Question

C. Diphtheria: Gray Black colonies with brown halos on what type of agar

a) Blood agar
b) MacConkey agar
c) Mannitol salt agar
d) Loeffler's medium

Answer 1

Corynebacterium diphtheriae, the bacteria that causes diphtheria, produces characteristic gray-black colonies with brown halos on Loeffler's medium, which is the correct type of agar for its growth.

Step-by-step explanation:

Diphtheria Cultivation

The causative agent of diphtheria is Corynebacterium diphtheriae, which is a gram-positive rod. When culturing this bacterium, it forms gray-black colonies with brown halos on Loeffler's medium.

This medium is specifically designed to support the growth of C. diphtheriae due to its enrichment which is essential for the slow-growing nature of this bacterium. Other agars mentioned such as blood agar, MacConkey agar, and mannitol salt agar are not the correct media for observing the characteristic gray-black colonies of C. diphtheriae.

Answer 2

Corynebacterium diphtheriae, which causes diphtheria, forms gray-black colonies with brown halos on Loeffler's medium. This is the correct agar type for isolating and cultivating C. diphtheriae, which is a club-shaped, gram-positive bacterium. Therefore, the correct option is d) Loeffler's medium.

Step-by-step explanation:

The question is about identifying the correct type of agar for observing the characteristic growth of Corynebacterium diphtheriae, the bacterium that causes diphtheria. Corynebacterium diphtheriae is known for its club-shaped, gram-positive form and is part of the Actinobacteria phylum. When cultured for laboratory diagnosis, C. diphtheriae forms grayish to black colonies with a brown halo on a specific type of agar that is suitable for demonstrating these characteristics. The correct type of agar is Loeffler's medium, which is an enrichment medium specifically designed for the isolation and cultivation of Corynebacterium diphtheriae.

The Mannitol salt agar is used for differentiating Staphylococcus species, and MacConkey agar and EMB agar are designed for the growth and differentiation of gram-negative bacteria. Blood agar can show certain hemolytic properties of bacteria, but for C. diphtheriae, Loeffler's medium is the specialized medium that provides the required nutritional support and visual growth pattern. In conclusion, the correct option for the type of agar that supports the growth of C. diphtheriae and demonstrates the characteristic gray-black colonies with brown halos is Loeffler's medium (d).