chapter 10 microbiology

drugs to treat a disease

interfere with the growth of microbes within a host

substance produced by a microbe that inhibits another microbe

a drug that kills harmful microbes without damaging the host

• began in 1909 with Paul Ehrlich
• arsenic compound for treatment of syphilis
• salvarsan
• 1929- Fleming discovered penicillin, produced by Penicillium mold
• cointed ter antibiotic
• 1932- Gerhard Domagk discovered sulfanilamide
• first to use agent to treat wide array of bacterial infections
• prontosil: red dye

naturally produced antimicrobial agent

chemically altered antibiotics that are more effective than naturally occurring one

completely synthesized in a lab

an agent that works against a single gram negative, gram positive, or a few organisms

an agent that is effective against a wide variety of gram positive and gram negative organisms

an agent that kills the organisms

an agent that temporarily inhibits the growth of the organism long enough for the bodys defense mechanism to take over

• selectively toxic
• bacteriocidal

• competitvely bind with transpeptidase (penicillin binding protein)
• inhibits cross linking of peptidylglycan
• cell wall sythesis is arrested and the bacterial dies

• penicillin
• amoxicillin
• ampicillin

• kflex
• ceclor
• cefzil
• vantin

azactam

• bacteria defend themselves from the penicillin family in four ways
• alter porins
• Gm+ and Gm- possess beta-lactamase enzymes that cleave beta-lactam ring
• penicillinase
• alter structure of transpeptidase so antibiotics cant bind
• methicillin-resistan staphylococcus aureus (MRSA)
• Gm+ and Gm- may develop the ability to actively pump out beta-lactams before it binds to the transpeptidase

• these enzymes are inhibitors of beta-lactamase
• they are given in combination with penicillins to create a beta-lactamase resistant combination
• clavulanic acid
• amoxicillin and clavulanic acid: augmentin
• sulbactam
• ampicillin and sulbactam: unasyn
• tazobactam
• piperacillin and tazobactam: zosyn

• bacitracin
• inhibits lipid carrier, bactoprenol
• prevents transport of NAM subunits through cell wall
• effective as a topical treatment against gram positives
• staphylococci
• streptococci
• vancomycin
• glycopeptide derived from streptomyces
• prevents insertion of NAMs and NAGs into PTG wall
• important "last line" against antibiotic resistan s. aureus

• members of the genus mycobacterium have an atypical cell wall
• contain mycolic acid
• acid fast stain
• cause leprosy and tuberculosis
• antimycobacterium antibiotics
• isoniazid (INH)
• inhibits the enzyme, fatty acid synthase
• drug of choice, generally used in combination with rifampin and ethambutol

• target synthesis of b-glucans and result in an incomplete cell wall
• echinocandins
• binds to 1,3 b-glucan synthase
• used to treat candida and pneumocystis
• caspofungin (cancidas)

• polymyxin B: made from a specific form of bacillus
• caues disruption of the plasma membrane by attaching to the phospholipids
• effective against gram negative bacteria
• pseudomonas
• toxic to human kidneys
• topical
• combined with bacitracin and neomycin in over the counter preparation

• amphotericin B
• attaches to ergosterol and dirupts membrane and causes lysis
• azoles
• inhibits lanosterol a-demethylase
• enzyme converts lanosterol to ergosterol
• dirupts plasma membrane
• miconazole/clotrimazole
• triazoles (fluconazole and itraconazole)

• recall prokaryotes ribosomes are structurally different from eukaryotes
• 70S ribosome
• 50S unit
• 30S unit
• allows creation of antimicrobials that target these structures

• broak spectrum
• binds 50S subunit, inhibits peptide bond formation
• serious toxicity
• suppression of bone marrow

• streptomycin, neomycin, gentamicin, tobramycin
• broad spectrum
• bind to 30S and cause misreading of mRNA
• toxicity can cause hearing impairment and/or kidney damage

• bread spectrum
• effective against Gram + and Gram-, rickettsias, and chlamydia
• interferes with tRNA attachment
• forms complexes with calcium and can strain developing teeth and affect strength of developing bones

