Biofilms pose a significant danger to the body's ability to treat infections. They are able to evade the immune system, tolerate antibiotics and withstand environmental stresses. These factors lead to the development of antibiotic resistance and chronic infection. Biofilms are colonies of bacteria that grow on the surface of medical implanted devices, such as dental implants, joint prosthetics, sutures, catheters and crosslinked hyaluronic acid dermal fillers (Costerton et al, 1999; de la Fuente-Núñez et al, 2013). The concept of biofilm is complex; however, in basic terms, bacteria can either exist in a free planktonic state or develop a communal lifestyle, known as a biofilm. In the latter state, they orchestrate the production of a variety of chemicals, including adhesins and extracellular polymeric substances, that link and encase the bacteria. This cell-to-cell connecting structure is beneficial for bacterial survival. It helps them to communicate, attach to surfaces and, perhaps most importantly, provides a mechanism for resistance to antimicrobial agents (Tolker-Nielson, 2015).
It is important to note that biofilm formation is species-specific and requires certain environmental factors to be present to initiate the microcolony formation (Tolker-Nielson, 2015). Not all infections and infective states involve biofilm.
The issues of biofilm
A biofilm formation is a series of well-regulated steps. To understand the problem that they pose, it is important to understand the mechanism of how they form and function. The bacteria must attach to a substrate, grow and aggregate into microcolonies and then mature and maintain the biofilm structure (O'Toole, 2003). Biofilm communities have altered metabolic activities compared to ‘normal’ planktonic bacteria. Their protective structure and altered metabolism provide protection from altered pH, osmolarity, lack of nutrients and mechanical and shearing forces. It also blocks the access of the host immune cells and antimicrobial agents. The development of a biofilm and these protective mechanisms are what lead to the emergence of antimicrobial resistance. Biofilm infections can only be treated by their removal, and, hence, removal of the medical implant (Costerton et al, 2005; Hoiby et al, 2011).
Infections associated with biofilm
Generally, it is estimated that 80% of chronic and recurrent infections can be attributed to biofilm formation (Donlan, 2001). It is also estimated that bacteria in a biofilm, as opposed to in a free planktonic state, are 100–1000-times more resistant to antibiotic therapy. Biofilms can form on two types of surfaces: abiotic surfaces (such as medical devices) or on the host tissue (Donlan, 2001), and it is the former that is of significance when administering crosslinked hyaluronic acid dermal filler.
Resistance to antibiotics can still occur in normal planktonic bacteria; however, the mechanism is different. These mechanisms include efflux pumps, enzymes that inactivate drugs and neutralising proteins. Whereas pertaining to a biofilm, the mechanism of resistance is slow and incomplete penetration, presence of bacterial spores and altered microenvironment (Sharma et al, 2019).
The significance of biofilm in delayed onset nodules
Biofilms are problematic for the aesthetic clinician. Dermal filler implants can be infected by injection of skin flora (Staphylococcus and Streptococcus Spp) directly onto the material during the procedure. They can also become seeded with bacteria through contiguous direct extension or haematological spread, meaning that any bacterial infection in proximity (i.e. a dental source or a bacterial infection from any other part of the body) may seed the implant (Ibrahim et al, 2018).
Transient bacteraemia, and, therefore, seeding of the dermal filler implant, can also result from brushing one's teeth, dental flossing and other everyday activities (Cassuto and Sundaram, 2013). In short, there is always a risk that the dermal filler can become colonised at any point from the initial treatment itself, to seeding once in situ.
To differentiate between acute infection and likely biofilm, it is important to consider the timeframe of infective signs. Infection may occur within hours of the injection, and this may lead to development of acute infection—amendable with first-line treatment with flucloxacillin (if no allergy to penicillin is identified)—or result in formation of an early biofilm. In the latter instance, a dormant period can follow, which may last for weeks or over a year. When bacteria do arise from their sessile state, they can cause acute infection, abscesses or granulomatous inflammation (DeLorenzi, 2013).
Dermal filler implants can be infected by injection of skin flora directly onto the material during the procedure
The presentation may appear as an exaggerated foreign-body response, mimicking a type 4 allergic reaction clinically and microscopically. However, administering steroids can accelerate the infective sequalae and lead to worsening of infective complications.
It is very difficult to identify whether a biofilm is present without doing invasive testing. However, infectious nodules tend to be localised, are unlikely to be symmetrical (Graivier et al, 2018) and, in the periorbital region, are more likely to be indolent. Biofilms can main dormant until a triggering event. A triggering event can constitute trauma, infection or inflammation from another source or further dermal filler procedure. An activated biofilm can cause acute purulent infections and sepsis or chronic inflammation with a subsequent granulomatous response (Wagner et al, 2016).
This is the reason why a steroid and antibiotic combination, without the consideration of a working diagnosis, can lead to clinical deterioration and chronic issues.
