Sampling is to be performed by your staff and is out of the control of Biotech Laboratories. Please ensure your staffs are informed of the following requirements. All documents referred to are available from the laboratory. When sampling, it essential that you do the following:
- Ensure that the sample taken is representative of the source under investigation. This may require multiple samples to ensure you have a statistically relevant representation.
- The collection technique must ensure that the sample is not compromised during the collection procedure. Do not use eskies or courier bags as sample containers as these are reused and not sterile.
Sample size and containers for different analyses
Chemical analyses: Contact the laboratory and specify the analyses to be performed and we will advise the containers or amount of sample required. This information is provided to us by the Australian Government laboratory, National Measurement Institute.
Microbiological analyses: Ensure you have on file the applicable documents from the following list. These can be obtained by contacting the laboratory.
- Sample size requirements, Collection and TAT - Food Samples
- Sample size requirements, Collection and TAT - Water Samples
- Sample size requirements, Collection and TAT - Miscellaneous Samples
Water sampling: Direct collection into sample bottle or, only if flow is excessive, transfer into a sample bottle from a collection vessel. Bottle only to be uncapped during sample collection and at no other time. Do not rinse.
- Potable water: Request a copy of Procedure 48
- Legionella: contact the public health unit in your area for guidelines and procedure
Food and food products:
It is optimal to supply the food in the same container or packaging as it will be presented for sale or consumption. Fresh loose food products such as fruit and vegetables are to be aseptically transferred to sterile or clean/dry containers which are sealed and labelled clearly.
Biosolids, soil and other environmental samples: Samples are to be aseptically transferred to sterile or clean/dry containers which are sealed and labelled clearly.
Air samples / Exposure Plates: Agar plates are exposed to the required volume of air with the lid removed. Immediately replace the lid after exposure without touching the agar surface. Seal the plate with adhesive tape. A small amount on opposite sides is sufficient.
Swab samples: Ensure you have on file
- Surface Swab collection procedures
All containers are to be labelled on the side of the container and never on the lid.
The minimum labelling requirements are:
- Company or facility name
- Full sample identification *
* Note that in some cases, such as swab samples, the area available on the container is not sufficient to record the full sample identification. In these cases it is acceptable to record the sample number on the container as long as this number is matched on the Analysis Request Form where the full identification is recorded. Ensure that the numbers 6 and 9 are written with an underscore ( 6 / 9 ) so that they cannot be misread.
Agar plates are labelled on the base and never on the lid.
Sample storage and transportation requirements
All samples are to be stored and transported to the laboratory as per the following guidelines:
Water for Legionella testing: Ambient, if it will be processed within 24 hours. Refrigerated, if the samples will be received and processed within 48 hours.
Water for all other microbiological analyses: Refrigerated and transported on the same day as collection so that the samples are processed within 24 hours.
Frozen food: Frozen (this includes samples for histamine testing)
Refrigerated food: Refrigerated
Room temperature stable food: Ambient
Air samples: Refrigerated and transported on the same day as collection so that the samples are processed within 48 hours.
Ambient or refrigerated and transported on the same day as collection so that the samples are processed within 24 hours.
Analysis request forms
All samples submitted must be accompanied by an Analysis Request Form. This form must detail at least the following:
- Full client or company name. The company address is required if there are multiple listings for the company in our computer system.
- The full identification of each sample as it is to appear on the final laboratory report.
- Clear indication of what analyses are required for each sample.
Provision of other relevant information
Any further information that is relevant to processing samples or reporting results can either be emailed to the laboratory or noted on the Analysis Request Form. This information will then be added to your company profile.
To enable mixing of the sample in the laboratory before processing, leave ample air space (at least 2.5cm) above liquid level. Collect samples that are representative of the water being tested. Keep container closed until ready to sample. Do not contaminate inner surface of lid. Flush sample ports. Then fill container without rinsing using aseptic technique to avoid sample contamination. Close container immediately.
