Vibrio

Vibrio

The genus Vibrio belongs to family Vibrionaceae, they are enteric pathogens of humans or part of normal flora. Gram negative comma-shaped, straight or curved rods, motile by means of a single polar flagellum. Oxidase positive, facultative anaerobic. Most species require 2-3% NaCl or sea water base for optimal growth.
The genus vibrio includes two important human pathogens, Vibrio cholera causes cholera, While vibrio parahaemolyticus causes a less severe diarrhoae.
Cholera (frequently called epidemic cholera) is a severe diarrheal disease caused by the bacterium Vibrio cholera .
Diarrhea occurs-as much as 20-30 L/d-with resulting dehydration, shock and death.

Vibrio Cholera:
Classification:

Vibrio cholerae




Serogroup produce serogroup that do not
cholera toxin produce cholera toxin


serogroups 1 and 139 non 1 and non 139
serogroups


Biotype 139 Bengal non toxigenic strain some
classical 139 alcuta time associated with sporadic
and El Tor diarrhea
serogroup

Inaba Ogawa Hikojima
A and C A and B A and B and C


Toxigenic strain usually associated
with a large out break



Pathogenicity:
Rice water diarrhea (through ingestion of food or drink often sea food). A person with normal gastric acidity may have to ingest as many as 1010 or more V.cholerae to become infected when the vehicle is water, because the organisms are susceptible to acid. When the vehicle is food, as few as 102 - 104 organisms are necessary because of the buffering capacity of food.
The cells of V.cholereae attach to but do not invade the intestinal mucosa. Pathogenicity is due to secretion of an enterotoxin, which binds to ganglioside receptors on mucosal cells. After a large period of 15- 45 min, adenylate cyclase is activated and the cyclic adenosine monophosphate concentration inside the intestinal cells increases. This in turn leads to excretion of electrolytes and water and subsequent diarrhea, leading to severe dehydration.

Specimens:
Rice – water stool contains numerous numbers of vibrio, mucus and epithelial cells.

Laboratory diagnosis:
1- May be seen directly in stool samples by dark- field microscopy.
a) APW ( Alkaline Peptone Water ): transport media (pH= 8.6 )
b) TCBS (Thiosulfate – Citrate – Bile salt Sucrose agar) for culture yield yellow colonies.
C) Pepton agar.
2- Indol: positive.
3- TSI: A/A, K/A (due to sucrose fermentation).
4- Blood agar: ?-hemolytic colonies.
5- MacConKey agar: colorless (NLF)
6- Gelatinase : positive.
7- Slide agglutination tests using anti- O group 1 or 139 antisera.

Characteristics of ElTor biovar:-
?- hemolytic on sheep Blood agar
VP: positive.
Polymyxin B (50 IU): resistant.
Resistant to phage group IV.
Classic V.cholera strain give the opposite reactions in these tests.
Non – cholera vibrios
1. Vibrio mimicus
? Diarrhea after ingestion of under cooked sell fish.
? Ear infection after exposure to marine environment.

2. Halophilic Vibrios
? Vibrio parahemolyticus: diarrhea, wound infection.
? Vibrio alginolyticus: ear infection, wound infection.
? Vibrio vulnificus: septicemia, ear infection.

Laboratory diagnosis for Non-cholera vibrios:-

They do not ferment sucrose (TCBS) green colonies.
Halophilic vibrios require 1 % NaCl in all test media.

Treatment and prevention
-Intravenous administration of fluid and electrolytes .
-Oral administration of a solution contain glucose and electrolytes.
-Antibiotics(Tetracycline).
-Immunization with a whole- cell vaccine(limited use).