Exploring the Intricate World of Chlamydiae: Unraveling Their Biology, Pathogenesis, and Implications for Human Well being
Chlamydiae are obligate intracellular micro organism (i.e., they’ll
develop solely inside cells). They’re the brokers of widespread sexually
transmitted ailments, comparable to urethritis and cervicitis, in addition to
different infections, comparable to pneumonia, psittacosis, trachoma, and
Further data concerning the scientific facets of
infections attributable to the organisms on this chapter is supplied
in Half IX entitled Infectious Ailments starting on web page 589.
Chlamydia trachomatis causes eye (conjunctivitis, trachoma),
respiratory (pneumonia), and genital tract (urethritis, lympho-
granuloma venereum) infections. Chlamydia trachomatis is
the most typical bacterial explanation for sexually transmitted
illness in the US. (Human papilloma virus an infection
is the most typical sexually transmitted an infection general in
the US.) An infection with C. trachomatis can also be related
with Reiter’s syndrome, an autoimmune illness. Roughly
40% of nongonococcal urethritis is attributable to C. trachomatis.
Chlamydia pneumoniae causes atypical pneumonia. Chlamydia
psittaci causes psittacosis, additionally a illness characterised primarily by
pneumonia (Desk 25–1).
Chlamydia pneumoniae and C. psittaci are sufficiently differ-
ent molecularly from C. trachomatis that they’ve been reclas-
sified into a brand new genus known as Chlamydophila. Taxonomically,
they’re now Chlamydophila pneumoniae and Chlamydophila
psittaci. Nevertheless, from a medical perspective, they’re nonetheless
referred to as Chlamydia pneumoniae and Chlamydia psittaci, and
these are the names which might be used on this e-book.
Chlamydiae are obligate intracellular micro organism. They lack the
capacity to provide adequate power to develop independently and
due to this fact can develop solely inside host cells. They’ve a inflexible cell
wall however shouldn’t have a typical peptidoglycan layer. Their cell partitions
resemble these of gram-negative micro organism however lack muramic acid.
Chlamydiae have a replicative cycle totally different from that of all
different micro organism. The cycle begins when the extracellular, meta-
bolically inert, “sporelike” elementary physique enters the cell and
reorganizes into a bigger, metabolically lively reticulate physique
FIGURE 25–1 Life cycle of Chlamydia. The extracellular, inert elementary physique enters an epithelial cell and adjustments right into a reticulate physique
that divides many occasions by binary fission. The daughter reticulate our bodies grow to be elementary our bodies and are launched from the epithelial
cell. The cytoplasmic inclusion physique, which is attribute of chlamydial infections, consists of many daughter reticulate and elementary
our bodies. (Reproduced with permission from Ryan Okay et al. Sherris Medical Microbiology. third ed. Initially printed by Appleton & Lange. Copyright 1994, McGraw-Hill.)
(Determine 25–1). The latter undergoes repeated cycles of binary
fission to type daughter reticulate our bodies, which then develop
into elementary our bodies, that are launched from the cell. Inside
cells, the location of replication seems as an inclusion physique within the
cytoplasm, which might be stained and visualized microscopically
(Determine 25–2). These inclusions are helpful within the identification
of those organisms within the scientific laboratory.
All chlamydiae share a group-specific lipopolysaccharide
antigen, which is detected by complement fixation assessments. They
additionally possess species-specific and immunotype-specific antigens
FIGURE 25–2 Chlamydia trachomatis—gentle microscopy of cell cul-
ture. Lengthy arrow factors to cytoplasmic inclusion physique of C. trachomatis;
brief arrow factors to nucleus of cell. (Supply: Dr. E. Arum and Dr. N. Jacobs,
Public Well being Picture Library, Facilities for Illness Management and Prevention.)
(proteins), that are detected by immunofluorescence.
Chlamydia psittaci and C. pneumoniae every have one immuno-
kind, whereas C. trachomatis has no less than 15 immunotypes.
Transmission & Epidemiology
Chlamydia trachomatis infects solely people and is often
transmitted by shut private contact (e.g., sexually or by pas-
sage by the start canal). People with asymptomatic
genital tract infections are an vital reservoir of an infection
for others. In trachoma, C. trachomatis is transmitted by finger-
to-eye or fomite-to-eye contact.
Chlamydia pneumoniae infects solely people and is transmit-
ted from individual to individual by aerosol. Chlamydia psittaci infects
birds (e.g., parrots, pigeons, and poultry, and plenty of mammals
together with people). People are contaminated primarily by inhaling
organisms in airborne dry chook feces.
