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Chlamydiacae
The taxonomy of Chlamydiacae has been revised on the basis of
genomic studies; and accordingly they have been divided into 2
genera:
Chlamydia
Chlamydia trachomatis
2 biovars
Trachomatis & LGV
Chlamydophila
Chlamydia psittaci
Chlamydia pneumoniae
They were once considered as viruses because :
They are small enough to pass through o.45µ filters
They are obligate intracellular parasites.
They are now considered as bacteria because:
1.They have inner & outer membranes similar to gram negative
bacteria.
2. They contain both DNA &RNA
3.They can synthesize their own proteins, nucleic acids & lipids
4.They are susceptible to many antibiotics.
Antigenic structure
1. They have a genus-specific lipopolysaccharide detected by
complement fixation test.
2. They have species &strains-specific outer membrane proteins
Staining
1. Giemsa………….stains the elementary bodies , the reticulate
bodies &inclusions (not for definitive diagnosis )
2. Gram……………gram negative or gram variable (difficult )
3. Immunofluorescense
4. Iodine……………for intracellular inclusions which contain
glycogen
Developmental cycle of Chlamydia
-EB (elementary body ) attaches to the
surface of susceptible cell & enters the
cell by phagocytosis
-The elementary body organizes into
RB ( Reticulate body ).
-The reticulate body divides by binary
fission.
-After 24-48 hrs ,EBs are released and
initiate a new cycle of infection
-The mass of EBs → Inclusion
body→detected by histologic stains
NB 1-After internalization,bacteria remain
within the cytoplamic phagosome &
replicate.
2-Fusion of cellular lysosomes &
EBs containing phagosome , and
subsequent intracellular killing is
inhibited (bacteria not affected by
lysosymes
Growth
Eukaryotic cell lines : Hela cells-229 , Mc Coy cells , BHK -21 , Buffalo green
monkey kidney cells.
Sensitivity is increased by pretreatment with cycloheximide (to decrease host
metabolism ), use of shell vial technique ( growth of host cell monolayer on
glass cover slips rather than in small microtiter plates), use of Iodine stain or
Fluorescein-conjugated antibodies to detect intracellular inclusions.
- Embryonated egg yolk sac.
- Mice (rarely used )
Reaction to physical & chemical agents
Heat …………….at 60°C,for 10 min leads to their inactivation
Ether……………..for 30 min………..leads to rapid inactivation
Phenol 0.5%, for 24h…………………leads to inactivation
Freeze drying…………………………decreases their infectivity
Dryness……………………………….does not affect infectivity
Treatment
- Both sex-parteners should be simultaneously treated
- Tetracyclins are commonly used in non-gonococcal urethritis and in
non-pregnant females.
- Azithromycin is also effective.
- Erythromycin may be an alternative in pregnant females
- Topical Tetracyclin or Erythromycin………for inclusion
conjunctivitis.
- In LGV……….Sulfonamides & Tetracyclins for the early stages;but
late stages require surgery.
Chlamydia Trachomatis
It has a very limited range of infection (infects humans only)
It has 2 Biovars:
Trachoma (15 serovars A,B,Ba,C,D-K )
LGV
(4 serovars L1,L2,L2a,L3)
Clinical syndromes
1. Infections in Adults
Non-gonococcal urethritis (NGU) in males
- 50% of cases of NGU are sexually acquired.
- 25% are asymptomatic but are able to transmit the organism.
- When symptoms occur (urethral discharge,difficult micturition),they are
mild (unlike gonococcal urethritis).Serious complications are rare.
Mucopurulent cervicitis in females
- It is the female counterpart of male NGU
- It is acquired through sexual intercourse.Many remain asymptomatic.
- The Gram stain of the endocervical swab shows yellow-green mucous and
more than 10 PNLs/ HPF.(Neisseria must be excluded)
- Complications include PID
Pelvic inflammatory disease (PID)
- It is an ascending infection.
- Although symptoms may be mild yet laparoscopy may show severe
inflammation.
- Complications include salpingitis, endometritis,peritonitis,
Prihepatitis(Fitz-Hugh Curtis syndrome).These may lead to
infertility,chronic pelviabdominal pain & ectopic pregnancy.
Lymphogranuloma venereum
- It is a sexually transmitted disease.
