Research Question
What is the effect of different shampoos on the growth of bacteria on different hair types?
Materials
- 9 Petri dishes
- Agar gel
- Cotton buds
- Three different shampoos
- Test tubes
- Droppers
- Test tube rack
- Labels
Independent variable
Different types of shampoos
Different hair types
The condition of the different hair types.
Dependent variable
The rate of growth of bacteria on Petri dishes
The amounts of bacteria from different hair types.
Types of bacteria on the Petri dishes
The size of bacteria in different hair types.
Controlled variables
The brand of shampoos used
The volume of the shampoos
The amount of bacteria on the Petri dishes
Procedure
- Rub your hands thoroughly in the first hair type (the dry hair) to ensure that the required bacteria are attached to the hands; 5-6 rubs will be sufficient.
- The bacteria collected should be smeared on the first agar plate 5-6 times and labeled correctly.
- Add three drops of the shampoo to the Petri dish containing smeared bacteria.
- This procedure should be repeated for the other remaining two hair types.
- Different types of shampoos should be collected and put in their respective test tubes.
- All the shampoos should be put under the same temperature in their respective test tubes.
- The bacterial cultures should be removed from the incubators at the same temperatures.
- Measure 2 ml of shampoos to be added to the growing bacteria on the Petri dishes.
- The volume of the shampoos to be added to the growing bacteria has to be kept constant throughout the experiment.
- Each test tube should have its own dropper to prevent mixing of the contents in the test tubes.
- All test tubes containing the three different shampoos should be well labeled.
- The Petri dish plus its contents should be kept in the incubator for them to start growing.
- All the Petri dishes containing the growing bacteria should be well labeled to avoid mixing them up and creating confusion.
- Place the first Petri dish containing bacteria undergrowth and add 2 drops of the first shampoo (Pantene) to the bacteria.
- Place the second Petri dish containing bacteria and add in it the same volume of a different shampoo (head and shoulders).
- Place the third Petri dish containing growing bacteria and add drops of a third shampoo (Baby Johnson) like the other two. The same volume of the shampoos should be maintained for the other remaining samples.
- After adding Shampoo to the Petri dish the dropper should be returned to the respective test tube.
- Repeat the same procedure for the other two hair types, normal and oily.
- Take all the Petri dishes plus their contents back into the incubator at a suitable constant temperature and pressure to facilitate their growth.
- After a predetermined duration of time, observations should be made in the Petri dishes.
- Observe and record the growth of the bacteria on the different Petri dishes.
- The different shampoos would have an impact on the growth of the bacteria from the three different hair types, and this can be recorded in terms of the differences in growth in the respective Petri dishes.
Data Collection
Recording raw data
Table 1.
The uncertainties at this stage concerned the number of bacteria that were counted from the Petri dishes. In some cases, the number was estimated.
Some people had washed their hair a day before and some had applied oils and chemicals that might have interfered with the number of bacteria present in their samples. These include things like sprays, curlers, and hair gels which may have either increased or reduced the number of bacteria in their hair.
Some bacteria because of being too small, they could not be counted after the two days period.
While adding the shampoos on the Petri dishes, the number of drops might have differed therefore affecting the number of bacteria.
The number of types the cotton buds was rubbed on the agar gels might also have affected the number of bacteria.
The process of rubbing hands in the hair might also have affected the bacteria as the concentration of bacteria in the hair cannot be determined. Some parts of the hair had different numbers of bacteria for instance on the surface and deep inside the hair, the concentration differs.
The effect of the chemicals in the shampoos is likely to have killed some strains of bacteria and this is likely to have reduced the number of bacteria counted in some Petri dishes.
There is also a possibility that on the cotton buds bacteria might have been present even before collection in the different hair types. This consequently might have led to inflated numbers after growth on the Petri dishes.
Data Processing
An average number of bacteria = Sum total number of bacteria counted in the samples/ the number of samples.
