micro 3 Flashcards
how many different mutation has been found of the CFTR protein?
over 1800
what is the most common CFTR mutation?
Phe508del most common (>80% of cases)
what is the mucocillary elevator?
- Cilia in the lung beat which then moves mucus up to the throat and swallowed
- Cl-secreted into ASL via CFTR
what happens in the mucocillary elevator in someone with CF?
In Phe508del CF, CFTR protein absent
•Cl-cant be pumped out
•ASL dehydrates, mucus attracted to cell surface and cilia unable to beat properly
•Mucus becomes stuck
what are the comvectional CF pathogens?
P. aeruginosa
S. aureus
H. influenzae
B. cepaciacomplex
how does the prevalence of microorganisms differ?
varies by country-•MRSA in adults: UK ~3%; USA >30%
what did Muhlebachet al 2018 find in his study?
- Took BAL samples and looked at different types of microbes (particularly bacteria in lung) using 16s rRNA sequencing
- Initial microbial load is similar to that found in oral cavity
- Transitions to pathogen dominated by age 4
how do bacteria change in infections in CF patients over time?
- Initially with H. influenza and S. aureus
* Progresses to intermittent and chronic P. aeruginosa
what are the two main types of Staphylococcus aureus that are in CF infections in the lung?
- MRSA
* Small colony variants (SCV)
how big are small colony variants?
<1mm, nonpigmented, non haemolytic
what happens if the growth rate decreases in small colony variants?
increased resistance
what are the clinical implications of scv?
Children with SA SCV had lower mean % of predicted FEV1(85.5% Vs 92.4%)
•SCVs which were thymidine dependent →strongest association with lung function
what is Pseudomonas aeruginosa?
Gram negative facultatively anaerobic bacillus •Environmentally ubiquitous, generally an opportunistic pathogen
•Found in UTIs, sepsis, non-CF lung infections, GI etc
what is the main priority on WHO list of antibiotics to make?
Pseudomonas aeruginosa
Intrinsically resistant to multiple antimicrobials;
•Multiple efflux systems
•Multiple secreted and cell based virulence factors
what is Pseudomonas aeruginosa’s role in CF?
Generally thought of as an opportunistic pathogen;•Several groups of strains have become more specialised pathogens and are associated with CF infection
how can New infections with PA can be eradicated?
- Combination of oral/IV antibiotics AND inhaled antibiotic
- Non consensus on what is the best combination
- Can be successful in approx. 80% of cases
what is Chronic colonisation with PA associated with?
- Worse lung function outcome
* Higher inflammation
how does Pseudomonas aeruginosa adapt in the CF lung?
- Has to overcome challenges in the CF lung•Protection from immune system•Less oxygen in mucus layer
- Switches gene expression•Begins to adapt•Numerous mechanisms
how are the PA adaptations in the lung regulated?
Many of the changes are regulated by quorum sensing system
what is Quorum sensing?
Ability to detect and respond to cell population density by gene regulation
•Expression or repression of specific genes which produce phenotypes which will be beneficial
what are the 3 characteristics bacteria must have to be able to us QS?
- Ability to produce a signalling molecule (an autoinducer)
- Be able to detect the change in [signalling molecules]
- Regulate gene expression as a result
how can PA use QS?
- Biofilm formation
* EPS production
what is type 3 secretion system?
- T3SS is needle like machinery that lets bacterial effectors translocate directly into the cell
- Causes tissue injury and cytotoxicity
- Can also activate innate immune response via IL-1β
- Chronic PA infections select against T3SS expressing PA
what are the 4 T3SS dependent effectors PA has?
- ExoS, ExoT, ExoY, and ExoU(reviewed in Hauser, 2009)
- ExoS, T and U disrupt host cell cytoskeleton
- ExoUcan cleave phospholipases (leads to cell death)
what happens to PA’s LPS?
O antigen lost during early CF infections
•Lipid A structure in CF clinical isolates changes
what effect can LPS modifications have?
LPS modifications may make PA less visible to immune system
what are free floating bacterica called?
platonic
what happens in chronic cf - biofilm?
- In chronic CF bacteria attach to a surface and become embedded in an acellular matrix
- Surface is damaged epithelia of airway
- Matrix varies by bacteria (also includes mucus)
- PA has Alginate, PEL, PSL, extracellular DNA etc
what are biofilms?
- Biofilms are intricate structured bacterial communities
- Generally polymicrobial
- Different micro-environments present within them
what are the 5 steps in biofilm formation?
- Initial attachment
- Irreversible attachment•Needs various factors (flagella, type IV pili)
- Microcolonyformation•Starts to produce EPS
- Maturation•Formation of complex 3D structures•Creates oxygen gradient (more anaerobic nearer centre of the biofilm mass
- Dispersion
what can PA do in chronic infections?
n chronic infections PA can switch from non-mucoid to mucoid phenotype
•Generally due to large amounts of alginateproduced
what is alginate? what are its properties?
•Linear polysaccharide
•Initially produced as homopolymer of D-mannuronic acid residues
Information from Franklin et al 2011, Colvin et al 2011, Jennings et al 2015•Modified by different enzymes (AlgI, AlgJ, AlgF)
•Epimerized by AlgG(converts D-mannuronic acid to L-guluronic acid
•Best characterised of the PA EPS
•Negatively charged
what is PSL and what does it do?
•Neutral pentasacchariderepeat •contains glucose, mannose, and rhamnose
what is pel?
- Suggested to be cationic amino sugars
* 1→4 linked partially acetylated galactosamine and glucosamine sugars
what is PA invasion of the hosts response?
- PAiscapable of evading the immune response;
- Complement evasion important during early stages of infection
- Produces enzymes (alkaline protease and elastase) degrade C3b
- Neutrophils produce reactive oxygen species and epithelial cells produce hypothiocyanite •P. aeruginosa produces pyocyanin
- PA biofilms can both stimulate and supress the immune system
- Expression of flagellin and T3SS down regulated•↓ inflammation and cytotoxicity
- PA in biofilms can trigger neutrophil cell death•↑ inflammation and tissue damage
what is Burkholderiacepaciacomplex (BCC) ?
•Comprised of at least 18 different species of Burkholderia•Most common are; B. cenocepacia(most virulent), B. multivorans, B. dolosa•Associated with;•More severe lung disease•Transmissible between CF patients•Unpredictable clinical outcomes
what is Non tuberculosis mycobacteria?
Over 150 NTM species•Majority (95%) of NTM isolates in CF patients are from 2 “complexes”•Mycobacterium avium•Most common•Includes 4 M. avium species and M. intracellulare•Mycobacterium abscessuscomplex•Impact on health outcome is variable
