Community Acquired Bacterial Infections Flashcards
Define virulence factor.
Molecules produced by pathogens that contribute to the pathogenicity of the organism
List some common bacterial virulence factors and include their function.
- Flagella – movement and attachment
- Pili – adherence
- Capsule – protects against phagocytosis
- Endospores – metabolically dormant forms of bacteria – they are heat, cold, desiccation and chemical resistant
5, Biofilms – organised aggregates of bacteria embedded in a polysaccharide matrix – antibiotic resistant
Give examples of bacteria that possess the following virulence factors:
a. Capsule
b. Endospores
c. Biofilms
Capsule
Streptococcus pneumoniae
Endospores
Bacillus sp.
Clostridium sp.
Biofilms
Pseuodmonas aeruginosa
Staphylococcus epidermidis
What are exotoxins?
A toxin released by a living bacterial cell into its surrounding
What are the four main different types of exotoxin? Give examples of bacteria that produce such toxins.
- Neurotoxins -act on nerves or motor-end plates
- Botulinum toxin
- Tetanus - Enterotoxins- act on GIT
- Infection diarrhoea –Vibrio cholerae, E. coli, Shigella dysenteriae, C.jejuni
- Food poisoning –Bacillus cereus, Staph. aureus - Pyrogenic exotoxins- stimulate realise of cytokines
- Staph. aureus
- Strep. pyogenes - . Tissue invasive toxins - enzymes that allow bacteria to tunnel through tissue
- Staph. aureus
- Strep. pyogenes
- Clos. perfringens
What is an endotoxin?
This is the lipid A part of lipopolysaccharide that is found on the outer membrane of Gram-negative cells
NOTE: so ONLY Gram-negative cells can produce endotoxins
Why can treating patients with Gram-negative infection sometimes worsen their condition?
Antibiotics can cause lysis of the bacteria meaning that the endotoxins are released into the circulation in large quantities
This can trigger an immune response that leads to SEPTIC SHOCK
What is an outbreak?
sudden increase in the incidence of a disease in a particular time at a particular place
How can an outbreak be identified?
Surveillance
Good and timely reporting systems are necessary
PCR
What was the 2011 E. coli outbreak in Germany caused by?
outbreak due to fusion of EHEC and EAHC strains to form EAHEC
EHEC- enterhohaemorrhagic E.coli
EHAC- enteroaggregative E.coli
What were the symptoms of infection by this EHEC bacterium?
Gastroenteritis
Haemolytic uraemia syndrome (acute renal failure + haemolytic anaemia + thrombocytopenia
What was special about the bacterial strain that caused by outbreak?
The bacterial strain was an enteroaggregative E. coli strain (EAEC) that had acquired the ability to produce shiga toxin (through phagetransfer)
Shiga toxin production is a feature of Enterohaemorrhagic E. coli(EHEC)
This produced a new strain called Enteroaggregative haemorrhagic E. coli (EAHEC
Describe the structure of shiga toxin.
There is an A subunit that is non-covalently associated with a pentamer of protein B
(AB5 subunit composition)
Describe the action of shiga toxin.
Subunit A is the enzymatically active domain (StxA)
Subunit B is pentamer responsible for binding to the host cell membrane
Subunit A cleaves 28S ribosomal RNA in eukaryotic cells thus inhibiting protein synthesis
Bacterial ribosomes are also a substrate for subunit A so it can lead to decreased proliferation of susceptible bacteria (e.g. commensal microflora of the gut)
How was the shiga toxin gene transferred between bacteria?
Bacteriophage
What is the important virulence factor in EAEC?
Aggregative adherence fimbriae (AAF) –
- this is required for adhesion to enterocytes and stimualtes IL-8 response
- AAF also allows biofilm formation
What type of bacterium is Legionella pneumophila and what is the route of infection?
Gram negative
It is transmitted through inhalation of contaminated aerosols
Which cells within the human host does L. pneumophila infect and grow inside?
Alveolar macrophages
What is the important virulence factor for L. pneumophila?
Type IV secretion system
What feature of Mycobacterium tuberculosis makes it more difficult to treat?
It has a mycolic acid outer membrane – this prevents normal antibiotics from getting into the cell
State three bacterial sexually transmitted diseases including the species of bacteria that cause the diseases.
Chlamydia - Chlamydia trachomatis
Syphilis –Treponema pallidum
Gonorrhoea –Neisseria gonorrhoeae
What is a major consequence of Chlamydia in the developing world?
