Lecture 20 - Biofilms Flashcards
(19 cards)
define sessile and planktonic
- sessile = attached
- planktonic = free floating
what are biofilms?
- structured/organised community of microbes
- enclosed in extracellular polysacc (EPS) + fluid channels
- adhesion
list some device and tissue related biofilm infections
- device = contact lenses, tracheal tubes, grafts, catheters, valves, pacemakers, implants, prosthetics
- tissue = chronic infections/wounds, plaque, kidney stones
describe the 3 steps involved in plaque formation by biofilms
- primary colonisers (normal flora) adhere to glycoproteins on tooth pellicle
- secondary colonisers adhere to primary by coaggregation, binding CHO receptors
- repeat until multispecies plaque
describe how corn cob coaggregation and calculus formation occurs with dential plaques
- corn cob = coccal strep binding filamentous bacteria eg fusobacterium nucleatum
- calculus = Ca2+ and H2PO4 + toxins = inflammation
describe the shift of bacteria in a healthy vs unhealthy tooth
- healthy = G+ve aerobic cocci eg strep
- unhealthy = G-ve anaerobic bc plaque = anaerobic
List 4 opportunistic G-ve anaerobes involved in dental plaque formation
- Fusobacterium nucleatum
- Porphylromonas gingivalis
- Trepanema denticola
- Actinobacillus
why are biofilm infections difficult to treat?
- antibiotics can’t penetrate whole biofilm
- capsule inhibits macrophages and blocks enzymes
what are 4 phenotypic changes in biofilms that contribute to their resistance?
- capsule reduces diffusion
- increased gene expression eg pumps
- inner cells quiescent with no antibiotic target
- dormant persister cells
describe the pathology of cystic fibrosis
- mutated CF transmembrane conductance regulator (CFTR) ion channel
- increased Cl secretion + decreased NaCl uptake = excess mucus = impaired clearance
- increased opportunistic RT infection = chronic
list the 5 steps in Ps aeruginosa biofilm formation in CF
- attachment
- microcolony
- maturation by quorum sensing
- detachment from biofilm
- dispersal
explain the initial attachment step of ps aeruginosa biofilm formation
- Surface adherence deficiency (sad) genes
- motility essential for biofilms = fla +ve only
- type 4 pilus to asialoGM1 host receptor
- Ps1 exopolysac for galactose + mannose matrix
explain the microcolony step of ps aeruginosa biofilm formation
- positive feedback loop of Ps1 exopolysac making cells stay longer = increased Ps1 until microcolony
- type 4 pilus twitching by extension + bind + retract or slingshot by extension + bind + taught + detach
explain the quorum sensing maturation step of ps aeruginosa biofilm formation
- quorum sensing = detect cell density
- G-ve LuxI/R with acyl-homoserine lactones (AHLs) as auto-inducers (AIs)
- G+ve with peptide AI
- both use AI-2 for interspecies communication
explain the 2 step LuxI/R system of quorum sensing and the AHLs of the ps aeruginosa system
- LuxI AHL synthase makes AHL in propotion to cell density
- LuxR binds AHL = activates target genes eg capsule
- ps aeruginosa = las and rhl for capsule and VFs
how do bacteria detach from the biofilm in the detachment step of ps aeruginosa biofilm formation
shear forces = abrasion, erosion etc
explain the dispersal step of ps aeruginosa biofilm formation
- bacteria make matrix degrading enzymes = degrade EPS = planktonic cells
- alginate lyase, hydrolases, Dnases
what is quorum quenching and what are the 2 categories?
- QQ = inhibit quorum sensing to reduce biofilm = reduce virulence
1. structural AHL analogues
2. Enzymes hydrolysing homoserine lactone ring
list 2 medicinal research examples of QQ
- red algae halogenated furanones AHL analogue = enhanced ps aeruginosa lung clearance (mice)
- furanones + D-ribose targeting AI-2 in oral cavities to prevent periodontitis
