Standard Bacteriological Sampling Protocols
Standard Protocols for Bacteria Sampling
- To collect a portion of material small enough in volume to be transported conveniently and yet large enough for analytical purposes, while still accurately representing the material being sampled. The relative proportions or concentrations of all pertinent components, should be the same in the samples as in the material being sampled, and the sample should be handled in such a way that no significant changes in composition occur before the tests are made.
- Samples are potentially hazardous so gloves and other personal protective wear should be worn when sampling. When sampling for bacteriological parameters take extra care not to introduce contaminants.
- Use sterile swabs. Many have a moisture pad in the end or contain liquid in a tube to keep the sample moist after sampling and during shipment to the lab.
- Remove the outer packaging of the sterile swab.
- It is often recommended to follow the instructions on the outer packaging to moisten the swab before sampling to help improve collection efficiency. The swab may require crushing a capsule to release liquid into the pad or the pad may be pre-wetted. Push the swab into the wetted pad to moisten it slightly.
- Swab the area of concern. Wipe the area with the wetted swab to remove surface material and potential bacterial growth. If results are required in colony forming units per square inch or square centimeter, then carefully measure the area swabbed or use a template of known area and report this area to the lab.
- Return the swab into the tube.
- Remove a one or two square inch piece of suspect material and place it inside of a clean plastic bag.
- Collect samples for microbiological examination in non-reactive borosilicate glass or plastic bottles that have been cleansed and sterilized. Many laboratory suppliers carry pre-cleaned and pre-sterilized containers, with and without chlorine neutralizers.
- Use chlorine neutralizers (e.g. thiosulfate) when sampling potable waters.
- When the sample is collected, leave ample air space in the bottle (at least 2.5 cm) to facilitate mixing by shaking, before examination. Keep sampling bottle closed until it is to be filled. Do not contaminate the inner surface of stopper or cap and neck of bottle. Fill container without rinsing. Replace stopper or cap immediately.
- Open tap fully and let water run to waste for 1 or 2 minutes or for a time sufficient to permit clearing the service line. Reduce water flow to permit filling bottle without splashing. If tap cleanliness is questionable, choose another tap.
- Collect between ten (10) to fifty (50) representative grams of soil and place it inside of a clean plastic bag.
- Samples must be shipped to the laboratory for overnight delivery as it is recommended to begin analysis within 24 hours from sampling.
- If the samples are sent on Friday, it is usually best to ship for arrival on Saturday, not Monday. It is advisable to use a shipping company that offers tracking of packages.
- Place samples within a cooler with ice packs. Wrap samples in bubble wrap to prevent them from coming in direct contact with ice packs. Make sure that samples are well packed and protected to prevent damage during transport.