Which organism may be identified as the swarming gram-negative bacterium on agar plates?

Which organism may be identified as the swarming gram-negative bacterium on agar plates?

• A. Pseudomonas sp.
• B. Staphylococcus sp.
• C. Proteus sp.
• D. Escherichia coli

Answer: (C)

Swarming motility is rapid, coordinated movement of a bacterial population across a semisolid surface, producing expanding fronts and often concentric rings. This behavior relies on abundant flagella and surface-active factors to move as a group across the agar. Among the options, Proteus species are the classic swarming bacteria on agar plates; Proteus mirabilis, in particular, spreads quickly across the surface and can overtake the plate with a characteristic spreading pattern. The other organisms do not display this textbook swarming behavior: Staphylococcus species are gram-positive and generally non-motile; Escherichia coli, while motile, does not typically form the distinctive swarming fronts seen with Proteus; Pseudomonas species are gram-negative and motile but do not produce the classic Proteus swarming pattern on standard media.

Swarming motility is rapid, coordinated movement of a bacterial population across a semisolid surface, producing expanding fronts and often concentric rings. This behavior relies on abundant flagella and surface-active factors to move as a group across the agar. Among the options, Proteus species are the classic swarming bacteria on agar plates; Proteus mirabilis, in particular, spreads quickly across the surface and can overtake the plate with a characteristic spreading pattern. The other organisms do not display this textbook swarming behavior: Staphylococcus species are gram-positive and generally non-motile; Escherichia coli, while motile, does not typically form the distinctive swarming fronts seen with Proteus; Pseudomonas species are gram-negative and motile but do not produce the classic Proteus swarming pattern on standard media.