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Vibrionaceae and Aeromonadaceae
Vibrionaceae and Aeromonadaceae
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Classification – contain three medically
important genera
Vibrio
 Aeromomas
 Pleisiomonas
 All members of these families are oxidase +,
catalase +, ferment glucose, indole +, and
are motile by means of polar flagella.
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Vibrionaceae and Aeromonadaceae
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To differentiate amongst the different genera:
6.5% NaCl ODC DNAse LDC O/129*
Vibrio
G
Aeromonas NG
Pleisiomonas NG
+/+
+/+
-
+/+
+
S
R
S
*O/129 is a vibriostatic agent (2,4-diamino-6,7dilsopropylpteridine)
Vibrionaceae
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Vibrio species – are found in fresh and salt
water and in the intestines of humans and
other animals
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Morphology and cultural characteristics
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Gram negative straight or curved rods with polar
flagella
Vibrio general and cultural
characteristics
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Will grow on routinely used bacteriologic media. On CBA
look similar to other Gram-negative bacteria, but may have a
greenish hue.
TCBS – Thiosulfate-Citrate-Bile salts-Sucrose – was
developed for the selective isolation of Vibrios
Sodium citrate, high pH (8.6) and bile salts (collectively
inhibit G + and many enterobacteriaceae) are the
selective ingredients
Sucrose and bromthymol blue( turns yellow in acid
conditions), plus sodium thiosulfate and ferric citrate are
the differential ingredients .
Organisms that ferment sucrose (V. cholera and V.
alginolyticus) produce yellow colonies. Non-sucrose
fermenting colonies remain colorless (V.
parahaemolyticus and V. vulnificus).
Organisms that produce H2S produce a black
precipitate.
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V. cholera on TCBS
Vibrio species
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Vibrio biochemistry
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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.
Stringing after emulsification
Vibrio species
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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
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Virulence factors
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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?
Cholera toxin activity
Vibrio virulence factors
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Other Vibrio species may produce cholera-like enterotoxins
V. cholera may produce an enterotoxin called ZOT which
increases leakage of electrolytes and fluid into the intestinal
lumen by disrupting the tight junctions between intestinal
enterocytes
V. cholera may also produce an enterotoxin called ACE
which may insert into intestinal membranes forming an ion
channel
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 nonfimbrial (outer membrane proteins, including the LPS) are
involved in attachment to intestinal mucosa cells.
Motility – help V. cholera reach the intestinal mucosa
Vibrio
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Protease (previously called a mucinase)- produced by V.
cholera – degrades fibronection, lactoferrin and cholera
toxin – may be important for allowing bacteria to leave
mucosal cells that are being sloughed from the mucosa.
The bacteria could then reattach to newly formed mucosal
cells.
Cytolysin – is important in species other than cholera
Clinical significance
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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) containing
large 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 markedly
dehydrated, and go into hypovolemic shock and
metabolic acidosis.
This can lead to cardiovascular collapse and death.
V. parahaemolyticus – causes gastroenteritis after ingestion
of raw, improperly cooked, or contaminated seafood
(common in Japan).
The disease is usually self-limited and symptoms
include abdominal pain, vomiting, watery diarrhea, and
slight fever.
V. parahaemolyticus occasionally causes infections of
wounds in individuals exposed to contaminated sea
water.
V. vulnificus – in patients with liver dysfunction and
syndromes with increased serum iron levels, ingestion of V.
vulnificus from contaminated shellfish can result, within
hours, in septicemia with a mortality rate of 40-60%!
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Vibrio – clinical significance
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V. vulnificus infections of wounds can also occur
and, in immunocompromised individuals, this can
rapidly progress to necrosis, septicemia and
death.
Early lesion
Necrosis
Septicemia
Vibrionaceae and Aeromonadaceae
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Treatment
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For gastroenteritis – replace lost fluid and electrolytes
Systemic infections – tetracycline
Aeromonas and Pleisiomonas species – now
considered to be in the new family
Aeromonadaceae
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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 enteric
media
On CIN Aeromonas hydrophila produces pink colonies and
Pleisiomonas shigelloides produces colorless colonies –
What does this tell you?
Aeromonas and Pleisiomonas
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Biochemistry
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Virulence factors
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TSI A/A plus gas, H2S – for Aeromonas; A/a or K/A no gas or
H2S for Pleisiomonas
LIA K/K or K/A for Aeromonas; K/K for Pleisiomonas
DNAse + for Aeromonsa; - for Pleisiomonas
Aeromonas – may produce heat labile enterotoxins and
cytotoxins
Pleisiomonas – may produce an enterotoxin
Clinical significmce
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Aeromonas – gastroenteritis infection occurs from ingestion
of contaminated water or seafood.
Large numbers of organisms must be found in the stool for it
to be reported out as the pathogen.
Five different diarrheal presentations may occur:
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 and
septicemia
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
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Treatment
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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.