practical one

what are bioassays used for and why

to estimate the concentration of antibiotics in solution

monitor the concentration of an antibiotic in the blood

what does zone of growth inhibition indicate in bioassays

the edge of the zone occurring when the antibiotic is too dilute to inhibit growth of the bacteria

in bioassays what does it mean if there is a wider zone of growth inhibition

the antibiotic is more concentrated

how graph can be drawn using bioassays

standard curve can be drawn by plotting the zone of inhibition diameter against the antibiotic concentration. This curve can then be used to determine the antibiotic concentration in an unknown sample

what are antibiotics synthesized by

bacteria and fungi

how is the sensitivity if bacteria to antibiotics determined

disc diffusion; zones of growth inhibition for test organism are compared with those of a known standard sensitive strain

zones obtained with different antibiotics cannot be directly compared

what needs to be considered for antibiotic sensitivity testing

culture medium, inoculum density, antibiotics discs, incubation conditions, and interpreation of zone size and break points

what are two ways antibiotic resistance is aquired

chromosomal mutations or transfer of plasmid determined resistance

how do chromosomal mutations work

they impact the functionality of an antibiotic by altering the antibiotic target so it is no longer susceptible however the functionality is maintained

how does rifampicin work

binds to enzyme RNA polymerase blocking the ability of the bacteria to transcribe DNA to RNA

chromosomal mutations and Rifampicin

mutations in the chromosomal genes coding for RNA polymerase result in an altered enzyme to which rifampicin no longer binds while maintaining correct enzyme functionality

does plating on rifampicin containting media induce RifR mutants

no it does not induce mutants since mutants are already present it only selects for the mutants

how is the frequency of rifampicin resistant mutants deterined

no of RIFr coloines/ml divided by starting culture viability count

what is bacterial conjugation

transfer of genetic material between bacterial cells via cell to cell contact of the pilus

what does the R plamsid carry

carries the gene for chloramphenicol resistance (CmR), conferring resistance to the antibiotic on bacteria harboring this mobile genetic element

what is the R- bacteria sensitive to

nalidixic acid

MIC

minimum inhibitory concentration=lowest concentration of a substance that inhibits growth of an organism

how is MIC determined

agar dilution method which testing several strains on doses at once