7/25/2019 10B - Infectious Disease
6/6
Why antibiotics do not affect viruses?We have seen that viruses
are non-living particles (Chapter 1). A virus lacks cell
structureand has no metabolism of its own to be interfered with or
disrupted. Instead, virusesreproduce using metabolic pathways in
their host cell that are not affected by antibiotics.Antibiotics
cannot be used to prevent viral diseases.
Antibiotic resistanceThere are a variety of mechanisms:
- Some bacteria produce penicillinase, an enzyme that breaks
down penicillin(Bacteria developed ability to produce this
enzyme)
- Some bacteria have a capsule / wall and membrane complex that
does not allowpenicillin to penetrate or that pumps the penicillin
straight out again (Bacteria withstructural advantage)
All that happens is that one solitary bacteria has a mutation a
chance error in DNAreplication that changes the way this bacteria
metabolises / builds its wall etc. Thisbacteria resists the course
of antibiotics because of the selective advantage that itsmutation
gives it. Dividing mitotically through binary fission, all of the
daughter bacteria areresistant, whilst all those without the
mutation are being wiped out. Soon, hundreds ofthousands of
individuals are resistant.
Bacteria become resistant to antibiotics because of mutation.
Not finishing the course of
antibiotics does not create resistant bacteria, but helps in
their widespread.
What creates resistant bacteria?
- Mutation (which is every day event and random) alters genetic
code of organisms.- When mutation occurs in bacteria, it may so
happen create genetic code that gives
the bacteria resistance to the antibiotic.
- This affects a small number of bacteria initially.- In the
absence of the antibiotic, the resistant bacteria confers no
selective advantage
at all. The resistant bacteria must compete for resources with
non-resistant bacteria.
- When we abuse antibiotic (take them but do not finish them),
we help kill thenonresistant competitors of the resistant
bacteria.
- As a result, the resistant bacteria will grow and reproduce
rapidly, all their offspringare resistant to the antibiotic.
- Through coughing etc., the resistant bacteria are released to
the environment.
However, if we complete the course of antibiotics, the total
number of bacteria will be incheck (under control) and there is a
chance that our bodys immune system may be able tokill all of them,
including the resistant bacteria. Therefore, to avoid antibiotic
resistance, weshould finish all antibiotics once we have started
taking them.
