides – needs to create a new
cell wall
– Interrupt this leads to new microbes being
susceptible to external influences
– Cell ruptures  Microbe death
Eg. Penicillinsm cephalosporins,
vancomycin and bacitracin
Disruption of the microbial cell
membrane
Essentially, affect cell membrane transportation in
and out
Increases permeability of membrane
– External influences have greater effect
– Microbe death
Eg. Polymyxin, Colistin
Note: These agents are more toxic systemically
than those agents that inhibit cell wall
synthesis.
Inhibition of Protein Synthesis
Proteins vital for growth and repair
Act either at:
– Site of protein synthesis (ribosome)
– Within the nucleus by inhibiting synthesis of nucleic
acids
•
DNA replication / RNA synthesis = TRANSCRIPTION
Eg. Tetracyclines, aminoglycosides and macrolides
(erythromycin)
Exploit structural differences between microbial
and human cells
– High dose can lead to toxicity
Interference with metabolic
processes
• Agents are structurally similar to Paraaminobensoic acid (PABA) – component
of folic acid
– Essential for nucleic acid synthesis, without it
microbes can not produce the proteins for
growth
– Exploits: microbes need to create their own
folic acid, whilst we get it in our diets.
• Eg Sulphonamides, Trimethoprim
Examination of susceptibility of
bacteria to antibiotics
Serial dilutions:
- in a liquid medium
- in a solid medium
Disc diffusion method
Rapid methods
Demands to nutrient media
1. to be standard and provide optimal
conditions for microbial growth;
2. do not have inhibitors of bacterial
growth and a lot of stimulators;
3. do not have substances, which
inhibit antibiotic activity
Disc diffusion method
Serial dilution in liquid medium
Serial dilution in solid medium
Minimal Inhibitory
Concentration (MIC)
􀂅􀂅Lowest concentration of antibiotic that
prevents visible growth
• 􀂅Broth or tube dilution method􀂅Serial 2-fold
dilutions of the antibiotic
• 􀂅Accurate but time-consuming
• 􀂅Disk sensitivity test􀂅Rapid, but must be related
to results from the tube dilution method
Minimal Bactericidal
Concentration (MBC)
􀂅􀂅Lowest concentration of antibiotic that reduces
the number of viable cells by at least 1000-fold
• 􀂅Performed in conjunction with MIC by the tube dilution
method􀂅Aliquots from the tubes at and above the MIC are
plated onto agar media
• 􀂅The antibiotic is diluted, so that the remaining viable cells
grow and form colonies
– 􀂅The MBC of a truly bactericidal agent is equal to or
just slightly above its MIC
Rapid methods
 examination
of changes of microbial
enzymes activity under the influence of
antibiotics;
 examination
indicators;
of
color
of
redox-
 cytological evaluation of morphological
changes;
 automatic
Automatic metod of examination of bacterial
susceptibility
Criteria
that determines the effectiveness of
antimicrobial agents used in the
treatment of infectious diseases:
1. Selective toxicity - destroys or inhibits microbe
without affecting host cells
2. Broad spectrum - effective against a wide
variety of organisms
3. Non-mutagenic - does not induce development
of resistant strains
4. Soluble in body fluids - distributed through body
(in bloodstream)
Criteria
that determines the effectiveness of
antimicrobial agents used in the
treatment of infectious diseases:
5. Stable in body fluids - not easily broken down
or excreted, to maintain constant and effective
levels
6. Absorbed by tissues - to reach site of infection
7. Non-allergenic to host - should not cause
adverse reactions in host
8. Should not disturb host’s normal flora
(organisms normally living in body) causing
secondary (super) infections produced by
opportunists
General principles
1. The first question to ask before prescribing an
antibiotic is whether its use is really necessary. There is
no point in prescribing it if, for instance, the disease is not
due to an infection (fever does not always indicate the
presence of an infection), or if the infection is due to
agents such as viruses, which do not respond to
antibiotics.
All therapy is a calculated risk in which the probable
benefits must outweigh the drawbacks, and antibiotics are
no exception to this rule. To use them when they are not
indicated and when the "probable benefits" are nonexistent means exposing the patient to the risk of adverse
reactions, or worse.
2. Patients with similar infections react differently.
This may be due to previous contact with the same
pathogen or to the individual immune response. The
presence of hepatic or renal disease may necessitate
changes in the dosage or the choice of antibiotic.
