Information on Sample Collection


Quick Nav - Water Sampling | Food Sampling | Surface Swab Sampling | Air Sampling | Sample Identification | Sample Transportation

 

Water Sampling Procedures

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.

 

Potable waters

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.

 

Potable waters - Legionella Testing

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.

 

Raw Potable or Raw Non-Recreational Waters

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.

 

Surface Waters


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.

 

Recreational Water - Not Swimming Pools

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.

 

Swimming and Spa Pools

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.

 

Sediments and Sludges

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.

 

Cooling Towers

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.

 

Sample Size

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.

 

Table 1

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Food Sampling

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

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Surface Swab Sampling

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.

Food Surfaces

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.

Air-conditioning surfaces

There are no standard acceptable levels for bacteria or fungi counts on air-conditioning surfaces or in air-conditioning ducts. Companies who perform these analysis usually also collect air samples to assist in the evaluation. In-house guidelines are generally used based on historical laboratory results.

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Air Sampling

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.

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Sample Identification

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

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Sample Transportation

All samples are to be held in an esky or similar insulated container with one or multiple ice bricks. Samples should be returned to the laboratory for processing immediately after collection.