Transcript 4. Microbial Products

Microbial Products
A. Primary Metabolites: log phase, use nutrients fast, produce PM
B. Secondary Metabolites: depletion of nutrients, growth retards,
produce SM
Primary Metabolites: Vitamins
Vitamins: cannot be synthesized by higher organisms
But microorganisms are capable of synthesizing (gut)
 Studies reveal vitamin deficiencies
Thiamine
 Reported beneficial health effects
Riboflavin
 Growing vitamin market demand (cost
Pyridoxine
effective)
Folic acid
 Genetically engineered MO as alternatives to
Pantothenic acid
chemical synthesis
Biotin
Vitamin B12
Ascorbic acid
b- carotene (provitamin A)
Ergosterol (vitamin D)
Vitamins
Fat soluble
Carotenoids
b-carotene (provitamin A)
Astaxanthin
Poly unsaturated Fatty acids (PUFA; vitamin F)
Docosahexaenoic acid (DHA)
Arachidonic acid (ARA)
Ergosterol (vitamin D)
Water soluble
Riboflavin (vitamin B2)
Cobalamin (vitamin B12)
L-Ascorbic acid (Vitamin C)
R-Pantothenic acid (vitamin B5)
D-Biotin (vitamin H or B7)
Vitamin B1 (Thiamine)
Vitamin B6 (pyridoxol)
Folic acid
Vitamin B12 or Cyanocobalamin
• Water soluble vitamin ; complex sructure
• Has role in functioning of brain and nervous system, formation of
blood
• Contains rare element cobalt
• Deficiency causes pernicious anemia which is an causes low Hb, less
RBCs
• Pernicious anemia: autoimmune disorder, parietal cells (stomach)
responsible for secreting intrinsic factor are destroyed. Intrinsic
factor is crucial for the normal absorption of B12, so a lack of
intrinsic factor, as seen in pernicious anemia, causes a deficiency of
Vitamin B12
• dietary reference intake for an adult ranges from 2 to 3 µg per day
• used in treating cyanide poisoning, prevents brain atrophy in
Alzheimer’s patients
• COMMON INGREDIENT IN ENERGY DRINKS
C63 H88 CoN14 O14P
Pyrrole nitrogen
4 Pyrrole units
cobinamide
• Corrin ring
• Deep red colour due to corrin
ring
• Central Co atom
• Coordination state 6
• 4 of 6 coord sites have pyrrole
ring
• 5 has dimethylbenzimidazole
group
• 6 is center of reactivity,
variab;e
• CN, OH, Me, 5-deoxyadenosyl
for 4 types of B12
nucleotide
6
2
1
3
4
5
5,6-dimethyl
benzimindazole
Commercial production
Chemical syn not feasible
Genera known to produce vit B12
Most commonly used for industrial production are
20mg/L
Streptomyces griesus
Pseudomonas denitrificans (aerobic)
Salmonella typhimuriu (anaerobic)
Propionibacterium shermanii
GRAS by FDA
(anaerobic)
(Generally Regarded As Safe)
Sanofi-Aventis (FRENCH) use genetically engineered versions to produce vit
B12 under specialized conditions from Propionibacterium since they have no
endotoxins or exotoxins
P. denitrificans also used after strain modification; mutant more efficient
than wild type
Commercial production
•
Produced in continuous culture with 2 fermenters in series
Addition
of
5,6dimethylbenzimidazol (0.1%)
Glucose
Corn steep
Betaine (5%)
Cobalt (5ppm)
pH 7.5 +
Propionibacterium
freudenreichii
Anaerobic
70h
Aerobic
50h
Cobinamide production
and accumulation
KCN added
CYNACOBALAMIN
80% purity
Used as feed additive
Betaine: sugar beet molasses
Filtrate
Nucleotide synthesized
Combined with cobinamide
To yield 2ppm of cobalamin
Acidification of culture
To 2-3pH/ 100oC
Filter to remove cell debris
Commercial production
ANAEROBIC PHASE
AEROBIC PHASE
2-4 DAYS
5-deoxyadenosylcobinamide produced
5,6-dimethylbenzimidazole
is
added and gets incorporated to
form 5’-deoxyadenosylcobalamin
During the 7-day fermentation run, adenosylcobalamin is predominantly
secreted from the biomass and accumulates in the fermentation broth in
milligram amounts.
