Vibrio ecology and virulence Flashcards
Min. temperature for Vp
15 deg C
tdh and trh
thermostable direct hemolysin and thermostable related hemolysin, considered the major virulent factors for Vp
First used to test for Vp virulence on Wagatsuma agar in the 1970s
tdh and trh virulence (what they do–3 items)
lyse RBCs, cause cytotoxicity in cell culture, enterotoxins that cause diarrhea
Both genes exhibit similar biological activity
how similar are the aa sequences for trh and tdh?
trh is 67% homologous w/ tdh
have tdh and trh ever been isolated from E-strains?
Yes, though both genes are primarily associated with C-strains
Vp chromosome I size
3.3 gb (mostly housekeeping genes)
Vp chromosome II size
1.8 gb (more variable)
indicators of horizontal gene transfer on Vp chromosome II (4)
phage genes, transposons, mobile genetic elements (MGEs), interesting GC regions
all indicative of recent horizontal gene transfer
genes of interest in Vp pathogenicity island on chromosome II
TTSS gene sets (2), tdh (2 copies), + homologues to other well studied virulence factors
TTSS (type 3 secretion system) function
allows the transport of cytoplasmic proteins across the cell membrane
how many sets of TTSS does Vp have?
2 sets– TTSS1 and TTSS2
Each secretory system recognizes distinct proteins and is expressed under different conditions
Which TTSS is found in all Vp strains?
TTSS1
Which TTSS is found in only KP-positive strains?
TTSS2
Does Vc have a TTSS?
no; likely linked to the inflammatory response in Vp infection
YopD and VopD
Vp virulence factors
form holes in the host membranes and mediate the injection of effector proteins to disrupt immune defenses, excreted by TTSS1 ((Vop) and TTSS2 (Yop)
how many copies of T6SS (type 6 secretion system) does Vp have?
2– T6SS1 and T6SS2
which T6SS is more active under marine conditions for Vp and which chromosome is it located on?
T6SS1
chromosome I
which T6SS is more active under lower salinity conditions for Vp and which chromosome is it located on?
T6SS2
chromosome 2, only functions in adhesion not cytotoxicity
do non-pandemic strains of Vp have T6SS
only partial gene sets
MAM7 (multivalent adehesion molecule 7) function in Vp
host adhesion which can then lead to the upregulation of virulence factors, needed for TTSS-mediated cell death
how was toxR first identified?
as the regulatory gene for cholera toxin
how much homology is there between Vp and Vc toxR genes
Vp toxR aa sequence is 52% similar to Vc toxR
is toxR specific to C-type Vp?
No, tox R is also found in E-type Vp and other Vibrio species (though it is thought to be “perfectly” conserved in Vp)
(Kim et al. 1999)
what is the function of toxR?
part of the toxRS (toxR +toxS) operon that regulates “virulence-associated genes” including tdh
(Matsumoto et al. 2000)
Which Vp virulence factors are primarily associated w/ KP-pos strains?
tdh and trh
how many cases of Vv require hospitalization each year in the US?
50, responsible for 95% of seafood-related deaths
what is the fatality rate of Vv infection?
50-60%, up to 79% (parker et al. 1991)
how was Vv described prior to 1976?
“lactose positive” Vibrio (w/o gas), before being identified as a specis by the CDC in 1976
(15% of Vv are actually lac-; 15% are suc+)
Vv biotype 2
associated with infection of eels
all biotype 2 strains have the same LPS (serotype E), different type of LPS than biotype 1
Vv biotype 3
associated with Israeli wound infections (Bisharat et al. 1999)
all have vvha (like biotype 1), but vvha are all identical (unlike biotype 1)
what time of year are Vp and Vv infections most common
March-October, when waters are warmer
Optimum salinity range for Vv
5-10 ppt, up to 25 ppt (Blackwell and Oliver 2008)
Optimum salinity for Vp
23 ppt (10-34 ppt salinity range)
How many genomes of Vv +Vp have been completed?
~10
How many genes make up a TTSS?
20-30
How long does it take for a Vv infection to advance to primary septicemia?
Hours to days, 36h on average
What is the incubation period for a Vv wound infection?
3h to 8d
Vv capsule (CPS) function
anti-phagocytic
Is CPS importance for Vv virulence?
YES, it is essential.
What is th difference between transluscent and opaque strains of Vv?
Transluscent– no CPS, LD50>10^6-10^8 CFUs
Opaque– much more virulent; have CPS, LD50
How is CPS related to biofilm formation in Vv?
CPS+ strains are not as good at forming biofilms; possible reason E-strains (CPS-) do better in the environment than C-strains.
Function of LPS in Vv
lipid polysaccharide
causes symptoms related to endotoxic shock
What happens when mice are treated w/ Vv LPS (no live cells)
they die in 30-60 mins; Vv LPS is very very virulent!
vvha
Vv hemolysin
linked to virulence but no change in mutant strains
vvpE
Vv metalloprotease
linked to virulence but no change in mutant strains
flgC &flgE
Vv flagellar proteins
mutants have reduced cell adherence
RTX toxin
Vv toxin involved in cytoskeletal rearrangements in host cells, more toxin is produced when Vv is in contact with host cell
luxR (smcE)
Vv quorum sensing genes
Mutants have increased virulence
RpoS
Vv stress response factor
Has effects on adherence and cytotoxicity
hlyU
Vv transcriptional activator associated with virulence
What is the problem with mouse models of Vv infection?
lab experiments indicate that ALL strains of Vv are virulent based on animal lethality, but there are
how many oysters are consumed in the US each year?
