Integrated Assignment 05
Antiseptic wipes
This is an extended activity that requires a high standard of self-organisation and record-keeping. Students should be encouraged, and given time, to carry out the tests at a suitable pace. The activity is as much about scientific thinking, and clear presentation of ideas, as about practical investigations. The aim is to produce a report which could be read and understood by a scientifically literate third party.
Teamwork is important. Performing tests on several brands of wipes both wet and dry, involves much repetition. Students should therefore share tasks between team members. For efficiency, each student (or pair) could focus on one aspect of testing. However, this would still involve repetition, and limit the students’ experience and skills development. One alternative is to allocate responsibility for testing one particular brand while wet, with other students testing the dry version and other brands.
Students need to be familiar with procedures for testing tensile strength, antimicrobial effectiveness, and microscopy techniques. Ideally, they should have tackled the appropriate Practice Assignments in this resource.
Practical tips
Tensile strength
Preliminary testing is recommended to decide what width of sample gives reasonable breaking loads across a range of brands of wipes. Comparative tests must be performed on samples of the same width.
Sticky tape is unlikely to be effective on wet wipes. One alternative is to use a large bulldog clip instead of wrapping the sample around a dowel.
Antimicrobial effectiveness
Students who read the standard procedure carefully may spot an apparent anomaly. Paragraph 2 defines antiseptics and disinfectants. There are two types of wipe commonly available and both may be called antiseptic. However wipes for use on wounds contain antiseptic, and wipes for use on surfaces contain a mild disinfectant. Antiseptics are generally milder than disinfectants, to avoid damaging living tissue.
Either type of wipe can be used for this Assignment.
Students should be able to deduce that they can use 5mm circles cut from wipes in place of assay discs. Instead of testing different concentrations, they can divide the dish into three sectors (wet wipe, dry wipe and control).
Fibre quality
The antiseptic is held between the microfibres, so the porosity of the fibre ‘mat’ is important. The finer the fibres, the more porous the mat, but the more easily it is likely to pull apart. When compiling their results to compare brands, students could check whether there is any correlation between the fineness of fibres and strength of the wipes.
To show how liquid is absorbed, they should also compare the texture of wet and dry wipes.
Health and safety note
Antiseptic wipes are likely to be soaked with ethanol (surgical spirit), so must be kept away from naked flames. In particular, when drying out wipes, direct heat should be avoided.
Apparatus and reagents
- Standard Procedures:
- SP0001:2005 Methods for setting up and adjusting a light microscope
- SP0002-1:2005 Methods of preparing slides for microscopy - Part 1
- SP0004:2005 A method for evaluating the effectiveness of anti-microbial products
- SP0012-1:2005 Comparing the tensile strength of sheet materials
For testing strength
- scissors for cutting test pieces
- clear sticky tape
- metre rule
- clamp and stand
- wooden blocks
- strong thread
- dowel with a pin or pointer attached to one end
- bulldog clip
- 100 g mass hanger
- 100 g masses
- 10 g masses
For testing antimicrobial effectiveness
- sterile apparatus:
- bottle containing 20 cm3 of molten nutrient agar, suitable for micro-organism being tested
- Petri dish
- dropper
- bacterial culture (such as Bacillus subtilis, Escherichia coli, or Micrococcus luteus)
Caution: biohazard - plain antibiotic assay discs (or 5 mm diameter discs of filter paper) – for use as blanks
- forceps
- marker pen to write on glass
- adhesive tape
- • incubator set at 30 ±1oC
For microscopic examination
- microscope with low and high power objectives
- light source (lamp or good daylight)
- various antiseptic wipes
- microscope slides and cover slips
- disposable dropper
- forceps
- mounted needle
- mountant (e.g. DPX Caution: contains xylene [dimethylbenzene] – harmful, irritant) Available form BDH Chemicals (VWR International, Poole, BH15 1TD 01202 669700 www.vwr.com