Eikenella corrodens

Ei·ken·el·la cor·ro·dens (k-nl k-rdnz)
n.
A rod-shaped, gram-negative, facultatively anaerobic bacterium normally in the adult human oral
cavity but which may become an opportunistic pathogen, especially in immunocompromised
individuals.

The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.

Eikenella corrodens
Kim Hydeman
Eikenella corrodens was first described in 1948 as a slow-growing, anaerobic, Gram-negative rod.  
A distinguishing feature of this organism is the ability to pit or corrode the agar in plated culture.  
The colonies grow in the little grooves and for this reason it was called a corroding bacillus.  It was
classified as Bacteroides corrodens.  Further studies proved that the classification had been
applied to two organisms.  The major difference between the two being that one was a facultative
anaerobe and the other was an obligate anaerobe.  The facultative anaerobe was renamed
Eikenella corrodens.
E. corrodens inhabits the mucous membrane surfaces of humans, most commonly the respiratory
tract.  E. corrodens can cause infections in humans when their immune system is weak.  Once an
infection has occurred it can travel to other parts of the body.  E. corrodens is usually found with
other bacteria in infections, commonly streptococci. E. corrodens is also responsible for about a
quarter of human hand-bite wound infections and clenched-fist injuries.  It is also a putative
periodontal pathogen, found at high levels in humans with periodontitis. E. corrodens infections
can be treated with antibiotics such as penicillin, ampicillin and tetracycline.

E. corrodens does not grow on selective media.  When it is incubated aerobically it requires hemin.
 However, when it is incubated anaerobically it does not require hemin.  Plate growth may be
stimulated in a 3-10% CO2 enviroment, even though CO2 is not required.  E. corrodens grows so
slowly that sometimes it is hidden by other faster-growing bacteria.  However, adding 5 ug/ml of
clindamycin increases recovery.

E. corrodens must be incubated for 2-3 days before the colonies grow to a size sufficient for
counting.  When plated the organism is dry, flat and has a yellow-pigmented colony.  The colony
growth has three zones.  There is a clear and moist center, a highly visible ring that appears like
droplets, and an outer growth ring.  The organism can produce either a musty smell or a bleach
smell.

E. corrodens is small, straight, nonsporeforming, nonencapsulated and nonmotile.  It is
biochemically inactive for most biochemical tests.  It does not produce catalase, urease, indole or
H2S2.  It is oxidase positive and it can reduce nitrate.

REFERENCES:

Balow, A.  The Prokaryotes: a hand book on the biology of bacteria; Springer-Verlag: New York,
1992.

http://www.usc.edu/hsc/dental/faculty/CHEN.html