The down- stream steps comprise filtration, cyanide treatment,
chromatography, extraction, and crystallization yielding vitamin B12 in
high purity.
If to be used for treatment further purification (95-98% Purity)
Commercial production
Pseudomonas denitrificans: strain improvements resulted in increase in yeild
From 0.6mg/L to 60mg/L
Glucose : common carbon
Alcohols (methanol, ethanol, isopropanol)
Hydrocarbons(alkanes, decane, hexadecane)
With methanol 42mg/L was obtained using Methanosarcina barkeri
Riboflavin (Rf) or Vitamin B2
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Water soluble
Essential for growth and reproduction; key role in energy metabolism, ketone bodies,
fats, CHO and protein metabolism
Deficiency leads to cheliosis (fissures around mouth), glossitis (purple tounge) and
dermatitis
Required in coenzymes FAD (flavin adenine dinucleotide) and FMN (flavin
mononucleotide)
Used as an orange-red food colour additive, designated in Europe as E101
7,8-dimethyl-10- (D-19-ribityl) isoalloxazine
Participates in O-R reactions
Flavin is ring moiety with yellow
colour to oxidized form
Isoalloxazine ring
Isoalloxazine ring
H
H
Ribitol
FAD
E101
FMN
E101a
genes encoding the riboflavin biosynthetic enzymes are well conserved among bacteria and fungi
INDUSTRIAL USE
Processed food is often fortified by the use of riboflavin as a colorant or vitamin
supplement.
The main application (70%) of commercial riboflavin is in animal feed, since productive
livestock, especially poultry and pigs, show growth retardation and diarrhea in case of
riboflavin deficiency.
According to a report by SRIC, a consulting company in Menlo Park (California), in 2005
the need for industrially produced riboflavin was estimated at 6500–7000 tons per
year.
Commercial production
Glucose
1/3rd production by
direct fermentation
Acetone butanol fermentation
Clostridium acetobutylicum
C. butylicum riboflavin as
by product
50% by biotransformation
using Bacillus pumulis
D-ribose
20% production by Chemical synthesis
Riboflavin
Ashbya gossypii
Candida famata
Bacillus subtillis (genetically modified)
Commercial production
Phase I
use of glucose, accumulation of pyr, pH acidic, growth stops, no Riboflv
Phase II decr pyr, incr in ammonia, alkalinity incr, prod of Riboflv in form of FAD and FMN
Phase III autolysis, cell disruption, release of free FAD, FMN and riboflv
Carbon sources: glucose, acetate, methanol, aliphatic hydrocarbons
Major riboflavin producers are DSM Nutritional Products
(Switzerland) and Hubei Guangji (Hubei Province, China), both using
genetically engineered B. subtilis production strains, and BASF (first in
Germany but now in South Korea), employing genetically engineered A.
gossypii.
Ascorbic acid or Vitamin C
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•
Used in collagen biosynthesis, protects against nitrosamines, free radicals
Deficiency causes scurvy
Precursor for its chemical synthesis can be obtained by biological methods
feed applications of L-ascorbic acid account for only 10%, whereas the main
uses are in the
pharmaceutical industry (50%),
food (25%), and
beverages (15%).
Pharmaceutical applications include stimulation of collagen synthesis
(especially cosmetic products) and high antioxidant capacity, used for the
reported health benefits in the prevention of flu, heart diseases, and cancer,
as well as an antidote for poisoning.
The food and beverage industry predominantly exploits the antioxidant
capacity of L-ascorbic acid to extend durability, prevent discoloration,
and to protect flavor and nutrient contents of their products.
Submerged bioreactor fermentation
Erwinia sp.
Acetobacter sp.
Gluconobacter sp.
2,5-diketogluconic acid
2,5-diketogluconic acid
reductase
D-glucose
(200g)
Glucuronic acid
Corynebacterium sp.
