Lead Acetate Agar

Intended Use

Recommended for detection of hydrogen sulphide producing enteric bacteria from clinical and non-clinical samples.

Composition

Final pH ( at 25°C): 6.6±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 36.28 grams in 1000 ml purified/distilled water. Heat to boiling to dissolve the medium completely. Dispense into test tubes and sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Allow to cool the tubes in a slanted position to obtain slants with generous butts. Inoculate pure culture by surface streaking slant and stabbing the butt.

Principle And Interpretation

Salmonella, Shigella, Yersinia species and certain strains of Escherichia coli cause severe gastroenteritis and life- threatening systemic illness in human (1,2). Of these, Salmonella Typhi can be differentiated due to their ability to form hydrogen sulphide (3). Lead Acetate Agar is the modification of the original formulation of Spray (4). This medium was successfully used to study hydrogen sulphide production (4,5). Lead Acetate Agar can also be used to differentiate between Salmonella Paratyphi A and Salmonella Paratyphi B (6). The latter produces hydrogen sulphide, observed as browning of the medium, within 18-24 hours, whereas the former fails to produces hydrogen sulphide.

Peptone, proteose peptone and dextrose provide all the essential nutrients for the growth of bacteria. Bacteria capable of using sulphur from sodium thiosulphate in their metabolic activities produce hydrogen sulphide. Lead acetate acts as an indicator of hydrogen sulphide production observed as browning of the medium. Dextrose is the fermentable carbohydrate source. Production of gas from dextrose is indicated by the presence of bubbles in the butt.

Type of specimen

Pure isolate from clinical and non-clinical specimen.

Specimen Collection and Handling

For clinical samples, follow appropriate techniques for sample collection and processing as per guidelines (7,8). After use, contaminated materials must be sterilized by autoclaving before discarding.

Warning and Precautions

In Vitro Diagnostic use. For professional use only. 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.

Performance and Evaluation

Performance of the medium is expected when used as per the direction on the label within the recommended temperature.

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder.

Gelling: Firm, comparable with 1.5% Agar gel

Colour and Clarity of prepared medium: Medium amber coloured clear to slightly opalescent gel forms in tubes as slants

Reaction: Reaction of 3.63% w/v aqueous solution at 25°C. pH : 6.6±0.2

pH: 6.40-6.80

Cultural Response Cultural characteristics observed after an incubation at 35-37°C for 18-24 hours.

Key : (*) Corresponding WDCM numbers. (#) Formerly known as Enterobacter aerogenes

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. Product performance is best if used within stated expiry period.

Disposal

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 clinical sample must be decontaminated and disposed of in accordance with current laboratory techniques (7,8).

Reference

1. Balows A., Hausler W. J. Jr., Hermann K. L., Isenberg H. D., Shadomy H. J., (Eds.), Manual of Clinical Microbiology, 5th Ed., ASM, Washington, D.C.
2. Murray P. R., Baron J. H., Pfaller M. A., Jorgensen J. H. and Yolken R. H., (Ed.), 2003, Manual of Clinical Microbiology, 8th Ed., American Society for Microbiology, Washington, D.C.
3. Orlowski, 1897, Dissert, St. Petersburg.
4. Spray R. S., 1936, J. Bacteriol., 32:135.
5. Morrison L. E. and Tanner F. W., 1922, J. Bacteriol., 7:343.
6. Jordan E. O. and Victorson R., 1917, J. Infect. Dis., 21:554.
7. Isenberg, H.D. Clinical Microbiology Procedures Handbook 2nd Edition.
8. Jorgensen, J.H., Pfaller, M.A., Carroll, K.C., Funke, G., Landry, M.L., Richter, S.S and Warnock., D.W. (2015) Manual of Clinical Microbiology, 11th Edition. Vol. 1.