The Effects of Chlorine on Harmful Bacteria

Group 1-010Leow Shawn Tao (1A413, Leader), Sow Jeng Wei (1O220),

Justin Soh (1P111), Soh Yee Kiat (1P127)

Contents

OverviewMaterials and MethodologyResults and DiscussionConclusion

Rationale

To test the ability of chlorine as an disinfectant while also suggesting an alternative to chlorine, in which is Silver Nanoparticles for our case.

Hypothesis

Chlorine water is ineffective in killing common harmful bacteria.

MATERIALS AND METHODOLOGY

Variables

Controlled Dependent Independent

Dilution of bacteria and silver nanoparticles

Colonies of bacteria left

Type of disinfectant used

Amount of bacteria

Area of collection of water

Materials

Agar PlatesSterile SwabsChlorine Water (Collected from HCI swimming pool)Pipette & MicropipetteCentrifuge TubesNutrient Agar & Nutrient BrothMeasuring CylinderDe-ionized waterE.coli

Materials

METHODOLOGY

DAY 1Pre-Experimental Procedures

Water Collection

Water was collected using centrifuge tubes from the HCI Swimming Pool at the times of 7.50am, 2.30pm and 5.00pm.

Broth and Agar Preparation

For broth, 3.25g were displaced into a bottle and mixed with 250ml of de-ionized water.

For agar, 14g were displaced into a bottle and mixed with 500ml of de-ionized water.

Broth and Agar

DAY 2Preparation

Synthesis and Dilution of Silver Nanoparticles

1. 30ml of sodium Borohydride is poured into a small beaker. This small beaker is then placed into a larger beaker. Ice is placed into this larger beaker. Stir for 20 minutes.

2. 2ml of silver nitrate is then dropped into the sodium Borohydride. 1.28g of polyvinyl alcohol is then added into the mixture and heating is carried out.

Agar Spreading

Using our agar, the agar was displaced onto Petri dishes to half the Petri dishes height. They were then left to solidify for approximately 15 minutes.

Overnight Culture

1. 10ml of our nutrient broth was displaced into 4 centrifuge tubes each.

2. Then, using a bacteria streaking rod, bacteria was displaced into the tubes. The centrifuge tubes were then placed in the shaking incubator for 1 day.

DAY 3Experimentation

Dilution

1. Our aim was to reach 1 x 10-⁶ of bacterial dilution. We filled 6 centrifuge tubes each with 9ml of nutrient broth.

2. Using a micropipette, we displaced 1ml of the bacterial broth from the overnight culture into a centrifuge tube labeled 1 x 10-¹. This procedure was repeated on the tubes labeled 1 x 10-²to 1 x 10-⁶.

Bacterial Spreading

1. The plates were labeled accordingly to their content. Triplication was carried out. Also, 3 controls involving sterile water instead of silver nanoparticles or chlorine water was set up.

E.g.: First plate consisting of 2.30pm water will be labeled as: 2.30pm, C.Water, 1.

Bacterial Spreading

2. Next, according to the labels, 50 microlitres of bacteria and 50 microlitres of silver nanoparticles or chlorine water accordingly was displaced onto the agar dish with a micropipette. This mixture was then spread and sealed with Parafilm, before being kept in the incubator at 36 Degrees Celsius.

RESULTSDAY 4

Chlorine Water

Controls 7.50am 2.30pm 5.00pm

Dish 1 27 N/A 15 33

Dish 2 16 29 15 35

Dish 3 22 26 8 23

Average 21.67 27.5 12.67 30.34

Results of Chlorine Experiment

7.50am 2.30pm 5.00pm Control05

10152025303540

No. of Bacterial Colonies

No. of Bacterial Colonies

Results of Chlorine experiment

7.50am 2.30pm 2.30pm05

101520253035

No. of Bacterial Colonies

No. of Bacterial Colonies

Silver Nanoparticles

Controls Silver Nano 1x10-4

Dish 1 18 9

Dish 2 21 3

Dish 3 21 7

Average 20 6.34

Q&A

Biblography

http://aem.asm.org/content/44/4/972.short

https://mrsec.wisc.edu/Edetc/nanolab/silver/

http://www.medicalnewstoday.com/articles/68511.php

http://natsci.edgewood.edu/wingra/wingra_bacteria.htm

http://www.cbc.ca/news/health/story/2009/07/02/f-ecoli-recall-food-safety.html

http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_p013.shtml

http://proquest.umi.com.libproxy.nlb.gov.sg/pqdweb?index=9&did=2037658811&SrchMode=1&sid=2&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1332762445&clientId=13402

Thank You!