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Transcript of Antibiotics
During ancient times;
Greeks and Indians used moulds and other plants to treat infections.
In Greece and Serbia, mouldy bread was traditionally used to treat wounds and infections.
Warm soil was used in Russia by peasants to cure infected wounds.
Sumerian doctors gave patients beer soup mixed with turtle shells and snake skins.
Babylonian doctors healed the eyes using a mixture of frog bile and sour milk.
Sri Lankan army used oil cake (sweetmeat) to server both as desiccant and antibacterial.
Antibiotics can be loosely defined as the variety of substances derived from bacterial sources (microorganisms) that control the growth of or kill other bacteria.
However, Synthetic antibiotics, usually chemically related to natural antibiotics, have since been produced that accomplish comparable tasks.
Antibiotic resistance occurs when a bacteria acquires a genetic mutation either spontaneously, by a gene transfer, or it can acquire the resistance gene from other bacteria by horizontal gene transfer via conjugation, transduction or transformation.
Antibiotic resistance genes are found on plasmids making their transfer easier. Antibiotic resistance plasmids frequently contain genes conferring resistance to several different antibiotics.
Plasmids are usually found in prokaryotes. They are small, extra DNA molecules,
for the cell but
to basic life processes.
Genes for antibiotic resistance are often found on plasmids - meaning they can form multi-drug resistance.
Antibiotics are screened for any negative effects on humans or other mammals before approval for clinical use.
Some antibiotics have been associated with a range of Side-effects.
Side-effects range from mild to very serious depending on the antibiotics used, the microbial organisms targeted, and the individual patient.
Side effects of antibiotics :
Infections are very common and responsible for a large number of diseases adversely affecting human health. Most of the infectious diseases are caused by bacteria.
Infection caused by bacteria can be prevented, manged and treated through anti-bacterial group of compounds known as antibiotics.
Classification of Antibiotics
Antibiotics can be also classified based on their chemical structure. A similar level of effectiveness, toxicity and side-effects is rendered by the antibiotics of the same structural group. Broad spectrum antibiotics are effective aganist a broad range of microorganisms in comparison to narrow spectrum antibiotics. Bactericidal antibiotics kill the bacteria whereas bacteriostatic antibiotics halt the growth of bacteria.
Sir Alexander Fleming
Sir Alexander Fleming, a Scottish biologist, defined new horizons for modern antibiotics with his discoveries of enzyme lysozyme (1921) and the antibiotic substance penicillin (1928). The discovery of penicillin from the fungus Penicillium notatum perfected the treatment of bacterial infections such as, syphilis, gangrene and tuberculosis. He also contributed immensely towards medical sciences with his writings on the subjects of bacteriology, immunology and chemotherapy.
''One sometimes finds what one is not looking for''
- Sir Alexander Fleming
His research and study during his military career inspired him to discover naturally antiseptic enzyme in 1921, which he named lysozyme. This substance existed in tissues and secretions like mucus, tears and egg-white but it did not have much effect on the strongly harmful bacteria.
Six years later, as a result of some intelligent serendipity, he stumbled on discovering penicillin. It was in 1928 when he observed while experimenting on influenza virus that a common fungus, Penicillium notatum had destroyed bacteria in a staphylococcus culture plate. Upon subsequent investigation, he found out that mould juice had developed a bacteria-free zone which inhibited the growth of staphylococci. This newly discovered active substance was effective even when diluted up to 800 times. He named it penicillin.
He was knighted in 1944 and was given the Nobel Prize in Physiology or Medicine in 1945 for his extraordinary achievements which revolutionized the medical sciences.
How do they work then ?
Antibiotics are designed to attack unfriendly bacteria inside your body
Different antibiotics do so in different ways
A bactericidal, like penicillin, kills the bacteria by attacking its cell wall
A bacteriostatic, like amoxicillin, stops the bacteria from multiplying
Mechanisms of antibiotic action
- There are Five Basic Mechanisms of Antibiotic Action against Bacterial Cells:
1. Inhibition of Cell Wall Synthesis (most common mechanism)
2. Inhibition of Protein Synthesis (Translation) (second largest class)
3. Alteration of Cell Membranes
4. Inhibition of Nucleic Acid Synthesis
5. Antimetabolite Activity
1-Inhibition of Cell Wall Synthesis
Inhibition of peptidoglycan synthesis (bactericidal)
(1) Fails to cross membrane (gram negatives).
