Swarming/Motile Bacteria

Swarming is a function of motility in bacteria and is seen in both G+ bacteria (ex:  Bacillus spp) and G- bacteria (ex: Proteus, Pseudomonas, E. coli, Serratia,  Yersinia, Salmonella, Vibrio, Aeromonas) and is associated with incresed virulence.  Swarming ability can be influenced by nutrients, media composition (agar concentration), the ability of the organism to produce biosurfactants, and the presence of flagella.  Biosurfactant production is thought to lower the surface tension of the growth media allowing the bacteria to move and can be a variety of different chemical compositions from fatty acids, phospholipids, glycolipids, surface active anitibiotics,  and polymeric microbial surfactants (1).  

(A)                                                                                                     (B)

(A)  Streak plate of Proteus vulgaris.  After 48 hours of incubation at 37 degree C swarming finger like projections can be seen.  (B) unknown organism form a floor swab after 48 hour incubation at 37 degree's C with swarming finger like projections.



(A)











(B)


(A)  A sample of Proteus mirabilis was inoculated onto a blood agar plate by taking a swab and placing a drop of culture onto the plate.  The plate was then incubated at 37 degree's C for 8 hrs, culture was young to image the start of swarming.  Swarming motility can  be seen as a halo around the inoculation site forming a bulls-eye with waves of swarming followed by differentiation into vegetative cells then back again into swarming cells (2).  This will eventually lead to a colony of concentric circles around the inoculation site.
(B) using the same technique Proteus mirabilis was also inoculated on TSA and imaged using transmitted light.  Again after 8 hours swarming was seen from the initial site of inoculation.




Unknown colony, presumably a Bacillus spp, taken from a swab of a students backpack.  Swarming can be seen a blebs from the initial site of growth.  Image taken form underside of the plate using transmitted light.





(A)


(B)
(A) Streak plate isolation of Alcaligenes faecalis grown on TSA, swarming seen as finger like projections around the colonies.   A. faecalis is know for swarming as well as pleiomorphic gram stain morphology.  (B) Straight line inoculation of A. faecalis demonstrating swarming.






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(1) N. G. K. Karanth, P. G. Deo and N. K. Veenanadig*:  Microbial production of biosurfactants and their importance
Pesticide Residue Abatement Lab, Food Protectants and Infestation Control Department, Central Food Technological Research Institute,
Mysore 570 013, India
(2)Nicole Valentini, Swarming motility in Proteus mirabilis: causitive agent of UTI's.  Microbewiki, the student edition


All images copyright Sturm

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