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Salmonella enteritidis is a rod-shaped, gram negative, non-motile bacteria, that does not form spores.  Unlike other strains of Salmonella that are primarily adapted to people, Salmonella enteritidis is primarily adapted to animal hosts, at least for the beginning of its life cycle.  S. enteritidis are considered facilitative anaerobes, which means that these bacteria can survive with or without oxygen. This broadens the environments in which they can be found.Flagella as observed on Salmonella (Image located at








Nice ride

Salmonella enteritidis move through their host’s intestines via flagella.  As shown in the images, S. enteritidis was grown and observed on HMM plates using an oil immersion objective.  Take note of the numerous flagella that extend from the bacteria cells. 


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Migration of Salmonella (Image located at

To the left is another image of S. enteritidis as it can be observed migrating on HMM and GI motility media.  This culture migrated 5-10 mm from the initial inoculation site over a period of 6 hours.  It is also interesting to note that equal migration distances were observed when conducting this experiment aerobically verses anaerobically.  This provides evidence that these bacteria are facilitative anaerobes.  This experiment was also conducted on a different species, S. pullorum, that lacks flagella.  As expected, no apparent migration was observed.  The flagella drastically affects the motility and, therefore, the ability of the bacteria to migrate and cause disease. S. enteritidis is currently the leading species of Salmonella that causes illness in the United States; S. pullorum is much easier to contain where as the non-motile state drastically impacts the ability to cause disease.


 Inter-Bacteria Communication (Impressive for a uni-cellular bacteria)

Communication (Image from Microsoft Clip Art)

Although bacteria are uni-cellular, new technology has enabled scientists to discover a new inter-bacteria communication between Salmonella enteritidis cells.  S. enteritidis has recently been discovered to release acyl-homoserine lactone (AHL), which is a chemical that acts as a communication signal between cells.  This chemical enhances the growth of the cells and increases virulence.  As the bacteria use their flagella to swim along, they release small amounts of AHL.  Once the concentration of the AHL is strong enough in a particular area, this serves as a signal to all of the cells to attack so that the hen’s egg can be infected.  The idea that bacteria cells can communicate chemically is known as quorum-sensing. 


Where can Salmonella be found?