(2) Fails to bind to altered PBP’s.
(3) Hydrolysis by beta-lactamases.
Disrupts peptidoglycan cross-linkage
(1) fails to cross gram negative outer membrane (too large).
(2) some intrinsically resistant (pentapeptide terminus).
Disrupts movement of peptidoglycan precursors (topical use).
*Resistance ---> fails to penetrate into cell.
Disrupt mycolic acid or arabinoglycan synthesis (bactericidal).
(1) reduced uptake.
(2) Alteration of target sites.
2-Inhibition of Protein Synthesis (Translation)
30S Ribosome site
Irreversibly bind 30S ribosomal proteins (bactericidal)
(1) Mutation of ribosomal binding site
(2) Decreased uptake
(3) Enzymatic modification of antibiotic
Block tRNA binding to 30S ribosome-mRNA complex (b-static)
(1) Decreased penetration
(2) Active efflux of antibiotic out of cell
(3) Protection of 30S ribosome
50S Ribosome site
Binds peptidyl transferase component of 50S ribosome, blocking peptide elongation (bacteriostatic)
(1) plasmid-encoded chloramphenicol transferase
(2) altered outer membrane (chromosomal mutations)
Reversibly bind 50S ribosome, block peptide elongation (b-static)
(1) Methylation of 23S ribosomal RNA subunit
(2) Enzymatic cleavage (erythromycin esterase)
(3) Active efflux
Binds 50S ribosome, blocks peptide elongation; Inhibits peptidyl transferase by interfering with binding of amino acid-acyl-tRNA complex
*Resistance ---> methylation of 23S ribosomal RNA subunit
3-Alteration of Cell Membranes:
Cationic detergent-like activity (topical use)
*Resistance ---> inability to penetrate outer membrane
Disrupt cytoplasmic membranes
*Resistance ---> inability to penetrate outer membrane
4-Inhibition of Nucleic Acid Synthesis:
Inhibit DNA gyrases or topoisomerases required for supercoiling of DNA; bind to alpha subunit
(1) alteration of alpha subunit of DNA gyrase (chromosomal)
(2) Decreased uptake by alteration of porins (chromosomal)
Metabolic cytotoxic byproducts disrupt DNA
(1) Decreased uptake
(2) Elimination of toxic compounds before they interact
RNA Effects (Transcription)
Binds to DNA-dependent RNA polymerase inhibiting initiation & Rifabutin of RNA synthesis
(1) Altered of beta subunit of RNA polymerase (chromosomal)
(2) Intrinsic resistance in gram negatives (decreased uptake)
Inhibits RNA transcription
*Resistance ---> inability to penetrate outer membrane.
5- Antimetabolite Activity:
Sulfonamides & Dapsone
Compete with p-aminobenzoic acid (PABA) preventing synthesis of folic acid
*Resistance ---> permeability barriers (e.g., Pseudomonas)
Inhibit dihydrofolate reductase preventing synthesis of folic acid
(1) Decreased affinity of dihydrofolate reductase
(2) Intrinsic resistance if use exogenous thymidine
Compound may help in fight against antibiotic-resistant superbugs
These so-called superbugs are actually bacterial strains that produce an enzyme known as New Delhi metallo-β-lactamase (NDM-1). Bacteria that produce this enzyme are practically impervious to antibiotics because NDM-1renders certain antibiotics unable to bind with their bacterial targets. Since NDM-1 is found in Gram-negative bacteria like K. pneumoniae, which causes pneumonia, urinary tract, and other common hospital-acquired infections, it is of particular concern.
It had been found that a compound derived from a class of molecules known as 2-aminoimidazoles "recharged" existing antibiotics, making them effective against Gram-positive antibiotic-resistant bacteria like the Staphylococcus strain MRSA.
Provided by North Carolina State University
New antibiotic cures disease by disarming pathogens, not killing them
-New drugs are badly needed for treating infections with the bacterium Acinetobacter baumannii, a pathogen that most often strikes hospital patients and immune- compromised individuals through open wounds, breathing tubes, or catheters. The bacterium can cause potentially lethal bloodstream infections. Strains of A. baumannii have acquired resistance to a wide range of antibiotics, and some are resistant to every FDA-approved antibiotic, making them untreatable.
