Adherence of psychrotrophic bacteria to dairy equipment surfaces

Psychrotrophic bacteria isolated from raw milk were tested for their ability to adhere to steel, two types of rubber, and glass, materials employed in the construction of milking equipment. The adherence assays were carried out by exposure of the materials to radioactively labelled bacteria in both a buffering solution (Ringer's) and milk. The degree of adherence of Gram-positive bacteria was lower (P less than 0.001) than that of Gram-negative bacteria. Glass was the material least prone to bacterial adherence (P less than 0.001); there were no significant differences between the other three materials. Milk was found to inhibit adhesion significantly (P less than 0.05), this inhibition being more evident with the most adherent bacteria. There was no statistically significant correlation between bacterial surface hydrophobicity and adherence. Our results suggest that intrinsic bacterial adherence cannot be considered a relevant factor in the contamination of milking equipment.