Bacterial Biofilm as a Complication of Respiratory Disease Treatment
One of the unique characteristics of certain microorganisms is their ability to form organized communities enveloped in extracellular polymeric matrix and firmly attached to a solid surface or interphase or forming aggregates, collectively referred to as biofilm. Clinically, the major issue is the formation of pathogenic and conditionally pathogenic organisms' biofilm on tissues (such as respiratory tracts) or the surfaces of various medical devices (including catheters and implants), as it represents a dangerous complication leading to the development of chronic, recurrent, and scarcely treatable conditions.
Increased Resistance of Pathogens
Existence in the form of a biofilm provides microorganisms with a number of advantages and allows them to survive even in challenging conditions. The formation of biofilm increases resistance to the host immune system's defensive mechanisms and to the treatments used, thanks to several factors. Biofilm is composed of a heterogeneous community of microbial cells in different physiological and metabolic states, and the expression of some genes in biofilm cells significantly differs from that in planktonic cells.
The Role of Extracellular Matrix
A key factor is the extracellular polymeric matrix produced by biofilm cells, which can constitute up to 90% of the biofilm biomass. The properties of the extracellular matrix vary among different biofilms, but in general, it is composed of polysaccharides, proteins, lipids, and in some cases, extracellular DNA. Numerous water pores run through this extracellular matrix, used for the transport of nutrients and oxygen to the cells.
The presence of the extracellular matrix is one of the reasons behind the significantly increased resistance of biofilm cells to antimicrobial agents, as it limits their penetration into the deeper structures of the biofilm and can also lead to their inactivation (for example, by the action of present enzymes). It is reported that the concentration of antibiotics targeted at cells present in the biofilm must be up to 1000 times higher than the concentration needed when targeting freely occurring pathogenic microbial cells. Thus, the extracellular matrix provides both a living environment and a crucial protective means for biofilm cells.
Complications Associated with Biofilm Formation in Clinical Practice
Microbial biofilms are most frequently associated with lung infections, such as in patients with cystic fibrosis (typically Pseudomonas aeruginosa infections, often multiresistant to many antibiotics), with chronic infections caused by the mold Aspergillus fumigatus (aspergillous bronchitis, tracheobronchitis, allergic bronchopulmonary aspergillosis, and others), and with chronic middle ear inflammation (biofilm formation is, for example, associated with Streptococcus pneumoniae).
Complications resulting from biofilm formation can also be encountered in many other fields, including cardiology, dentistry, ophthalmology, gastroenterology, dermatology, and urology. The issue of colonization of medical devices (such as venous catheters or implants) by biofilm-forming pathogens, accompanied by secondary infection of the surrounding tissue, constitutes a separate chapter.
Strategies for Preventing the Formation or Elimination of Biofilm
The formation of biofilm and its specifics must be considered when planning effective therapy for the mentioned diseases. Given the high resistance of pathogens in the biofilm form, it is necessary to consider alternative strategies (or a combination of various strategies) for their elimination rather than simply administering antimicrobial drugs. First and foremost, it is essential to focus on preventing biofilm formation (for example, through effective pre-operative prophylaxis and the use of anti-adhesive biomaterials). Different strategies are being developed that interfere with the structure of already present biofilm to enable its elimination, although this approach currently appears to be less successful.
Despite the considerable efforts of research teams, many questions related to the treatment of infections accompanied by biofilm formation remain unanswered. Given that these infections pose a significant societal risk, especially in connection with growing antibiotic resistance, it is crucial to develop effective strategies for their prevention or eradication that can be applied in practice.
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