Proteus SWARM (like a blog swarm)

Swarming Proteus strains exhibit the Dienes phenomenon (the mutual inhibition of swarming), and this forms the precise basis of differentiation among strains. Test organisms are inoculated onto the surface of an agar plate, and those that show no line of demarcation in areas where the swarming growths meet are regarded as identical.

Here is what they look like on different media:

1) CLED: 




2) CLED:



3) CLED:



4) Blood Agar:



5) Blood Agar:



6) Blood Agar:




These bacteria are capable of swarming motility as they differentiate from typical enterobacterial bacilli expressing fimbriae and flagellae into highly elongated rods with thousands of flagellae that translocate rapidly across the surface of agar plates.

Here, a swarming growth of P. mirabilis inoculated centrally onto a blood agar plate is incubated overnight @ 37 degrees celcius. The distinctive "pong" occurs due to the break down of urea.

How then can these be mistaken on a blood culture for GPCs?
Boy, that's a tough question! Proteus are gram negative rods, but due to the Gram staining process, they can appear as cocci in the centre of the innoculum with an increase in length of the microbes picked from the periphery.

Each of the clinical bacteria has its own claim to fame. This genera has two species which swarm over the agar plate in waves. Which species? Hint: swarming is a vulgar miracle.

How do you prevent the swarm?
Either grow it on a CLED  [(Cystine-Lactose-Electrolyte-Deficient) - inhibits the proteus swarm] or a MacConkey, use a selective media (e.g. cipro)  or to use alcohol "shock" therapy. Here the mixed culture is put into a broth and mixed with a "shot" of alcohol. This kills the Gm -ves but allows others to survive.

NOTE. P. mirabilis is fully sensitive, while P. vulgaris is not. Both produce a urease enzyme which break down urea. This produces ammonia with allows precipitation of calcium and thus stone formation. Klebsiella sp also predispose to stone formation. Note that this urease reaction forms part of the diagnostic pathway for Helicobacter pylori.


Proteus, Providencia & Morganella are inextricably linked, and there has been much confusion over the taxonomy. The genera Proteus, Providencia, and Morganella are related members of the family Enterobacteriaceae.

Although there is considerable morphological varaition amongst the various species, on agar they look like most coliforms. They grow well on nutrient media. Both P. vulgaris & P. mirabilis SWARM, but the Dienes phenomenon is particular to P. mirabilis.

The 3 species are:

  • lactose negative
  • motile
  • produce phenylalanine deaminase. This is tested for by innoculating the isolates onto media containing phenylalanine. The phenylpyruvic acid is the PPA test.
  • Providencia can be differentiated from Proteus and Morganella on the basis of their ability to utilize citrate and ferment D-mannitol.
  • Morganella morganii is citrate negative.

There are several species of Proteus, but P. mirabilis and P. vulgaris account for the vast majority of clinical isolates in this genus.


  • produce urease
  • P. vulgaris is indole positive.
  • produce H2S.

N.B: The name "Proteus" was chosen from a character in Homer's Odyssey, who was capable of changing form. 



And the answer is ...??