Fecal contamination indicators

Fecal contamination indicators

Enterococcus fæcalis (Streptococcus fæcalis), Enterococcus fæcium (Streptococcus fæcium), Enterococcus durans (Streptococcus durans) and Streptococcus equinus (Streptococcus bovis)

---

Morphology: Cocci

Gram: Positive

Catalase: Negative

Respiratory system: Facultative anaerobe
Characteristic: bile-resistant

---

Characteristics

• Growth at 10° C and 45° C
• Temperature resistance - 60° C for 30 minutes
• Methylene blue reduction - Sherman's milk
• NaCl-resistant: 6,5 %

Identification tests

• Tellurite resistance - Potassium tellurite agar
• Tetrazolium chloride (TTC) reduction - Barnes medium
• Hemolysis - Sheep blood agar (5 %)
• Gelatinase - gelatine broth
• Sugar fermentation (lactose, sucrose, mannitol, arabinose, sorbitol)

Culture

Slanetz & Bartley medium

Selective enumeration of Enterococci in water

Sodium azide inhibits the growth of Gram-negative bacteria. TTC is an indicator of bacterial growth. It is reduced to an insoluble formazan inside the cells. This reaction is seen by the formation of red to maroon colonies.

Retain only membranes containing fewer than 100 colonies. Red, maroon or pink colonies are 

considered as characteristic. Carry out confirmation of typical colonies using Bile Esculin Azide Agar.

Reference: Biokar Diagnostics [Link]

Bile Esculin Agar

Organisms positive for esculin hydrolysis hydrolyze the esculin to esculetin and dextrose. The esculetin reacts with the ferric citrate to form a dark brown or black complex. Oxbile is used to inhibit Gram-positive bacteria other than enterococci. Beef Extract and Enzymatic Digest of Gelatin are the carbon and nitrogen sources used for general growth requirements in Bile Esculin Agar. Agar is the solidifying agent.

Reference: Neogen [Link]

Please, feel free to comment if there is any mistake.