2-keto L-gluconic acid
Bacillus
megaterium
L-ASCORBIC ACID
Cloning of gene
2,5-diketogluconic acid
Reductase of
Corynebacterium into
Erwinia herbicola
D-sorbitol
sorbitol dehydrogenase
Acetobacter xylinum,
A,suboxydans
L-Sorbose
chemical oxidation
2 keto L gulonic acid
Enol form of
2 keto L gulonic acid
Reichstein Grussner synthesis
Gluconolactone
acid treatment
L-ASCORBIC ACID (100g)
L-Gluconolactone
L-Gluconolactone
dehydrogenase
L-ASCORBIC ACID
b- carotene or provitamin A
Provitamin A -----> Vitamin A (intestine)
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Fat soluble
Deficiency leads to night blindness
Best source is liver and whole milk also coloured fruits and vegetables
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Isoprene derivatives
Tetraterpenoids with eight isoprene residues
400 naturally occurring carotenoids: b-carotene, a-carotene, d-carotene, lycopene,
zeaxanthin
Carotenoids Used as food colorants and animal feed supplements for poultry
and aquaculture, carotenoids play an increasing role in cosmetic and
pharmaceutical applications due to their antioxidant properties.
The pigments are often regarded as the driving force of the nutraceutical
boom, since they not only exhibit significant anticarcinogenic activities but also
promote ocular health, can improve immune response, and prevent chronic
degenerative diseases.
Commercial production
Microbial fermentation
Submerged Fermentation process
Blakeslea trispora (high yeild; 7g/L)
Phycomyces blakesleeanus
Choanephora cucurbitarum
Corn starch, soyabean meal, b-ionone, antioxidants
stimulators
Trisporic acid: act as microbial sex hormone, improves yield
b-Ionone: incr b-carotene syn by incr enzyme activity
Purified deodorized kerosene increases solubility of hydrophobic
substrates
Recovery: b- carotene rich mycelium used as feed additive
Mycelium is dehydrated by methanol, extracted in methylene chloride
and crystallized which is 70-85% pure
DSM Nutritional Products (Switzerland) and BASF (Germany)
dominate the market with their chemical synthesis processes,
but Chinese competitors are catching up.
Halophilic green microalgae Dunaliella salina. It accumulates the pigments in oil
glo- bules in the chloroplast interthylakoid spaces, protecting them against
photoinhibition and photodestruction.
Excessive pigment formation in D. salina is achieved by numerous stress factors
like high temperature, lack of nitrogen and phosphate but excess of carbon, high
light intensity, and high salt concentration, the latter two having the highest
impact.
Dried D. salina biomass for sale contains 10–16% carotenoids, mainly b-carotene.
In addition crystalline material obtained after extraction with edible oil is also
sold.
Primary Metabolites: Organic Acids
Organic acids are produced by through metabolisms of carbohydrates. They accumulate in
the broth of the fermenter from where they are separated and purified.
Glycolysis
Krebs cycle
I. Terminal end products
(pyruvate, alcohol)
lactic acid
Propionic acid
II. Incomplete oxidation of sugars
(glucose)
citric acid
Itaconic acid
Gluconic acid
III. Dehydrogenation of alcohol with O2
acetic acid
Manufactured on large scale as pure products or as salts
CITRIC ACID: industrial uses
Flavoring agent
In food and beverages
Jams, candies, deserts,
frozen fruits, soft
drinks, wine
Antioxidants
preservative
and
Chemical industry
Antifoam
Treatment of textiles
Metal
industry,
pure
metals +citrate (chelating
agent)
Acidifyer
Flavoring
Chelating agent
Primary metabolite
Present in all organisms
Agent for stabilization of
Fats, oil or ascorbic acid
Stabilizer for cheese
preparation
Pharmaceutical industry
Trisodium citrate (blood
preservative)
Preservation of ointments
and cosmetics
Source of iron
Detergent cleaning industry
Replace polyphosphates
Commercial Production
Strains that can tolerate high sugar and low pH with reduced
synthesis of undesirable by products (oxalic acid, isocitric acid,
gluconic acid)
Glucose
Glucose
Pyruvate
Aspergillus niger
A. clavatus
Pencillium luteum
MEDIUM
CYTOPLASM
Pyruvate
CO2
Pyr carboxylase
OXA
Malate
Pyruvate
Pyr Dehydrogenase
Acetyl CoA
MITOCHONDRIA
Malate
CO2 OXA
Fumarate
Succinyl CoA
Citrate
synthase
citric acid
a-KG
100g sucrose --- 112g any citric acid or 123g citric acid-1hydrate
