Clinical Implication for Biofilms Flashcards
What are biofilms?
- Microorganisms living in self-organised community attached to surfaces, interfaces or each other, embedded in matrix of extracellular polymeric substances of microbial origin while exhibiting altered phenotypes with respect to growth rate and gene transcription
Surfaces supporting biofilm growth
Manmade objects: pipes/ ships Environmental: rocks/ riverbeds Biological: wounds
Medical devices: catheters
Biofilms are Ubiquitous: commonly found in various environments and composed of diverse microbial communities
Components of biofilms
What do they provide?
▪ Microbes (mono- vs. multi-species) and a self-produced matrix – biofilms >90%
▪ Components:
Polysaccharides – often heteropolysaccharides: mixture of neutral and charged sugar residues. Proteins – enzymes: degrade biopolymers, structural proteins. Nucleic acids – not just a by-product of cell lysis (adhesion). Lipids – surface attachment
▪ Provides:
▪ Mechanical stability
▪ Enhance adhesion
▪ 3D polymer network – interconnects and transiently immobilises cells
▪ External digestive system
Biofilm formation steps
Reversible attachment: planktonic (free floating) bacteria in surrounding environment encounter surface->undergo reverisble attachment. Bacterial cells temporarily adhere to surface through weak and reversible reactions: van der Waals forces, electrostatic interactions and hydrophbic interactions. Allows bacteria to explore surface and establish initial contact. Irreversible Attachment: some bacteria attach firmly to the surface using stronger adhesive mechanisms. Involves production and secretion of extracellular polymeric substances (EPS) e.g: poly saccharides, proteins and DNA forming protective matrix arround attached cells stabilising bacterial attachment and providing structural support for developing biofilm. Maturation: Bacterial cells within biofilm undergo proliferation and further EPS production once attached to the surface. Biofilm architecture becomes more complex: formation of microcolonies, water channels and mushroom like structures. Bacterial cells in biofilm community communicate using quorum sensing and other signaling mechanisms, coordinating gene expression and metabolic activities.
Mature biofilm: resistant to environmental stresses, antimicrobial agents and host immune responses. Detachment: of cells from biofilm occurs as a continuously natural process despite biofilms stability. Occurs via sloughing ( shedding of outer layers of biofilm due to shear forces/ mechanical disturbances), gradual erosion of biofilm matrix components causing bacterial cell release, or dispersion ( active release of planktonic cells from the biofilm via action of specific enzymes or regulatory factors). Needed for dispersal of bacterial cells/colonisation of new surfaces/ dissemination of biofilm-associated infections.
Characteristics of biofilms
Mono- or multi-specie functional community.
Many gradients: Nutritional, Oxygen: Surface of biofilm more aerobic, Bottom of biofilm more anaerobic. Not flat: complex three-dimensional (3D) structures
Characteristics of Biofilms - AMR
Mechanisms of antimicrobial
resistance in biofilms:
▪ Resistance
at the biofilm surface, within biofilm
microenvironment, of bacterial “persister” (higher tolerance to antibiotics)
cells
QS
Allows bacteria to sense if they have a high density population
Requires Auto inducers produced by cells. More AI produced triggers an luminescence response.
Lux system: mediates bacteria luminescence
usually expressed at a low level
produces LuxI and Lux R
LuxI: produced auto inducer (acyl homoserine lactone) that quickly diffuses out of the cell typically without a chance to interact with the lux system.
But when there is a high concentration of AI outside of teh cells, the AI is likely to diffuse back in and bind to LuxR.
LuXR-AI binds to operon and activates transcription enhancing expression of the target gene- more Lux I and AI are produced further enhancing the expression of the operon,
Luciferase (causes light production) consist of Lux A and Lux B gene products. Requires energy to make this
Cells turn this on when they are in are crowded or when appropriate such as squid for camoflague.
as in a squid providing luminesence for it at night for camoflague in moonlight reflecting on the seas surface
Biofilms: Uses chemical language to assess bacterial cell density and diversity to determine the best time to perform a behaviour such as when to glow or when to launch an attack in the body.
Clinical Biofilms - Why are they Problematic?
- ## More tolerant against antibiotics, disinfectants and host immune mechanismsMIC (Minimum Inhibitory Concentration) and MBC (Minimum Bactericidal Concentration) of antibiotics to biofilm growing bacteria may be up to 1000-fold higher than planktonic bacteria
- Biofilm resistance/tolerance mechanisms to antimicrobials have been best
studied in Pseudomonas aeruginosa. - Biofilms allow infections to persist, causing chronic
disease or repeated re-infection from a foreign body
Resistance mechanisms of biofilm bacteria (P.
aeruginosa)
Slow growing biofilm bacteria are predominantly more resistant to antibiotics. Increased production of Beta-lactamases.
Production of modified lipopolysaccharide: confers resistance to Colistin. Possible matrix antibiotic binding (and retardation of diffusion). P. aeruginosa in biofilms has increased mutability: increased chance that mutations will lead to antibiotic resistance. Hypermutator strains persist in people with CF
P. Aeruginosa biofilms in Cystic Fibrosis
How does CF increase bacterial infections?
CF: genetic disorder. affects 1 in 2000 newborns in Caucasian populations. recurrent and chronic infections. mutation(s) in CF transmembrane conductance regulator gene (CFTR) => malfunction of
chloride channel. impaired clearance of inhaled microbes. recruitment of inflammatory defence mechanisms.
-People with CF suffer from recurrent and chronic respiratory tract infections