Blindness (due to eye infection)
How does N. gonorrhoeae establish infection in the urogenital tract?
It interacts with non-ciliated epithelial cells
What are the important virulence factors of N. gonorrhoeae?
Pili
Antigenic variation escapes detection and clearance by the immune system
What is the most commonly reported infectious GI disease in theEU?
Campylobacter jejuni
What is the route of infection of Campylobacter and Salmonella?
Ingestion of undercooked poultry
State some important virulence factors of Campylobacter jejuni.
Adhesion and invasion factors
Type IV secretion system
Toxin
Which subset of the population has the highest incidence of Salmonella and Campylobacter infection?
Young children (0-4 years)
What is an important virulence determinant of Salmonella sp.?
Type III secretion system
NOTE: Salmonella sp. can cause outbreaks whereas Campylobactertends to be sporadic cases
What are the important virulence factors of Vibrio cholerae?
Cholera toxin
Type IV fimbria
Explain how cholera toxin works.
It has A and B subunits
A is the active toxin
B allows entry of the toxin into the epithelial cell
The A subunit activates adenylate cyclase, thus increasing the production of cAMP
The cAMP then binds to CFTR and causes Cl- efflux
Water follows the ion movement so you get massive movement of water into the lumen of the intestine
Which subsets of the population are at risk of infection by Listeria monocytogenes?
Immunocompromised
Elderly
Pregnant and their foetus
What are some special features of Listeria?
They can enter non-phagocytic cells and cross tight barriers (e.g. BBB and maternal-foetal barrier)
Name some bacterial vector-borne diseases.
Q fever
Plague
List some vaccine-preventable diseases. Identify which are viral.
- Diphtheria (clostr. diptheriae)
- gram +ve - Invasive pneumococcal infections (strep. pneumoniae)
- gram +ve - Invasive meningococcal infections (neiss. meningitidis)
- gram -ve - Pertussis (bordetella pertussis)
- gram -ve - Tetanus (clos. tetani)
- gram +ve - Invasive Haemophilus influenza
- gram -ve
Viral Measles * Mumps* Rubella* Polio*
What aspects of EHEC and EAEC did the PCR identify?
EAEC- 2 plasmids
- pAA type plasmids which contain aggregative adhesion fibril operon
- ESBL plasmids- gene for encoding for extended spectrum beta lactamase (AB resistance)
EHEC
-prophage encoding shiga toxin
prophage is when a bacteriophage inserts genome into circular bacteria DNA
List two communicable respiratory tract infections, giving their virulence factors and route of infection by their bacterium.
- Legionnaire’s diseases ( legionella pneumophilila)
- gram -ve
- v factors are type 4 secretion systems
- roi- inhalation of aerosols - Tuberculosis (mycobacterium tuberculosis)
- gram +ve
- v factors are it has an extra lipid layer and can enter a dormant state for reactivation
List three communicable sexually transmitted infections, giving their virulence factors and route of infection by their.
- Chlamydia (chlamydia trcahomatis)
- gram -ve obligate intracellular parasite
- most common STI in Europe and causes more than 3% worlds blindness - Gonorrhoea (neisseria gonorrhoea)
- gram -ve
- UTI affecting non-ciliated epithelial cells
- v factors are pili, antigenic variation mechanisms - Syphilis ( treponema pallidum)
- also gram -ve
List four communicable food./waterbourne/zoonoses infections, giving their virulence factors and route of infection by their.
- Campylobacterosis mostly (C. jejuni)
- most infectious GI disease in EU
- gram -ve
- small children 0-4 highest risk group
- infection route via uncooked poultry, but does NOT causes outbreaks
- v factors are adhesion, flagella, T4 secretion system - Salmonellosis (salmonella species)
-gram -ve
- again uncooked poultry but DOES cause outbreaks
- highest risk in small children 0-4
- main v factor is T3 secretion system;
SPI1 for invasion and SPI2 for intracellular accumulation - Cholera (vibrio cholera)
- gram -ve
- acute severe diarrhoeal disease
- main v factors are T4 fimbria and cholera toxin (increased cAMP- opening of Cl- channels and expulsion of water from cells)- carried on bacteriophages - Listerosis ( listeria monocytogenes)
- gram +ve
- risk groups are immunocompromised and pregnant people
State two emerging and vector borne disease?
- Plague (yersina pestis)
- gram -ve - Q fever (coxiella burnetti)
- gram -ve
smallpox has been eradicated
What infectious disease has mass vaccination eradicated?
Smallpox
Poliomyelitis