-it was found that in laboratory mice it was possible to mitigate the potentially lethal effects of the bacterium by blocking one of its toxic products rather than killing it. Blocking the synthesis ofthe endotoxin with a small molecule called LpxC-1 prevented infected mice from getting sick. Unlike traditional antibiotics, Spellberg says, LpxC-1 doesn't kill the bacteria, it just shuts down the manufacture of the endotoxin and stops the body from mounting the inflammatory immune response to it that is the actual cause of death in seriously ill patients.
Journal reference: mBio
Provided by: American Society for Microbiology
Do we need antibiotics?
-There are certain illnesses that nearly always need antibiotic treatment: are pneumonia, bacterial meningitis, urinary tract infections and sexually transmitted diseases caused by bacteria (a number are caused by viruses) and often, skin infections don't get better without antibiotic treatment.
-In all other cases, though, one could use alternative methods, in consultation with a doctor.
-Again, antibiotics only work on bacterial infections, and can do nothing to heal a viral infection like the flu or the common cold.
- You take the antibiotics to kill all the bacteria, so you have to take all the antibiotics prescribed to avoid any bacteria being left in your body and becoming resistant to antibiotics.
-You need to use
all the antibiotics
prescribed to avoid any bacteria being left in your body and becoming resistant to antibiotics, even though you feel better after a few days of taking antibiotics.
- If you have leftover medication , do not take them unless your doctor tells you it's okay. The leftover antibiotics may not work on whatever is making you sick. If they do work, there probably will not be enough leftover medicine to completely kill all the bacteria in your body.
Medical importance :
Most common side effects of antibiotics are
• Severe watery diarrhea and abdominal cramps.
• Allergic reaction (shortness of breath, hives, swelling of lips, face, or tongue, fainting)
• Vaginal itching or discharge.
• White patches on the tongue.
Allergic reactions :
Adverse effects range from fever and nausea to major allergic reactions, including photodermatitis and anaphylaxis.
These mild to moderate allergic reactions can usually be successfully treated by taking a medication known as antihistamines.
Around one person in 15 has an allergic reaction to antibiotics, especially penicillin and cephalosporins.
In rare cases (estimated to be somewhere between one and five in 10,000) an antibiotic can cause a severe and potentially life-threatening allergic reaction known as Anaphylaxis. Initial Anaphylaxis is often the same as above and can lead to:
Mild allergic reactions :
• a raised itchy skin rash (urticaria or ‘hives’)
• tightness of the throat, which can cause breathing difficulties
• a rapid heartbeat
• increasing breathing difficulties due to swelling and tightening of the neck
• a sharp and sudden drop in your blood pressure, which can make you feel light-headed and confused
How is an antibiotic medication allergy diagnosed?
-Your healthcare provider will ask about your medical history and allergies. You may also need any of the following:
: You may need blood taken to give caregivers information about how your body is working. The blood may be taken from your hand, arm, or IV.
A patch test
means a small amount of the antibiotic is put on your skin. The area is covered with a patch that stays on for 2 days. Then your healthcare provider will check your skin for a reaction.
A skin prick test :
means a small drop of the antibiotic is put on your forearm and your skin is pricked with a needle. Your healthcare provider will watch for a reaction.
An intradermal test :
means a small amount of antibiotic liquid is put under the surface of your skin. Your healthcare provider will watch for a reaction.
A drug provocation test :
is also known as an antibiotic challenge test. Your healthcare provider gives you increasing doses of the antibiotic medicine and watches for a reaction.
How does antibiotic resistance transfer?
plasmids are released
when a prokaryotic cell dies,
and another cell of a different species absorbs it. This can happen between different bacterial species
when new generations inherit antibiotic resistance genes
**antibiotic resistance spreads as bacteria themselves move from place to place . Bacteria can travel via airplane, water and wind. People can pass the resistant bacteria to others; for example, by coughing or contact with unwashed hands.
While humans are creating stronger chemicals, pesticides and antibiotics that have resulted in a stronger version of viruses and germs, nature has come to our rescue again. Herbs packaged with antidotes can help to fight against stronger versions of bacteria and viruses.
Many pharmaceutical antibiotics are isolated chemical constituents. They are one compound/one chemical – penicillin is penicillin, tetracycline is tetracycline and so on. This makes them easier for bacteria to adapt to and counteract. In contrast, herbs are much more complicated. Garlic has over 33 sulfur compounds, 17 amino acids and a dozen other compounds.
