VRBG TLHTh Agar

Description

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 35 ± 2 °C for 24 ± 2 hours 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.

Physical/chemical control

Microbiological control

Inoculate: 10-100 CFU according to the European Pharmacopoeia and 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ CFU (selectivity) according to ISO.

Microbiological control according to ISO 11133:2014/Amd 1:2018.

Analytical methodology according to ISO 11133:2014/Amd 1:2018; A2:2020.

Aerobiosis. Incubation: 30-35 °C, reading at 24 h (E.P.) / 37 ± 1 °C, reading at 24 h (ISO).

Note: results ATCC 8739/6538/9027 (30-35 °C) and ATCC 8739/25922/19433/14028 (37 °C).

Sterility control

Incubation 48 h at 30-35 °C and 48 h at 20-25 °C: NO GROWTH.

Check at 7 days after incubation in same conditions.

• MOSSEL, D.A.A. (1985) Media for Enterobacteriaceae. Int. J. Food Microbiol. 2:27-35.
• MOSSEL, D.A.A., H. MENGERINK & H.H. SCHOLTS (1962) Use a Modified MacConkey Agar Medium for the selective growth and enumeration of all Enterobacteriaceae. J. Bact. 84:381.
• MOSSEL, D.A.A., M. VISER & A.M.R. CORNELISSEN (1963) The examination of foods for Enterobacteriaceae using a test of the type generally adopted for the detection of salmonellae. J. Appl. Bact. 26:444-452.
• MOSSEL, D.A.A. & M.A. RATTO (1970) Rapid detection of sub-lethally impaired cells of Enterobacteriaceae in dried foods. Appl. Microbiol. 20:273-275.
• PASCUAL ANDERSON, Mª R. (1992) Microbiología Alimentaria. Díaz de Santos, S.A. Madrid.