is a slender, spirally curved, motile Gram-negative
rod belonging to the Campylobacteraceae family (Figure
1). The bacterium is approximately 4 μm
length by 0.2 μm to 0.5 μm in width, and possesses
a single polar flagellum at one or both ends of
the cell. If environmental
pressures are placed on the bacteria, such as
drying, heating, disinfectants or acidic
conditions, they are capable of converting to a coccal form from their native spiral morphology.
This is one reason why identifying this pathogen
poses a challenge to microbiologists.
This scanning electron micrograph depicts a Campylobacter jejuni
bacterium [11734 X].
C. jejuni is optimally grown on sheep
blood agar with limited exposure to oxygen (5
to 10% of that found in the atmosphere) (Figure 2).
Its requirement for reduced levels of oxygen suggests that this
species is microaerophilic.
Furthermore, C. jejuni utilizes a
relatively large supply of serine, proline,
aspartate, and glutamate; this may be a way to
identify the bacteria if whether it can grow
well in a culture enriched with these amino
Campylobacter jejuni culture grown on
Skirrow's and Butzler's medium. Butzler and
Campylobacter agar (Skirrow) are selective media
for the isolation of Campylobacter species from
clinical and other specimens.
Infection by C. jejuni
is common, resulting in 400 million
cases of human
enterocolitis every year.
infections caused by C. jejuni are higher
in countries with low sanitation. Poor countries
with poor water treatment tend to have water
sources infected with
this pathogen. The most troubling symptoms
are observed in children than in adults simply
because the immune system does not respond
effectively to repeated infections at a young
age. The sites of tissue injury include the
jejunum, the ileum, and the colon. It has been
noted that when a host cell is infected with
C. jejuni, there are at most three bacteria
per cell, since their entrance rate into
epithelial comprising the gastrointestinal tract
is not optimal.
of C. jejuni produce a toxin,
cytolethal distending toxin (Cdt), that
hinders the cells from dividing and activating
the immune system. Cdt is produced by
several pathogenic bacteria. The toxin is
of three subunits, CdtA, CdtB and CdtC, which
together form a ternary complex (Ohara et al.,
2004). CdtB is the
active component, and CdtA and CdtC are involved
in delivering the CdtB into the cells. The
sophisticated strategy of Cdt to control host
cells is CdtB-mediated limited DNA damage of the
host cell chromosome, which triggers the
response of the cell cycle checkpoint and
results in Gap 2 phase (G2) arrest in the cells
(Ohara et al., 2004). Recall that the
G2 phase is the phase just before mitosis, the gap between DNA
synthesis and mitosis. Cdt also induces
apoptotic cell death of lymphocytes, which may
be relevant to onset or persistence of chronic
infection by the producing bacteria. This helps
the bacteria to evade the immune system and
survive for a limited time in the cells. Another
way C. jejuni evades its host's defenses
is by genetically rearranging the genes that
encode its flagella. By slightly changing the
amino acid composition of the protein coding the
flagella, it prevents antibodies specific for
the flagella from binding, and so the host is
unable to bind and induce a humoral or
cell-mediated response against the pathogen.
Normally, the flagellin would bind toll-like
receptors (TLR-5) or B-cell receptors as a
T-independent antigen and induce the activation
of phagocytes and antigen-presenting cells to
destroy the bacteria.
Ohara, M., Oswald, E. Sugai,
M. (2004). Cytolethal Distending Toxin: A
Bacterial Bullet Targeted to Nucleus. Journal of
Biochemistry, 136(4); 409-413.