Bacterial adhesion to sausage casings: development of a model experimental system

An experimental system was developed to study bacterial adhesion to cooked sausages, using natural sheep casing, 100% collagen casing, or collagen-sorbitol-cellulose casing as model surfaces. Square pieces ( c. 1 cm 2) of the casings were inserted into specially designed flow chambers. Bacteria were introduced ( c. 10 8 cfu ml −1) and allowed to sediment on the casings for 20 min. The chambers were then rinsed under controlled conditions (shear stress of 0·05 N m −2) and the remaining (adherent) bacteria were stained and enumerated under light microscopy. Typically, Brochothrix thermosphacta cells adhered to casings in large numbers ( c. 10 5 cfu cm −2), regardless of the casing type and mode of rehydration (30 min in water or 5 min in a 10% NaCl solution; room temperature). A Lactobacillus sp. was found to adhere to the casings in lower numbers ( c. 10 4 cfu cm −2) and this was due to a low level of sedimentation rather than to weak adhesive properties. Preliminary results indicate that the method developed will be applicable to pieces of casings peeled from cooked sausages.