Microbio 310 1st EditionExam # 3 Study Guide Lectures: 21-32Lecture 21 (March 30)How Antibiotic Resistance Happens1. Lots of Germs. A few are drug resistant.2. Antibiotics kill bacteria causing the illness, as well as good bacteria protecting the body from infection.3. The drug resistant bacteria are now allowed to grow and take over.4. Some bacteria give their drug-resistance to other bacteria, causing more problems.- You kill off the competitors of the MOST drug-resistant bacteria by not taking your antibiotics for the full amount of time.Antibiotics in Food Supply- 80% of all antibiotics are used on factory farm animals.- Pros– 4-5% increase in feed conversion rate– Increase in lifespan– Disease suppression- Cons– Selection for multi-drug resistant (MDR) pathogens– MDRs are a result of antibiotic feed– Food supply contaminated with drug resistant pathogens26.1 Heat Sterilization• Heat sterilization is the most widely used method of controlling microbial growth autoclave• Some bacteria produce resistant cells called endospores– Can survive heat that would rapidly kill vegetative cells• The autoclave is a sealed device that uses steam under pressure– Not the pressure that kills things, but the high temperature• Pasteurization is the process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids– Does NOT kill all organisms, so it is different than sterilization26.2 Radiation Sterilization• Microwaves, UV, X-rays, gamma rays, and electrons can reduce microbial growth• UV has sufficient energy to cause modifications and breaks in DNA– UV is useful for decontamination of surfaces– Cannot penetrate solid, opaque, or light-absorbing surfaces• Ionizing radiation– Electromagnetic radiation that produce ions and other reactive molecules– IRRADIATED no contact NOT RADIOACTIVE• Radiation is used for sterilization in the medical field and food industry– Radiation is approved by the WHO and is used in the USA for decontamination of foodsparticularly susceptible to microbial contamination26.3 Filter Sterilization• Filtration avoids the use of heat on sensitive liquids and gases– Pores of filter are too small for organisms to pass through– Pores allow liquid or gas to pass through26.4 Chemical Growth Control• Antimicrobial agents can be classified as bacteriostatic (slow it down), bacteriocidal (kill it), and bacteriolytic (bust it open)- Minimum inhibitory concentration (MIC) is the smallest amount of an agent/drug needed toinhibit growth of a microorganism– Varies with the organism used, inoculum size, temp, pH, etc.• Disc diffusion assay– Antimicrobial agent added to filter paper disc– MIC is reached at some distance• Zone of inhibition– Area of no growth around disc– Can be quantified: diameter of circle is proportional to the amount of antimicrobial agent added to the disc, the solubility of the agent, the diffusion coefficient, and the overall effectiveness of the agent.Lecture 22 (April 1)Antimicrobial Agents Used In Vivo• Classified on the basis of: – Molecular structure– Mechanism of action(ex: affect cell wall synthesis, protein synthesis)– Spectrum of antimicrobial activity 26.6 Synthetic Antimicrobial Drugs• Product of organic synthesis • Sulfa drugs: Inhibit growth of bacteria (inhibit nucleotide synthesis) – High Therapeutic Index* = low host toxicity – We don’t make folate so we take vitamins – Resistance bacteria learn to absorb folate from environment * Also HTI Isoniazid is a growth analog effective only against Mycobacterium – prodrug Interferes with synthesis of mycolic acid • Nucleic acid base analogs have been formed by the addition of bromine or fluorine • Quinolones are antibacterial compounds that interfere with DNA gyrase, which unwinds DNA 26.7 Naturally Occurring Antimicrobial Drugs: Antibiotics • Antibiotics are naturally produced antimicrobial agents – Less than 1% of known antibiotics are clinically useful • Can be modified to enhance efficacy (semisynthetic)• The susceptibility of microbes to different antibiotics varies greatly – Gram-positive and gram-negative bacteria vary in their sensitivity to antibiotics – Broad-spectrum antibiotics are effective against both groups of bacteria 26.8 eta-Lactam Antibiotics: Penicillins and Cephalosporins• eta -Lactam antibiotics are one of the most important groups of antibiotics of all time – Include penicillins, cephalosporins, and cephamycins – Over half of all antibiotics used worldwide • Penicillins M – Discovered by Alexander Fleming; in his experiment he saw a zone of exclusion(circle of mold) where no bacteria were growing, therefore he concluded the mold is producing antibacterialM – Primarily effective against gram-positive bacteria M – Some synthetic forms are effective against some gram-negative bacteria (Ex: Ampicillin)M – Target cell wall synthesis 26.10 Antiviral Drugs • Most antiviral drugs also target host structures, resulting in toxicity • Most successful and commonly used antivirals are the nucleoside analogs (e.g., azidothymidine aka AZT) – Block reverse transcriptase and production of viral DNA (inhibits HIV)– Also called nucleoside reverse transcriptase inhibitors (fake A’s and T’s)• Nonnucleoside reverse transcriptase inhibitors (NNRTI) bind directly to RT and inhibit reverse transcription • Protease inhibitors inhibit the processing of large viral proteins into individual components • Fusion inhibitors prevent viruses from successfully fusing with the host cell• Interferons are small proteins that prevent viral multiplication by stimulating antiviral proteins in uninfected cells 26.12 Antimicrobial Drug Resistance • Antimicrobial drug resistance – The acquired ability of a microorganism to resist the effects of a chemotherapeutic agent to which it is normally sensitive • At least six reasons that microorganisms are naturally resistant to certain antibiotics: – Organism lacks structure the antibiotic inhibits – Organism is impermeable to antibiotic (waxy membrane organism-need to acid treat them to get through)– Organism can inactivate the antibiotic – Organism may modify the target of the antibiotic (mutations)– Organism may develop a resistant biochemical pathway – Organism may be able to pump out the antibiotic (efflux) • Most drug-resistant bacteria isolated from