Lec 6 Vibrionaceaelec

7/29/2019 Lec 6 Vibrionaceaelec

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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.




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)



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



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.



V. cholera on TCBS



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.



Stringing after emulsification



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



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?



Cholera toxin activity





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



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.



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%!



Vibrio – clinical significance

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




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?



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:




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




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.

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