Sponge sampling of red meat carcasses

A sponge sample must be taken and tested for Salmonella.  The sponge can additionally be tested for Total Aerobic count and Enterobacteriaceae in place of wet and dry swabbing.  That is: one sample can be taken and analysed for all three tests. It is important to note that wet and dry swabs cannot be used as a sample for Salmonella but can be used for Total Aerobic count and Enterobacteriaceae.

To sample each individual carcass, you will require a sterilised sponge swab (inside a plastic bag to keep it sterile), 10 ml of diluent and (optionally), a permanent marker pen.  These are shown in the photograph below.

 

Photograph 1:  Sterile sponge swab and container of diluent

Most commercial testing laboratories will be able to supply you with these consumables.  

The sponge should have an area of at least 50cm².  The width of the sponge should be no larger than 10cm.  The diluent should be 0.9% unbuffered saline (sodium chloride solution) for lab-prepared cellulose waffle dishcloths.  Commercially-purchased sponge swabs may come pre-moistened in their own diluent.  Pre-moistened swabs are acceptable for use as long as it can be shown any diluent residues which may remain on the carcass after sampling are not harmful to consumers.

Taking care not to contaminate the inside of the bag, manipulate the folded sponge so that the fold points towards the end of the bag that opens.  If required, tip the entire 10ml of diluent onto the sponge.  The diluent will soak into the sponge and moisten it as shown in Picture 2 below.  If the sponges were hydrated and stored frozen, there is no need to add additional diluent at this stage.  Frozen sponges should however, be properly thawed before use.

 

Photograph 2:  Diluent soaking through the sponge swab

To help distribute the diluent evenly throughout the swab, you can gently massage the sponge as long as you keep your fingers outside of the bag.  If the sponge is not already folded, it should be folded at this stage to resemble the one shown in photograph 3.

Grasp the bottom of the sponge through the bag as shown in photograph 3 below.

Photograph 3:  Begin by grasping bottom of the sponge through bottom of the bag

Peel the open end of the bag back over your hand in the direction of the arrow in photograph 4A below.  The bag will become turned inside out, your hand will be covered by the bag, and the folded end of the sponge will be exposed as shown in photograph 4B.

        Photographs 4A and 4B:  Turn the bag inside out over your hand to expose the swab

Samples should be taken after the carcasses have been finally inspected by Meat Hygiene Service officials and before chilling has occurred.

Begin by randomly choosing a side of the carcass to sample.  Swab by starting at the back leg and using a firm pressure rub the sponge across the carcass in a sweeping  motion as shown in photograph 5. 

Photograph 5:  Sponge swab sampling of red meat carcasses

 

The direction and path that the swab should follow are shown on photographs 6A (cattle), 6b (sheep) and 6C (pigs) below.  It is important that each of the four carcass sampling sites are sampled with the sponge.  Agitate the swab by moving it by a few centimetres using a side-to-side movement as you swab the carcass.   For sides of full-grown beef, it may be hazardous to attempt a single carcass swabbing from a ladder.  If the sampler considers the operation hazardous, samples from the rump can be collected from a ladder, and the remaining three sites can be sampled from the ground.

         Photographs 6A,  6B and 6C:  Path to use across a carcase when sampling using sponge swabs

It is not necessary to accurately measure the area of carcass surface that was swabbed.  The person who collects the sample should estimate the surface area that was swabbed. 

You can estimate the area that you swabbed by multiplying together the approximate length of the carcass that you swabbed in cm by the width of the swab in cm.

For example, if you swabbed approximately one metre (which is 100cm) length of a pig carcase surface using a swab with a width of 10cm, then the calculation is 10cm x 100cm = 1000cm².

Record the area that was swabbed so that your laboratory can properly report the bacterial numbers per cm².

Additional information that you need to retain for each sample is:

• A unique carcass reference (most commonly this will be the kill number)

• The name and postcode of the farm that supplied the carcass

• The carcass species

If your plant has an on-site laboratory, you should keep the samples cool and deliver to your lab within 2 hours of sampling.  If you use an offsite lab, immediately put the sample into an insulated cool box containing frozen freezer blocks or crushed ice.  Keep the samples cold (but don’t freeze them).  Keeping samples chilled at 0^oC to 4^oC will help prevent bacteria from multiplying and make sure your counts accurately reflect the bacteria present on the carcass surface.  Sample testing should commence a maximum of 24 hours after sample collection.

Testing frequency and interpretation of results

For red meat plants, sampling must be undertaken weekly, and  5 carcass samples per session must be tested. There are reduced frequencies based on throughput.  To check the frequency that applies to your plant click here.

An important change is that 5 samples for each species processed need to be sampled during each sampling interval (i.e. unlike the previous requirement for TVC and Enterobacteriaceae tests you don't sample one single species each week). Salmonella test results are  assessed over 10 consecutive sampling sessions on a species-by-species basis.  That is in batches of 50, taken over a 10 week period.  These 50 samples will be assessed in a rolling manner whereby after 10 weeks, the samples collected from weeks 1 to 10 will be assessed.  At week 11, the samples collected from weeks 2-11 will be assessed i.e. the test results from week 1 drop off the rolling window at week 11. 

Salmonella test results are reported as either positively detected or absent. The assessment criteria that you must use are:

More than 2 out of 50 samples with Salmonella detections for cattle or sheep are unacceptable.

More than 5 out of 50 samples with Salmonella detections for pigs are unacceptable.

Exceeding 2 out of 50 Salmonella detections for cattle or sheep carcasses or 5 out of 50 Salmonella detections for pigs should result in appropriate and proportionate corrective actions being initiated by the plant operator.  It does not mean the carcasses are unfit for consumption if Salmonella detections are unacceptable.

For Total Aerobic Counts and numbers of Enterobacteriaceae, the assessment criteria haven't changed since July 2002.   The assessment criteria are available here.  The sampling frequency for each species are available here.   Pictorial summaries of the assessment criteria are shown below.  If you enter your data into the Meat Test Results Database, the mean log values are calculated automatically for you.

Mean log bacterial numbers in the red regions are unacceptable; in the amber are marginal, and in the green area are fully acceptable.