Vibrionaceae

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.

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

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

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

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

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

Recognize the serotypes – Inaba and Ogawa

Hemolysis effect in Greig test

Resistant to Mukerjee’s V.cholerae group IV phage

Resistance to polymyxin B, but V.cholerae sensitive to it

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

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 .

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).

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

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 is primarily a gram negative, motile,

non-sporulating rod that requires a plant host. Species under this genus:

1. R. phaseoli

2. R. leguminosarum

3. R. trifolii

Other genus are cowpeas Rhizobium and

Bradyrhizobium

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.