It is important to ascertain from the client what they require to be tested. For example, analysis of a drinking water sample from a residence utilizing a rain water tank, or storage tank from a bore, would require the sample to be collected from the tap used for obtaining the water directly for use. This sample will then test the whole system, direct water supply, pipe work, collection system and storage tank. If a mains water sample was required, it must be ensured that the tap utilised is connected directly to the mains supply and does not connect to a cistern or storage tank.
Open tap fully and let water run to waste for 2 to 3 minutes or sufficient time to allow clearing of the service line. Leave tap running, reduce water flow rate if necessary to avoid splashing or loss of additives and fill container.
If well water is to be collected and a hand pump is fitted, pump water to waste for 5 minutes before collecting sample. If a mechanical pump is fitted collect sample from a tap on the discharge, run tap to waste for 2 to 3 minutes before collecting sample. If a pump is not fitted collect sample directly from well by lowering a sterile container with a weight attached to the base.
When collecting a first catch sample it is essential that you realise that you only want the water associated with the tap, thermostatic mixing valve (TMV) and pipework between the outlet and the main water line. This is generally only about 20mL of water. When collecting a first catch sample it is useless to collect a 100mL sample as you are collecting a first catch and then diluting that sample with the water from the main line. To collect a first catch sample fill just under half of a 70mL sterile container.
When collecting a flush sample it is essential that you first remove the water associated with the tap, TMV and pipework between the outlet and the main water line. The volume of water can vary but running the tap for one minute should generally be sufficient to remove this water.
When collecting samples directly from a river, stream, lake, reservoir, spring or shallow well collect a sample which is representative of the source of supply. It is preferable to collect samples from such a position that equates to the draw off point. Take samples by holding bottle by its base and plunging it below the surface. Then turn the bottle slowly upward and the mouth is directed towards the current (if no current, move slowly away from hand). Where samples are collected from a boat, sample from the upstream side of vessel. If it is not possible to collect samples in this manner, attach a weight to the container and lower it into water. In any case avoid contact with the bank or stream bed.
Stream waters sampling locations will be decided upon based on the purpose of the study. It is preferable to collect a baseline sample, upstream from the study area. Where investigation of the dispersion of waste waters is to be analysed, preliminary cross section studies may be necessary to determine completeness of mixing. Where a tributary stream is involved, select a sampling point near the confluence with the main stream. Samples may be collected from a boat or from bridges near critical study points. Sample collection is as described in Section 2, above. Choose a sampling frequency which is reflective of the stream conditions. For example, to evaluate waste discharges, sample every 4 to six hours and advance the time over a 7 to 10 day period.
Sample locations should be selected based on the reason for analysis. Where discharge water contamination is suspected, samples should be collected adjacent to drains or natural contours that would discharge storm water or septic waste. Collect samples in a swimming area at a uniform depth of 1 meter. Sampling of the shallow water may also be required because of the exposure of young children at the water's edge. Samples should be collected at the peak bathing time, usually on weekends. Sample collection is as described in Section 2, above.
When using the sampling cocks in the filter return or discharge lines, run to waste for 3 to 5 minutes before collecting sample. Where samples are to be collected directly from pool or spas sample where water depth is approximately 1 meter. Use a second sterile container to collect sample. To collect sample hold the second container (with lid off) upside down and plunge into water to a depth of approximately 20cm. Then invert container to fill and remove. Decant the sample into the container with Sodium Thiosulphate Na2S2O3.
Collect sample by aseptically scraping sediment into sterile container. Sampling frequency for reservoirs and lakes may be related to seasonal changes in water temperature. Sludges from water and waste water treatment purposes should be collected as directed by the client.
Fill container directly from free flowing water in tower basin by holding open container at approximately 45 degrees and immerse in water. Filling slowly to ensure there is no loss of Sodium Thiosulphate Na2S2O3, if present. When collecting from a sampling cock or discharge pipe, run to waste for sufficient time to allow removal of "dead" water from tubing. Minimal volume is 10mL. A preferred sample volume is 100mL.