Sexually transmitted illness attributable to C. trachomatis happens
worldwide, however trachoma is most steadily present in develop-
ing international locations in dry, sizzling areas comparable to northern Africa. Tra-
choma is a number one explanation for blindness in these international locations.
Sufferers with a sexually transmitted illness are coinfected
with each C. trachomatis and Neisseria gonorrheae in approxi-
mately 10% to 30% of instances.
Pathogenesis & Medical Findings
Chlamydiae infect primarily epithelial cells of the mucous
membranes or the lungs. They not often trigger invasive, dissemi-
Chlamydia trachomatis has greater than 15 immunotypes (A–L).
Varieties A, B, and C trigger trachoma, a persistent conjunctivitis
endemic in Africa and Asia. Trachoma might recur over many
years and should result in blindness however causes no systemic sickness.
Varieties D–Okay trigger genital tract infections. In males, it’s a
widespread explanation for nongonococcal urethritis (usually abbreviated
NGU), which is characterised by dysuria and a watery, nonpu-
rulent urethral discharge (Determine 25–3). The discharge could also be
slight, detectable solely by staining of underwear in a single day. This
an infection might progress to epididymitis, prostatitis, or proctitis.
In ladies, cervicitis accompanied by a vaginal discharge devel-
ops and should progress to salpingitis and pelvic inflammatory
illness (PID). Repeated episodes of salpingitis or PID may end up
in infertility or ectopic being pregnant. Urethritis accompanied by
dysuria additionally happens.
Asymptomatic infections are quite common in each males and
Infants born to contaminated moms usually develop mucopuru-
lent conjunctivitis (neonatal inclusion conjunctivitis) 7 to 12 days
after supply, and a few develop chlamydial pneumonia 2 to
12 weeks after start. Chlamydial conjunctivitis additionally happens in
adults because of the switch of organisms from the genitals
to the attention.
Sufferers with genital tract infections attributable to C. tracho-
matis have a excessive incidence of reactive arthritis and Reiter’s
syndrome, which is characterised by urethritis, arthritis, and
uveitis. These are autoimmune ailments attributable to antibodies
fashioned in opposition to C. trachomatis cross-reacting with antigens on
the cells of the urethra, joints, and uveal tract (see Chapter 66).
Chlamydia trachomatis L1–L3 immunotypes trigger lym-
phogranuloma venereum, a sexually transmitted illness with
lesions on genitalia and in lymph nodes.
An infection by C. trachomatis results in formation of antibodies
and cell-mediated reactions however to not resistance to reinfection
or elimination of organisms.
FIGURE 25–3 Nongonococcal urethritis. Word watery, nonpuru-
lent discharge attributable to Chlamydia trachomatis. The urethral
discharge attributable to Neisseria gonorrheae is extra mucoid and
purulent. (Used with permission from Seattle STD/HIV Prevention Coaching Heart.)
Chlamydia pneumoniae causes higher and decrease respiratory
tract infections, particularly bronchitis and pneumonia, in younger
adults. Most infections are delicate or asymptomatic. The clini-
cal image resembles different atypical pneumonias, particularly
that attributable to Mycoplasma pneumoniae. It’s unclear whether or not
C. pneumoniae causes higher respiratory infections comparable to
sinusitis and otitis media.
Chlamydia psittaci infects the lungs primarily. The an infection
could also be asymptomatic (detected solely by a rising antibody titer)
or might produce excessive fever and pneumonia. Human psittacosis
will not be usually communicable from human to human.
Though most infections are delicate, some are fairly extreme and
contain organs aside from the lung. The respiratory an infection
usually manifests with fever, cough, dyspnea, myalgias, and
headache. The commonest extrapulmonary organs concerned
are the liver (hepatomegaly, jaundice), coronary heart (myocarditis, peri-
carditis), and nervous system (listening to loss, transverse myelitis,
Chlamydiae type cytoplasmic inclusions, which might be seen
with particular stains (e.g., Giemsa stain) or by immunofluorescence
(see Determine 25–2). Basically, the Gram stain will not be helpful because the
organisms are too small to visualise throughout the cytoplasm.
Nevertheless, a Gram stain of a urethral discharge that exhibits neutro-
phils however no gram-negative diplococci resembling N. gonorrheae
is presumptive proof for an infection by C. trachomatis.
Nucleic acid amplification assessments (NAATs) utilizing the affected person’s
urine are broadly used to diagnose chlamydial sexually trans-
mitted illness. Checks not involving tradition, comparable to NAAT, are
now extra generally used than culture-based assessments (see later).
In exudates, the organism might be recognized inside epithelial
cells by fluorescent antibody staining or hybridization with a
DNA probe. Chlamydial antigens will also be detected in exu-
dates or urine by enzyme-linked immunosorbent assay (ELISA).
