Which statement best describes Escherichia coli on sheep blood agar and related media?

Which statement best describes Escherichia coli on sheep blood agar and related media?

• A. Most strains are beta-hemolytic on sheep blood agar
• B. Most strains are beta-hemolytic on chocolate agar
• C. Most strains are non-hemolytic on sheep blood agar
• D. They produce pink colonies on MacConkey agar

Answer: (A)

Escherichia coli is usually non-hemolytic on blood-containing media, so on sheep blood agar most strains show gamma-hemolysis (no lysis around colonies). This means you wouldn’t expect a clearing or a distinct beta-hemolytic pattern for the typical E. coli isolates. On chocolate agar, growth is enhanced due to the enriched nutrients, but hemolysis isn’t a defining feature there either. The key identifying feature on MacConkey agar is lactose fermentation: E. coli ferments lactose, producing acid that changes the colonies pink. So, the consistent description you’d expect across these media is non-hemolysis on sheep blood agar and pink lactose-fermenting colonies on MacConkey. The notion that most strains are beta-hemolytic on sheep blood or on chocolate agar doesn’t fit the usual pattern for E. coli.

Escherichia coli is usually non-hemolytic on blood-containing media, so on sheep blood agar most strains show gamma-hemolysis (no lysis around colonies). This means you wouldn’t expect a clearing or a distinct beta-hemolytic pattern for the typical E. coli isolates. On chocolate agar, growth is enhanced due to the enriched nutrients, but hemolysis isn’t a defining feature there either. The key identifying feature on MacConkey agar is lactose fermentation: E. coli ferments lactose, producing acid that changes the colonies pink. So, the consistent description you’d expect across these media is non-hemolysis on sheep blood agar and pink lactose-fermenting colonies on MacConkey. The notion that most strains are beta-hemolytic on sheep blood or on chocolate agar doesn’t fit the usual pattern for E. coli.