Lecture 10 Flashcards
What is the goal of antimicrobial chemotherapy?
administer a drug to an infected person that destroys the infective agent without harming the host’s cells (selective toxicity)
Chemotherapeutic drug
any chemical used in the treatment, relief, or prophylaxis of a diease
Prophylaxis
the use of a drug to prevent imminent infection of a person at risk
Antimicrobials
all inclusive term for any antimicrobial drug no matter its origin
Antibiotics
substances produced by the natural metabolic processes of some microorganisms that can inhibit or destroy other microorganisms
semisynthetic durgs
natural resources that are chemically modified in the lab
synthetic drugs
drugs produced by chemical reactions
Why are antibiotics produced and what are they derived from?
- are common metabolic products of aerobic bacteria and fungi
- produced to inhibit the growth of competing microbes in the same habitat
Derived from
bacteria in the genera Streptomyces and Bacillus
molds in the genera Penicillium and Cephalosporium
What is the kirby-baurer techinque testing for drug susceptibility?
surface of an agar plate is spread with bacteria
small discs containing a prepared amount of antibiotic are placed on the plate
zone of inhibition surrounding the discs is measured and compared with a standard for each drug
antibiogram provides data for drug selection
this method is less effective for anaerobic, fastidious, or slow-growing bacteria
What is the tube dilution test for testing for drug susceptibility?
more sensitive and quantitative than the Kirby- Bauer test
antimicrobial is diluted serially in tubes of broth
each tube is inoculated with a small uniform sample of pure culture
useful in determining the effective dosage and providing a comparative index against other antimicrobials
What is the therapeutic index?
-the ratio of the dose of the drug that is toxic to humans as compared to its minimum effective (therapeutic) dose
-the smaller the ratio, the greater the potential for drug reactions
Toxic dose ÷ MIC
The closer this is to 1, the more toxic it is.
What are the goals of antimicrobial drugs?
disrupt cell processes or structures of bacteria, fungi, or protozoa
inhibit virus replication
interfere with the function of enzymes required to synthesize or assemble macromolecules
destroy structures already formed in the cell
What is selectively toxic?
kill or inhibit the actions or synthesis of molecules in microorganisms but not vertebrate cells
What do drugs with excellent selective toxicity do?
block the synthesis of the bacterial cell wall (penicillins)
What drugs are most toxic to humans?
drugs that act upon a structure common to both the infective agent and the host cell (cell membrane)
What is minimum inhibitory concentration (MIC)?
the smallest concentration (highest dilution) of drug that visibly inhibits growth
What are the goals of chemotherapy?
identifying structural and metabolic needs of a living cell and removing, disrupting, or interfering with these requirements
What are the antimicrobial drug categories?
inhibition of cell wall synthesis
inhibition of nucleic acid structure and function
inhibition of protein synthesis
interference with cell membrane structure and function
inhibition of folic acid synthesis
facts about penicilins
original penicillin was narrow-spectrum and susceptible to microbial counterattacks
molecule has been altered and improved upon over the years
later penicillins overcome the limitations of the original molecule
Are Biofilms unaffected or affected by the same antimicrobials that work against them when they are free living?
unaffected
What are the stragies for treating biofilm infections?
interrupting quorum sensing signals
adding DNase to antibiotics helps with penetration
impregnating devices with antibiotics
What is quinine?
principal treatment of malaria for hundreds of years
has been replaced by synthesized quinolones, chloroquine and primaquine
several species of Plasmodium and many stages in its life cycle means that no drug is universally effective
What is metronidazole?
widely used amoebicide
treats intestinal infections and hepatic disease caused by Entamoeba histolytica
also treats Giardia lamblia and
Trichomonas vaginalis
What are the challenges of antihelminthic drug therapy?
flukes, tapeworms, and roundworms are larger parasites
their physiology is much more similar to humans
blocking reproduction does not affect adult worms
most effective drugs immobilize, disintegrate, or inhibit the metabolism of all stages of the life cycle
What are the unique challenges of antiviral chemotherapeutic agents?
infectious agent relies on a host cell for the vast majority of its metabolic functions
disrupting viral metabolism requires disruption of cellular metabolism
measles, mumps, and hepatitis are prevented through the use of vaccines
AIDS, influenza, and the common cold attest to the need for more effective medications for the treatment of viral infection
What are the modes of action of antiviral agents?
barring penetration of the virus into the host cell
blocking transcription and translation of viral molecules
preventing maturation of viral particles
What is drug resistance?
an adaptive response in which microorganisms begin to tolerate an amount of drug that would normally be inhibitory
due to the genetic versatility and adaptability of microbial populations
can be intrinsic as well as acquired
When do microbes become newly resistant to a drug?
pontaneous mutations in critical chromosomal genes
acquisition of entire new genes or sets of genes via horizontal transfer from another species
What was the original wonder drug and how was it formed?
pencilin and by fungus
What is chromosomal drug resistance and what does it result from?
usually results from spontaneous random mutation
slight changes in drug sensitivity can be overcome with larger doses of drug
can be the result of a phenotypic, rather than a genotypic change; slowing or stopping of metabolism so that the microbe can’t be harmed by the antibiotic
