Antibiotics by kirby-bauer method Flashcards
What is an antimicrobic/antimicrobial agent?
any chemical or physical agent that inhibits the growth of a microorganism or kills it
what is a chemotherapeutic drug?
- antimicrobial agent
2. chemical compounds that are taken internally to ease the symptoms of a disease or to speed the patient’s recovery
what three criteria must a chemotherapeutic drug meet to be considered an antibiotic?
- its a chemical substance produced by a microorganism
- it stops the growth of or kills other microorganisms
- it is effective in very small doses.
True or false: antibiotic production by microorganisms is common. If true, where is it most common?
True, most common in soil microbes.
What are antibiotics effect against and what are they not effective against
- effective against bacteria and fungi
2. not effective against viruses
The course of an infection depends upon what?
the race between the pathogen’s ability to grow in the host tissue and the tissues ability to capture and destroy that invading pathogen
Purpose of antibiotics?
to weaken or kill some of the invading pathogens; hopefully the body’s tissues can then destroy the rest.
what is a chronic infection?
its marked by long duration or frequent recurrence ( if pathogen did not go away)
What happens if there is a chronic infection?
the pathogen is isolated and an antibiotic it is easily weak to is found for it.
what results with overuse of antibiotics and over prescription of broad-spectrum antibiotics ?
- risk of increasing antibiotic resistance
2. affecting balance of non-target populations (wiping out important bacteria needed by body)
What happens after isolating the pathogen to determine its susceptible antibiotic?
the plates are heavily streaked and antibiotic sensitivity disks are used to determine the antimicrobial activity for each antibiotic.
conditions for the antibiotic disks on the agar surface?
they are placed on the agar surface after inoculation and BEFORE incubation.
what happens to the antibiotic disk during incubation?
it diffuses from the disk into the agar, creating a concentration gradient such that the greatest concentration is at the edge of the disk
what happens to the cells during the incubation of the plate with the antibiotic discs?
it grows confluently to form a thick loawn of microbial growth except where the microorganisms are either killed or stopped from growing by the antibiotic.
What is a zone of inhibition?
a clear zone in which there is no microbial growth
How is the effectiveness of the antibiotic preliminarily determed ?
its determined by the size of the zone of inhibition
the type of medium used
what does the zone of inhibition vary according to?
to how easily the antibiotic diffuses through the agar
What is special about the kirby-bauer method?
it is highly standardized to avoid varying results due to alterations in procedure
What agar is used in the kirby-bauer method?
only the mueller hinton agar is used
what is the components of the mueller hinton agar?
it has the same composition as TSA
but is prepared under exacting conditions such that its chemical composition is always the same
pH = 7.2 to 7.4
what two things are the size of the zone of inhibition related to?
- minimum concentration that kills or inhibits that microbe (minimum inhibitory concentration (MIC))
- ability of the antibiotic to diffuse through the agar
what is MIC
This is the lowest concentration of an antimicrobial drug that prevents visible growth of a microorganism after overnight incubation with media.
