Medical Technologist Test Microbiology

Question 1

Which culture medium is selective for gram-negative enteric bacteria?

Accepted Answer

MacConkey agar

Answer

MacConkey agar contains bile salts and crystal violet that inhibit gram-positive organisms while supporting gram-negative growth.

Question 2

A positive catalase test followed by a positive coagulase test identifies which organism?

Accepted Answer

Staphylococcus aureus

Answer

Catalase-positive and coagulase-positive results are the key biochemical tests identifying S. aureus among staphylococci.

Question 3

Which stain is used to visualize acid-fast bacilli such as Mycobacterium tuberculosis?

Accepted Answer

Ziehl-Neelsen (carbol fuchsin) stain

Answer

The Ziehl-Neelsen stain uses carbol fuchsin retained by mycolic acid in the cell wall of acid-fast organisms despite acid-alcohol decolorization.

Question 4

Colonies with a green metallic sheen on EMB agar are characteristic of which organism?

Accepted Answer

Escherichia coli

Answer

E. coli produces a green metallic sheen on eosin methylene blue (EMB) agar due to strong lactose and acid production.

Question 5

Which organism is the MOST common cause of community-acquired pneumonia in the US?

Accepted Answer

Streptococcus pneumoniae

Answer

Streptococcus pneumoniae (pneumococcus) remains the leading bacterial cause of community-acquired pneumonia in all age groups.

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