JW - Biofilms and Bacteriophage I Flashcards
(18 cards)
What is Vibrio cholerae and how does it appear microscopically? (5)
- Gram-negative, curved rod
- 0.5–0.8 μm wide and 1.4–2.6 μm long
- Facultative anaerobe
- Has a single polar flagellum
- Optimal growth at 20–30°C
How is Vibrio cholerae transmitted? (3)
- Water (infectious dose = 10⁹)
- Food (infectious dose = 10³)
- Person-to-person contact
What are the clinical events in cholera? (4)
- Entry
- Colonisation
- Disease, hypovolemic shock, acidosis, vomitting, diarrhoea, muscle cramps
- Exit (in one to many liters of fluid per day)
What are the clinical manifestations of cholera? (5)
- Severe diarrhea – up to 20–30 L/day
- Dehydration
- Shock
- Acidosis
- Can be fatal if untreated
Describe the pathology of cholera infection. (4)
- Non-invasive – bacteria do not reach bloodstream
- V. cholerae colonizes intestinal microvilli
- Secretes cholera toxin, mucinase, and endotoxin
- Acts locally in the intestine
How is V. cholerae classified? (2)
- Serogroups – bacteria of the same species with different antigenic determinants on the cell surface
- Biotypes (biovars) – different strains of the same bacterial species
distinguished by a group of phenotypic or genetic traits - 150 serogroups exist, but only two are epidemic-causing
How is toxigenic Vibrio cholerae classified? (3)
- Divided into two epidemic serotypes:
- O1
- O139
- These two serotypes are responsible for cholera outbreaks
- Other serotypes exist in the environment but are not epidemic-causing
What is the classification hierarchy for the O1 serotype of V. cholerae?
- O1 is further divided into two biotypes:
- Classical – caused the first six pandemics
- El Tor – replaced Classical in 1961
- Each biotype has three serotypes (ribotypes):
- Inaba – A & C antigens
- Ogawa – A & B antigens (mostly A, little C)
- Hikojima – A, B & C antigens
What is significant about the O139 serotype of V. cholerae? (3)
- Emerged in Southeast Asia in 1992
- Replaced O1 as the predominant pandemic-causing strain
- Demonstrates the potential for new epidemic serotypes to emerge
Why are only O1 and O139 of over 150 V. cholerae serotypes toxigenic? (3)
- These two serotypes have acquired key virulence factors (e.g. CTXϕ phage and TCP pili)
- Environmental strains lack these elements and do not cause severe disease
- Highlights the role of horizontal gene transfer in pathogenic evolution
What is transduction in bacteria and what are its types? (4)
- Transduction is the transfer of genetic information from one bacterium to another via a bacteriophage
- The DNA is carried inside the phage particle
- There are two types of transduction:
- Generalized transduction – random bacterial DNA is packaged into phage heads
- Specialized transduction – specific bacterial genes near the prophage insertion site are transferred
What is the structure of the V. cholerae genome? (2)
Two circular chromosomes
- Chromosome I (2.96 Mbp) – essential functions and housekeeping
- Chromosome II (1.07 Mbp) – includes integron island
What two bacteriophages are associated with V. cholerae virulence in chromosome 1 (2)?
- VPI phage – encodes Toxin-Coregulated Pilus (TCP) for host attachment
- CTXϕ phage – encodes cholera enterotoxin; integrates into Chromosome I
What is the Toxin-Coregulated Pilus (TCP) (4)?
- Filamentous surface structure on V. cholerae
- Required for efficient colonization of the small intestine
- Major subunit = TcpA
- Genes for TCP production are located on pathogenicity island (VPI) in Chromosome I
How is cholera toxin encoded and regulated? (4)
- Genes: ctxA and ctxB (on phage CTXϕ)
- Transcription regulated by host and phage proteins
- Integration site in genome = attRS
- Toxin expression requires TCP (receptor for CTXϕ)
How does the cholera toxin (CT) function at the cellular level? (5)
- A-B type toxin: 1 A subunit + 5 B subunits
- Binds to GM1 ganglioside on host cells
- Internalized via endocytosis → ER
- A1 subunit modifies GTPase → increases cAMP
- High cAMP → secretion of Cl⁻, HCO₃⁻, and water → diarrhea
Why doesn’t V. cholerae always cause disease? (3)
- Only becomes toxigenic after infection with CTXϕ phage
- Phage uses TCP to enter the bacterium
- Integration of CTX genome enables toxin production
What broader lesson does V. cholerae teach about phage biology? (3)
- Phage-mediated gene transfer is key in evolution of virulence
- Many bacterial pathogens acquire virulence factors via phages
- Phages may also enhance survival and pathogenicity in biofilms