Factors for regulation
 CARBOHYDRATE SOURCE: sugar should be 12-25%
 Molasses (sugar cane or sugar beet)
 Starch (potato)
 Date syrup
 Cotton waste
 Banana extract
 Sweet potato pulp
 Brewery waste
 Pineapple waste
High sugar conc incr uptake and production of citric acid
 TRACE METALS:
 Mn2+, Fe3+, Zn2+ incr yield
 Mn2+ incr glycolysis
 Fe3+ is a cofator for enzymes like aconitase
 pH: incr yield when pH below 2.5, production of oxalic acid and gluconic acid is
suppressed and risk of contamination is minimal
 DISSOLVED O2: high O2, sparging or incr aeration can affect if interrupted
 NITROGEN SOURCE: addition of ammonium stimulates overproduction, molasses is
good source of nitrogen
Citric acid production
Surface fermentation
Solid
liquid
submerged fermentation
Stirred
Bioreactor
Airlift
bioreactor
N alkanes (C9-C23) can also be used to produce citric acid; can
result in excess production of isocitric acid
ACETIC ACID: industrial uses
ACETIC ACID
Incomplete oxidation of ethanol
Vinegar is prepared from alcoholic liquids since ceturies
NAD+
NADH +H+
NADP+
NADP +H+
CH3 CH2OH---- CH3CHO-------- CH3CH(OH)2 -------
Ethanol
acetaldehyde
acetaldehyde hydrate
Alcohol
dehydrogenase
CH3COOH
acetic acid
Acetaldehyde dehydrogenase
Gluconobacter, Acetobacter with acid tolerant A. aceti
One molecule of ethanol one molecule of acetic acid is produced
12% acetic acid from 12% alcohol
Clostridium thermoaceticum
It is an obligate anaerobe, Grampositive, spore-forming, rod-shaped,
thermophilic
organism
with
an
optimum growth temperature of 55–
60 o C
and optimum pH of 6.6–
6.8.
VINEGAR: 4% by volume acetic acid with alcohol, salts, sugars and esters
flauoring agent in sauces and ketchups, preservative also
Wine, malt, whey (surface or submerged fermentation process)
Surface: trickling generator; fermentale material sprayed over surface, trickle thro
shavings contaning acetic acid producing bacteria; 30oC (upper) and 35oC (lower).
Produced in 3 days.
Submerged: stainless steel, aerated using suction pump, production is 10X higher
Clostridium thermoaceticum (from horse manure) is also able to utilize fivecarbon sugars:
2C5H10O5 --- 5CH3COOH
A variety of substrates, including fructose, xylose, lactate, formate, and
pyruvate, have been used as carbon sources in an effort to lower substrate
costs. This factor is also important if cellulosic renewable resources are to be
used as raw materials.
Typical acidogenic bacteria are Clostridium aceticum, C. thermoaceticum,
Clostridium formicoaceticum, and Acetobacterium woodii. Many can also reduce
carbon dioxide and other one-carbon compounds to acetate.
1mol
2moles
1mol
2moles
1mol
CODH
These enzymes are metalloproteins; for example,
CODH contains nickel, iron, and sulfur; FDH
contains iron, selenium, tungsten, and a small
quantity of molybdenum; and the corrinoid enzyme
(vitamin B12 compound) contains cobalt. C.
thermoaceticum does not have any specific amino
acid requirement; nicotinic acid is the sole essential
vitamin
LACTIC ACID: industrial uses
Technical grade
20-50%
>90%
Intestinal treatment
(metal ion lactates)
Food additive
(sour flour and
dough)
Ester manufacture
Textile industry
Glucose
G3P
G3P dehydrogenase
Pharmaceutical grade
Food grade
>80%
NAD+
Lactic acid
NADH +H+
1,3-biphosphoglycerate
Pyruvate
LDH
(Lactate dehydrogenase)
LACTIC ACID
2 isomeric forms L(+) and D(-) and as racemic mixture DL-lactic acid
First isolated from milk
Toady produced microbial
Heterofermentation
Homofermentation
Other than lactate products
only lactate as product
Lactobacillus
L. delbrueckii
L. leichmanni
Mostly one isomer is produced
Glucose
L. bulgaricus
L.helvetii
Whey (lactose)
L.lactis
------L.amylophilus -------L.pentosus
------
Maltose
Starch
Sulfite waste liquor
LACTIC ACID: production process
1mol of glucose gives 2 moles of lactic acid; L lactic acid is predominantly produced
Fermentation broth (12-15% glucose, N2, PO4, salts micronutrients)
pH 5.5-6.5/temp 45-50oC/75h
Heat to dissolve Ca lactate
Addition of H2SO4
(removal of Ca SO4)
Filter and concentrate
Addtion of Hexacyanoferrant
(removes heavy metal)
Purification (Ion exchange)
Concentration
Lactic acid
GLUCONIC ACID: Applications
1. Used in stainless steel manufacturing, leather (can remove rust and
calcareous deposits)
2.