• gram positives
• binds 50S, prevents translation
• erythromycin
• azithromycin
• clarithromycin

• fomiversen
• cytomegalovirus and eye infections
• prevents formation of 70S initiation complex
• oxazolidinones (zyvox)
• vancomycin and methicillin-resistant staphylococcus aureus

• sulfonamides (sulfa drugs)
• structural similar to PABA
• inhibit folic acid synthesis
• broad spectrum

• compounds can interefere with function of nucleic acids (nucleoside analogs)
• nucleoside analogs can distort shapes of nucleic acid molecules and prevent further replication, transcription, or translation
• most often used agains viruses; viral DNA polymerases moer likely to incorporate and viral nucleic acid synthesis more rapid than that in host cells
• also effective agains rapidly dividing cancer cells

• binds to bacterial RNA polymerase
• antituberculosis

• inhibits DNA gyrase
• broader spectrum synthetic versions
• ciprofloxacin: anthrax
• limited use in children

• produced by a species of penicillium
• used for superficial mycoses of hair and nail (tinea capitis or ringworm)
• binds slectively to keratin
• blocks microtubles and inhibits mitosis

• mechanism of action: not known
• used for athletes foot

• no peptidoglycan wall
• no ribosomes
• no plasma membrane
• current anti-viral medications attack steps in viral replication
• only attack actively replicating viruses
• most are fake viral nucleotides, derail viral replicaton

• protease inhibitors
• indinavir:
• prevents HIV protease to trim viral proteins down to working size
• prevents capsid formation
• inhibit attachment
• zanamivir
• influenza
• inhibit uncoating
• amantadine
• influenza
• interferons prevent spread of viruses to new cells
• viral hepatitis
• reverse transcriptase inhibitors: RNA to DNA
• HIV

• also known as the kirby-bauer test
• petri plate is "seeded" with test organism
• filter paper disks are impregnated with chemotherapeutic agents are place of surface
• zone of inhibition
• the larger the zone the more sensitive the microbe is to the drug

• more advace diffusion test
• can measure minimal inhibitory concentration (MIC)
• lowest antibiotic concentration that prevents visible bacterial growth

• used to determine MIC
• plus minimal bactericidal concentration
• wells that show no growth (higher concentration than MIC) are cultured in drug free broth
• no growth= bacteriocidal
• growth= basteriostatic

topical: application of dug if infection is external

oral: simplest; lower drug concentrations; no reliance on health care provider; patients do not always follow prescribing information

intramuscular: requires needle; contration never as high as IV administration

• intravenous: requires needle or catheter; drug contration diminishes as liver and kidneys remove drug from circulation
• must know how antimicrobial agent will be distributed to infected tissues

• exact cause of many adverse reactions poorly understood
• drgs may be toxic to kidneys, liver or nerves
• considerations needed when prescribing drugs to pregnant women

• although allergic reactions are rare, they may be life threatening
• anaphylactic shock
• disruption of normal flora

• a variety of mutations can lead to antibiotic reistance
• mechanisms of antibiotic resistance
• enzymatic destruction of drug
• prevention of penetration of dug
• alteration of dugs target site
• alter their metabolic activity
• rapid enjection of the drug
• mycobacterium tuberculosis produces MfpA protein, which binds to DNA gyrase preventing the binding of fluoroquinolone drugs
• resistance genese are often on plasmids or transposons that can be transferred between bacteria

• misuse of antibiotics selects for resistance mutants
• misuse includes
• using outdated, weakened antibiotics
• using antibiotics for the common cold and other inappropriate conditions
• use of antibiotics in animal feed
• failure to complete the prescribed regimen
• using someone elses leftover prescription

• patient should finish entire course of antimicrobial
• limit use of antimicrobials to necessary cases
• use synergistic antimicrobials
• develop new variations of existing drugs
• second-generation drugs
• third-generation drugs
• search for nw antibiotics, semi-synthetics, and synthetics
• bacteriocins
• design drugs complementary to the shape of microbial proteins to inhibit them