Citrate Agar
Intended use
Recommended for cultivation of iron bacteria from soil samples.
Composition
Ingredients Gms / Litre
Ammonium sulphate 0.500
Sodium nitrate 0.500
Magnesium sulphate 0.500
Dipotassium phosphate 0.500
Calcium chloride 0.200
Ferric ammonium citrate 10.000
Agar 15.000
Final pH ( at 25°C)
Directions
Suspend 27.2 grams in 1000 ml purified/ distilled water. Heat to boiling to dissolve the medium completely. Sterilize by
autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 45-50°C. Mix well and pour into sterile Petri plates.
Principle And Interpretation
The iron bacteria oxidize ferrous iron to ferric state, which precipitate as ferric hydroxide around cells. These bacteria
are usually non-filamentous and spherical or rod shaped. Certain algae also transform ferrous salts to ferric state and
deposit the precipitation around the colonies. The ferric hydroxide deposits give a brown or rust red colour to these organisms.
Citrate Agar is recommended by Subba Rao (5 ) for the isolation and detection of iron bacteria. A modification of the
original formulation of Subba Rao is recommended by APHA (1) for the isolation of heterotrophic iron-precipitating
bacteria (2). Dipotassium phosphate provides buffering to the medium. Magnesium sulphate, ammonium sulphate and
calcium chloride are sources of ions that stimulate metabolism. Ferric ammonium citrate is used as a source of carbon and
sodium nitrate acts as a source of nitrogen.
Intended use
Recommended for cultivation of iron bacteria from soil samples.
Composition**
Type of specimen
Soil samples; Water samples
For soil samples, follow appropriate techniques for sample collection and processing as per guidelines (5).
For water samples, follow appropriate techniques for sample collection, processing as per guidelines and local standards.(1)
After use, contaminated materials must be sterilized by autoclaving before discarding.
Specimen Collection and Handling:
Warning and Precautions :
Read the label before opening the container. Wear protective gloves/protective clothing/eye protection/ face protection.
Follow good microbiological lab practices while handling specimens and culture. Standard precautions as per
established guidelines should be followed while handling specimens. Safety guidelines may be referred in
individual safety data sheets.
Limitations :
1. This medium is general purpose medium for soil bacteria and may not support the growth of fastidious
organisms.
Performance and Evaluation
Performance of the medium is expected when used as per the direction on the label within the expiry period when stored
at recommended temperature.
Quality Control
Appearance
Cream to greenish yellow homogeneous free flowing powder
Gelling
Firm,comparable with 1.5% Agar gel
Colour and Clarity of prepared medium
Light amber coloured, clear to slightly opalescent gel forms in Petri plates
Reaction
Reaction of 2.72% w/v aqueous solution at 25°C. pH : 6.7±0.1
pH
6.60-6.80
Cultural Response
Cultural characteristics observed after an incubation at 35-37°C for upto 7 days.
Organism Growth
Escherichia coli ATCC
25922 (00013*)
inhibited
Sphaerotilus natans ATCC
13338
good-luxuriant
Storage and Shelf Life
Store between 10-30°C in a tightly closed container and the prepared medium at 20-30°C. Use before expiry date on
the label. On opening, product should be properly stored dry, after tightly capping the bottle in order to prevent lump
formation due to the hygroscopic nature of the product. Improper storage of the product may lead to lump formation.
Store in dry ventilated area protected from extremes of temperature and sources of ignition Seal the container tightly
after use. Use before expiry date on the label.
Product performance is best if used within stated expiry period.
User must ensure safe disposal by autoclaving and/or incineration of used or unusable preparations of this product. Follow
established laboratory procedures in disposing of infectious materials and material that comes into contact with sample must
be decontaminated and disposed of in accordance with current laboratory techniques (3,4).