: Goldenseal is an amazing herbal antibiotic that can fight against bacteria and fungi. Goldenseal is also anti-inflammatory, improves liver and gastrointestinal problems.
: Thyme has antiseptic, antimicrobial and antibacterial properties. Thyme is so effective for treating coughs, asthma and breathing problems, bronchitis and digestive problems.
3. Aloe Vera:
Aloe vera is a traditional native plant that grows in hot and dry climates. Aloe vera leaves are known for treating rashes, wounds, inflammation, arthritis and constipation.
4. Grapefruit seeds Extract
: Grapefruit seeds extract is driven from organic grapefruit and has great antibacterial, antimicrobial and antifungal properties. Grapefruit seeds have been known to fight more than 800 different kinds of bacteria and more than 100 different kinds of fungi. Grapefruit seeds destroy bad bacteria without destroying the good bacteria in the body.
Treatment of :
Bacterial infection caused by Gram-negative bacteria, such as Escherichia coli and Klebsiella particularly Pseudomonas aeruginosa ( treated by Garamycin ) .
Bactericidal for both Gram-positive and Gram-negative organisms and therefore useful for empiric broad-spectrum antibacterial coverage.
*** Vancomycin : Active against aerobic and anaerobic Gram-positive bacteria including MRSA
***Erythromycin :Streptococcal infections, syphilis, upper respiratory tract infections, lower respiratory tract infections, mycoplasmal infections, Lyme disease .
***Sulphonamides : Urinary tract infections (except sulfacetamide, used for eye infections, and mafenide and silver sulfadiazine, used topically for burns)
• Prevention of infection :
1. Surgical wound.
2. Dental antibiotic prophylaxis .
Conditions of neutropenia e.g, cancer-related
Evaluation of Antibiotics
Broth dilution test :
One of the earliest antimicrobial susceptibility testing methods was the macro broth or tube-dilution method.
The procedure involves :
1) preparing two-fold dilutions of antibiotics (e.g., 1, 2, 4, 8, and 16 µg/mL) in a liquid growth medium dispensed in test tubes .
2)The antibiotic-containing tubes were inoculated with a standardized bacterial suspension of 1–5×105CFU/mL. Following overnight incubation at 35°C.
3) The tubes were examined for visible bacterial growth as evidenced by turbidity. The lowest concentration of antibiotic that prevented growth represented the minimal inhibitory concentration (MIC).
of this technique was the generation of a quantitative result (i.e., the MIC)
The principal disadvantages
of the macro dilution method were the tedious, manual task of preparing the antibiotic solutions for each test, the possibility of errors in preparation of the antibiotic solutions, and the relatively large amount of reagents and space required for each test.
Antimicrobial gradient method.
The antimicrobial gradient diffusion method uses the principle of establishment of an antimicrobial concentration gradient in an agar medium as a means of determining susceptibility.
The Etest is a commercial version available in the United States. It employs thin plastic test strips that are impregnated on the underside with a dried antibiotic concentration gradient and are marked on the upper surface with a concentration scale. As many as 5 or 6 strips may be placed in a radial fashion on the surface of an appropriate 150-mm agar plate that has been inoculated with a standardized organism suspension like that used for a disk diffusion test.
After overnight incubation, the tests are read by viewing the strips from the top of the plate. The MIC is determined by the intersection of the lower part of the ellipse shaped growth inhibition area with the test strip.
Disk diffusion test
. The disk diffusion susceptibility method is simple and practical and has been well-standardized.
The test is performed by applying a bacterial inoculum of approximately 1–2×108CFU/mL to the surface of a large (150 mm diameter) Mueller-Hinton agar plate.
Up to 12 commercially-prepared, fixed concentration, paper antibiotic disks are placed on the inoculated agar surface .
Plates are incubated for 16–24 h at 35°C prior to determination of results.
The zones of growth inhibition around each of the antibiotic disks are measured to the nearest millimeter. The diameter of the zone is related to the susceptibility of the isolate and to the diffusion rate of the drug through the agar medium.
The zone diameters of each drug are interpreted using the criteria published by the Clinical and Laboratory Standards Institute (CLSI, formerly the National Committee for Clinical Laboratory Standards or NCCLS) or those included in the US Food and Drug Administration (FDA)-approved product inserts for the disks.
Definition & Classification.
Mode of action.
Made by :
-Aya Abd El Fatah
-Aya Abd El Rady
-Basma Abd El Rady
Supervised by :
Section : B