Which organism is not gram-positive?

Which organism is not gram-positive?

• A. Suttonella wadsworthensis
• B. Eubacterium lentum
• C. Bifidobacterium dentium
• D. Propionibacterium acnes

Answer: (A)

Grams staining hinges on cell wall structure: thick peptidoglycan in Gram-positive bacteria traps the crystal violet-iodine complex and appears purple, while Gram-negative bacteria have a thinner peptidoglycan layer with an outer membrane and do not retain the dye as strongly. The three well-known Gram-positive anaerobic bacteria listed—Eubacterium lentum, Bifidobacterium dentium, and Propionibacterium acnes—have the thick peptidoglycan layer that reliably retains the violet stain, so they consistently appear Gram-positive. Suttonella wadsworthensis, however, does not consistently stain as Gram-positive; it can appear Gram-negative or Gram-variable depending on conditions and strain. That makes it not a reliable Gram-positive organism, unlike the others.

Grams staining hinges on cell wall structure: thick peptidoglycan in Gram-positive bacteria traps the crystal violet-iodine complex and appears purple, while Gram-negative bacteria have a thinner peptidoglycan layer with an outer membrane and do not retain the dye as strongly.

The three well-known Gram-positive anaerobic bacteria listed—Eubacterium lentum, Bifidobacterium dentium, and Propionibacterium acnes—have the thick peptidoglycan layer that reliably retains the violet stain, so they consistently appear Gram-positive.

Suttonella wadsworthensis, however, does not consistently stain as Gram-positive; it can appear Gram-negative or Gram-variable depending on conditions and strain. That makes it not a reliable Gram-positive organism, unlike the others.