Differentiation and ID Media for Salmonella

Today’s use of classical culture methods to identify Salmonella, a potent food-borne pathogen

Salmonella contamination is the second leading cause of food-borne illness worldwide. Controlling outbreaks of Salmonella is an important task for food regulators, restaurants and the food industry in general.

The Salmonella family includes over 2,300 serotypes of bacteria, but two types, Salmonella enteritidis and Salmonella typhimurium, are responsible for about half of all human infections. Most outbreaks of Salmonella are traced back to dairy, poultry and meat products, but Salmonella can grow on nearly any food. Chicken, eggs and their derivative products are particularly high risk.

Figure 1. Salmonella Bacteria

Microbiological control in the food industry plays a critical role in preventing Salmonella outbreaks. Tests and media used for identification of Salmonella take advantage of unique aspects of Salmonella physiology or biochemistry relative to other genera within the family Enterobacteriaceae. For example, bacteria from the genus Salmonella are mostly facultative anaerobes, oxidase-negative, catalase-positive and gramnegative rods. Most strains are motile and ferment glucose with production of both acid and gas. The media used currently for the differentiation and identification of Salmonella are still based on the detection of carbohydrate fermentation indicated by a pH indicator (see also Table 1 for carbohydrate fermentation ability), the detection of proteolytic activity, hydrogen sulphide production and selectivity. Most modern media also combine some of this detection system to make the media more reliable. A listing of the most common selective and differential media appears in Table 2.

Table 1. Typical carbohydrate fermentation ability of Salmonella

	Fermentation		Cat. No.
Carbohydrate	Acid	Gas	Cabohydrate Discs
Adonitol	-	-	55876
Arabinose	+/-	+/-	80372
Cellobiose	-	-	56481
Dextrose	+	+/-	63367
Dulcitol	+/-	+/-	73044
Fructose	+/-	+/-	53901
Galactose	+	+/-	89608
Inositol	+/-	+/-	89614
Lactose	-	-	28816
Maltose	+	+/-	77653
Mannitol	+	+/-	94438
Mannose	+/-	+/-	94445
Melibiose	+	+	93196
Raffinose	-	-	94226
Rhamnose	+/-	+/-	93999
Salicin	-	-	92971
Sorbitol	+	+/-	93998
Sucrose	-	-	94309
Trehalose	+	+/-	92961
Xylose	+	+/-	07411

Table 2.Salmonella selective and differential media (list not complete. For more see sigma-aldrich.com/salmonella)

