Antimicrobials Flashcards
Chemotherapeutic agents
a chemical used to treat a disease; ex: salvarsan and prontosil (produces sulfa)
Also called antimicrobials
Penicillin
Fleming found that colonies around a mold were being killed. The mold had penicillin. It kills many different bacteria. He was not able to purify the penicillin substance so he stopped studying it.
First antibiotic found
Penicillin G is the best serotype
Antibiotics are naturally produced by microorganisms
The chemical structure can be altered to kill other bacteria as well; ampicillin, methicillin
Streptomyocin
second antimicrobial susbstance found; produced by a bacterium (S. griseus)
Where do most antibiotics come from?
Soil
Semisynthetic antibiotics
a substance that is chemically altered to kill other bacteria; ampicillin (derived from penicillin)
hard to make because it is expensive and the microorganisms can being to resist the new antibiotics and then it will be harder to cure
Selective toxicity
Medication is more toxic to the microbe than the human
Therapeutic index; high-less toxic (acts against an essential biochemical process of the microorganism, humans lack this process…EX: Penicillin G)…Low therapeutic index- more toxic to humans (if its too toxic for bloodstream use, they use a topical application which is applying it to the skin)
Antimicrobial action
Bactericidal (chemical kills the bacteria; depends on dosage and stage of bacteria) vs Bacteriostatic (relies on the humans immune defenses to eliminate the microorganims after it has been inhibited and stops growing)
Spectrum of activity
Narrow range (less disruptive to the normal microbiota vs Broad range (important for treating acute life threatening diseases because there isn’t time to identify the pathogen…but can also affect normal microbiota so it can be harmful)
Tissue distribution/metabolism/excretion
Meningitis; needs med. that crosses the blood into the cerebrospinal fluid
Meds that are unstable at low pH are destroyed by stomach acid when swallowed….so they are given by an IV
Dosage; depends on the half life of the med. If the med is excreted fast, you need to be given more doses per day…if the med is excreted slow (kidney or liver damaged patients), you need to be given less doses per day to avoid toxicity
Effects of combinations
Has to be chosen carefully to prevent antagonistic combinations (one antimicrobial prevents the action of the other antimicrobial)
Ideal combination; Synergistic (one antimicrobial enhances the action of the other)
Additive; one microbial doesn’t effect the other one at all
Adverse effects
Allergies; given an alternative antimicrobial
Toxic Effects; low therapeutic index causes damage.
Pregnant women should avoid some because it could give adverse effects to the fetus
Suppression of normal microbiota; causes dysbiosis (an imbalance in the microbial pop)…can cause other pathogens to multiply without competition and cause disease
Resistance to antimicrobials
Intrinsic resistance (inherently resistant to the med…mycoplasm lacks cell wall needed for the antimicrobial to work)
Acquired resistance; previously sensitive microorganism that becomes resistant (through spontaneous mutation or horizontal gene transfer)
Target of antibacterial medications (cell wall synthesis…peptidoglycan)
b lactam antibiotics; competitively inhibit enzymes that help from cross-links between adjacent glycan chains…human cells dont have peptidogylcan…ex; penicillin carbapenems, monobactams, and cephalosporin (they all have the b lactam ring and have a high therapeutic index)…the b lactam antibiotics are bactericidal only against growing bacteria
Gram negative is more resistant, because their cell wall and because the penicillin binding proteins are different.
B lactamase; enzyme that breaks down b lactam ring…bacteria that have this are resistant…carbapenemases inhibit most
Glycopeptide antibiotics; bind to the amino acid side chain of NAM molecules which blocks formation of cross links between the gylcan chains…only effect gram positive bactera…ex vancomycin
Bacitracin; interferes with the transport of peptidoglycan precursors across the cytoplasmic membrane
Target of antimicrobial mediations
Nucleic acid synthesis; fluoroquinolones; bactericidal against a wide range of bacteria.
Rifamycins; block transcription…bactericidal agains a wide range and mycobacterium
Metronidazole; only effects anaerobic microorganisms (metabolism of anaerobic mirco. converts the medication to its active form)
Cell membrane integrity; polymixins, daptomycin
Metabolic pathways (folate biosynthesis); sulfomaides, trimethoprim
Protein synthesis; target the 70s ribosome of bacteria…ex aminoglycosides, tetracyclines, glyclyclines, macrolides, chloramphericol, linocosamides, oxazolidinones, pleuromutilins, streptogramins
Different types of penicillins
Natural penicillins;
Penicillinase-resistant penicillins; methicillin and dicloxacillin…some S. aureus are MRSA (methicillin resistant s. aureus)…only cephalosporins are effective against MRSA
Broad-spectrum penicillins; inactivated by b lactamases, ex ampicillin and amoxicillin
Penicillin family + b lactamase inhibitor; combination of agents, ex; augmentin (amoxicillin and clavulanic acid)