Molecular Basis of Bacterial Infection Flashcards
WoM (21 cards)
What is Symbiosis?
An association of two or more different species of organisms
What is an Ectosymbiont?
An organism located on surface of another organism (usually larger)
What is an Endosymbiont?
An organism located within another organism
What is a Symbiont?
Physical contact between dissimilar organisms of similar size
What is a Consortium?
Interaction of one host with more than one symbiont
Microbial Interactions - Commensalism
Two organisms interact and only the commensal benefits, while the other is unaffected
Example: Nitrification
- Waste product from one organism is exploited by a second
- Final beneficiary : the plant host
Microbial Interactions - Cooperation
Two organisms establish an interaction from which they both benefit, but this interaction is not obligatory; hence separation leaves both partners viable
Example:
1. Connection of carbon and sulphur cycles of Desulfovibro & Chromatium spp.
Microbial Interactions - Mutualism
Two organisms establish a very close interaction with reciprocal (mutual) benefit (on which they both depend)
- involves syntrophy, an association where growth og either organism depends on or it improved by e.g. nutrients provided by the partner
Examples :
- plant + rhizobium
- tube worm + bacteria
Microbial Interactions - The Human Microbiome
- historically considered as commensalism; however recent discoveries suggest mutualism
- humans need benefits of microbiota
- specific microbiota communities seem to depend on human interaction
- at individual cell level all three types can be found as well as many antagonistic interactions
MIcrobial Interactions - Amensalism
Interaction in which one organism has an adverse effect on another without benefiting
Examples:
1. Untargeted release of antimicrobials which kill other microbes
2. Toxic effects of algae bloom on fish population
Microbial Interactions - Competition
Occurs when two organisms try to use the same resource
Two possible outcomes
1. “winner takes it all” - exclusion
2. Two organisms share a resource - both survive at lower population levels
Outcome might be determined by :
- different affinities of nutrient transporters
- use of weapons to disable or destroy the competitor
Microbial Interactions - Parasitism
An organism that lives in (endoparasite) or on (ectoparasite) another (host) to its own advantage - to the disadvantage of the host
Microbial Interactions - Predation
- the classical “food chain”
- organism attacks, kills and feeds on prey organisms
Formation of Microbial Communities
- Microbial interactions usually are complex
- Many microbes grow on surfaces (sessile) rather than free-floating (planktonic)
- These attached microbes form slime enclosed communities called biofilms
- Biofilms are ubiquitous in nature in water
- Can be formed on any conditioned surface - the surface properties strongly influence the nature of the biofilm
- Bacteria are often main inhabitants, but phages, protozoa and other organisms can play vital roles to shape the biofilm
- Different types of microbial interactions occur within
Formation of Biofilms
- Substratum preconditioning by ambient molecules
- Cell deposition
- Cell adsorption
- Desorption
- Cell-to-cell signaling and onset of exopolymer production
(bacterial communication to signal synchronous switch to sessile life style) - Convective and diffusive transport of O2 and nutrients
- Replication and growth
- Secretion of polysaccharide matrix
- Detachment, erosion, and sloughing
(bacterial communication to signal synchronous production of release factors)
Key Factors involved in biofilm formation and dispersal
- Attachment factors
- surface preconditioning factors which improve a surface for attachment
- bacterial adhesions or surface structures which mediate lasting surface contact - Matrix - extracellular polymeric substance (EPS)
- bacterial products such as polysaccharides proteins and DNA
- can make up 75-90% of the biofilm mass - Release factors
- dispersins - bacterial proteins which break down the matrix
- flagella - increased motility to break free
Pro’s of being in a biofilm
- matrix glues biofilm to the surface - resistance to washout by flow
- proximity of other bacteria allow to benefit from commensal or cooperative interactions
- matrix blocks penetration of antibiotics, disinfectants and antibodies and UV light - protection against antimicrobials
Con’s of being in a biofilm
- high density of bacteria
- nutrients and oxygen can be limited
- static - exposed to predators
Visualising Biofilms
Crystal Violet Staining - quick, quantitative method to compare bacterial strains, mutants or growth conditions
Electron Microscopy - high resolution, gives 3D impression of the biofilm ultrastructure
3D fluorescence microscopy - higher resolution, assessment of architecture, growth conditions, dynamic behaviour and subpopulations
Medically important sites of biofilm formation
- Catheters
- Implants
- Teeth
- Wounds/Healing
- Lung - cystic fibrosis patients
- Plumbing/Heating
- persistence in water systems
- constant exposure
- increased antibiotic tolerance and lasting shedding of planktonic bacteria from a biofilms are associated with treatment failure and chronic infections
Intervention Strategies for biofilm formation
- “smart” surfaces e.g. coated with silver nanoparticle or antimicrobial peptides
- anti-adhesion agents: caps for attachment factors, biofilm disrupting polysaccharides
- Biodispersion - surfactants and recombinant bacterial dispersins
- Lytic phages
- Inhibition of bacterial communication which controls community behaviour