- The IP is about 4w.
- The primary lesion occurs at the site of infection:vesicle,papule or
ulcer,small,painless heals rapidly so it might be overlooked.
- The second stage which occurs after2-5w shows marked inflammation&
swelling of the lymph nodes (usually inguinal)
- There is constitutional symptoms (usually severe).Fistulae may form
(especially after needle aspiration)
Acute urethral syndrome
Occurs in young women in the form of recurrent dysuria,pyuria& sterile
culture
Ocular infections
1- Trachoma :( A,B,Ba,C ) keratoconjunctivitis,invasion of blood vessels into
the cornea,bacterial infection&scarring.
2- Inclusion conjunctivitis :( A,B,Ba,D-K) in sexually active adults. It may
occur as an autoinfection.
Proctocolitis &epididymitis
Reiter' s syndrome: conjunctivitis,reactive arthritis and urethritis.
2. Infections in infants
Newborns………..from infected birth canal
Infants pneumonia (1-6 mo ) : usually associated with
conjunctivitis.
Infants conjunctivitis :It is the commonest cause of neonatal
conjunctivitis& is associated with mucopurulent discharge(2-3w
after birth).Most cases resolve without sequelae. However,some
may develop chronic ocular infection
Diagnosis
1. Culture
2. Non-cultural methods:
- Cytology : cell scrapings for inclusions,but is insensitive compared to culture
&immunofluorescence.
- Antigen detection: by direct immunofluorescence,
than culture)
ELISA(less sensitive
- Nucleic acid probes: test the presence of a specific species-specific sequence
of 16S rRNA.It is rapid & relatively inexpensive.
- PCR,LCR,TMA (transcription mediated amplification), SDA (standard
displacement ).They have a sensitivity of
90-98% In the very near future,they will be the test of choice.
- Serology: has a limited value in Chlamydia trachomatis causing genital
infections in adults,because antibody titers persist for a long period so,do not
differentiate between concurrent and past infections; although a significant rise
in antibody titer is useful.
Chlamydia Psittaci
Causes Psittachosis, Ornithosis, Parrot fever
Humans are infected by contact with birds, inhalation of dried
bird excrement, urine or resp. secretions.
IP 4d
C/ P: From mild inapparent or flu like inf. to severe pneumonia
with sepsis and high mortality rate (20%) now decreased to 2%.
Path: RT
lungs.
Blood
Liver, Spleen, Kidneys and
Diagnosis
1) Serology: 4 fold rise by CFT confirm by MIF
Sometimes specific IgM Antibody can be demonstrated.
2) Cell culture: rarely performed
Treatment
Te, Macrolides
Chlamydia Pneumoniae
Was 1st isolated from conj. of a child in Taiwan (TW-183) and
was found to be related to a pharyngeal isolate (AR-39)
TWAR C. pneumoniae
Chlamyolophila ( only a
single serotype)
Transmitted by resp. secretions (person to person)
Human pathogen
Common in adults
Clinical Picture
Usually mild or asymptomatic
May cause bronchitis, pneumonia, sinusitis
Cannot be diff. from other atypical pneumonias (Mycopl,
Legionella,….)
Associated with atherosclerosis
Diagnosis
difficult
Do not grow
Amplification techniques √
Serology:
Complement Fixation: not specific (positive for both
Chlamydia and Chlamydophia)
IF √√ : the most sensitive and specific. It uses EBs as
antigens
Treatment
E, Te, Lev
10-14d
Characteristics of the Chlamydiae
C. Trach.
C. Pneum.
C. Psittaci
Inclusion
Morphology
Round, Vaeuolar
Round, Dense
Large, Variable
Shape, Dense
Glycogen in Inclu.
Yes
No
No
E B Morph.
Round
Pear Shaped
Round
Suspect. To Sulph.
Yes
No
No
Serovars
19
Natural Host
Humans
Mode of
Transmission
Person to person
Mother to infant
Trachoma
STDs
Infant pneumonia
LGV
Major Disease
1
Humans
Air borne
Person to person
Pneumonia
Bronchitis
Pharyngitis
Sinusitis
≥4
Birds
Air borne (bird
excreta to human )
Psittacosis
Pneumonia
Fever of U.O