BK - Biofilm physiology and antibiotic resistance II Flashcards
What role does flagellar-mediated motility play in Pseudomonas aeruginosa biofilm formation? (2)
- It facilitates initial surface attachment
- Works in tandem with other structures for biofilm development
How do polar-localized type IV pili contribute to P. aeruginosa biofilms? (2)
- They create twitching motility
- Enable formation of 3D biofilm structures (regulated by catabolite repression control, Crc)
What is the role of the global virulence regulator GacA in P. aeruginosa biofilms? (2)
- It is involved in forming the 3D structure of the biofilm
- Acts as a key regulator of virulence factors
How does the ndvB gene contribute to antibiotic resistance in P. aeruginosa biofilms? (3)
- It is required for synthesizing periplasmic anionic glucans
- These glucans sequester aminoglycosides, preventing them from reaching the inner cell membrane
- Also influences 8 ethanol oxidation genes related to tobramycin resistance
What is the significance of the RpoS stress response in P. aeruginosa infections? (3)
- It protects cells from heat shock, cold shock, pH changes, and chemical agents
- Induced by high cell density, leading to production of trehalose and catalase
- Detected in clinical samples from chronic biofilm infections (e.g., CF sputum)
How does quorum sensing affect the biofilm phenotype in P. aeruginosa? (3)
- Modulates cell transformation into the biofilm phenotype
- Deletion of the lasI gene leads to loss of EPS production and biofilm defects
- Involves production of signaling molecules like N-(3-oxododecanoyl)-L-homoserine lactone (odDHL)
What were the key findings from the Whiteley et al. microarray study on P. aeruginosa biofilms? (3)
- Only about 1% (73 genes) showed differential expression between biofilm and planktonic cells
- A significant portion of regulated genes code for hypothetical proteins
- Activation of filamentous bacteriophage (Pf1) and repression of pili/flagella synthesis were noted
How do changes in gene expression in P. aeruginosa biofilms relate to antibiotic resistance? (3)
- Upregulation/downregulation of genes affects LPS structure and aminoglycoside affinity
- tolA gene product affects LPS structure, resulting in decreased aminoglycoside affinity for the outer membrane
- Tobramycin induces a stress response, activating chaperones (dnaK, groES) and efflux systems
What are persister cells and why are they critical in biofilm-related infections? (3)
- They are dormant cells highly tolerant to antibiotics
- Their survival leads to relapsing chronic infections
- Shielded within biofilms, they evade both antimicrobials and the immune system
What mechanisms underlie persister cell formation in bacteria? (6)
- Downregulation of energy production and biosynthesis
- Activation of toxin-antitoxin (TA) modules
- RelE and MazF toxins: Cleave mRNA, leading to dormancy.
- HipA toxin: Inhibits translation by phosphorylating elongation factor Ef-Tu.
- TisB toxin: Forms membrane pores, reducing proton motive force (pmf) and ATP levels
- Involvement of various TA system types (I–VI) that neutralize toxins through different mechanisms
What is an important molecule involved in Toxin-antitoxin modules and persister formation?
guanosine pentaphosphate; (p)ppGpp
What pathways play a role in formation of persister cells (3) and what are their mechanisms (2)?
- Obg/HokB pathway: Triggered by (p)ppGpp signaling.
- Polyphosphate/Lon/mRNA interferase pathway: Also controlled by (p)ppGpp signaling.
- TisB pathway: Activated by strong SOS response (a DNA damage response).
Mechanisms:
- HokB and TisB (Type I toxins): These membrane-associated peptides disrupt the proton motive force (PMF), leading to energy depletion and dormancy.
- 10 mRNA endonuclease type II toxins: These toxins cleave mRNA, interfering with ribosomal translation and causing dormancy. This pathway involves both positive feedback (via HipA toxin) and negative feedback (via reduced mRNA levels)
What is the effect of nitric oxide (NO) on P. aeruginosa biofilms? (3)
- At nanomolar concentrations, NO decreases biofilm formation
- Enhances removal of biofilms when combined with antimicrobials
- Increases bacterial susceptibility to antibiotics
How can nitric oxide donors and scavengers influence biofilm dispersal? (2)
- They modulate biofilm structure and removal
- e.g. PTIO (1 mM) partially alleviates NO effects, increasing biofilm surface area coverage
What is MRSA and why is it a concern in hospital settings? (3)
- MRSA; Methicillin-resistant Staphylococcus aureus (Gram +ve)
- It has become endemic in hospitals, contributing to thousands of infections
- Increasing resistance even to last-resort antibiotics like vancomycin
What impact does a single nucleotide polymorphism (SNP) have on MRSA biofilm susceptibility? (2)
- It does not change the biofilm structure or detachment
- But it makes MRSA significantly more susceptible to antimicrobials, especially vancomycin
How does nitric oxide (NO) increase the susceptibility of MRSA and other biofilms to antimicrobials? (4)
- Diguanylate cyclases (GGDEF domain) synthesize c-di-GMP from GTP
- Phosphodiesterases (EAL or HD-GYP domain) degrade c-di-GMP into pGpG
- Feedback Inhibition: c-di-GMP can directly inhibit the activity of diguanylate cyclases, creating a negative feedback loop to regulate its own levels
- NO activation of Phosphodiesterase reduces c-di-GMP
What are the downstream effects of c-di-GMP binding to receptors in bacteria? (6)
Promotes
- sessility
- biofilm formation
- cell adhesion
- cell cycle progression
Reduces
- flagellar motility
- virulence factor expression
How does the interplay between σS subunit of RNA polymerase (RpoS) and c-di-GMP affect biofilm formation? (2)
- During slow growth or stationary phase, RpoS accumulates and activates specific genes (e.g., CsgD, GGDEF)
- This leads to increased c-di-GMP production and enhanced biofilm formation
Represents a feedback loop reinforcing the sessile lifestyle
