Antibiotic resistance Flashcards
measuring antibiotic activity process
- We make a suspension of the bacteria and lawn it with a cotton swab all over an agar plate equally
- Add plates embedded with antibiotics
- Incubate overnight
- Measure area of clear agar to show antibiotic resistance
the larger the area clear area of agar
The larger the area the less resistance
how is antibiotic susceptibility measured
Minimum inhibitory conc (MIC)
how can MIC be measured (2)
- broth microdilution
- E-test
what is MIC
The first conc of antibiotics which inhibits the growth of bacteria
E-test
- Lowest conc of antibiotics at the bottom
- Highest conc of antibiotics at the top
o Zonal clearing
More clearing at the top
Least clearing at the bottom
• First no. that you get no growth–> MIC
resistance to antibiotics started
almost as long ago as antibiotics (2 bill to 40 mill years old)
all exposure of bacteria to antimicrobials will result in
resistance
is resistance reversible
no
types of resistance
intrinsic
acquired
adaptive
intrinsic resistance
the bacteria have no target for the drug to work on e.g. a penicillin can’t act on a microbe without a cell wall as this is its site of action.
(usually permanent)
acquired resistance
this is done either through mutation or horizontal gene transfer.
adaptive resistance
The bacteria only are resistant when exposed to an antibiotic as they adapt to the environment. This form of resistance is unstable, therefore when the antibiotic is removed, the bacteria become susceptible once again. (This is a reason for why efficacy of an antibiotic regimen may fall with treatment.)
e.g. sub inhibitory level of antibiotics
mode of action of antimicrobial resistance (3)
- Enzymatic modification or destruction of antibiotics
- Enzymatic alteration of antibiotic targets
- Mutation of bacterial target sites
development of resistance by mutation
1) n Within a population of bacteria, through random mutation, some bacteria will develop antibiotic resistant traits.
2) This is of no real concern as these bacteria are few and far between with in the larger population.
3) On the introduction of a selection pressure i.e. the introduction of an antibiotic, only these resistant cells will survive and are thus selected for.
4) This causes issues now as because now only the resistant bacteria are alive to reproduce. 5) This leads to a population which is entirely resistant to the antibiotic, compared to one with only a few resistant individuals.
