Dextrose Sabouraud Agar with Neutralings. Triple Wrapped. Irradiated

Description

Its selectivity is due to a low pH and a high glucose concentration, which together with incubation at a relatively lower temperature (25-30 °C) favours the growth of fungi while discouraging that of bacteria.

The mixture of peptones employed has been selected to provide the fungi with all their nitrogen requirements.

The addition of the neutralizing agents TLHTh (Tween 80 - Lecithin - Histidine - Sodium Thiosulphate) may inactivate a variety of disinfectants.

• The combination of lecithin, polysorbate 80 and histidine neutralizes aldehydes and phenolic compounds.
• The combination of lecithin and polysorbate 80 neutralizes the quaternary ammonium compounds.
• The polysorbate 80 neutralizes hexachlorophene and mercurial derivatives.
• Sodium thiosulphate neutralizes halogen compounds.
• Lecithin neutralizes chlorhexidine.
• Histidine neutralizes formaldehyde.

Technique

Contact plates are used in the microbiological control of disinfection and cleaning of surfaces. They act simultaneously as a sampler and incubation culture medium without the need for any other intermediate steps.

The plates come in a form appropriate for this function and can be used with different culture media depending on the type of microbe that needs to be controlled. On average the plates provide a contact surface of approximately 25 cm².

To use, remove the cover and gently press the culture medium on the surface to be controlled, ensuring contact between the two surfaces. The contact plate is removed and covered with the lid to prevent air contamination. It is advisable that the lid is secured with adhesive tape and the bottom labelled with the sampling data (place, date and time).

If the sample surfaces are rough, the contact plates will not make good contact, even when the pressure is increased. In these cases it is advisable to delineate a sample surface area of 25 cm² and rub this area vigorously with a wet sterile swab and then rub the swab over the contact plate.

If verifying the effectiveness of a cleaning or disinfection process, contact plates should be used within two hours after the end of the process, ensuring that the sample surface is dry. It is advisable to always include positive controls, sampling the area before disinfection or dirty areas beside the disinfected area.

The technician will determine the frequency of sampling and disinfection according to performance criteria. Apply the agar directly onto the surface to be monitored ensuring that the pressure is distributed over the whole plate for 10 seconds. Clean the surface where the sample was collected in order to remove any traces of agar.

The inoculated plates are incubated at 32-35 °C for 24-48 hours and examined daily. For fungi, the incubation is carried out at 22-25 °C for 5 days and examined daily.

Note: Contact plates are used for monitoring the microbiological contamination of surface and air inside cleanrooms, isolators, RABS, food industries and hospitals. The double/triple irradiated wrapping ensures that the package itself doesn't contaminate the environment as the first wrapper is removed just before entering the clean area.

Physical/chemical control

Microbiological control

Inoculate 10-100 CFU per unit according to the harmonized European Pharmacopoeia.

Aerobiosis. Incubation at 20-25 °C, reading after 24-72 hours for bacteria and 3-5 days for yeasts and moulds.

Sterility control

Check at 7 days after incubation in same conditions.

• AJELLO, L. (1957) Cultural Methods for Human Pathogenic Fungi. J. Chron. Dis. 5:545-551.
• COLIPA (1997) Guidelines on Microbial Quality Management (MQM). Brussels.
• EUROPEAN PHARMACOPOEIA 8.0 (2014) 8th ed. § 2.6.13. Microbiological examination of non-sterile products: Test for specified microorganisms. Harmonised Method. EDQM. Council of Europe. Strasbourg.
• GEORGE, L.K., AJELLO, L. & PAPAGEORGE, C. (1954) Use of Cycloheximide in the Selective Isolation of Fungi Pathogenic to Man. J. Lab. Clin. Med, 44 (422-428).
• HANTSCHKE, D. (1968) Mykosen, 11, (769-778).
• ISO 11133:2014/Amd 1:2018. Microbiology of food, animal feed and water. Preparation, production, storage and performance testing of culture media.
• ISO 16212 Standard (2017) Cosmetics - Microbiology - Enumeration of yeast and mould.
• PAGANO, J. LEVIN, J.D. and TREJO, W. (1957-58) Diagnostic Medium for Differentiation of Species of Candida. Antibiotics Annual, 137-143.
• SABOURAUD, R. (1910) Les Teignes. Masson, Paris.
• USP 33 - NF 28 (2011) <62> Microbiological examination of non-sterile products: Test for specified microorganisms. Harmonised Method. USP Corp. Inc. Rockville. MD. USA.