3.
4.
5.
6.
Food additive for breverages
Used in Ca and Fe therapy
Na gluconate used in sequestering agent in detergets
Desizing polyester or polyamide fabric
Manufacture of frost and cracking resistant concrete
Bacteria: Gluconobacter, Acetobacter, Pseudomonas, Vibrio
Fungi: Aspergillus, Penicillium, Gliocladium
intracellular
PQQH2
PQQ
Glucose
dehydrogenase
D-gluconolactone
D-Glucose
Extracellular
Inducible
Glucose
oxidase
FAD
H2O2
extracellular
Bacteria
H2O
Lactonase
Gluconic Acid
fungi
FADH2
Catalase
Fungi
O2
High conc of glucose and pH above 4
H2O2 antagonist for other micro-organisms
Submerged fermentation process
Use glucose from corn
H 4.5-6.5
28-30oC for 24h
Incr supply of O2 enhances yield
PQQ: pyrroliquinoline quinone
coenzyme
ITACNIC ACID: Applications
Aspergillus itoconicus and A.terreus
1. Used in plastic industry, paper industry
2. Manufacturing of adhesives
Cis-aconitic acid undergoes decarboxylation
Itaconic acid Oxidase
Itaconic acid
Itatartaric acid
(-) By Ca to incr yield
SECONDARY METABOLITES
ANTIBIOTICS
BROAD SPECTRUM
Control growth of
wide
range
of
unrelated organisms
Tet, Cm
NARROW SPECTRUM
Control growth
selected number
organisms
Pen, Str
Streptomyces,eg. Tetracyclin, actinomycin D,
of
of
ANTIBIOTICS: applications
1. Antimicrobial agents for chemotherapy
2. Antitumour antibiotics eg. Actinomycin D and mitomycin D
3. Food preservative antibiotics eg in canning (chlortetracycline) or fish or meat
preservation (pimarcin, nisin)
4. Antibiotics in animal feed and veterinary medicine eg enduracidin, tylosin and
hygromycin B, theostrepton, salinomycin
5. Control of plant diseases eg blasticidin, teranactin, polyoxin
6. Molecular biology
MODE OF ACTION OF ANTIBIOTICS
DNA GYRASE
RNA ELONGATION
CELL WALL SYNTHESIS
DNA DIRECTED RNA POLYMERASE
DNA
THF
RIBOSOMES
DHF
RNA
PROTEIN SYNTHESIS
(50S INHIBITORS)
PROTEIN SYNTHESIS
(30S INHIBITORS)
PROTEIN SYNTHESIS
(tRNA)
CYTOPLASMIC
MEMBRANE STRUCTURE
AND FUNCTION
PABA
LIPID BIOSYNTHESIS
SYTHETIC ANTIBIOTICS
Selective toxicity: concept, Paul Ehrlich
1. GROWTH FACTOR ANALOGS:
structurally similar to a growth factor required in a micro-organism;
small differences of analogs in authentic growth factor prevent analog to
function in the cell.
A.
SULFA DRUGS: specifically inhibit bacteria (streptococcal infections)
eg. SULFANILAMIDE: is an analog of PABA (p-aminobenzoic acid) which is
part of folic acid and nucleic acid precursor. Combination:
sulfamethoxazole and trimethoprim; disadvantages and advantages
B. ISONIAZID: important growth factor with narrow spectrum only against
Mycobacterium. It interferes with synthesis of mycolic acids, a cell wall
component. It is an analog of nicotinamide (vitamin). Single most effective
drug against tuberculosis.
2. NUCLEIC ACID BASE ANALOGS
URACIL
PHENYLALANINE
THYMINE
5-FLOUROURACIL (Uracil analog)
p-FLOUROPHENYLALANINE
5-BROMOURACIL (thymine analog)
Addition of F or Br does not alter the shape but changes chemical properties
such that the compound does not function in the cell metabolism, thereby
blocking the nucleic acid synthesis.
These analogs are used in treatment of viral and fungal infections and many of
these occur as mutagens.
