CAIE grade 11

1. *
Distinguish between bacteriostatic
& bactericidal antibiotics
Describe how to investigate the
effect of different antibiotics on
bacteria

2. *
One of the best examples of natural selection &
Adaptation is the evolution of genetic resistance in
pathogens.
Pathogenic bacteria rapidly develops resistance to
antibiotics.
This results in an evolutionary race between the bacteria
& humans, in which the participants are engaged in a
continuous struggle against each other with no long term

3. *

4. *
An antibiotic is given for the treatment of an
infection or a disease caused by bacteria.
Antibiotics target microorganisms such as
bacteria, fungi & parasites. However, they are
not effective against viruses.

5. *
It was thought that the battle against disease
would be won with the use of antibiotics
But….
Bacteria that cause disease rapidly develop
resistance to antibiotics
As quickly as we evolve mechanisms to
combat pathogens, they evolve new methods
of overcoming our immune system.

6. *
Mutations cause resistance to antibiotics:
The bacteria may produce an enzyme that
enable the cell to break down the antibiotic
They may change the structure of it’s protein so
antibiotics no longer have an effect
It might code for a protein pump that removed
the antibiotic from the bacterial cell.
Genes for
antibiotic
resistance
may be
transferred to
other non-
resistant
bacteria by
conjugation,
transformatio
n or
transduction.

7. *

8. *
The presence of antibiotics produces a selection
pressure
Those bacteria which does not have the gene for the
resistance are selected against & are likely to be
destroyed
Those with the gene are selected for, they survive,
grow & reproduce.
The gene frequency for resistance increases within
the population

9. *

10. *
Transformation
The problem further continues as bacteria transfers
resistant genes between species. They spread by;
Bacteria take up fragments of DNA from a lysed
bacterial cell & incorporates to its own DNA.

11. *
Transduction
Bacteriophages (viruses which target bacteria) can pick up
bacterial genes by accident & transfer these genes to other

12. *
Conjugation
Genes for resistance are commonly kept on bacterial plasmids.
Bacteria can share plasmids through conjugation. It forms
cytoplasmic bridges (pili) between their cytoplasms. Once the
pili is formed, plasmids are replicated & one copy of the
plasmid passes from one bacteria to another via the pili.

13. *

14. *
Antibiotic
A used
Antibiotic
B used
Antibiotic
C used
Bacteria are now
resistant to
Antibiotic A, B & C
X Y Z
Bacterialpopulation
Time
X- Antibiotic A kills the non resistant
bacteria. The survivors are mutant
bacteria which are resistant to antibiotic
A. These resistant ones are now selected
by nature to survive &  in no., as they
cannot be killed by antibiotic A
Y- Antibiotic B kills the bacteria that are non
resistant to antibiotic B, but does not kill all the
bacteria. The survivors are mutant bacteria
which are resistant to Antibiotic A & B. the
resistant ones are selected by nature to survive
&  in no. as they cannot be killed by both
antibiotic A & B. The survivors are mutant
bacteria which now have genes for resistance
to antibiotic A & B.
Z- exposure to antibiotic C will now select & favor the
survival of mutant bacteria which have genes for
resistance to antibiotic A, B & C. These are called as
superbugs or multiple drug resistant bacteria. They
are commonly found in hospitals, where many
antibiotics are frequently used. Thus, natural
selection is responsible for the  in abundance of
resistant bacteria.

15. *
1. Bactericidal: antibiotics destroy bacteria. E.g.
Penicillin is a bactericidal.
2. Bacteriostatic: antibiotics prevent the multiplication of
the bacteria. The hosts own immune system then
destroy the bacteria

16.  Inhibition of bacterial cell wall synthesis
 Disruption of the cell membrane causing changes
in permeability
 Inhibition of nucleic acid synthesis & replication
 Inhibition of protein synthesis
 Inhibition of specific enzymes found in bacterial
cell wall