Vibrionaceae

Introduction of Vibrio Three members pathogenic to human, other species are pathogenic for animal and insects. The genus Vibrio consists of Gram negative straight or curved rods, motile by mean of single polar flagellum. Most common in surface of waters. Occur in both marine and freshwater habitat. Most disease causing strains are associated with gastroenteritis but can also infect open wounds and cause septicemia.

Vibrio cholera Found in fresh and brackish (slighly salt) water, shellfish and other seafood Major reservoir is not known. Long assumed to be human but some evidence suggests that it is the aquatic environment. Factor of transmission –through water or food. Eg: inadequate sanitation, lack of person and food hygiene, use a polluted water to prepare food, inadequate cooked shellfish etc

Pathogenicity (V.cholerae) Cause Cholera (Asiatic cholera or epidermic cholera). Causing watery diarrhoea producing ‘rice water’ stool containing vibrios, epithelial cells and mucus. Produce enterotoxin (exotoxin) that activates enzyme adenylate cyclase Adherence factor – motility and extracellular enzymes such as proteases Acute cholera – rapid loss of fluid and electrolytes in stool, vomit leads to muscular cramps and severe dehydration (fatal), acidosis, blood urea increase, urine increase in albumin

Microscopy Curved rods with rounded ends 3 x 0.5µm Gram negative Actively motile with single polar flagellum. To- and fro- movement (dark-field micsroscopy) Non-capsulated, Non-sporing Some strain is pleomorphic and lateral flagellum Facultative anaerobic rods

Culturation Aerobic Wide temperature. Optimum 37oC Grow in ordinary media but sensitive to acid pH (alkaline; 8.2) 2-3 mm in size after 18 – 24 hr incubation in optimum temp. Low convex with an entire edge, whitish and translucent Older colonies develop a light ochre tinta tube of peptone water with a flake of mucus from stool and incubating for only 6 – 8 hrs

Biochemical tests Ferment glucose, sucrose, mannitol and maltose without gas production Does not utilise lactose or dulcitol Positive in indole and nitrites test Non-hemolytic in sheep blood agar (Greig test) Can be tested in H2SO4

Serological test Recognize the serotypes – Inaba and Ogawa

Vibrio el tor Hemolysis effect in Greig test Resistant to Mukerjee’s V.cholerae group IV phage Resistance to polymyxin B, but V.cholerae sensitive to it

Vibrio parahaemolyticus Halophilic (salt-loving) vibrio Growth best in 2-4% NaCl culture media V.cholerae and V.el tor produce large yellow sucrose-fermenting colonies in thiosulphate bile sucrose (TCBS) V.parahaemolyticus colonies are blue-green in TCBS medium

4.5 AZOTOBACTER AND RHIZOBIUM

Introduction Both are soil bacteria Azotobacter and Rhizobiaceae bacterial species are nitrogen fixers Azotobacter is a free-living bacteria Rhizobium basically in soil Most bacteria in soil are about one micron in length or diameter. Their size varies with their environment. Bacteria in -high levels of nutrients ,larger than those in nutrient- poor .

Azotobacter

Azotobacter - Soil bacteria The majority of bacteria in soil usually occur as single cells. Bacteria sometimes join together in chains or clusters. They mainly have one of two shapes - spheres (called cocci) and rods (called bacilli). Other bacteria have more varied shapes including spirals and long thin hyphae (although these are less common).

As nitrogen fixer These bacteria take nitrogen from the air (which plants cannot use) and convert it into a form of nitrogen called ammonium (NH4+), which plants can use. The nitrogenase enzyme controls the process, called nitrogen fixation, and these bacteria are often called "nitrogen fixers".

It converts atmospheric nitrogen into ammonium, but in the condition of : An easily degradable carbon source is available Any nitrogen compounds such as ammonium or nitrate, are not already present in substantial concentrations Soil pH levels are between 6 and 9 High levels of phosphorus are present Very low levels of oxygen are present

Benefits as biofertilizer These are primarily used to enhance the growth of several species of plants and crops. A correct proportion of bacterial growth could ensure a high quality of biofertilizer. Its capability in maintaining the pH, safe to use and compatible as chemical fertilizer

Rhizobium Rhizobium is primarily a gram negative, motile, non-sporulating rod that requires a plant host. Species under this genus: R. phaseoli R. leguminosarum R. trifolii Other genus are cowpeas Rhizobium and Bradyrhizobium

In agricultural Rhizobia belong to a specific group of bacteria that form a mutually beneficial association, or symbiosis, with legume plants. Rhizobia are found in soils of many natural ecosystems. They may also be present in agricultural areas where they are associated with both crop legumes (like soybean) and pasture legumes (like clover). Usually, the rhizobia in agricultural areas have been introduced at sowing by applying an inoculum to the exterior of the seeds as liquid formations or pellets.

Rhizobium