Question

Phage resistant medium for the growth of lactic acid bacteria shall NOT contain

• A. Magnesium
• B. Manganese
• C. Calcium
• D. Zinc

Hint:

Phage Resistant Media (PRM PIM): Formulated to EXCLUDE CHELATE CALCIUM ($\text{Ca}^{2+}$) using phosphates. Phages cannot adsorb without calcium.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bacteriophage control in dairy starter cultures: bacteriophage adsorption to the cell wall receptor of lactic streptococci obligately requires free calcium ions ($ ext{Ca}^{2+}$); therefore, Phage Inhibitory Media (PIM) strictly exclude or chelate calcium.
Key Formula or Approach:
\[ \text{Phage Adsorption Requirement: } \text{Bacteriophage Tail} + \text{Host Cell Wall Receptor} \xrightarrow{\mathbf{Ca^{2+} \text{ (Obligate Cofactor)}}} \text{Irreversible Phage Injection} \]

Step 2: Detailed Explanation:
In dairy starter culture propagation and bacteriophage management:
- Virulent bacteriophages represent the single greatest cause of starter culture failure ('dead vats' and slow acid development) during cheese and dahi manufacturing.
- The irreversible attachment and DNA injection of lytic phages into Lactococcus lactis and Streptococcus thermophilus cells strictly requires free divalent Calcium ions ($\text{Ca}^{2+}$) as an indispensable cofactor.
- Phage Inhibitory Media (PIM) Phage Resistant Media (PRM) are specifically formulated using high concentrations of phosphate or citrate chelating salts (such as ammonium phosphate or sodium tripolyphosphate) to completely bind and precipitate free calcium, ensuring the medium shall NOT contain free Calcium, thereby rendering phages incapable of infecting starter cells while permitting normal bacterial proliferation.

Step 3: Final Answer:
Hence, phage resistant medium shall NOT contain Calcium, matching option (C).