3. QUINOLONES:
Antibacterial compounds interfere with bacterial DNA gyrase, prevent
supercoiling (packaging of DNA) eg Flouroquinolones like ciprofloxin (UTI,
anthrax). B. anthracis maybe resistant to pencillin. These are effective in both
G+ve and G-ve bacteria since DNA gyrase is present in all.
Also used in beef and poultry for prevention and treatment of respiratory
diseases.
New generation
Flouroquinolnes
Ouinolones
NATURALLY OCCURING ANTIBIOTICS
FROM BACTERIA, FUNGI
LESS THAN 1% OF 1000S OF ANTIBIOTICS ARE USEFUL BECAUSE OF TOXICITY
OR LACK OF UPTAKE BY HOST CELLS
Natural antibiotics can be artificially modified to enhance their efficacy then they are
semi-synthetic antibiotics
Broad spectrum antibiotics: effective against both gram +ve and gram-ve
Narrow may also be beneficial to target specific group of bacteria eg. Vancomycin:
narrow spectrum effective for gram positive pencillin resistant Staphylococcus,
Bacillus, Clostridium
Targets for antibiotics maybe
ribosomes (Cm and Str for Bacteria and Cyclohexamide for eukarya), Cell
wall, cytoplasmic membrane, lipid biosynthesis, enzymes, DNA replication and
transcription elements
Protein synthesis, Transcription (RNA poly, RNA elongation etc)
Produced By Fungi
B-LACTAMS (b-lactam ring)
Penicillin
Cephalosporins
Produced by Prokaryotes
AMINOGLYCOSIDES (amino sugars with glycosidic linkage)
MACROLIDES (lactone ring bonded to sugars)
TETRACYLINES (Streptomyces)
PEPTIDE ANTIBIOTICS (Daptomycin, (Streptomyces)
PLATENSIMYSIN (Streptomyces)
Beta Lactam Antibiotics
1.
2.
3.
4.
PENICILLINS,
CEPHALOSPORINS,
MONOBACTAMS AND
CARBAPENEMS
PENCILLIN--------b-LACTAM ANTIBIOTIC
Alexander Fleming
Pencillin G and V (natural)
Penicillium chrysogenum
Pencillin G first clinically useful antibiotic
For Gram positive bacteria
Used for
Pneumococcal
Streptococcal infections
6-AMINOPENICILLIANIC ACID
Ampicillin, carbencillin
Slight modification in N-acyl groups results in semi synthetic penicillin which is able to
act on gram negative bacteria (goes past outer membrane) to act on cell wall
MANY BACTERIA HAVE BETA LACTAMASE HENCE THOSE BACTERIA ARE
PENCILLIN RESISTANT
EG. Oxacillin and Methicillin beta lactamase resistant semi synthetic antibiotics
MECHANISM OF ACTION
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•
Pencillins block cell wall synthesis: transpeptidation (cross linking 2 glycan peptide
chains)
Transpeptidases bind to pencillin hence they are called PENCILLIN BINDING
PROTEINS (PBP)
Newly synthesized bacterial wall is no longer cross linked and has poor strength
PBP also stimulates release of AUTOLYSINS (ENZYMES TO DIGEST CELL WALL)
Osmotic pressure differences cause lysis
VANCOMYCIN: does not bind PBPs but D-alanyl- Dalanine peptide to block
transpeptidation
BECAUSE OF SELECTIVE PROCESS B-LACTAMS DO NOT AFFTECT HOST CELLS
AND MECHANISM IS UNIQUE TO BACTERIA
MECHANISM OF ACTION
Natural penicillin: i.e. V and G are effective against several gram positive bacteria
They are effective against b-lactamase producing MO (enz which can hydrolyze penicillins)
Eg. Staphylococcus aureus
Production of penicillin is used: 45% (human), 15% (animal health) and
45% for production of semi synthetic penicillin
P. notatum, P.chrysogenum and its mutant strain which is a high yeilding strain (Q176)
Genetically engineered strains for improved pencillin production are being used now
UDP deriv of NAM and NAG are
synthesized
Sequentially aa are added to UDPNAM to form NAM -pentapeptide
ATP is used, no tRNA or ribosomes
involved in peptide bond formation
UDP tansfers NAG to bactoprenolNAM peptapeptide. For
pentaglycine use special glycyltRNA moc but not ribosomes
Transfer of UDP-NAMpentapeptideto bactoprenol PO4
LIPID I
Bactoprenol carrier moves back
across membrane by losing one PO4
for a new cycle
Transport of completed NAMNAG-pepntapeptide across
membrane
LIPID II
Attached to growing end of PG
chain and incr by one repeat unit
Bactoprenol is a 55 carbon alcohol and linked to NAM by pyrophosphate
In S. aureus pepntapeptide has L-lys and in
E. coli DAP
UDP glucose
Final step is TRANSPEPTIDATION which creates peptide cross links between PG
chains. The enzyme removes terminal D-alanine as cross link is formed
The b-lactam group of antibiotics includes an enormous diversity of natural
and semi-synthetic compounds that inhibit several enzymes associated with the final
step of peptidoglycan synthesis.