Chlamydiae might be grown in cell cultures handled with cyclo-
heximide, which inhibits host cell however not chlamydial protein
synthesis, thereby enhancing chlamydial replication. In tradition,
C. trachomatis types inclusions containing glycogen, whereas
C. psittaci and C. pneumoniae type inclusions that don’t con-
tain glycogen. The glycogen-filled inclusions are visualized by
staining with iodine. Exudates from the eyes, respiratory tract,
or genital tract yield constructive cultures in about half of instances.
Serologic assessments are used to diagnose infections by C. psittaci
and C. pneumoniae however are not often useful in diagnosing illness
attributable to C. trachomatis as a result of the frequency of an infection is
so excessive that many individuals have already got antibodies.
All chlamydiae are inclined to tetracyclines, comparable to doxycy-
cline, and macrolides, comparable to erythromycin and azithromycin.
The drug of alternative for C. trachomatis sexually transmitted
ailments is azithromycin. As a result of the speed of coinfection with
gonococci and C. trachomatis is excessive, any affected person with a diagno-
sis of gonorrhea also needs to be handled for C. trachomatis with
azithromycin. Intercourse companions needs to be supplied remedy.
The drug of alternative for neonatal inclusion conjunctivitis
and pneumonia attributable to C. trachomatis is oral erythromycin.
The drug of alternative for C. psittaci and C. pneumoniae infections
and for lymphogranuloma venereum is a tetracycline, comparable to
There isn’t a vaccine in opposition to any chlamydial illness. The most effective
safety measure in opposition to C. trachomatis sexually transmit-
ted ailments is to restrict transmission by protected intercourse practices and
immediate remedy of each the affected person and the sexual companions,
together with individuals who’re asymptomatic. Sexual contacts
needs to be traced, and people who had contact inside 60 days
needs to be handled. Screening of sexually lively, asymptomatic
younger ladies and remedy of those that are constructive is cost-
efficient as a result of it could stop PID and ectopic being pregnant.
A number of kinds of sexually transmitted ailments are sometimes pres-
ent concurrently. Thus, prognosis of 1 requires a seek for
different causative brokers.
Oral erythromycin given to new child infants of contaminated
moms can stop inclusion conjunctivitis and pneumonitis
attributable to C. trachomatis. Word that erythromycin ointment
used to stop neonatal gonococcal conjunctivitis is far much less
efficient in opposition to neonatal chlamydial conjunctivitis. Oral eryth-
romycin needs to be used.
Psittacosis in people is managed by proscribing the impor-
tation of psittacine birds, treating or destroying sick birds, and
including tetracycline to chook feed. Home flocks of turkeys and
geese are examined for the presence of C. psittaci.
1. Your affected person is a 20-year-old man with a urethral discharge. Gram
stain of the pus reveals many neutrophils however no micro organism. You
suspect this an infection could also be attributable to C. trachomatis. Which
one of many following is the laboratory consequence that greatest helps
your scientific prognosis?
(A) Gram stain of the pus reveals small gram-positive rods.
(B) The organism produces β-hemolytic colonies on blood agar
plates when incubated aerobically.
(C) The organism produces α-hemolytic colonies on blood agar
plates when incubated anaerobically.
(D) Fluorescent antibody staining demonstrates cytoplasmic
inclusions in epithelial cells within the exudate.
(E) There’s a fourfold or better rise in antibody titer in opposition to
2. Concerning chlamydiae, which one of many following is essentially the most
(A) Lifelong immunity often follows an episode of illness
attributable to these organisms.
(B) The reservoir host for the three species of chlamydiae that
trigger human an infection is people.
(C) Their life cycle consists of elementary our bodies exterior of cells
and reticulate our bodies inside cells.
(D) They will solely replicate inside cells as a result of they lack the ribo-
somes to synthesize their proteins.
(E) The vaccine in opposition to C. pneumoniae comprises the capsular poly-
saccharide because the immunogen conjugated to a provider protein.
3. Which one of many following is the drug of alternative for sexually trans-
mitted illness (urethritis, cervicitis) attributable to C. trachomatis?
SUMMARIES OF ORGANISMS
Temporary summaries of the organisms described on this chapter
start on web page 653. Please seek the advice of these summaries for a fast
evaluate of the important materials.
PRACTICE QUESTIONS: USMLE &
Questions on the subjects mentioned on this chapter might be discovered
within the Medical Bacteriology part of Half XIII: USMLE
(Nationwide Board) Apply Questions beginning on web page 715. Additionally
see Half XIV: USMLE (Nationwide Board) Apply Examination