Monday 7 March 2022

The Importance of Not Being Too Attached: Pharmaceutical Equipment Characteristics and Bacterial Attachment


The ability to attach to and subsequently detach from biotic and abiotic surfaces is a characteristic shared  by all bacterial cells. This is because the mechanisms of attachment are advantageous for survival in the natural environment. Moreover, attachment enables microorganisms to exert some control over their nutritional environment. The ability to, and likelihood of, attachment is as likely within a pharmaceutical or healthcare environment compared with any other environment, albeit with the expectation that populations are lower. It is important that as part of hygienic equipment design that surface characteristics are specified, especially with materials like stainless steel.


Attachment can lead to adhesion, and the two are different but related concepts. Attachment is a physical activity; as bacteria approach a surface, cell appendages (such as fimbriae, pili, and flagella) may stick to it. Adhesion can occur when adhesive molecules expressed on the bacterial surface bind to host surface receptors; this is associated with biofilm formation. In both cases, bacteria can sense that they are in contact with a surface and provide the initial cellular responses to surface contact and subsequent adhesion. Factors like temperature and pH influence the bacterial adhesion. It is important to note that surface roughness and cleanability have a relationship, but the relationship is complex. A rougher surface may increase the potential for microbial attachment although to a degree cleanability is subject to variations in terms of the presence of other substrates and time as microorganisms move from the reversible to the irreversible state.



An important factor related to this consideration, especially for when cleanroom equipment is selected, is the surface finish and surface roughness. This focus on topography is particularly useful for stainless steel given the commonality of this material, along with anodized aluminum, for the production of pharmaceutical processing equipment. Hence, specifying appropriate finishes and limits of roughness should form part of equipment and facility specifications, as informed by the principles of quality by design. Durability and resistance to corrosion represent important reasons as to why material grade, finish, and roughness matter. In addition, these specifications are also determinants of the likelihood of microbial attachment and hence they are essential considerations when developing a contamination control strategy. This review paper assesses the factors affecting finish and roughness, primarily in relation to microbial attachment to stainless steel. The objective is to aid with developing equipment design specifications and User Requirement Specifications.



Sandle, T. (2021) The Importance of Not Being Too Attached: Pharmaceutical Equipment Characteristics and Bacterial Attachment, Journal of GxP Compliance, 25 (5):


Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (

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