How do I employ contact plates and settle plates?

Contact plates can be used for the determination of viable counts on smooth, dry surfaces as well as for personnel hygiene monitoring (clothing, gloves or hands). The inner diameter of the standard contact plates is 55 mm. The bottom of the plate has a 1 cm² square grid, which facilitates the counting of grown microbes. The agar surface is convex.

For monitoring of surfaces, which might contain residues of antibiotics or disinfectants it is recommended to use agarmedia supplied with inactivating agents like lecithin, Tween 80, histidine, sodiumthiosulphate or enzymes like beta-lactamases.

Two different types of heipha contact plates are available:

• RT-Media: 10 plates each + desiccant in a bag, storage at 15-25°C, long shelf life, reduced condensation (e.g. Tryptic Soy Contact Agar with LTH-RT; Ref.-No. 234e)
• ICR-Media: 10 plates each + desiccant in a set of three bags, gamma irradiation of the final packaged product, storage at 15-25°C, long shelf life, reduced condensation (e.g. Tryptic Soy Contact Agar with LTHTh-ICR; Ref.-No. 2283e).

The bags of the ICR-contact plates can be removed prior to the use in material locks or the last one after gassing in an isolator (see also ICR culture media).

Sample preparation:

The plates are opened and the agar surface is evenly pressed onto the dry surface for approximately 10 seconds. Afterwards the plates are closed and incubated.

For qualitative or semi-quantitative determination of viable count of bacteria, yeast and moulds settle plates (90 mm) can be used for sedimentation. In the pharmaceutic industry settle plates are positioned at locations posing the greatest risk of product contamination (1).

For passive air monitoring in production areas, which might contain inhibitors for microbial growth it is recommended to use agar media supplied with inactivating agents like lecithin, Tween 80, histidine, sodiumthiosulphate or enzymes like beta-lactamases.

Three different types of heipha settle plates are available:

• standard plates: 10 plates each in a single cellophane bag, storage at 4-12°C (e.g. Tryptic Soy Agar; Art.-No. 307e)
• LI-Media: 10 plates each + desiccant, storage at 15-25°C, long shelf life, reduced condensation (e.g. Tryptic Soy Agar with LTHTh-LI 30 ml; Ref.-No. 030820e)
• ICR-Media: 10 plates each + desiccant in a set of three bags, gamma-irradiation in the final packaging, storage at 15-25°C, long shelf life, reduced condensation (e.g. Tryptic Soy Agar with LTHTh-ICR; Art.-No. 030826e).

Sample preparation:

The opened plates are positioned at critical locations concerning product contamination and left there up to 4 hours. Afterwards the plates are closed and incubated. Following the recommendations of the "Guidance for Industry" (1) the conditions for sedimentation should be validated concerning exposure time and the flow velocity acting upon the agar medium. The conditions should avoid desiccation of the agar medium and allow the detection of low viable counts.

Incubation:

The conditions for incubation may vary for different application areas and can be taken from the adequate guidelines. The conditions mentioned below are received from the "Guidance for Industry" (1) for the pharmaceutical industry.

• Bacteria: aerobic (or anaerobic) 2-3 days at 30-35°C
• Yeast and moulds: aerobic 5-7 days at 20-25°

For determination of anaerobic bacteria it is recommended to use lids of plates with ventilation spacers. This allows a rapid exchange of gaseos atmosphere for example in an anerobic chamber. The settle plates of heipha ICR- and LI-media do not contain ventilation spacers. We offer empty sterile settle plates with ventilation spacers on request (code 67000) in order to exchange the lid before anaerobic incubation.

(1) Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing - Current Good Manufacturing Practice.(September 2004) Pharmaceutical CGMPs br>