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Subances produced by a microorganism that (at low concentration) inhibit or kill other microorganisms
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Talking about chemical produce by living organisms that can kill or inhibit
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BASICALLY: life destroys life
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The use of drugs to treat a disease
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Any substance of natural, synthetic or semi-synthetic origin that kills or inhibits the growth of a microorganism
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Causes little or no host damage
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Requires knowing the following:
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- The organism's identity
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- The organism's susceptibility to a particular agent
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- The site of infection
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- Patient's factors
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- The safety of the agent
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- The cost of therapy
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Definition:
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Ability to kill or injure an invading microorganism without harming the cells of the host
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LD50
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Lethal dose at 50%; should be high
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MIC
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Minimal inhibitory concentration; should be low; the lowest concentration of antibiotic that INHIBITS bacterial growth; lowest concentration that will stop the growth of bacteria
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MBC
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Minimal bactericidal concentration; should be; minimum concentration of antibiotic that KILLS the bacteria
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Selective Toxicity: goal of antimicrobial drug therapy
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Example: inhibit pathways or targets critical for pathogen survival at drug concentrations lower than those required to affect host pathways
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Unique Pathways
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Also known as Cell Wall Synthesis Inhibitors; drug that inhibits the cell wall synthesis in microbes; the walls will lyse and the bacteria will die
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Selective Pathways
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Also known as protein synthesis inhibitors
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Common Pathways
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Also known as metabolites
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Type
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Example
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Cause inhibition of cell wall synthesis
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Beta-Lactamas
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Alter the function of the cytoplasmic membrane; destroy cytoplasmic membranes
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Isoniazid
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Inhibit protein synthesis
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Macrolides
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Inhibit nucleic acid synthesis
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Quinolones
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Inhibit metabolite activity
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Sulfonamides
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Narrow Spectrum
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Preferentially active
against single or limited group of microorganisms Tx eg: isoniazid |
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Extended Spectrum
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Effective against gram-positive and SOME gram negative bacteria
Tx eg: ampicillin |
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Broad Spectrum
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Active against BOTH gram positive and gram negative bacteria
Tx eg: tetracycline Tx eg: chloramphenicol |
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Cell Wall Inhibitors
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Fosfomycine
Cylcoserine Vancomycin Penicillin Cephalosporins Monobactams Carbapenems Ehambutol Pyrrazinamide Isoniazid |
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DNA Synthesis &
Integrity Inhibitors |
Sulfonamides
Trimethoprim Quinolones |
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Transcription &
Translation Inhibitors |
Rifampin
Axminoglycosdes Spectinomycin Tetracyclines Macrolides Chloramphenicol Streptogramins Oxazolidinones |
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INHIBIT the growth of pathogens without causing cell death
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Eg: sulfonamides (DNA synthesis & intercity inhibitor)
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Eg: chloramphenicol (transcription & translation inhibitor)
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Bacteriostatic effectiveness relies on an intact host immune system to CLEAR THE NONGROWING (but viable) bacteria
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KILL BACTERIA
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Eg: penicillin (cell wall inhibitor)
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Eg: streptomycin (transcription and translation inhibitor)
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Eg: give this to patients with AIDS because they don't have immunity
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Spirilla
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Spiral shaped bacteria
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Bacilla
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Rod shaped bacteria
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Cocci
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Spherical shaped bacteria
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Diplo-
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Pair
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Staphylo-
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Culsters
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Strepto-
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Chain
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Looks violet or dark blue in gram staining
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Retains the crystal violet stain
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Single layered membrane -- it lacks the second outer phospholipid bilayer
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Thick layer of peptidoglycan -- only this forms the cell wall
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Easier to treat with antibiotics because it only has one phospholipid bilayer
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Don't retain crystal violet dye from gram staining
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They are pink or red colored
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Thin peptidoglycan wall
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Two phospholipid bilayers (two membranes)
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Consist of outer membrane and thin peptidoglycan wall as cell wall
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The cell wall is thinner than gram positive
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This is harder to treat with antibiotics because it has two phospholipid bilayers
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Definition: bacteria which resist decolorization with an acid-alcohol mixture during the acid-fast stain procedure
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It retains the initial dye (carbofuchsin)
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Acid-fast bacteria (mycobacteria and some of the related actinomycetes) appear red
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Gram Positive Cocci
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Gram Positive Bacilli
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Gram Positive Cocci
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Gram Negative Bacilli
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Anaerobe Organisms
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Spirochetes
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Mycoplasma
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Chlamydia
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Other
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Reasons to Use Single Treatment Instead of Combinations of Antimicrobial Drugs
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1. Reduces the possibility of superinfection
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2. Reduces the emergence of resistant organisms
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3. Minimizes toxicity
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Advantage:
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Synergism
Eg: beta-lactams and aminoglycosides |
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Disadvantage:
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Drug antagonism
Eg: combining bacteriostatic drug with bactericidal drug Eg: giving a patient tetracycline with penicillin or cephalosporins |
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BASICALLY:
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Don't combine bacteriostatic drugs with bactericidal drugs
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- Use of antibiotics for prevention instead of treatment of infection
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- May cause resistance and superinfection
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- Use is limited
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1. Hypersensitivity
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2. Direct toxicity
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3. Superinfection
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Definition: relative or complete lack of effect of antimicrobial against a previously susceptible microbe
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Increase in MIC (remember MIC is lowest concentration needed to inhibit bacterial growth)
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May be innate (an escape from antibiotic effect)
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OR it may be acquired
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1. Spontaneous, random chromosomal mutations. The mutations are due to change in either a structural protein receptor for an antibiotic or a protein involved in drug transport
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2. Extrachromosomal transfer of drug-resistant genes
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2a. Transformation: transfer of naked DNA between cells of same species
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2b. Transduction through R plasmids: R plasmids are a sexual transfer of plasmid DNA in a bacteria virus between bacteria of the same species
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2c. Conjugation: the passage of gene from bacteria to bacteria via direct contact through a sex plus or bridge. Conjugation occurs primarily in GRAM NEGATIVE BACILLI. It is the principal mechanism of acquired resistant among enterobacteria
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2d. Transposition: occurs as a result of movement or "jumping or transposons" (stretches of DNA containing insertion sequences at each end) from plasmid to plasmid or from plasmid to chromosome and back
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1. Reduced entry of antibiotic into pathogen
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2. Enhanced export of antibiotic by pathogen efflux pumps
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3. release of microbial enzymes that destroy the antibiotic
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4. Alterations of microbial enzymes that are required to transform products to the effective moieties
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4. Alterations of target proteins
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5. Development of alternative biochemical pathways to those inhibited by the antibiotic
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1. Exposure to sub-optimal levels of antimicrobial
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2. Exposure to microbes carrying resistance genes
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- Prescriptions not taken correctly
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- Antibiotics for viral infections (you don't give antibiotics for viral infections)
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- Antibiotics sold without medical supervision
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- Spread of resistant microbes in hospitals due to lack of hygiene
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- Lack of quality control in manufacture of outdated antimicrobial
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- Inadequate surveillance of defective susceptibility assays
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- Poverty or way
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- Use of antibiotics in foods
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Antibiotics are used in animal feeds and sprayed on plants to prevent infection and promote growth
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Multi-drug resistant Salmonella typhi has been found in some people who eat beef fed antibiotics
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Methicillin-Resistant Staphylococcus Aureus
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Most frequent nosocomial (hospital-acquired) pathogen
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Usually resistant to several other antibiotics
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