Scanning electron microscopy of dairy equipment surfaces contaminated by two milk‐borne micro‐organisms

Abstract

Ethanol dehydration followed by Ar replacement induced drying (ARID) is a suitable method for the preparation of glass, stainless steel and rubber surfaces which had been in contact with inoculated milk and which were to be examined using scanning EM (SEM). This technique was used to examine samples of all 3 materials which were subjected to single and repeated inoculation with whole milk containing a Pseudomonas sp. or a Micrococcus sp. and incubated for various periods. Some samples were also prepared for SEM using a cryofixation technique. The Pseudomonas sp. proliferates on glass and stainless steel surfaces but not on rubber. Due to the clumping tendency of the Micrococcus sp., proliferation of this organism was more difficult to assess accurately. In general, there was no difference in results obtained between single and repeated inoculation. Various factors which may have aided attachment of microorganisms to surfaces were identified, i.e., surface channels present in stainless steel, milk deposits and the production of extracellular material. The value of using the cryofixation and chemical preparatory techniques for the identification of artifacts is discussed.