Salmonella Selective Enrichment Medium Containing Tetrathionate and Magnesium Salt

Abstract

The invention relates to a salmonella selective enrichment medium containing tetrathionate or a salt thereof and at least one type of magnesium salt and to a method for detecting salmonella in a sample by using said selective enrichment medium.

Description

EXAMPLE

Comparison of a liquid enrichment medium containing tetrathionate alone as a selective factor and a liquid enrichment medium containing tetrathionate and a magnesium salt in accordance with the invention.

Each sample consists of 25 ml of yogurt, in one case inoculated with a mixture of 100 Salmonella and 1,000,000 E. coli and in another case with 100 Salmonella and 1,000,000 Citrobacter, so that the salmonella are in a 1:10,000 ratio with respect to the competitive flora.

1. Reactivation

Each sample is mixed with 225 ml of a reactivation broth of formula (in grams per liter of water): peptone, 5; NaCl, 5; calcium carbonate, 10.

The mixture is incubated at 37° C. for 4 hours.

2. Enrichment

10 ml of said mixture are recovered in a container and the following are added:

• • in the case of the control medium, 0.38 g of a supplement of formula (in grams per liter of water): bile, 8; calcium carbonate, 10; brilliant green, 0.07; tetrathionate, 20; or,
  • in the case of the invention, 0.31 g of a supplement of formula (in grams per liter of water): bile, 8; calcium carbonate, 10; brilliant green, 0.07; tetrathionate, 3; magnesium chloride, 10 (Table 1).

TABLE 1
		Calcium	Brilliant		Magnesium
In g/l	Bile	carbonate	green	Tetrathionate	chloride
Control	8	10	0.07	20	—
medium
Medium	8	10	0.07	3	10
according
to the
invention

Enrichment is carried out by incubation of the medium at 37° C. for 22 hours.

3. Isolation

Approximately 10 μl of the culture obtained in step 2 above are isolated on a differential isolation medium and, after 18-24 hours of incubation at 37° C. , the Salmonella flora and the competitive flora are counted (Table 2).

	TABLE 2
	Proportion of Salmonella/competitive
	flora
	Salmonella/E. Coli	Salmonella/Citrobacter
	mixture	mixture
Control medium	85%	1%
Medium according	100%	80%
to the invention

Claims

1-8. (canceled)

9. A salmonella selective enrichment medium comprising tetrathionate, or a salt thereof, and at least one magnesium salt.

10. The medium according to claim 9, wherein the at least one magnesium salt is present at a concentration between 0.1 g/l and 50 g/l.

11. The medium according to claim 9, wherein the at least one magnesium salt is present at a concentration between 2 g/l and 40 g/l.

12. The medium according to claim 9, wherein the at least one magnesium salt is present at a concentration between 7 g/l and 35 g/l.

13. The medium according to claim 9, wherein the at least one magnesium salt is selected from the group consisting of magnesium carbonate, magnesium chloride, magnesium sulfate, and combinations thereof.

14. The medium according to claim 9, wherein the tetrathionate, or salt thereof, is present at a concentration between 0.1 g/l and 40 g/l.

15. The medium according to claim 9, wherein the tetrathionate, or salt thereof, is present at a concentration between 0.5 g/l and 30 g/l.

16. The medium according to claim 9, wherein the tetrathionate, or salt thereof, is present at a concentration between 1 g/l and 25 g/l.

17. The medium according to claim 9, comprising a tetrathionate salt selected from the group consisting of potassium tetrathionate and sodium tetrathionate.

18. A method for detecting salmonella in a sample, the method comprising: incubating the salmonella sample in a salmonella selective enrichment medium comprising tetrathionate, or a salt thereof, and at least one magnesium salt; andisolating the salmonella.

19. The method according to claim 18, wherein the method further comprises reactivating the salmonella sample prior to the step of incubating in the salmonella selective enrichment medium.

20. The method according to claim 19, wherein the reactivating step comprises incubating the sample in a reactivation medium.

21. The method according to claim 18, wherein the isolation step comprises an analysis procedure selected from the group consisting of enzymatic immunological analyses, nucleic acid probe hybridization analyses, pure culture analyses, analyses using biochemical indicators, and immunoimmobilization analyses.

22. The method according to claim 18, wherein the salmonella selective enrichment medium comprises at least one magnesium salt at a concentration between 0.1 g/l and 50 g/l.

23. The method according to claim 18, wherein the salmonella selective enrichment medium comprises at least one magnesium salt at a concentration between 2 g/l and 40 g/l.

24. The method according to claim 18, wherein the salmonella selective enrichment medium comprises at least one magnesium salt at a concentration between 7 g/l and 35 g/l.

25. The method according to claim 18, wherein the magnesium salt is selected from the group consisting of magnesium carbonate, magnesium chloride, magnesium sulfate, and combinations thereof.

26. The method according to claim 18, wherein the salmonella selective enrichment medium comprises tetrathionate, or a salt thereof, at a concentration between 0.1 g/l and 40 g/l.

27. The method according to claim 18, wherein the salmonella selective enrichment medium comprises tetrathionate, or salt thereof, at a concentration between 0.5 g/l and 30 g/l.

28. The method according to claim 18, wherein the salmonella selective enrichment medium comprises tetrathionate, or salt thereof, at a concentration between 1 g/l and 25 g/l.