under the microscope
By Rodney E . Rohde , PhD , MS , SM ( ASCP ) CMSV CM , MBCM , FACSc
The Microbial Battlefront : Surfaces
2021 review article in Frontiers Bioengineering and Biotechnology
A discusses what I am calling the “ microbial battlefront .” This so-called battlefront – the surface – alongside the many mechanisms of microbial attachment to surfaces has long been a topic of study . This interaction of microbes , particularly bacteria , with surfaces has far reaching and critical implications in a diverse range of areas , including infection and transmission dynamics , formation of biofilms , biofouling , and bioenergy to name just a few .
By definition , a biofilm is a three-dimensional structure formed because of microorganism ’ s surface sensing , initial adhesion to surfaces , followed by subsequent colonization and production of an extracellular polysaccharides matrix ( EPS ). The sticky and glue-like matrix substance is structured and act as “ smart communities ” by bacteria . Like enemies , the bacteria become entrenched , and the biofilm community creates actual channels much like trench warfare where there is a hidden and protected route from the external environment to the internal surface environment for delivery of nutrients and waste byproducts allowing for ongoing colonization and maturation for the embedded bacteria . Even more diabolical , once the microorganisms mature , they shed and move from the matured biofilm to join another biofilm community or to become a pioneer of a new one . True cunning by these microbial adversaries . Like any enemy or opposition , those of us in healthcare and other industries must work to better understand their makeup and mechanisms of action .
In the review article , the authors lay out the key research areas that help us to better understand the microbial battlefront – the surface . The two key areas discussed include surface properties and environmental factors . Briefly , I will highlight the primary areas with respect to the characteristics attributed to how they impact the healthcare environment .
The authors primarily focus on the following surface properties : surface charge density , surface wettability , surface roughness , surface topography , and surface stiffness . Due to the general makeup of bacterial cell walls from carboxyl , amino , and phosphate groups , the overall bacterial surface is a negative charge . Generally , we see more adhesion and biofilm EPS accumulation on positively charged surfaces although some studies show trends for initial attachment and later biofilm formation can be variable . In terms of sterilization and disinfection , one might consider surface selection . The interactions between solid and liquid phases define surface wettability . The liquid phase “ wets ” the surface of a solid surface by maximizing its area in contact with the surface . Surfaces with low surface energy and liquids with high surface tension tend to reduce surface wettability and vice versa in this direct relationship .
While the authors state that broad generalizations can ’ t be made , there is an argument for engineered materials and surface treatments creating an extreme water contact angle – either superhydrophobic or superhydrophilic surfaces that can limit bacterial adhesion – playing a part in this battlefront .
Surface roughness increases the surface area available for bacterial attachment and provides a scaffold for adhesion and can provide protection for bacteria versus shear forces which would help bound
bacteria to resist being detached . Research consensus shows that as surface roughness increases , bacterial adhesion and biofilm formation also increases . Interestingly , bacteria are capable of sensing mechanical cues associated with natural and artificial physical features , such as the topography of surfaces . For example , topography alternations can affect the expression of bacterial adhesins .
Topography has important implications for “ sheltering ” of bacteria and stronger adhesion when the dimensions ( e . g ., space ) is larger than a single bacterium . In a sense , the less topography helps to deter sheltering . Surface stiffness is an indication of if material is softer and more elastic or harder and less elastic . This review states that investigations on the underlying mechanism in this topic are not yet sufficient .
Fluid dynamics and bacterial motility are the primary focus areas regarding environmental factors . One might think about fluid dynamics in the sense of the human body – dental plaques are subject to salivary and gingival crevicular fluid flow and the way fluid flows in a catheter microenvironment . These hydrodynamic conditions can enhance or interfere with bacterial sensing and overall biofilm formation .
One study in the review showed that shear flow enhances biofilm formation by increasing the EPS production and strength of the EPS-matrix in Staphylococcus aureus . In other words , a strong flow likely triggers S . aureus to express more EPS genes for stronger attachment .
Bacteria and other microbes can be broadly divided into motile and non-motile bacteria . At the simplest understanding of motility , motile bacteria can “ search the environment ” for the most suitable surface areas to attach to while non-motile bacteria must rely on gravity and other forces to participate in sensing . Generally , bacterial surface appendages such as flagella can play an important role in the adhesion by inducing a more dynamic response of motile bacteria to surface properties than non-motile bacteria . Once bacteria adhere to surfaces , motile bacteria can settle biofilms faster than non-motile bacteria by attracting free bacteria through chemotaxis and quorum sensing .
It is critical for those involved in healthcare and community infection control and prevention to understand the theoretical and applied research at the battlefront of microbes and surfaces . Likewise , the industries that play a role in the development of antibacterial and antimicrobial surfaces must continue to conduct robust research that looks at more complex surface and environmental factors . For example , the focus must shift from a single surface parameter and its effect on adhesion to efforts assessing the impact of multiple surface parameters on bacterial adhesion , including the effect of temperature .
For a complete understanding of this review , refer to the paper : Sherry , et . al . Implication of Surface Properties , Bacterial Motility , and Hydrodynamic Conditions on Bacterial Surface Sensing and Their Initial Adhesion in Front . Bioeng . Biotechnol ., 12 February 2021 . https :// doi . org / 10.3389 / fbioe . 2021.643722
Rodney E . Rohde , PhD , MS , SM ( ASCP ) CM SVCM , MBCM , FACSc , serves as chair and professor of the Clinical Laboratory Science Program at Texas State University . Follow him on Twitter @ RodneyRohde / @ TXST _ CLS , or on his website : http :// rodneyerohde . wp . txstate . edu /