Knowledge of any past adverse reactions to antibiotics
is also essential.
3. The doctor must be familiar with the typical
response of infections to proper antibiotic treatment.
Acute infection with group A streptococci or
pneumococci responds rapidly (usually within 48 hours)
to penicillin G, while the temperature curve in typhoid
fever treated with chloramphenicol may not show any
change for four or five days.
4.
The doctor must know which bacteria are
commonly found in which situations, for instance
Pseudomonas in extensive burns (sepsis is frequent
and often fatal) and in the expectoration of children
with cystic fibrosis, or Streptococcus pneumoniae and
Haemophilus influenzae in chronic bronchitis of the
adult.
5. Ideally, treatment with antibiotics should not be
instituted before samples for sensitivity testing have
been collected. Such tests can be dispensed with,
however, when the causative organism is known and its
response to the antibiotic is predictable. But the
sensitivity of, for instance, many gram-negative strains
can change, even during treatment, making an
alternative treatment necessary. In addition, the clinical
results may be at odds with the findings of the
sensitivity tests. Even a severe infection may show a
satisfactory clinical response despite apparent lack of
sensitivity.
Failure of antibiotic therapy
Antibiotic treatment is considered a failure if no response
is seen within three days. Failure may be due to various
causes:
1. Wrong diagnosis (a viral infection does not respond
to antibiotics).
2. Wrong choice of antibiotic.
3. Wrong dosage (wrongly dosed by doctor or poor
patient compliance).
4. Development of resistance during therapy (as
sometimes occurs in tuberculosis and infections due to
gram-negative pathogens).
Failure of antibiotic therapy
5. Superinfection by resistant bacteria.
6. Accumulation of pus necessitating surgical
drainage (buttock abscess).
7. Underlying disease (lymphoma, neoplasia) of
which the infection is only an intercurrent
complication.
8. Drug fever.
Disadvantages
of Antimicrobial Therapy:
І. Allergic reactions
ІІ. Toxic effects on normal tissues
ІІІ. Disturbs host normal flora 
secondary infections (Dysbacteriosis)
Disadvantages
of Antimicrobial Therapy:
І. Allergic reactions
- dangerous for life (anaphylactic shock,
angioneurotic oedema of larynx)
- non-dangerous for life
(skin itching,
urticaria, rash, rhinitis, glossitis, conjunctivitis,
photodermatoses (tetracyclines)
Disadvantages
of Antimicrobial Therapy:
ІІ. Toxic reactions
- dangerous for life (agranulocytosis,
aplastic anemia, endotoxic shock)
- non-dangerous (neuritis of N. vestibularis
and N. auricularis aminoglycosides;
periferal neuritis, vomiting, nausea, diarrhea,
hepatotoxic
and
nephrotoxic
effects,
embriotoxic effect, pigmentation of the teeth)
Secondary action of antibiotics
ІІІ. Dysbacteriosis
- dangerous for life
(generalized
candidiases
sepsis,
staphylococcal
enterocolitis, secondary pneumonia, which
cause gram-negative bacteria)
- non-dangerous for life (local candidiases)
Types of resistance
 Natural resistance
 Acquired resistanse
 primary
 secondary
Mechanisms of Resistance
Development of resistant strains – spontaneous
mutations, DNA transfer
a. Ability to destroy AMA by producing enzymes
(Staph –penicillinase or -lactamase)
b. Mutations causing structural changes in cell so
bypass metabolic step inhibited by AMA (L-forms - no
cell wall)
c. Over produce target molecules  increase in
quantity overcomes action of AMA
d. R-factors (resistant genes) in plasmids
transferred to bacterial cells by conjugation,
transformation, transduction
R-Plasmids
Resistance transfer factors, or RTFs
Transposons
Staphylococci, Enterobacteria – transposon Tn551
(erythromycin),
Tn552
(penicillin),
Tn554
(erythromycin, spectinomycin). They can integrate
with R-plasmids and phages
Mechanism to Reduce Bacterial Resistance.
Proper selection of new antibiotics will be a major force
in slowing the development of antimicrobial resistance.
Proper hygiene practices will reduce plasmid transfer
and the establishment of multiple drug-resistant
bacteria in the hospital and will delay the appearance
of such species in the community. There are a number
of mechanisms to prevent bacterial resistance. The
health care provider must be continually alert to the
appearance of antibiotic resistance within the hospital
and community.