Practice Assignment 04
Measuring mouthwash activity
This assignment could also test toothpastes, skin creams, deodorants, antiseptics or disinfectants. For testing thick suspensions a slight modification of the procedure is necessary. Instead of using soaked paper discs, cut wells in the inoculated agar plate using a sterile 5 mm cork borer. Place the pieces removed in disinfectant for disposal and resterilise the borer. Then fill the wells with the appropriate test samples – one brand at three dilutions, or three brands.
The aseptic techniques needed should be demonstrated, and then practised by the students before they use live micro-organisms.
A suitable bacterial culture should be prepared in advance. A culture of Bacillus subtilis, Micrococcus luteus or Escherichia coli (K12 strain) should be inoculated in nutrient broth and incubated at 25 °C at least 48 hours before it is needed.
Health and safety note
Agar plates should not be opened after incubation. If necessary, extra tape should be used to seal the plates before examination.
Apparatus and reagents
- Standard Procedure:
- SP 0004:2005 A method for evaluating the effectiveness of anti-microbial products
- 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)
- forceps
- marker pen to write on glass
- adhesive tape
- incubator set at 30 ±1oC
Test Specimens
- 3 different brands of mouthwash at the manufacturer’s recommended concentration, labelled A to C.
- 3 different concentrations of the same mouthwash, for example:
- A - manufacturer’s recommended concentration,
- B - diluted to half strength with distilled water
- C - diluted to quarter strength with distilled water;
Note: Some groups should use the first trio, others the second trio.