Brand	Cat #	Name
Sigma-Aldrich	A0715	Andrade Peptone Water
Sigma-Aldrich	28943	Andrade peptone water, Vegitone
Sigma-Aldrich	95388	Bismuth sulfite Agar
Sigma-Aldrich	15835	BPL Agar
Sigma-Aldrich	70134	Brilliant Green Agar, modified
Sigma-Aldrich	16026	Brilliant Green Phenol Red Lactose Sucrose Agar
Sigma-Aldrich	36408	Bromcresol Purple Broth
Sigma-Aldrich	22520	China Blue Lactose Agar
Sigma-Aldrich	55420	CLED Agar
Sigma-Aldrich	70135	DCLS Agar
Sigma-Aldrich	90035	DCLS Agar No. 2
Sigma-Aldrich	D2935	Decarboxylase Broth Base, Moeller
Sigma-Aldrich	D7809	Deoxycholate Citrate Agar
Sigma-Aldrich	E5399	Endo Agar
Sigma-Aldrich	70137	ENDO Agar (Base)
Sigma-Aldrich	16447	Glucose Bromcresol Purple Agar
Sigma-Aldrich	51490	Hektoen Enteric Agar
Sigma-Aldrich	60787	Kligler Agar
Sigma-Aldrich	61792	Leifson Agar
Sigma-Aldrich	66304	Lysine Decarboxylase Broth
Sigma-Aldrich	62915	Lysine Iron Agar
Sigma-Aldrich	70143	Mac Conkey Agar No 1
Sigma-Aldrich	19352	Mac Conkey Agar No 1, Vegitone
Sigma-Aldrich	M8302, 94216	MacConkey Agar with Crystal Violet, Sodium Chloride and 0.15% Bile Salts
Sigma-Aldrich	70144	MacConkey Broth
Sigma-Aldrich	75717, 16377	MacConkey broth purple
Sigma-Aldrich	63014	MacConkey MUG Agar
Sigma-Aldrich	51405	MacConkey-Agar (without salt)
Sigma-Aldrich	69965	Mossel Broth
Sigma-Aldrich	43052	Muller-Kauffmann Tetrathionate Broth, Base (ISO)
Sigma-Aldrich	75315	OF Test Nutrient Agar
Sigma-Aldrich	81648	Pril® Mannitol Agar
Sigma-Aldrich	04584	Rappaport Vassiliadis Broth acc. to DIN EN ISO 6579:2002
Sigma-Aldrich	17173	Rappaport Vassiliadis Broth, modified
Sigma-Aldrich	R0773	Rappaport Vassiliadis Medium
Sigma-Aldrich	92322	Rappaport Vassiliadis medium (base), modified, semi-solid
Sigma-Aldrich	84368	Salmonella Agar according to Önöz
Sigma-Aldrich	84370	Salmonella Enrichment Broth
Sigma-Aldrich	70153	Selenite Broth (Base)
Sigma-Aldrich	84922	Selenite Cystine Broth
Sigma-Aldrich	85438	SIM Medium
Sigma-Aldrich	85463	Simmons Citrate Agar
Sigma-Aldrich	85640	SS-Agar
Sigma-Aldrich	86352	TBG Broth
Sigma-Aldrich	88151	Tetrathionate Broth
Sigma-Aldrich	88148	Tetrathionate Enrichment Broth according to Muller-Kauffmann
Sigma-Aldrich	44940	Triple Sugar Iron Agar
Sigma-Aldrich	51463	Urea Broth
Sigma-Aldrich	42376	Violet Red Bile Agar, Vegitone
Sigma-Aldrich	70189, 79873	Violet Red Bile Glucose Agar
Sigma-Aldrich	17213	Violet Red Bile Glucose Agar without Lactose
Sigma-Aldrich	53605	Violet Red Bile Glucose Agar without Lactose, Vegitone
Sigma-Aldrich	41270	Violet Red Bile Lactose Dextrose Agar
Sigma-Aldrich	95273	VRB MUG Agar
Sigma-Aldrich	95586	XLD Agar
Sigma-Aldrich	76721	XLT4 Agar (Base)

In addition, our current technology offers the chromogenic media, which makes identification even more reliable and faster as they detect a characteristic enzyme of the Salmonella. These reactions are based on the cleavage of a chromogenic substrate which results in a visible color change (see Table 3).

Table 3.Chromogenic media for Salmonella

Brand	Cat #	Name
Sigma-Aldrich	00563	HiCrome™ MM Agar
Sigma-Aldrich	90918	HiCrome™ RajHans Medium, Modified
Sigma-Aldrich	78419	HiCrome™ Salmonella Agar
Sigma-Aldrich	05538	HiCrome™ Salmonella Agar, Improved
Sigma-Aldrich	84369	Salmonella Chromogen Agar
Sigma-Aldrich	01993	Salmonella Chromogen Agar Set

Figure 2. HiCrome™ Salmonella Agar, Improved

Detection of hydrogen sulfide Production of microorganisms such as Salmonella

A large number of bacteria can produce H₂S in small amounts from sulfur containing amino acids in carbohydrate media. When combined with lead acetate, the H₂S will produce a black precipitate, giving rise to a visible black coloured reaction on the paper strip. The lead acetate method is very sensitive, allowing the detection of trace levels of hydrogen sulphide.

Test with strips: Inoculate peptone water (Cat. No. 70179) with the suspect organism. Insert a lead acetate paper strip between the plug and inner wall of tube, above the inoculated medium and incubate at 35 °C for 18-24 hours. A positive reaction appears as a blackening of the lower part of the strip. In the case of negative response, no blackening should appear (see Figure 3).

Figure 2.1. Test Organisms Test Organisms

Figure 3. Hydrogen Sulfide Test Strips

Figure 4. A rapid test based on the rRNA detection