All of this enormous family are derived from a b-lactam structure: a four-membered
ring in which the b-lactam bond resembles a peptide bond. The multitude of chemical
modifications based on this four-membered ring permits the astonishing array of
antibacterial and pharmacological properties within this valuable family of
antibiotics.
Clinically useful families of b-lactam compounds include the penicillins,
cephalosporins, monobactams and carbapenems. Many new variants on the b-lactam
theme are currently being explored. Certain b-lactams have limited use directly as
therapeutic agents, but may be used in combination with other b-lactams to act as
b-lactamase inhibitors.
Co-amoxyclav, for example is a combination of amoxycillin and the b-
lactamase inhibitor clavulanic acid. During cross-linking of the peptidoglycan
polymer, one D-alanine residue is cleaved from the peptidoglycan precursor and
this reaction is prevented by b-lactam drugs.
More recent studies have shown that the activity of this class of drugs is more
complicated and involves other processes as well as preventing cross-linking of
peptidoglycan.
B-lactamase
An increasing number of bacteria are penicillin resistant. Penicillinase-resistant
penicillins such as methicillin, nafcillin, and oxacillin are frequently employed
against these bacterial pathogens.
Although penicillins are the least toxic of the antibiotics, about 1 to 5% of the
adults in the United States are allergic to them. Occasionally a person will die of a
violent allergic re- sponse; therefore patients should be questioned about penicillin
allergies before treatment is begun.
MRSA
VRSA
CEPHALOSPORINS
Cephalosporium: Cephalosporin C
B-lactam ring
Dihydrothiazine ring (6 member)
cefatrioxone
Same mode of action with broader spectrum than penicillins
Resistant to b-lactamases
Hence used to treat infections which are penicillin resistant
Used to treat Nesseria gonorrhea (STD)
Most cephalosporins (including cephalothin, cefoxitin, ceftri- axone,
and cefoperazone) are administered parenterally.
Cefoperazone is resistant to destruction by b-lactamases and
effective against many gram-negative bacteria, including Pseudomonas
aeruginosa.
Cephalexine and cefixime are given orally rather than by injection.
7-ACA: 7- aminocephalosporanic acid nucleus structure in all cephalosporins
G+ = G-
G+ > G-
R1
R2
G+ < G-
TETRACYCLINES
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Broad spectrum
Effective for G+ and G- (mycoplasmas, rickettesia, chlamydia)
Used for combatting stomach ulcer (Helicobacter pylori)
Inhibit protein synthesis by blocking binding of amino acyl tRNA to ribosome (A site)
BASIC STRUCTURE
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Napthacene ring
Chlortetracycline and oxytetracycline are most commonly used in human and veterinary
diseases and for preservation of meat, fish and poultry
Three members of the tetracycline family.
Tetracycline lacks both of the groups that are
shaded. Chlortetracycline (aureomycin) differs
from tetracycline in having a chlorine atom
(blue); doxycycline consists of tetracycline
with an extra hydroxyl (purple).
TETRACYCLINES
Str. aureus. S.flavus
S. rimosus, S. antibioticus
Streptomyces aureofaciens
20 diff species producing mix of tet
Genetic modification
Polyketide synthesis
Antibiotics synthesized by successive condensation of small carboxylic acids
Like acetate, butyrate, propionate, malonate
High doses of tetracycline may result in nausea, diarrhea, yellowing of teeth in
children, and damage to the liver and kidneys.
AMINOGLYCOSIDES
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Oligosaccharide antibiotics
Structurally all contain a cyclohexane ring and amino sugars bound by glycosidic
linkages
Bind to the 30S small ribosomal subunit and interfere with protein synthesis in at least
two ways. They directly inhibit protein synthesis and also cause misreading of the
genetic message carried by mRNA…prolonged use can cause kidney damage and hearing
loss
Streptomycin, kanamycin, neomycin, and tobramycin are synthesized by
Streptomyces, whereas gentamicin comes from a related bacterium,
Micromonospora purpurea.
