• FAQs

    Redipor prepared media

    Q: How do I melt bottled agar?

    A: Ideally in free steam at 100°C. Alternatively in a waterbath just less than boiling.
    It is not recommended to heat bottled agar in a microwave oven or on a hot plate because there is a risk of serious injury from broken glass and hot agar.

    Q: What does the use by date mean on Redipor® prepared media?

    A: For Redipor media the Use By date is the last day on which the medium should be inoculated or exposed. Any incubation period that is normal for that product may begin on that day. For example a 14 day sterility test in TSB or a 5 day incubation for a TSA settle plate.

    Q: Once we have opened a pack of irradiated plates, how quickly should they be used?

    A: The final wrap of irradiated plates should be removed at the point of use and it is then a question of risk. For example in a grade A isolator it might be reasonable to rewrap a part pack of plates for use in the next session. If all the exposed plates show no growth it is a reliable result. However if one or more colonies appear on the plate it might not be possible to know during which session the contamination occurred and the OOT investigation becomes more complicated and expensive.

    Q: Which culture media should I use?

    A: We can provide a great deal of information so that the user can make an informed choice. Please phone or email with details.

    Q: What does triple wrap packaging mean?

    A: Not as obvious as it might sound. 3 layers of wrap between the agar plate and the outside world, of course, but Redipor can offer at least 3 different ways to achieve that with our standard product range. We then have even more bespoke solutions to meet individual needs. Let us know how and where you want to remove the layers and we can find the best solution.

    Q: Why might I want gamma irradiated media?

    A: The sterility of the packaged medium is assured and all but the outer layer of packaging is also sterile. Thus the risk to the environment to be sampled is greatly reduced. There is an additional benefit that the additional packaging and process extends the room temperature shelf life. This can be sufficient reason for small or irregular users to prefer irradiated.

    Q: Are there any benefits to dip slides?

    A: Dip slides can be less sensitive than contact plates or swabs and they often have less stringent QC release criteria. However there are circumstances where they have real advantages.
    They are convenient and easy to use by the relatively less skilled.
    They are ideal for testing water tanks and hygiene monitoring in food preparation and similarly clean but not aseptic environments. Most importantly they are ideal for field use because they are self contained and the slide can be incubated and assessed without opening the device.

    Q: What is the maximum exposure time for settle plates?

    A: Settle plates are used to monitor the level of viable particles in the environment through a process of passive air sampling. A viable particle settles on agar plates at a rate dependent on its characteristics and the airflow in the environment.
    EU GMP Guide Annex 1 has recommended that 90mm settle plates can be exposed in cleanroom environments for up to 4 hours. However, agar plates may dry out during long exposures where the rate of air exchange is high. So, it might be necessary to use deep filled settle plates, or replace the settle plate after a shorter time to ensure satisfactory growth promotion after exposure.

    Q: Is it OK to store prepared media in the fridge?

    A: The storage condition for the majority of our prepared media is Ambient not exceeding 25ºC, the exception being a couple of very specialist products. We have never specified storage in a fridge for our general media as this causes excessive condensation and can result in a very wet agar surface. This makes the product impossible to use.

    Q: We need a specific or bespoke prepared media type, can Cherwell help?
    A: Our Redipor Prepared Media range is extensive and isn’t all included in the price list, please contact our office to discuss your specific requirements. Also, due to flexibility within our manufacturing process, we are able to produce bespoke solutions if required.

    Q: What is the difference between general purpose and selective growth media?

    A: General purpose media have nutrients that support the growth of most non fastidious culturable microorganisms. Selective growth media contain components that will inhibit the growth of some types of microorganisms, while supporting the growth of others.
    General purpose media, such as Tryptone Soya Agar, are used to produce total counts. While selective media, such as XLD for Salmonella species, are used to test presence/absence of specific types of microorganism.

    SAS air samplers

    Q: How much air should we sample?

    A: Typical requirements suggest 1,000 litres per air sample in high risk areas, such as: grade A filling lines, grade B clean rooms, operating theatres etc. As the criticality of the area reduces, the sample size can be reduced. The aim is to achieve a representative sample; so where higher counts would be expected, a smaller sample produces a more realistic number of cfu to count.

    Q: Should I use contact plates or Petri dishes for environmental air monitoring?

    A: SAS samplers were originally designed for Contact plates, however, a Petri dish option has been available for a number of years. It is really a personal choice, although this should be decided at time of purchase, as the sampler will be specifically configured for the plate type chosen. There are advantages for each version and we would be happy to discuss your specific needs.

    Q: Can I autoclave my SAS sampler?

    A: No, do not put your SAS sampler in a steam autoclave. The only part that can be autoclaved is the drilled head. The unit can be wiped with alcohol wipes to decontaminate it. The only other exception is the SAS Pinocchio, parts of which can be autoclaved.

    Q: How frequently should my SAS air sampler be calibrated?

    A: Cherwell Laboratories recommends every 12 months and we will send a reminder for the month it is due. For some situations local procedures demand more frequent recalibrations so Cherwell is happy to offer tailored recalibration date labelling and reminders on request.

    Mar Cor Decontamination

    Q: Should I rotate cleanroom disinfectants?

    A: Not necessarily, but it might be best practice in most situations as many disinfectants leave a residue which needs to be removed.
    Alcohols leave no dry residue, but might encourage the formation of spores resistant to alcohol. Chlorine-based disinfectants tend to be corrosive and leave a residue, but will kill spores with sufficient contact time. Hydrogen peroxide alone, or with peracetic acid, kills spores and leaves no dry residue but is relatively expensive and the vapour has limits for operator exposure. So, rotation with intermittent use of sporicide might enable the most effective bio-decontamination at reasonable cost.

    Q: How long does a Dry Fog 2 cycle take?

    A: The processing cycle is made up of 3 phases – fog dispersion, exposure and venting.  Phase 1 and 3 will be dependent on clean room/suite size and complexity.  The fog dispersion phase will take 15 mins – 2 hours, exposure will then take 1 hour and the final venting phase will take 30 mins – 2 hours.  Therefore, total process time is only 2-5 hours and there is no need for cleaning of surfaces afterwards.

    Q: What are the residuals?

    A: The potential residuals from a Dry Fog process, using Minncare cold sterilant are water, oxygen & Acetic acid.  However, the residual levels are so low that there is no measurable residue left on surfaces.

    Q: What services are required to run Dry Fog?

    A: The Dry Fog 2 system only requires compressed air.  The system needs approximately 70 litres of compressed air per minute per Dry Fog nozzle at a minimum 5 Bar pressure.

    Q: How many Dry Fog nozzles do we use?

    A: If you provide us with your clean room layout, we can advise on how many Dry Fog units are needed and their positioning as well as how many nozzles per machine and the orientation.

    Q: Is Minncare compatible with clean room materials?

    A: Minncare cold sterilant is compatible with the majority of materials that are commonly found in pharmaceutical cleanrooms.  We have material compatibility reports available that summarise test results.


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