Purpose: To test how effectively a range of Hygiena swabs recover viable dried bacteria from surfaces in comparison to routinely used standard environmental contact plates.
Methods: One hundred µl of Listeria monocytogenesdilutions (Dil -1, -2 and -3) were pipetted onto sterile coupons. Dilutions were dried on coupons measuring 4” by 4” and 12” by 12”. The surface was left to dry for 24 h until visibly dry. Contact plates and three swab types (Dacron bud, small foam and large foam (InSite) swabs) were used to collect the dried bacteria from the surface and swabs were moistened with 100 to 400 µl of MRD depending on swab size. After sample collection, the coupons were put in whirl pack bags, 50 ml of MRD was added to the bag, each coupon was then mixed thoroughly to remove remaining bacteria. Each run used five replicate coupons both control and both tests (swab and contact plate). The unswabbed counts from the controls are considered 100% for comparison.
Results: The comparison of swabbing with any swabs proved that the pick-up was superior to the contact plates. The 4” by 4” coupons swabbed with Dacron bud swabs, small foam and large foam removed mean 91±6% (4” by 4”), 98±1% (4” by 4”) and 91±3% (12” by 12”) compared to contact plates which removed 72±16%, 71±7% and 50±12%. Comparing 4” by 4” to 12” by 12” coupons reduced the efficiency slightly but the pick-up was still superior to contact plates for Listeria.
Significance: Swabbing efficiency is better measured by using the residual bacteria method with proper controls.