lec 6 vibrionaceaelec
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Vibrionaceae and Aeromonadaceae
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Vibrionaceae and Aeromonadaceae
Classification – contain three medically
important genera
Vibrio
Aeromomas
Pleisiomonas
All members of these families are oxidase +,
catalase +, ferment glucose, indole +, andare motile by means of polar flagella.
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Vibrionaceae and Aeromonadaceae
To differentiate amongst the different genera:
6.5% NaCl ODC DNAse LDC O/129*
Vibrio G +/- +/- +/- S
Aeromonas NG - + + R
Pleisiomonas NG + - + S
*O/129 is a vibriostatic agent (2,4-diamino-6,7-dilsopropylpteridine)
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Vibrionaceae
Vibrio species – are found in fresh and saltwater and in the intestines of humans and
other animals
Morphology and cultural characteristics
Gram negative straight or curved rods with polar
flagella
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Vibrio general and cultural
characteristics
Will grow on routinely used bacteriologic media. On CBAlook similar to other Gram-negative bacteria, but may have agreenish hue.
TCBS – Thiosulfate-Citrate-Bile salts-Sucrose – wasdeveloped for the selective isolation of Vibrios
Sodium citrate, high pH (8.6) and bile salts (collectivelyinhibit G + and many enterobacteriaceae) are theselective ingredients
Sucrose and bromthymol blue( turns yellow in acidconditions), plus sodium thiosulfate and ferric citrate arethe differential ingredients .
Organisms that ferment sucrose (V. cholera and V.alginolyticus ) produce yellow colonies. Non-sucrosefermenting colonies remain colorless (V.parahaemolyticus and V. vulnificus ).
Organisms that produce H2S produce a blackprecipitate.
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V. cholera on TCBS
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Vibrio species
Vibrio biochemistry
Oxidase +
Fermentative, but usually anaerogenic
TSI A/A or K/A
LIA K/K or K/A
Urea –
Display a wide range of halotolerance.
NaCl stimulates growth, but the concentration
required for stimulation varies with species. Colonies string after emulsification in sodium
desoxycholate.
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Stringing after emulsification
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Vibrio species
Serologic ID
Vibrio cholera is divided into serogroups based on O
antigens.
Only those toxigenic strains belonging to serogroup 01 or
0139 have been found to be involved in epidemic infections.
The 01 serogroup is divided into two biotypes, Classical and
El tor, both of which can cause epidemics:
hemolysin VP Polymyxin B
Classical - - S
El tor + + R
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Vibrio species
Virulence factors
Vibrio cholera produces a heat labile enterotoxin that
binds to Gm1 gangliosides and has the same structure
and mechanism of action as the LT enterotoxin of
ETEC. So what is the net result of its activity?
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Cholera toxin activity
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Vibrio virulence factors
Other Vibrio species may produce cholera-like enterotoxins
V. cholera may produce an enterotoxin called ZOT whichincreases leakage of electrolytes and fluid into the intestinallumen by disrupting the tight junctions between intestinalenterocytes
V. cholera may also produce an enterotoxin called ACEwhich may insert into intestinal membranes forming an ionchannel
Endotoxin – more important in the pathogenesis of Vibrios other than V. cholera .
Hemolysins – important for V. parahaemolyticus , but not V.cholera infections
Colonization factors – fimbrial (hemagglutinin) and non-fimbrial (outer membrane proteins, including the LPS) areinvolved in attachment to intestinal mucosa cells.
Motility – help V. cholera reach the intestinal mucosa
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Vibrio
Protease (previously called a mucinase)- produced by V.cholera – degrades fibronection, lactoferrin and choleratoxin – may be important for allowing bacteria to leavemucosal cells that are being sloughed from the mucosa.The bacteria could then reattach to newly formed mucosalcells.
Cytolysin – is important in species other than cholera
Clinical significance
V. cholera – causes cholera which acquired by ingestion of contaminated food or water.
The organism attached to and multiplies at the mucosal
surface, but does not invade the mucosal cells. The cholera enterotoxin(s) are liberated causing a
purging, watery diarrhea (rice H2O stools) containinglarge numbers of Vibrios.
Up to 20 liters of fluid may be lost per day.
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Vibrio – clinical significance
If left untreated, the patient will become markedlydehydrated, and go into hypovolemic shock andmetabolic acidosis.
This can lead to cardiovascular collapse and death.
V. parahaemolyticus – causes gastroenteritis after ingestionof raw, improperly cooked, or contaminated seafood(common in Japan).
The disease is usually self-limited and symptomsinclude abdominal pain, vomiting, watery diarrhea, andslight fever.
V. parahaemolyticus occasionally causes infections of wounds in individuals exposed to contaminated seawater.
V. vulnificus – in patients with liver dysfunction andsyndromes with increased serum iron levels, ingestion of V.vulnificus from contaminated shellfish can result, withinhours, in septicemia with a mortality rate of 40-60%!
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Vibrio – clinical significance
V. vulnificus infections of wounds can also occur
and, in immunocompromised individuals, this can
rapidly progress to necrosis, septicemia and
death.
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Early lesion
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Necrosis
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Septicemia
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Vibrionaceae and Aeromonadaceae
Treatment
For gastroenteritis – replace lost fluid and electrolytes
Systemic infections – tetracycline
Aeromonas and Pleisiomonas species – now
considered to be in the new family Aeromonadaceae Found in fresh water and are more likely to cause
infections in cold-blooded animals than in humans.
Most grow on CBA and some grow on selective entericmedia
On CIN Aeromonas hydrophila produces pink coloniesand Pleisiomonas shigelloides produces colorless colonies – What does this tell you?
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Aeromonas and Pleisiomonas
Biochemistry
TSI A/A plus gas, H2S – for Aeromonas ; A/a or K/A no gasor H2S for Pleisiomonas
LIA K/K or K/A for Aeromonas; K/K for Pleisiomonas
DNAse + for Aeromonsa ; - for Pleisiomonas
Virulence factors Aeromonas – may produce heat labile enterotoxins and
cytotoxins
Pleisiomonas – may produce an enterotoxin
Clinical significmce
Aeromonas –
gastroenteritis infection occurs from ingestionof contaminated water or seafood.
Large numbers of organisms must be found in the stool for itto be reported out as the pathogen.
Five different diarrheal presentations may occur:
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Aeromonas and Pleisiomonas
Watery diarrhea with vomiting
Dysenteric form of diarrhea with blood and mucous
Chronic diarrhea
Choleric type of diarrhea with rice-water stools
Traveler’s diarrhea
Aeromonas may also cause wound infections andsepticemia
Pleisiomonas –may cause three different types of gastroenteritis:
Watery diarrhea
Subacute or chronic diarrhea
Dysenteric form of diarrhea
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Aeromonas and Pleisiomonas
Treatment
Aeromonas – if antimicrobics become necessary,
most are sensitive to penicillin, but susceptibility
testing should be done
Pleisiomonas - if antimicrobics become necessary,antimicrobic sensitivity testing should be done.