cornyebacterium dip Flashcards
Bacillus and Clostridium form spores where as Corynebacterium, Erysipelothrix and Listeria do not
Bacillus and Clostridium species are longer and more deeply staining than Corynebacterium and Listeria species.
Corynebacteria
general character
Gram positive
Non motile, non spore forming straight or slightly curved rods
Pleomorphic, tend to be clubbed or irregularly shaped
Have metachromatic granules
Aerobic, facultative anaerobic and catalase positive
The major disease caused by C. diphtheriae is
diphtheria
An infection of the local tissue of the upper respiratory
Medically important species
C. diphtheriae
C. ulcerans
C. pseudotuberculosis
Individual corynebacteria in stained smears tend to lie
parallel or at acute angles to one another
True branching is rarely observed in cultures
Arranged in angular fashion like
Chinese lettering or cuneiform arrangement
The “barred” appearance is due to the presence of
polyphosphate inclusions called metachromatic granules
On blood agar, colonies are
small, granular, and gray with irregular edges and may have small zones of hemolysis
There are four biovars (biotypes): on basis of growth characteristics such as colony morphology, biochemical reactions, and severity of disease
gravis, intermedius, mitis, and belfanti.
Virulence factor
Corynebacterium diphtheriae
Diphtheria toxin an exotoxin
Diphtheria toxin an exotoxin
characters
Is a heat-labile polypeptide produced during lysogeny of a phage that carries the “tox” gene.
Alkaline pH of 7.8- 8.0, aerobic conditions
A low environmental iron level
The toxin inhibits protein synthesis
by ADP-ribosylating elongation factor 2
The diphtheria toxin is a heat-labile polypeptide, composed of two fragments
A (active) and B (binding).
Human are the only known reservoir with the carriage in
Oropharynx
Gastrointestinal tract
Urogenital tract and on the skin surface
Clinical feature
Respiratory Diphtheria
Diphtheria - pseudomembrane
Cutaneous Diphtheria
Complication in patients with sever disease include
Breathing obstruction,
The more dangerous effects occur when the toxin becomes systemic and attacks the heart
Cardiac arrhythmia, coma and ultimately death
Nerve weakness or paralysis, especially of the cranial nerves
C. diphtheriae does not actively invade deep tissues and practically never enters the bloodstream
cultures of C. dip
loeffler
Tellurite blood agar:
Tinsdale medium:
each culture character
It is not advisable to use either Dorset egg or Loeffler serum medium as a primary medium for isolating
C. diphtheriae because commensal diphtheroids may overgrow the diphtheria bacteria.
This medium is widely used as a primary medium for isolating C. diphtheriae from throat and nasopharyngeal swabs
The brown colour is due to the hydrogen sulphide produced from the cystine interacting with the tellurite
commensals But the colonies are not surrounded by a brown halo like those of C. diphtheriae.
Biochemical tests
reduces nitrate to nitrites
Catalase Positive
Oxidase negative.
Urease negative.
ferments
glucose and maltose
gravis and mitis sucrose
gravis starch
Toxigenicity of C. diphtheriae can be tested by
the Elek gel precipitation test.
Toxin-producing C. diphtheriae is identified by
the presence of precipitin lines and arcs of identity
