00:01
Chlamydia, a bacteria.
00:03
The Chlamydia are very small, obligate intracellular
bacteria
and you can see the slide in front of you.
00:12
They lack a peptidoglycan layer, a typical cell wall
which means that there is no target for a beta-lactam
antibiotic to attach to.
00:22
Remember that beta-lactam antibiotics bind to peptidoglycan
in the cell wall
otherwise known as the penicillin binding protein.
00:31
However, Chlamydia is without that.
00:33
It has several different morphological forms which we’ll
discuss a bit further
when we talk about its growth pattern.
00:40
The elementary body which is the extracellular infectious
form
and which is resistant to many mechanisms,
both immunologic and antibiotic and then, the reticulate
body which is a intracellular form
when it is in its replicative or a replicating stage and at
this point,
it is dependent on its host cell to survive.
01:04
We think of three distinct pathogens in the Chlamydia
family, Chlamydia trachomatis
which is the most overt cause and it causes sexually
transmitted infections principally.
01:17
Chlamydia psittaci which also has been named Parrot Fever
and it is almost exclusively bird-associated but humans can
get disease too,
and then, Chlamydia pneumoniae which can cause an atypical
pneumonia.
01:33
Let’s start with the growth cycle of Chlamydia and this is
specific looking at trachomatis
although other Chlamydia grow this way as well.
01:42
We start with the free formed elementary body which attaches
to its target cell.
01:49
And at this case, we might think of this as a genital
epithelium.
01:53
After it binds, it is then ingested by the cell or in fact,
it gains entry into it entering via a phagosome
and as it converts or as it enters that cell within the
phagosome,
it starts to convert from the elementary body form to the
reticulate body form.
02:14
Then, it starts to replicate and as it does, so, it creates
this cluster of the reticular body forms
called an inclusion body.
02:24
This is one of the few times if one were to stain by iodine
the cell
that one could actually see under the microscope naked eye,
evidence of Chlamydia trachomatis infection.
02:36
Ultimately, after the replication progress has occurred,
then, the reticulate bodies converted
back to elementary bodies ready to be dissolved into the
free flowing community
and then they extrude or release themselves into the serum,
into their local area and prepare to go infect their next
target.
03:00
So, it’s an ongoing cycle in which the Chlamydia itself
changes its form depending on whether it’s intra or
extracellular.
03:09
Looking then in comparison at the three distinct Chlamydia
species that we’ll talk further about,
the host range for all three does include humans but for
trachomatis and pneumoniae,
it’s principally only humans that will actually develop some
sort of infection with the organism.
03:29
Chlamydia psittaci as you see in the middle primarily
affects animals and especially birds
but there can be accidental infection of humans especially
if they’re associated with parrot care.
03:42
As I briefly mentioned in the previous slide, the iodine
staining of inclusion bodies
most demonstrates presence of Chlamydia trachomatis only at
the inclusion body stain
but is not sensitive for looking for the other forms of
Chlamydia psittaci and pneumoniae.
04:00
And then, in terms of antibiotic or specifically sulfonamide
susceptibility,
only the Chlamydia trachomatis is truly sensitive, the other
forms are resistant.
04:10
Diseases, here’s where things are even further divergent.
04:15
Chlamydia trachomatis exists in further subtypes which you
see there,
types A to C which are associated with trachoma, types L1 to
L3
which are associated with lymphogranuloma venereum and types
D to K
which are associated with even further sexually transmitted
diseases,
also including infantile pneumonia and conjunctivitis which
is acquired by the infant
during passage through the birth canal.
04:43
Chlamydia psittaci is the cause of psittacosis or parrot
fever as mentioned
and Chlamydia pneumoniae is the cause of typically
sinopulmonary infections such as pharyngitis,
bronchitis, deeper pneumonia, and sinusitis.
05:00
The transmission of each is also somewhat divergent.
05:03
Chlamydia trachomatis as you’re starting to get the sense is
sexually transmitted
either through direct contact with partners, contact with
bodily infected fluids,
or by infants as they’re delivered through the birth canal.
05:19
Chlamydia psittaci is transmitted via inhalation of dry bird
feces.
05:23
The classic exposure history is a human being if they get
infected
who’s changing the newspapers at the bottom of the parrot
cage
and in fact, you might add this to your arsenal of
interesting and unusual questions
to ask in the exposure history.
05:39
Chlamydia pneumoniae then like many other respiratory
bacterial and even viral pathogens is transmitted
via inhalation of fine aerosols, fine or small respiratory
droplets from the infected person.