Identifying a suspected biofilm
In an ideal situation, a biofilm would be cultured (if present) and identified to guide treatment. However, a swab can only collect bacteria found on the surface, and not those embedded within the tissue. A biofilm sample typically requires treatment with ultrasound (sonication) to release the bacteria, and the use of antibiotics prior to tissue sampling may render bacteria unculturable. It is accepted that standard culture is inadequate when suspecting biofilm, due to the potential for atypical organisms, including mycobacteria. Therefore, both aerobic and anaerobic cultures should be properly obtained and monitored for 2–3 weeks (Wagner et al, 2016).
Many methods to detect biofilm have been described in the literature. Peptide nucleic acid fluorescence in situ hybridisation (PNA FISH) analysis provided the first direct visualisations of bacteria and their locations within tissues after filler injections (Bjarnsholt, 2013).
Polymerase chain reaction (PCR) is also routinely used when bacteria are slow-growing or difficult to culture (De Boulle and Heydenrych, 2015; El-Khalawany et al, 2015). PCR does not discriminate between live and dead cells, nor does the detection of a bacterium by PCR evidence that it is pathogenic (Bjarnsholt, 2013). For these reasons, testing remains a challenge.
These types of tests may not be accessible for regular aesthetic clinician. Therefore, it is extremely difficult to clinically distinguish inflammation due to a biofilm from a low-grade hypersensitivity reaction or a granuloma (Rohrich et al, 2010).
It is suggested that the presence of erythematous, indurated areas that appear at any time after treatment, should raise the suspicion of a biofilm. This is particularly the case if there is a single lesion or an asymmetric picture.
Prevention and management
In summary, treating a biofilm is difficult for three reasons:
- It is difficult to identify if there is a biofilm present
- Even with the correct combination of antibiotics, biofilms cannot be eradicated
- Identifying the lineage of the bacteria and sensitivity pattern to drive empiric antibiotic choice is challenging.
While biofilms can result from seeding of the dermal filler after implantation, the presence of coagulase-negative staphylococcus (CoNS) must be considered. Historically, CoNS was a classification described to separate Staphylococcus aureus from staphylococci that are less or non-pathogenic. However, it is now known that, generally, CoNS account for the majority of foreign body-related infections (FBRI). It has been stated that no inserted implanted medical foreign has ever failed to be colonised by CoNS of the Staph epidermidis group (Becker et al, 2015). Numerous human studies have detected bacteria present in delayed onset nodules. In a 2021 study, 98% of cases were indeed Staph epidermidis, a CoNS (Bachour et al, 2021).
The colonisation of the polymer surface occurs at the point of implantation. Once there, they can form colonies and develop into a more mature biofilm. When crosslinked hyaluronic acid is present, the number of bacteria needed to cause an infection reduces from 100 000 to 100 per gram of tissue (Convery et al, 2021). For this reason, prior to implanting the filler product, thorough skin cleansing and disinfection is of the upmost importance.
It is important to note that concurrent treatment with immunosuppressants lower the number of bacteria required to cause an infection/biofilm (Becker et al, 2015). Therefore, if immunosuppressants are being taken, this discussion must be included in the consultation process. During the procedure, scrupulous hygiene methods must be applied, and prompt action must be taken if there are any signs of infection.
When biofilm is suspected, the causative organism is usually not known, which adds further complexity to managing the problem. This lack of insight makes it difficult to select what antibiotic may be appropriate to temper the biofilm until the dermal filler is dissolved (if that is an option).
As discussed, identifying whether there is a biofilm present at all is difficult. Administering antibiotics prior to culture may give a false negative—this is also the case in acute infection and abscess (Convery et al, 2021). There is further difficulty in isolating a biofilm due to the fact that patients may not consent to a tissue sample, and the appropriate test may not be available.
Biofilms are also known for the fact that there is a large proportion of methicillin-resistant strains (not responsive to penicillins). In addition to high resistance rates to ciprofloxacin, clindamycin and erythromycin, CoNS bacteria demonstrate resistance to most cephalosporins and carbapenems. They were found to demonstrate lower resistance rates to tetracyclines. In general, biofilms demonstrate better responsiveness to older antimicrobial agents, such as rifampicin and fusidic acid. However, combination treatment is required to actively suppress the biofilm (Becker et al, 2015). The difficulty in treating biofilms is linked to the fact that they are much more difficult to penetrate, given their altered metabolic states and physical protection mechanisms present by virtue of the biofilm structure (Tolker-Nielson, 2015).
Conclusion
Biofilms are difficult to identify and manage, and antibiotics will not eradicate a biofilm. It important to consider tissue sampling if complex, or dissolving or removing the implant if a biofilm is suspected. Even if the antibiotics temper the sign of infection, a true biofilm will not stay suppressed for long.