Antimicrobial chemotherapy Microorganisms grow on and within other
Antimicrobial chemotherapy Microorganisms grow on and within other organisms and microbial colonization can lead to disease, disability and death. Thus the control or destruction of microorganisms residing within the bodies of humans and other animals is of great importance.
Chemotherapeutic agent versus antibiotic What is a chemotherapeutic agent? It is a chemical agent used to treat disease. Synthetic in origin. Examples include sulfonamides, isoniazid and ethambutol. What is an antibiotic? It is a microbial product or a derivative that can kill susceptible microorganisms or inhibit their growth. Antibiotics are low molecular weight molecules produced as secondary metabolites, mainly by microorganisms that live in soil. E. g. Penicillin, erythromycin, streptomycin.
What should be the ideal characteristic of antimicrobial drug? Selective toxicity: It must kill or inhibit microbial pathogen while damaging the host as little as possible. Selective toxicity is expressed in terms of Therapeutic dose: It is the drug level required for clinical treatment of particular infection. The larger therapeutic index, the better the chemotherapeutic agent.
Antibiotics Penicillins inhibit bacterial cell wall synthesis Cephalosporins inhibit cell wall synthesis Aminoglycosides (eg. Steptomycin) inhibit protein synthesis Tetracyclines inhibit protein synthesis Chloramphenicol inhibits translation
Antibiotics Penicillins inhibit bacterial cell wall synthesis Cephalosporins inhibit cell wall synthesis Aminoglycosides (eg. Steptomycin) inhibit protein synthesis Tetracyclines inhibit protein synthesis Chloramphenicol inhibits translation
Antibiotic resistance Microorganisms in the environment have been involved in chemical warfare with their neighbors for hundreds of millions of years. To counteract the production of antibiotics by some microbes, others developed selfprotective (resistance) mechanisms to the natural antibiotics. Thus it is not surprising that bacteria quickly develop resistance to the natural antibiotics used to combat diseases.
Antimicrobial Drugs Fading Miracle?
Fleming and Penicillin
Mechanisms of Antimicrobial Action • Viruses use host enzymes inside host cells • Fungi and protozoa have own eukaryotic enzymes • The more similar the pathogen and host enzymes, the more side effects the antimicrobials will have
Modes of Antimicrobial Action
Antifungal Drugs • Fungi are eukaryotes • Have unique sterols in their cell walls • Pathogenic fungi are often outside the body
Mechanisms of Antibiotic Resistance • Enzymatic destruction of drug • Prevention of penetration of drug • Alteration of drug's target site • Rapid ejection of the drug
What Factors Promote Antimicrobial Resistance? • Exposure to sub-optimal levels of antimicrobial • Exposure to microbes carrying resistance genes
Inappropriate Antimicrobial Use • Prescription not taken correctly • Antibiotics for viral infections • Antibiotics sold without medical supervision • Spread of resistant microbes in hospitals due to lack of hygiene • Use of antibiotics in foods
Proposals to Combat Antimicrobial Resistanc • Use more narrow spectrum antibiotics • Use antimicrobial cocktails • Restrict antimicrobial use
TEN STEPS TO SAFE KITCHEN Keep your refrigerator at 40° F (4° C) or less. A temperature of 40°F or less is important because it slows the growth of most bacteria. The fewer bacteria there are, the less likely you are to get sick from them.
Refrigerate cooked, perishable food as soon as possible within two hours after cooking. ·Date leftovers so they can be used within two to three days. ·If in doubt, throw it out!
Sanitize your kitchen dishcloths and sponges regularly. Wash with a solution of one teaspoon chlorine bleach to one quart water, or use a commercial sanitizing agent A contaminated dishcloth can house millions of bacteria after a few hours. Consider using paper towels to clean up and then throw them away immediately. Wash hands carefully after handling raw meat.
Wash your cutting board with soap and hot water after each use. ·Never allow raw meat, poultry, and fish to come in contact with other foods. Washing with only a damp cloth will not remove bacteria. ·Periodically washing in a bleach solution is the best way to prevent bacteria from remaining on your cutting board.
Cook ground beef, red meats and poultry products until they are no longer red in the middle. Make sure the juices run clear. ·Cooking food, including ground meat patties, to an internal temperature of at least 160 ° F (72° C) usually protects against foodborne illness. Well-done meats reach that temperature. ·Ground beef can be contaminated with potentially dangerous E. coli 0157: H 7 bacteria.
Don't eat raw or lightly cooked eggs. Many older cookbooks have recipes for ice cream, mayonnaise, eggnog and some desserts that call for raw eggs. These recipes are no longer recommended because of the risk of Salmonella. The commercial versions of these products are made with pasteurized eggs (eggs that have been sufficiently heated to kill bacteria) and are not a food hazard.
Clean kitchen counters and other surfaces that come in contact with food with hot water and detergent or a solution of bleach and water. Bleach and commercial cleaning agents are best for getting rid of pathogens. Hot water and detergent do a good job, too, but may not kill all strains of bacteria.
Allow dishes and utensils to air-dry in order to eliminate re-contamination from hands or towels. When washing dishes by hand, it’s best to wash them all within two hours--before bacteria can begin to form.
Wash hands with soap and warm water immediately after handling raw meat, poultry, or fish. Wash for at least 20 seconds before and after handling food, especially raw meat. If you have an infection or cut on your hands, wear rubber or plastic gloves.
Defrost meat, poultry and fish products in the refrigerator, microwave oven, or cold water that is changed every 30 minutes. ·Follow package directions for thawing foods in the microwave. ·Cook microwave-defrosted food immediately after thawing. ·Changing water every 30 minutes when thawing foods in cold water ensures that the food is kept cold, an important factor for slowing bacterial growth on the outside while inner areas are still thawing.
The world of prokaryotes Chapter 27: Campbell & Reece
Phylogenetics of prokaryotes • A natural or phylogenetic classification became the goal of taxonomy. • However prokaryotes with their simple morphologies resisted evolutionary classification until the development of molecular tools that could measure the similarity of molecular sequences.
Prokaryotes : Two Domains It is now generally believed that archaea and bacteria diverged from a common ancestor nearly 4 billion years ago.
Molecular systematics • Is leading to phylogenetic classification of prokaryotes • Immense diversity – 5000 spp. – Classification : Phenetic Phylogenies are based on common ancestries inferred from fossil, morphological and molecular evidence.
Concept of a species in prokaryotes is fundamentally different • Multiplication is entirely asexual • Mechanisms of genetic exchange are remarkably nonspecific and interbreeding between different genera and even kingdoms occurs. • The genome of each individual prokaryote is to some extent a mosaic.
How diverse are the prokaryotes? • Highly diverse. • About 5000 organisms known. • Estimated diversity ranges from 400, 000 to 4 million species.
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