Swab vs Sponge for environmental sampling,

Hello,

If I use sponge instead of swab for environmental sampling, would it change expected range of result for microbial count?

Thanks

KT

Hello,

 

 

If I use sponge instead of swab for environmental sampling, would it change expected range of result for microbial count?

 

Thanks

KT

Hi KT,

I'm not entirely sure what you mean by "swab". A large variety of "swabbing" devices are in use. Equipment terminologies may vary.

TBH, the variation (~ range) of repeated APC swab counts on a given surface area using the same technique is typically "considerable". Surface Standards often reflect this characteristic.

Offhand I'm not familiar with any generic, large-scale comparison studies of swabbing methodologies but they maybe exist. Different swabbing methodologies could have different recoveries/scatter giving different average counts/ranges. Ideally, assumed equivalence should be validated if significant decisions are to be based on the results.

 In practice, specific applications, eg surface shapes, may necessitate certain options, eg this comment -

Q. Should I use Q-tip type swabs only?  Why?
Answer:  A sponge is a more appropriate sampling tool since it can test a larger area. More pressure can also be applied when using a sponge to sample. Test areas as large as 1 ft. x 1 ft. can be sampled.  Q-tip swabs are good for hard-to-reach areas where a sponge cannot be used.

 

swa0 - Micro.testing Programs.pdf   706.26KB   128 downloads

Some Authorities do use the same count Standards with different swabbing options which implies assumed equivalence in sampling methodologies, eg - 

swa2 - Env. Monitoring Hygiene Guide for EHOs.pdf   116.16KB   94 downloads

Other authorities use a well-defined, specific sampling procedure/equipment, eg -

swa3 - Detection,enumeration of bacteria in swabs, etc,UK,2013.pdf   329.62KB   84 downloads

So the context of yr OP may be important.

See Charles' response for a thorough eval, he knows his stuff.

As far as providing a quickie answer: for enumeration utilize a swabbing method that will yield the results you expect to see. Ideally you want 100% of the media represented (swab with minimal absorption and let's you eliminate "<X" results to a point) on your plate/reader, and a workable area like 10cm² where you won't blow out the plate before your specified limit is reached. Classic and common example is a 3M quikswab that you then inoculate and incubate using an approved media for environmental samples (e.g. APC or EB petrifilm).

For presence/absence detection (like Salmonella or Listeria), the sponges (spongcicles) make more sense because they cover larger areas (like 50cm²), and the amount of media remaining in the bag or on the sponge is irrelevant because you'll use an enrichment incubation step to get your target organism to proliferate before testing, and the quantity is irrelevant to your goal of presence/absence per location swabbed.