Posted by The 6-panel comic posted on Human STEAM demonstrates a bit about the process of bacteria coming to dwell upon a surface and adhering to it. The last panel also shows the swelling and redness that can be caused by this build-up of bacteria and the infection that follows in that region (for the purposes of this project, at a titanium plate located in the thigh). In the replacement of the anterior cruciate ligament, the damaged ligament is replaced with a graft (either from one’s own muscle tissue or from a cadaver). After the graft is in place, it is fixed in place with two titanium plates, one in the shin and one in the thigh (Lu et al., 2023). These titanium plates are, in turn, a breeding ground for two vicious types of bacteria: Staphylococcus aureus and Staphylococcus epidermidis. Staphylococcus makes up four out of five of all bacteria that cause implant infections- of these, many of them produce biofilm. Bacteria that produce biofilm are particularly harmful to an individual because they have incredibly restricted penetration to nearly all antibiotics (Lewis, 2001).Staphylococcus aureus is a gram-positive bacterium, which means it has a thick peptidoglycan cell wall. Within the species S. aureus exists a frightening strain: MRSA (methicillin-resistant S. aureus.). Due to its incredible resistance to antibiotics, MRSA is an incredibly difficult strain to treat and has a 20%-50% mortality rate (Cleveland Clinic, 2024.) Staphylococcus epidermidis is gram-negative, meaning it has a thin peptidoglycan wall and a membrane on the outside of that. This gram-negativity, in addition to the biofilms produced by S. epidermidis, is a large contributor to the resistance to antibiotics that is characteristic of S. epidermidis. Though the two species of Staphylococcus are generally transmitted into the human body through different paths, they can both end up finding their way to medical implants (Ribeiro et al., 2012). When it comes to how they manage to colonize implants, bacteria must be able to bind to the surface. In order to do this, bacteria must have adhesins with the ability to interact with extracellular matrix components. In S. aureus, these adhesins are called microbial surface components recognizing adhesive matrix molecules (or MSCRAMMs for short). These MSCRAMMs each have a specific tissue that they can colonize, a specific biomaterial they adhere to as well as the ECM proteins on the surface of the biomaterial (in this case, the medical implants). S. epidermidis, on the other hand, do not produce MSCRAMMs. Their method of adhesion comes from the biofilm they produce. An important component of this biofilm is dubbed polysaccharide intercellular adhesin (hereout PIA). PIA is important for the production of the biofilm because it protects S. epidermidis from phagocytosis and other defense system responses (Ribeiro et al., 2012).According to Ribeiro et al, there are two accepted phases to how bacterial adhesion works. In phase one, bacteria either propel themselves or are moved by means of a physical force toward the surface to which the bacteria will attach and colonize. In phase two, the adhesins will aid the bacteria in binding to the surface through selective bridging. It is at this phase, generally speaking, that bacteria will begin to overgrow the biomaterial they’ve attached to, but if the environment suddenly becomes unwelcoming to them, they can employ methods to lay low until things are optimal for them again (Ribeiro et al, 2012). In both S. aureus and S. epidermidis, the ability to remain undetected for great lengths of time comes down to their ability to hide themselves from the immune system via a polysaccharide capsule. Another technique that S. aureus has to prevent recognition is through the release of an effector protein called staphylococcal protein A (SpA). SpA binds to antibodies produced by the immune system to prevent recognition of S. aureus, then binds to B-cell receptors to inactivate the protective immune response. In this way, S. aureus is not only unrecognized by the immune system as S. aureus but is also able to remain undetected as even a threat to the host at all (Bizzell, 2018).
Bizzell, E. (2018). Microbial Ninja Warriors: Bacterial Immune Evasion. American Society for Microbiology. https://asm.org/articles/2018/december/microbial-ninja-warriors-bacterial-immune-evasion#:~:text=Immune%20evasion%20strategies%20are%20those,Modification%2C%20Capsule%20Production%2C%20and%20Mimicry
Cleveland Clinic. (2024). MRSA (Methicillin-resistant Staphylococcus aureus). Diseases and Conditions. https://my.clevelandclinic.org/health/diseases/11633-methicillin-resistant-staphylococcus-aureus-mrsa
Lewis, K. (2001.) Riddle of Biofilm Resistance. American Society for Microbiology, 45(4). https://journals.asm.org/doi/full/10.1128/aac.45.4.999-1007.2001
Lu, W., Liu, D., Cai, Z., Pan, L., Xie, W., Jin, H., Liu, X., Li, Y., and Xiao, W. (2023.) Internal brace augmentation reconstruction versus standard anterior cruciate ligament reconstruction: a randomized controlled clinical trial study protocol. BMJ Open, 13(12). https://pmc.ncbi.nlm.nih.gov/articles/PMC10749018/#s2
Ribeiro, M., Monteiro, F., and Ferraz, M. (2012.) Infection of orthopedic implants with emphasis on bacterial adhesion process and techniques used in studying bacterial-material interactions. Biomatter, 2(4), 176-194. https://www.tandfonline.com/doi/full/10.4161/biom.22905#d1e116
Caden STEAM project is about how bacteria adhere to a surface, ultimately leading to an infection. Her comic shows a yellow circle that gets introduced as Ms. Staphylococcus. As we learned from a prior lab, staphylococcus is a group of bacteria with over thirty different types. Staph bacteria can cause different infections, including skin infections, which are the most common. Caden uses the example of a replacement of the anterior cruciate ligament with a graft. The graft comes from either one’s own muscle tissue or a cadaver, and the titanium plates are placed on the shin and the thigh. Caden mentions that these plates are a vicious feeding ground for two types of bacteria: staphylococcus aureus and staphylococcus epidermidis. MRSA is also mentioned in Caden’s report, which we learned about during our skin graft lab. MRSA is incredibly resistant to antibiotics, and it is difficult to treat and oftentimes difficult to get rid of. Caden explains how the two strains of staphylococcus are transmitted into the human body through several different pathways, but ultimately, the infection ends up finding their way to medical implants. An interesting thing I read in Caden’s report was that for the bacteria to bind to medical implants, they must have adhesins that can interact with extracellular matrix components. Staphylococcus aureus contains these adhesives, and they are called microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), which is the acronym. The latter does not contain these adhesions. Staphylococcus aureus is not recognizable by the immune system, which can be very concerning since you can have it without knowing it, which means it prolongs treatment.