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Selenite cystine broth
International Journal of Food Microbiology, 5 (1987) 265-267
265
Elsevidr JFM 00M31
Selenite cystine broth Description and history This is a selective enrichment medium used in procedures for the detection and isolation of salmonellae. Selectivity is conferred by the inclusion of sodium selenite in the medium, shown by Leifson (1936) to be much more inhibitory to other members of the Enterobacteriaceae than to many strains of Salmonella, in particular Salmonella typhi and Salmonella paratyphi. Selenite cystine broth is a modification (North and Bartram, 1953) of the original Leifson (1936) formula, differing only in the addition of L-cystine which is considered to enhance Salmonella growth by reduction of toxicity. Selenite cystine broth is an internationally accepted medium (see ICMSF, 1978; Anon., 1981; 1985; Speck, 1984).
Composition (grams) Tryptone Lactose di-Sodium hydrogen phosphate- 12H20 Sodium hydrogen selenite * L-Cystine Distilled or deionised water
5.0 4.0 10.0 4.0 0.01 1000.0
Preparation Base: dissolve the tryptone, lactose and disodium hydrogen phosphate in water by boiling for 5 rain. After cooling add the sodium hydrogen selenite. Adjust the pH to 7.0 4- 0.1 at 20 o C. Store at 4 o C.
L-Cystine solution: add 0.1 g cystine to 15 ml N / I NaOH. Dilute to 100 ml with sterile water in a sterile flask.
Complete medium: cool base and add L-cystine solution at the rate of 0.1 ml per 10 ml of base. Adjust the pH to 7.0 4- 0.1 at 20 o C. Transfer the complete medium in appropriate quantities e.g. 10 ml, 100 ml, etc. to sterile containers, to give a depth of 50-60 ram. * WARNING: Extreme care should be taken with the laboratory use of selenite solutions because of their potentially toxic effect.
Physical properties Appearance pH
Pale straw coloured; clear or may have a slight precipitate. A brick red precipitate indicates overheating. 7.0 4- 0.1 at 20 o C.
0168-1605/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
266
Shetf t,ye Ready to use medium
Use on day of preparation.
Inoculation method for samples 1.
Where damaged cells are sought transfer 10 ml (or 1 ml) of sample-inoculated and incubated pre-enrichment broth into 100 ml (or 10 ml) selenite cystine broth
or
2.
Add comminuted (food) sample to selenite cystine broth in the ratio 1 part sample to 10 parts medium.
Incubation method At 37 ° C for 24 to 48 h.
Reading of results and interpretation Inoculated and incubated medium is subcultured after 24 h and preferably again after 48 h onto selective diagnostic agar media in such a way as to obtain well-isolated colonies. Suspect colonies are subcultured and their identity confirmed by biochemical and serological tests.
Quahty assessment (i) Productivity Test strain
Inoculation method
Salmonella Salmonella Salmonella Salmonella Salmonella
enteritidis N C T C 5188 typhimurium A T C C 1 3 3 1 1 / N C T C 74 saintpaul N C T C 6022 virchow N C T C 5742 typhimurium Lfd TM 98
Dilution to extinction.
(ii) Selectivity Test strains
Citrobacterfreundii N C T C 6272 Escherichia coli ATCC 1 1 7 7 5 / N C T C 9001 Proteus mirabilis ATCC 29906 Pseudomonas aeruginosa A T C C 2 5 6 6 8 / N C T C 10662
Inoculation method
Dilution to extinction.
References Anon., 1981. International Organization for Standardization. Microbiology - General guidance on methods for the detection of Salmonella. ISO, 6579-1981. Anon., 1985. International Organization for Standardization. Milk and milk products - Detection of Salmonella. ISO 6785-2985 (E). ICMSF, 1978. Microorganisms in foods. 1. Their significance and methods of enumeration, 2nd edn., University of Toronto Press, Toronto, Ont. Leifson, E., 1936. New selenite enrichment media for the isolation of typhoid and paratyphoid (Salmonella) bacilli. Am. J. Hyg. 24, 423-432. North, W.R. and M.T. Bartram, 1953. The efficiency of selenite broth of different compositions in the isolation of Salmonella. Appl. Microbiol. 1, 130-134.
267
Speck, M.L., 1984. Compendium of methods for the microbiological examination of foods, 2nd edn., American Public Health Association. Comments
This medium may be markedly influenced by the following: 1. Source of ingredients of dehydrated complete medium 2. The presence of food or other organic material 3. The physiological state of the organisms sought 4. The competing microflora 5. Possibly by combinations of the above Successful performance of the medium tested in one set of standard conditions may not be achieved if any of those conditions are altered.
