Differentiation and Identification Media for Salmonella

By: Jvo Siegrist, Microbiology Focus Edition 1.3

Product Manager Microbiology…. ivo.siegrist@sial.com

Today’s usage 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.

  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 1 Typical carbohydrate fermentation ability of 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)
 
Table 2: Salmonella selective and differential media (list not complete. For more see sigma-aldrich.com/salmonella)

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).

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
 
Table 3: Chromogenic media for Salmonella

 

Figure 2: HiCrome™ Salmonella Agar, Improved

 

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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 3: Hydrogen Sulfide Test Strips

 

(55662), (49415)

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Materials

     
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