APMB: Salmonella

Salmonella coliform status? (Coliform/Non-coliform)

Non-coliform
- Do not convert lactose or sucorse to acid

Salmonella growth environments

Resistant to/can grow in:

• Low pH

• High concentrations of detergents: Bile salts & Brilliant Green compared to faecal coliforms

• Tetrathionate (S₄O₆²⁻)

Typical Salmonella vs Atypical Salmonella

Typical Salmonella:

Produce H₂S from Thiosulfate (S₂O₃⁻)

Atypical Salmonella:

Do NOT produce H₂S from Thiosulfate (S₂O₃⁻)

Sources of Salmonella

1) Contaminated hands

2) Reptiles

3) Raw Poultry (more frequently in Chicken)

4) Contaminated soil and water (from faecal matter)

5) X-contamination in the kitchen/from utensils

What is the most common strain of Salmonella and what are the symptoms?

Salmonella enteriditis — Foodborne, common cause for intestinal diseases

Symptoms:

1) Vomitting

2) Diarrhea

3) Nausea

4) Fever

5) Andominal Cramp

6) Headache

Why do Food & Pharmaceutical samples require resuscitationa and enirochment while Clinical samples can undergo direct isolation/enumeration on selective media?

Cells damaged after undergoing processing → Low number of damaged bacteria

The low nnmber of damaged bactera can still be resusicitated in a suitable environment and medium

Low numbers of salmonella is NOT negligible, and may still cause disease in people

Resuscitiation media for Salmonella

1) Lactose Broth

2) Brilliant Green water

3) Nutrient Broth

4) Buffered Peptone water

[Resuscitation Media] Why is Lactose Broth used?

• Salmonella does not use lactose (non-coliform)

• Can still grow in the medium due to other coliforms → acid produced → Lower pH

[Resuscitation Media] Why is Brilliant Green Water used?

• Does not inhibit enteric bacteria (Enteric bacteria resistant to detergents)

• Resuscitates salmonella from samples with higher fat content

Enrichment media for Salmonella

1) Selenite broth

2) Tetrathionate broths

[Enrichment Media] Why is Selentie broth used?

Selenite is inhibitory to many G+ and G- bacteria, including coliforms, and select for Salmonella

[Enrichment Media] Why is Tetrathionate Broth used?

Contains:

• Caesin & Meat peptones

• Bile salts (and Brilliant Green) bacteria → inhibit G+ and non-enteric bacteria

• CaCO3 → neutralising agent

• Sodium Thiosulfate

• Iodine solution

Thiosulfate + Iodine → Tetrathionate

• inhibits coliforms and Shigella

• alternative O2 source during anaerobic respiration

Differential Agars for Salmonella

1) Brilliant Green Agar

2) Xylose, Lysine, Desoxycholate (XLD) Agar

3) Bismuth Sulphite Agar

[Differential Agar] Brilliant Green Agar

Brilliant Green Agar
Differential agents	Selective agents	Appearance
Lactose Sucrose Phenol Red	Brilliant Green	Pink colonies Inability to ferment lactose/sucrose to produce acid

[Differential Agar] XLD Agar

XLD Agar
Differential agents	Selective agents	Appearance
Xylose Lysine Lactose Sucrose Phenol red S2O32- and Fe2+	Desoxycholate (detergent, selects for salmonella and other enteric bacteria)	(Typical) Black colonies Production of H2S (Atypical) Red colonies No production of H2S Don’t ferment: Lactose and Sucrose Ferment: Xylose and Lysine

Fermentation of Lactose, Sucrose, Xylose, Lysine in Shigella and E. coli

[Differential Agar] Bismuth Sulphite Agar

Bismuth Sulphite Agar
Differential agents	Selective agents	Appearance
FeSO4 (for detection of H2S formation) S2O32-	Brilliant green (inhibit G+ bacteria) Bismuth (inhibit G+ bacteria) Glucose (carbon source for sacchrolytic salmonella)	Black colonies with a metallic sheen (for typical colonies)

[Differential Media] Salmonella Shigella Agar

Salmonella Shigella Agar
Differential agents	Selective agents	Appearance
Ferric Citrate (for binding with H2S for detection) Neutral Red Lactose S2O32-	Bile and Brilliant green (inhibit G+ bacteria)	(Typical) Black colonies (Atypical) Yellow-brown colonies

What does Triple Sugar Iron Agar test for?

1) H2S formation → (+) Black agar

2) Ability to use Lactose and Sucrose

3) Gas production

[TSI Agar] Atypical Salmonella result

Buttt - Yellow (due to glucose fermentation)

Slant - Red (no fermentation of lactose/sucrose)

[TSI Agar] Atypical Salmonella result

Buttt - Black (H2S formation)

Slant - Red (no fermentation of lactose/sucrose)