75-80 million
How are C v. E-types of Vv differentiated?
using the virulence correlated gene
C strains have vcgC allele
E strains have the vcgE allele
Not a virulence genes, just correlated with virulence
What percent of C-type Vv strains are isolated from clinical samples?
90% (Rosche et al. 2005)
What percent of E-type Vv strains are isolated from environmental samples?
93% (Rosche et al. 2005)
What is the concentration of Vv in seawater?
Average of 1-50 CFUs/mL, up to 10^4 CFUs/mL
What percent of natural flora is Vv in SE esuarine populations?
0.15% (Pfefferel et al. 2003)
What is the concentraion of Vv in shellfish?
up to 10^6 CFUs/mL, varies dramatically and has a strong correlation with temperature
What are other reservoirs for Vibrio?
sediments, plankton, non-molluscan shellfish, fish
Large range of concentrations
What percent of attached bacteria found on plankton/sediment is Vv?
up to 57%, higher than Vv found in surrounding water (Heidelberg et al. 2002)
what salinities have the greatest concentration of Vv?
5-10 ppt, result independent of temperature (Randa et al. 2004)
At 20-25 deg C, temperature must be greater than _____ for Vv to grow.
20deg C
True or false: Vv responds to environmental parameters similarly to other Vibrios
True: Vv numbers correlate well with total Vibrios
True or false: environmental strains decline in human serum
True (Williams et al. 2014, Vv metatranscriptomics paper)
pilF
used to detect pathogenic Vv strains through a polymorphism in the pilF (pilin) gene
This gene ahs been implicated in human pathogenicity and is useful for distinguishing pathogens in all three Vv biotypes.
Min temp for Vv
20 deg C
Why is urease activity important for Vp?
Breaks down urea, an important nitrogen source
What percent salt is required by Vv/Vp?
Vv: 0.5%
Vp: 2-3%
What is the thermolabile hemolysin (tlh) gene used for?
Detection of Vp (present in Vp but not other vibrio species)
Are Vv/Vp oxidase positive?
Yes
What sugars can Vv/Vp both utilize?
mannitol, mannose
Are Vv urease positive?
Variable (Vp is usually urease+)
Which organisms (Vv or Vp) is lac+?
Vv
Which organisms (Vv or Vp ) is ara+?
Vp
What is the primary role of heterotrophs in the N cycle?
Remineralization and decomposition of dissolved and particulate N (may also be consumers of both inorganic and organic N)
Can Vibrio fix Nitrogen?
4 species in the Vibrionaceae can and may be associated with plants and urchins
What N cycle-related functions can Vibrio carry out? (3)
nitrogen fixation, reduction (assimilatory and dissimilatory), ammonification
No known role in nitrification
What is the half-saturation constant for Vp? What does this mean?
500 uM, very high
Is the concentration supporting 1/2 maximum glucose uptake, indicates rapid growth/turnover potential
During aerobic respiration, what percent of C is used for biomass?
30-50%
During fermentative metabolism, what percent of C is used for biomass?
10%; most products are excreted (C leaking)
Likely an important contributor to DOC
What important enzymes do Vibrio have for the breakdown/remineralization of phosphorus? (2)
5’ nucleotidases (cleave 5’ nucleotides)
alkaline phosphatase (cleaves inorganic phosphate)
List the three “core” genome features of Vibrios?
- motility
- morphological plasticity
- organic matter cycling
What is the primary bottom up control on Vibrio?
Substrate availability
What is the primary top down control on Vibrio?
Predation (viral lysis, selective grazing)
How do Vibrio help to stimulate the anaerobic foodchain?
Via substances (like H2) that are released during anaerobic respiration
What is the incubation period for a Vibrio infection?
3h-8d (average 24h)
What secretory system excretes the RTX toxin?
Type I
What Vv virulence factor do female hormones protect against?
LPS
What is the percentage of Vv in coastal estuaries?
~0.15% (total Vibrio usually
What percent of total Vv has been shown to be attached ?
57%
What does the pilF gene assay detect?
a polymorphism in the pilF gene associated with virulence
What does the pilF do?
Codes for a pilin protein, important for horizontal gene transfer via conjugation
What amount of rainfall constitutes a “storm event”
> 1.27 cm
Is the VNBC state unique to Vibrio?
No, has been documented in other taxa; possibly up to 30 species
How many Vp O serotypes are there? K?
O: 13
K: 71
When did Vp O3:K6 emerge?
mid-1990s in Japan and India
What are the biochemical characteristics of O3:K6?
tdh+, trh-, urease-
Does Vv have a TTSS?
Yes, but has only recently been studied and has not yet been implicated in virulence
Why is tdh problematic as a marker for virulence?
Present in some benign environmental strains, some tdh+ strains are negative for hemolysis activity, and tdh mutants still caused disease in the mouse model
Virulence of O4 serovar Vp can usually be predicted by ________ _________.
urease activity; O4 strains tend to be urease +
What are siderophores?
Iron storage proteins which are produced under iron-limiting conditions; important in both clinical and environmental strains
Higher concentration may give a competitive advangtage
What is the GC content of Vp’s pathogenicity island on Chromosome II? What is the GC content of the rest of the genome?
~40% – PI
~45% – rest of genome
This is indicative of horizontal gene transfer
When is the TTSS triggered in Vp?
When the organism comes into contact with other cells
What two antibiotics are all Vibrio resistant to?
colistin and polymixin B
