Modified Scholten’s Broth

Bacteriophages are viruses that can only infect and replicate within bacteria. In many cases, these are very specific relationships. Somatic coliphages specifically infect Escherichia coli and in water indicate contamination by human or animal faeces or by wastewater containing such material. They provide a rapid and simple method of determining faecal pollution in environmental waters.

The ability of Escherichia coli O157:H7 to induce cellular damage leading to disease in humans is related to numerous virulence factors, most notably the stx gene, encoding Shiga toxin (Stx) and carried by a bacteriophage. Stx is thought to be responsible for the most severe form of the infection causing the life-threatening hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS).

MSB is used in the preparation of stock, working and inoculum cultures, to rehydrate and enrich the host. The result of the infection is lysis of the cell and the production of visible plaques (clear zones).

Preparation

Suspend 28 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense in adequate containers and sterilize in autoclave at 121 °C for 15 minutes.

Instructions for use

1. Take the inoculum with a sterile loop.
2. Submerge the loop into the medium and shake gently.
3. Incubate at 35 ± 2 °C for 24 hours.

Then, add the original sample or dilutions that contain the phage into tubes of semisolid Modified Scholten's Agar (ssMSA) to later inoculate a plate of Modified Scholten's Agar (MSA).

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• American Public Health Association. Standard methods for the examination of water and wastewater. Washington, D.C.: American Public Health Association; 1992.
• Beutin L, Strauch E, Fisher I. Isolation of Shigella sonnei lysogenic for a bacteriophage encoding gene for production of Shiga-toxin. Lancet. 1999;353:1498.
• Beutin L, Geier D, Zimmermann S, Aleksic S, Gillespie H A, Whittam T S. Epidemiological relatedness and clonal types of natural populations of E. coli strains producing Shiga toxins in separate populations of cattle and sheep.
• Ferdous, M., Zhou, K., Mellmann, A., Morabito, S., Croughs, P., & de Boer, R. et al. (2015). Is Shiga Toxin-Negative Escherichia coli O157:H7 Enteropathogenic or Enterohemorrhagic Escherichia coli? Comprehensive Molecular Analysis Using Whole-Genome Sequencing. Journal Of Clinical Microbiology, 53(11), 3530-3538.