Antimicrobial agent : disinfectants : time of contact between bacteria and disinfectant agent : effective concentration antiseptics : Colgate, Listerine and Dettol : zone of inhibition (MIC)

1. Results
8.1 Disinfectants- Time of Contacts
Disinfectants agent is a chemical drug that can kill bacteria especially vegetative
bacteria. The growth of E. coli bacteria on nutrient agar plate which contain Dettol
agent with different time of contact s shown in Diagram 1. From the diagram, there are
heavy growth of bacteria with numerous of colony bacterial on the section of zero time,
and there is moderate growth of bacterial can be seen on the 5’ minutes section
whereas there no such growth on bacterial from 10-minute section to 45-minute section
which there are none colony that can found. This can conclude that Dettol agent is act
as disinfectants to kill all the E. coli bacterial in 10 minutes.
8.2 Disinfectants- Effective Concentrations
Antiseptic is an agent that inhibits the growth of bacteria without destroy and killing it.
From Diagram 2, there six tubes with different concentration of solution that Dettol
agent mixed with saline which are 10-1
, 10-2
, 10-3
, 10-4
, 10-5
, 10-6
. Saline is a sodium
chloride solution. Saline solution is an isotonic solution which contain concentrations of
salt vary from low to normal to high. After 48 hours, the intensity of solution in tubes
with 10-1
concentration is chalky colour, while the tubes with 10-2
and 10-3
concentration
of solution is turns cloudy then the tubes with 10-4
, 10-5
and 10-6
concentration of
solution is in slightly cloudy colour. This situation means that there is heavy growth of
bacteria in solution of 10-1
tube, moderate growth of bacteria in the tubes with 10-2
and
10-3
concentration of solution and light growth of bacteria in the tubes with 10-4
, 10-5
and 10-6
concentration of solution. This is because serial dilution method decreases the
concentration of E. coli bacteria in solution leads to the growth of bacteria decreases
from 10-1
to 10-6
solution as the Dettol agent and saline are inhibits the growth of E.
coli bacteria.

2. 8.3 Antiseptics- Zone of Inhibition
Minimum inhibitory concentration (MIC) is meant that the lowest concentration of an
antibiotic will stunted the growth of E. coli bacterial or calculate the zone of inhibition
of bacterial. From Diagram 3, zone inhibition of Listerine mouthwash on E. coli bacteria
which is 2 mm which is excluded the diameter of sterile disk which is 5mm and this is
smaller than Colgate mouthwash which is 22mm. Thus the Listerine mouthwash is
sensitive to the E. coli bacteria which is the zone of inhibition is smaller than 8mm is
determined out Listerine mouthwash is effective against the E. coli. Whereas the
Colgate mouthwash is resistant or ineffective against the E. coli bacteria as the zone of
diameter is larger than 12mm. From Diagram 4, zone inhibition of Listerine mouthwash
on sterile mouth swabs bacteria which is 8 mm which is excluded the diameter of sterile
disk which is 5mm and this is larger than Colgate mouthwash which is 7mm after
excluded the disk. Thus the Listerine mouthwash and Colgate mouthwash are sensitive
to the sterile mouth swabs bacteria which is the zone of inhibition is smaller and equal
to 8mm is determined out both mouthwash are effective against the sterile mouth
swabs bacteria.
Conclusion
Antimicrobial agent are acts as inhibitor and destructor of bacteria. disinfectant agent
is a strong agent to kill all the bacteria and antiseptic is an agent that inhibits the growth
of bacteria. From experiment, we can conclude that effect of disinfectants are depend
on the time of contact with bacteria which is Dettol agent killed all the E. coli in
10minutes. The concentration of E. coli bacteria in solution affect the effect o f
disinfectants, the lower the concentration of E. coli bacteria in tube, the lower the
growth of E. coli bacteria which is inhibit by disinfectants. Furthermore, the wider the
zone of inhibition, the more susceptible the bacteria against the disinfectant agent.
From the result of the zone of inhibition or the minimal inhitbitory concentration of
disinfectant, Listerine mouthwash is sensitive to the E. coli bacteria whereas Colgate
mouthwash is resistant against the E. coli bacteria. Lastly, Listerine mouthwash and
Colgate mouthwash are sensitive to the sterile mouth swabs bacteria.

3. Reference
1. Books
(a) Laboratory manual and workbook in microbiology eleventh edition
Paul A. Granato, Verna Morton, Josephine A. Morello
Pg85-90
(b) Prescott’s Microbiology 9th
edition
Joanne M. Willey, Linda M. Sherwood, Christopher J. Wolverton
Published by Mc Graw Hill
pg 742