Faculty of Applied Medical Science

Graduation project

Vibrios and Aeromonas


 Introduction:
The second major group of Gram-negative facultatively anaerobic, fermentative rods are the genera Vibrio and Aeromanas .These organisms were at one time classified together in the family Vibrionaceae and were separated from the Enterobacteriaceae on the basis of positive oxidase reaction and the presence of polar flagella . These organisms were also classified together because they are primarily found in water and are able to cause gastrointestinal disease . However , molecular biology techniques have established that this genera are only distantly related and belong in separated families ; Vibrio and Aeromonas are now classified in the families Vibronaceae and Aeromonadaceae, respectively .Despite this taxonomic reorganization , it is appropriate to consider these bacteria together because their epidemiology and range of diseases are similar .
Vibrios
 Introduction:
The genus Vibrio has undergone numerous changes in recent years, with a number of less common species described or reclassified .Currently,the genus is composed of more than 60 species of curved rods with 10 species implicated in human infections . Vibrio cholera , Vibrio parahaemolyticus are the most important members ( and Vibrio vulnificus in some books ) (1) . Vibrios are short and curved Gram-negative bacilli which are motile, nonsporing and oxidase positive organisms . This genus comprises of 33 well defined species of which 11 have been isolated from clinical specimens obtained from human beings (2) .

[ (1)- ( Ken S. Rosenthal , et.al.) in 2005 ] [ (2)- 9 Rajesh Bhatia and Rattan Lal Ichhpujani ) in 2004 . ]

• Physiology , Structure and Classification of Vibrios :
Vibrio species can grow on variety of simple media within a broad temperature range from 14 to 40 . V.cholera can grow in the absence of salt ; most other species that are pathogenic in human require salt ( halophilic species ) . Vibrios tolerate a wide range of pH ( eg., pH of 6.5 to 9.0 ) but are susceptible to stomach acids . If gastric acid production is reduced or neutralized patients are more susceptible to Vibrio infection .
Most Vibrios have a single polar flagellum ( in contras with peritrichous flagella in the family Enterobacteriaceae ) . These bacteria also have various pili that are important for virulence . For example, epidemic strains of V.cholera , the etiologic agent of cholera , have the toxin co-regulated pilus.
The cell wall structure of Vibrios is also important . All strains possess lipopolysaccharides consisting of lipid A ( endotoxin ) , core polysaccharide and an O polysaccharide side chain . The O polysaccharide is used to subdivide Vibrio species into serogroups ; there are more than 140 serogroups of V.cholera ( O1 _ O140 ) , 7 O serogroups of V.fulnificu and 13 O serogroups of V.parahaemolyticus . The interest in this classification scheme is more than academic . (1)