265
Elsevidr JFM 00M31
Selenite cystine broth Description and history This is a selective enrichment medium used in procedures for the detection and isolation of salmonellae. Selectivity is conferred by the inclusion of sodium selenite in the medium, shown by Leifson (1936) to be much more inhibitory to other members of the Enterobacteriaceae than to many strains of Salmonella, in particular Salmonella typhi and Salmonella paratyphi. Selenite cystine broth is a modification (North and Bartram, 1953) of the original Leifson (1936) formula, differing only in the addition of L-cystine which is considered to enhance Salmonella growth by reduction of toxicity. Selenite cystine broth is an internationally accepted medium (see ICMSF, 1978; Anon., 1981; 1985; Speck, 1984).
Composition (grams) Tryptone Lactose di-Sodium hydrogen phosphate- 12H20 Sodium hydrogen selenite * L-Cystine Distilled or deionised water
5.0 4.0 10.0 4.0 0.01 1000.0
Preparation Base: dissolve the tryptone, lactose and disodium hydrogen phosphate in water by boiling for 5 rain. After cooling add the sodium hydrogen selenite. Adjust the pH to 7.0 4- 0.1 at 20 o C. Store at 4 o C.
L-Cystine solution: add 0.1 g cystine to 15 ml N / I NaOH. Dilute to 100 ml with sterile water in a sterile flask.
Complete medium: cool base and add L-cystine solution at the rate of 0.1 ml per 10 ml of base. Adjust the pH to 7.0 4- 0.1 at 20 o C. Transfer the complete medium in appropriate quantities e.g. 10 ml, 100 ml, etc. to sterile containers, to give a depth of 50-60 ram. * WARNING: Extreme care should be taken with the laboratory use of selenite solutions because of their potentially toxic effect.
Physical properties Appearance pH
Pale straw coloured; clear or may have a slight precipitate. A brick red precipitate indicates overheating. 7.0 4- 0.1 at 20 o C.
0168-1605/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
266
Shetf t,ye Ready to use medium
Use on day of preparation.
Inoculation method for samples 1.
Where damaged cells are sought transfer 10 ml (or 1 ml) of sample-inoculated and incubated pre-enrichment broth into 100 ml (or 10 ml) selenite cystine broth
or
2.
Add comminuted (food) sample to selenite cystine broth in the ratio 1 part sample to 10 parts medium.
Incubation method At 37 ° C for 24 to 48 h.
Reading of results and interpretation Inoculated and incubated medium is subcultured after 24 h and preferably again after 48 h onto selective diagnostic agar media in such a way as to obtain well-isolated colonies. Suspect colonies are subcultured and their identity confirmed by biochemical and serological tests.
Quahty assessment (i) Productivity Test strain
Inoculation method
Salmonella Salmonella Salmonella Salmonella Salmonella
enteritidis N C T C 5188 typhimurium A T C C 1 3 3 1 1 / N C T C 74 saintpaul N C T C 6022 virchow N C T C 5742 typhimurium Lfd TM 98
Dilution to extinction.
(ii) Selectivity Test strains
Citrobacterfreundii N C T C 6272 Escherichia coli ATCC 1 1 7 7 5 / N C T C 9001 Proteus mirabilis ATCC 29906 Pseudomonas aeruginosa A T C C 2 5 6 6 8 / N C T C 10662
Inoculation method
Dilution to extinction.
References Anon., 1981. International Organization for Standardization. Microbiology - General guidance on methods for the detection of Salmonella. ISO, 6579-1981. Anon., 1985. International Organization for Standardization. Milk and milk products - Detection of Salmonella. ISO 6785-2985 (E). ICMSF, 1978. Microorganisms in foods. 1. Their significance and methods of enumeration, 2nd edn., University of Toronto Press, Toronto, Ont. Leifson, E., 1936. New selenite enrichment media for the isolation of typhoid and paratyphoid (Salmonella) bacilli. Am. J. Hyg. 24, 423-432. North, W.R. and M.T. Bartram, 1953. The efficiency of selenite broth of different compositions in the isolation of Salmonella. Appl. Microbiol. 1, 130-134.
267
Speck, M.L., 1984. Compendium of methods for the microbiological examination of foods, 2nd edn., American Public Health Association. Comments
This medium may be markedly influenced by the following: 1. Source of ingredients of dehydrated complete medium 2. The presence of food or other organic material 3. The physiological state of the organisms sought 4. The competing microflora 5. Possibly by combinations of the above Successful performance of the medium tested in one set of standard conditions may not be achieved if any of those conditions are altered.