Welshimers Broth, Modified

Welshimer's Broth, Modified is a chemically defined minimal medium for the growth of Listeria monocytogenes.

Composition**

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 34.44 grams(equivalent weight of dehydrated medium per litre) in 1000 ml distilled water. Heat, if necessary, to dissolve the medium completely. Dispense as desired and sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.

Principle And Interpretation

Welshimer's Broth, Modified is an improved medium developed by Premaratne et al, which supports good growth of Listeria monocytogenes (1). This medium is a modification of Welshimer's Broth (2), having additional amino acids L - Histidine and L - Tryptophan.

Listeria monocytogenes is widespread in the environment and continues to present a potential health risk in raw, minimally processed, and some fermented foods. This chemically defined medium allows the growth of Listeria monocytogenes in widely diverse environment. All the aminoacids and vitamins act as the growth factors required by Listeria monocytogenes. Ferric citrate stimulates the growth whereas the potassium and sodium phosphates provide buffering system. Glucose and glutamine are the primary sources of carbon and nitrogen.

Quality Control

Appearance White to cream homogeneous free flowing powder

Colour and Clarity of prepared medium Light amber clear having white precipitate.

Cultural Response Cultural characteristics observed after an incubation at 35-37°C for 24-48 hours.

Storage and Shelf Life

Store below 30°C and the prepared medium at 2 - 8°C. Use before expiry date on the label.

Reference

1. Premaratne, R. J., W. Lin, and E. A. Johnson. 1991. Development of an improved chemical defined minimal medium for Listeria monocytogenes. Appl. Environ. Microbiol. 57: 3046-3048.
2. Welshimer,H.J. 1963. Vitamin requirements of Listeria monocytogenes J. Bacteriol. 85: 1156-1159.