The average number of bacteria in the different hair types keeps into account that in some cases the number of bacteria was affected by chemicals and other substances that might have been applied before the collection was done.
The numbers also keep into account that during the application of bacteria to the agar gel some might have been lost for instance being stacked on the cotton buds.
Some bacteria were too small and therefore they could not be counted after the two days.
Table 2.
There was notable differences in the bacteria that were observed on the Petri dishes. Some bacteria were large while others and others were small. This can be attributed to the fact that there was a collection of different strains of bacteria which differ in size and shape. Color differences were also evident because of the effect of shampoos which had different colors.
Conclusion and Evaluation
Conclusion
From the experiment, it has been demonstrated that indeed the type of hair affects the concentration of bacteria. This has been evident in the way some hair types like the dry and the normal types have more bacteria than the oily hair types which have been noted to have a fewer number of bacteria. Oily hair types might be having other factors within them that do not allow the growth of bacteria in them. Indeed research has shown that Head & shoulder shampoo helps to manage dandruff by reducing proliferation of bacteria on the scalp. Pantene and Baby Johnson also have an effect on growth of bacteria. The effect of the three shampoos varies with the hair type. (Campana 2006)
The different shampoos also have been shown to have influence on the growth of bacteria. Pantene shampoo has been depicted to be the one that promotes growth of bacteria in both dry and normal hair types. From this experiment people can analyze for themselves and find out which shampoo suites their specific hair types.
Evaluation
Limitations and sources of errors
The procedure can be said to be reliable for determining the effect of shampoos and different hair types on the growth of bacteria.
The limitations of this procedure included the handling of materials like the droppers whereby they were releasing more shampoos than required thus interfering with the overall number of bacteria in the Petri dishes.
The collection of the bacteria from the different hair types was also a weakness in the sense that the rubbing was done all over and may be the bacteria were colonial to some spots in the hair. This means that such types of bacteria were not sufficiently collected and hence this affected the overall counts after growth period of 2 days.
The procedure did not have a mechanism of ensuring that all the bacteria collected in the different hair types were transferred to the agar gels for growth. Possibilities are high that some bacteria remained on the cotton buds and thus their numbers were left out in the counts after the growth period in the Petri dishes.
The time for performing the experiment was also limiting as it did not allow for more samples which could lead to more reliable results. The growth period of the bacteria also limited the number of bacteria that could be observed. Some bacteria were too small to be counted.
The issue of some bacteria being minute and not being counted is also a weakness that has to be mentioned in this procedure.
There was no sterilization of the cotton buds before collection of bacteria and this might have altered the expected results since some bacteria might have been presents on the cotton buds.
The chemical composition of some shampoos might have killed some bacteria hence altering the number of bacteria after growth consequently leading to no counts and reduced counts.
Suggestions for further investigations
For better and more accurate results in this experiment adjustments should be made on the apparatus for instance instead of using droppers graduated measuring cylinder should be used to give out the same volumes of the shampoo.
Given additional time more samples of hair types could be added to the procedure to increase the reliability of the results. During the transfer of the bacteria to the agar gels from the cotton buds care should be taken to ensure that adequate rubs or smears are made to avoid the bacteria from going to the agar gel and then back to the cotton buds. This can improve on the number of counts after the growth period as most of the bacteria would remain on the Petri dish.
Future arrangements should be made such that the bacteria are given more time to ensure that all of them are included in the count.
All future improvements should be focused on maximizing on the number of bacteria collection from the different hair types such that during the counting after growth correct figures are recorded.
A more elaborate procedure can be pursued after this experiment to investigate the number of bacteria that can be killed by different shampoos so as to provide consumers with reliable information concerning the best choice of shampoos for their specific hair types.
References
Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill.
Campana, R., Scesa, C., Patrone, V. 2006. Microbiological study of cosmetic products during their use by consumers: health risk and efficacy of preservative systems. Letters in Applied Microbiology. 43: 301-6.