ch 9 antimicrobial chemotherapy Flashcards
antibiotic
natural products and their derivatives that kill susceptible microorganisms or inhibit their growth
antimicrobial agents
includes both natural and chemically synthesized compounds
Ehrlich
identified dyes that effectively treated African sleeping sickness
Hata - identified arsenic compounds that effectively treated syphilis
-> all antimicrobial (based on dyes)
penicillin
first discovered by Ernest Duchesne 1896
rediscovered by Alexander Fleming 1928
Florey, Chain, and Heatley purified penicillin from culture and injected into mice 1939
streptomycin
an antibiotic active against tuberculosis discovered by Waksman 1944
golden era of antibiotics
saw the rapid development of new antimicrobial agents that changed how infectious disease was treated and how medicine was and continues to be practiced
1950-1960s
selective toxicity
ability to kill or inhibit microbial pathogen while damaging the host as little as possible
the degree of selective toxicity can be expressed in terms of
1 The therapeutic dose - the drug level required for the treatment of a particular infection
2 the toxic dose - the drug level at which the agent becomes too toxic for the host
3 therapeutic index - the ratio of the toxic does to the therapeutic dose
- the larger the therapeutic index, the better the chemotherapeutic agent in general
narrow-spectrum drugs
effective only against a limited variety of pathogens
broad-spectrum drugs
target many different kinds of bacteria
cidal
kills the target pathogen, may be static at low levels
static
reversibly inhibit growth
minimal inhibitory conc (MIC)
lowest conc of a drug that prevents growth of a particular pathogen
minimal lethal conc (MLC)
lowest drug conc that kills the pathogen
dilution susceptibility test
used to determine MIC and MLC values
involves inoculating media containing different concs of drugs
- broth or agar with lowest conc showing no growth is MIC
- MLC is ascertained when tubes that show no growth are then cultured into fresh medium lacking antibiotic - lowest antibiotic conc that fails to support the microbe’s growth is MLC
disk diffusion test
often used to analyze rapidly growing bacteria
- disks impregnated with different antibiotics are place on agar plates inoculated with a microbe
- observe zones of clearing around disks
kirby-bauer method
most common disk diffusion test
relates zone diameter with microbial resistance
used to determine if effective conc of drug in body can be reached
Etest
used in sensitivity testing
Etest strips contain a gradient of an antibiotic, intersection of elliptical zone of inhibition with strip indicates MIC
- can only test 1 agent at a time, expensive
main modes of antibacterial drug action
- inhibitors of cell wall synthesis
- most selective against bacteria bc they target structures and functions not found in eukaryotes
- protein synthesis inhibitors
- metabolic antagonists
- nucleic acid synthesis inhibition
beta-lactam ring
the cyclic chemical structure composed of one nitrogen and three carbon atoms, it has antibacterial activity, interfering with bacterial cell wall synthesis - block transpeptidation
most crucial feature of penicillin
essential for bioactivity