Vibrionaceae and Aeromonadaceae

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.

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)

Vibrionaceae Vibrio species – are found in fresh and salt water 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 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 H 2 S produce a black precipitate.

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 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 non- fimbrial (outer membrane proteins, including the LPS) are involved 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 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 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 H 2 O stools) containing large numbers of Vibrios. Up to 20 liters of fluid may be lost per day.

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%!

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

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 enteric media On CIN Aeromonas hydrophila produces pink colonies and Pleisiomonas shigelloides produces colorless colonies – What does this tell you?

Aeromonas and Pleisiomonas Biochemistry TSI A/A plus gas, H 2 S – for Aeromonas; A/a or K/A no gas or H 2 S 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 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

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.