Known as reserve antibiotics as they develop resistance quickly
AMINOGLYCOSIDES producing organisms
Streptomycin
Streptomyces griesus
Neomycin B and C
S.fradiae
Kanamycin A, B and C
S.kanamyceticus
Hygromycin B
S.hygroscopicus
Gentamycin
Micromonospora purpurea
Sisimicin
M.inyoensis
MACROLIDES
Antibiotics with a large lactone ring (macrocyclic lactone ring)
Which consists of 12-, 14- and 16-membered lactone rings with 1-3 sugars linked
by glycosidic bond
Effective agaist penicillin resistant MO, G+ org, inhibitb y binding to 50S
ribosome
Clarithromycin (Erythromycin derv)
Used to treat stomach ulcers
Erythromycin : Streptomyces erythreus
14-membred connected to 2 sugars
Genetic modifications by polyketide synthesis
MACROLIDES
Polyene macrolides: lactone rings in range of 26-28
Eg. Nystatin, amphotericin
Actinomycetes are most common organisms which produce them
Erythromycin is a relatively broad-spectrum antibiotic effective against grampositive bacteria, mycoplasmas, and a few gram-negative bacteria. It is used
with patients allergic to penicillins and in the treatment of whooping cough,
diphtheria, diarrhea caused by Campylobacter, and pneumonia from Legionella
or Mycoplasma infections.
Newer macrolides are now in use.
Clindamycin is effective against a variety of bacteria including staphylococci
and anaerobes such as Bacteroides.
Azithromycin is particularly effective against Chlamydia trachomatis.
AROMATIC ANTIBIOTICS
Aromatic rings in structure
Chloroamphenicol, griesofluvin, novobiocin
CHLORAMPHENICOL
Broad spectrum antibiotic against G+ and G- bacteria, rickettesia, chlamydia,
actinomycetes
chloramphenicol binds to 23S rRNA on the 50S ribosomal subunit. It inhibits
the peptidyl transferase and is bacteriostatic.
Streptomyces venezuelae and S.omiyanesis
This antibiotic has a very broad spectrum of activity but unfortunately is quite toxic. One may see allergic responses or
neurotoxic reactions. The most common side effect is a temporary or permanent depression of bone marrow function, leading
to aplastic anemia and a decreased number of blood leukocytes. Chloramphenicol is used only in life-threatening situations
when no other drug is adequate.
GRIESOFULVIN
Penicillium patulum
Maybe attacks chitin biosynthesis hence acts as anti fungal antibiotic
Following a 40-year hiatus in discovering new classes of antibacterial compounds,
three new classes of antibacterial antibiotics have been brought into clinical use:
Cyclic lipopeptides (Daptomycin), Glycylcyclines (tigecycline) and Oxazolidinones
(Linezolid)
PEPTIDE ANTIBIOTICS
Daptomycin : Streptomyces roseosporus used to treat MDR infections
Tigecycline: Tygacil® marketed by Wyeth used to treat MDR strains of
Staphylococcus aureus and Acineotobacter baumanii. Mechanism similar to
tetracycline.
Also shows suceptibility to NDML (New Delhi metallo-b-lactamase multidrug
resistant Enterobacteriaceae)
NDML is an enzyme which makes bacteria resistant to broad range of b-lactam antibiotics.
This includes antibiotics of carbapenems for treatment of antibiotics resistant infections.
Termed as “SUPERBUGS” Such bacteria susceptible to polymixins and tigecyclines
MECHANISM OF DRUG RESISTANCE
Plasmids
R-Plasmids
Superinfection: Clostridium difficile, Candida albicans
Transformation, conjugation, transduction, ABC transporters
Phage therapy
There has been some recent progress in developing new antibiotics that are
effective against drug-resistant pathogens.
Two new drugs are fairly effective against vancomycin-resistant enterococci.
Synercid is a mixture of the streptogramin antibiotics quinupristin and dalfopristin
that inhibits protein synthesis.
A second drug, linezolid (Zyvox), is the first drug in a new family of antibiotics, the
oxazolidinones. It inhibits protein synthesis and is active against both vancomycinresistant enterococci and methicillin-resistant Staphylococcus aureus.