The following table gives the sample size required for different analyses and water types. Primary recreational water is described as water used for bathing where immersion of body occurs. Secondary recreational water is described as water used for wading only.
A representative sample that is appropriately transported to the laboratory is the first priority in the microbiological or chemical examination of any food product. Laboratory results and their interpretation are valid only when appropriate samples are examined. Samples must be representative of the entire lot of material under evaluation, must be the proper type for the determination to be made, and must be protected against extraneous contamination and improper handling. This is especially due to temperature during holding and transportation to the laboratory, for example microbiological growth can be significant above 10 ºC and samples for histamine and sulphur dioxide that are not help and transported in a frozen state can yield inaccurate results.
Refrigeration must be provided to prevent destruction or growth of organisms in a sample. Unfrozen samples, except food products that are stable at room temperature, must be refrigerated, preferably at 0 to 4.4 ºC, from the time of collection to receipt at the laboratory. Samples collected while frozen should be kept solidly frozen. As a general rule, samples should be examined within 36 hours of sampling whenever possible. Perishable items that cannot be examined within 36 hours should be frozen or retained at refrigeration temperatures, depending upon the type of product, reason for analysis, and type of analysis being performed. Samples and associated request forms must be clearly and completely identified.
Reference: Compendium of methods for the microbiological examination of foods 4th Ed 2001
The size of the area to be sampled greatly effects the quality of the result. We recommend an area no greater than 25 sq cm (5cm x 5cm template). Some laboratories recommend a 100 sq cm area, considering the surface area of a standard swab is approximately 1 sq cm, it is impossible to accept that it can "pick up" all the bacteria from a 100 sq cm area. What, in fact, will happen is that only a proportion of the bacteria will be collected on the swab, the rest will be smeared around the sampling area, the final laboratory result will be falsely lower that the true value.
The sampling of food contact surfaces is often required as a monitoring process of the cleaning/sanitising for the Food Safety Plan. In these cases there is no requirement or necessity to analyse for bacteria pathogens such as Salmonella, Listeria, Staphylococcus etc., or the presence of faecal coliforms or E. coli. To evaluate the efficiency of the sanitisation process of a surface a standard plate count of a set sized area will adequately provide the necessary information. A result of less than 6 bacteria per square centimetre of surface (expressed as CFU/ sq cm) is regarded as an acceptable result for a properly cleaned and disinfected surface. Applicable surfaces are large cutting knives, benches, plates and storage containers. Sample collection should not be performed immediately after cleaning/sanitising, it is more useful to sample just prior to use.
There are no standard acceptable levels for bacteria or fungi counts on air-conditioning surfaces or in air-conditioning ducts. Companies who perform these analyses usually also collect air samples to assist in the evaluation. In-house guidelines are generally used based on historical laboratory results
Before the introduction of simplified air sampling apparatus, agar drop plates were used to evaluate air-borne bacteria and/or fungi. This method used the exposure of the agar surface for a number of hours. Drop plates are now generally regarded as a useless means to evaluate air-borne micro-organisms, this is because bacteria can remain suspended in the air tens of hours without falling onto a surface. In general the only micro-organisms that will appear on a drop plate are those attached to dust particles.
The examination for air-borne bacteria, fungi and thermoactinomycetes can be performed by collecting air samples onto 0.45um or 0.2 um filters (one filter is required for each analysis requested) and forwarding these to the laboratory. Alternatively if using an air sampling apparatus that forces a volume of air onto the agar surface, the specific agar for each analysis can be obtained from the laboratory. Agar strips, as used in the Biotest air sampler, require a strip to be used for bacteria and a second strip to be used for fungi. Thermoactinomycetes can not be analyses from Biotest strip samples as the specific media required is not available in the Biotest strip range.
When submitting air samples collected by any method it is essential that the volume of air sample be recorded and documented on the sample and/or the supplied analysis request form.
Samples must be labelled on the side of the container and never solely on the container lid. The minimal sample label will include:
• Sample identification with code or name to enable accurate identification of source
• Date and time of collection
• Clients' or organisation's name