Chlamydiae

23/4/22 microbiology 8-year course 1

Chlamydiae


Biological Features Structure and chemical composition Developmental cycle Staining properties Antigens Growth and metabolism Characteristics of host-parasite relationship Classification


Structure and chemical composition

a nonreplicating, infect

ious particle called the

elementary body (EB)

an intracytoplasmic for

m called the reticulate

body (RB)


Structure and chemical composition


Structure and chemical composition The elementary body, which is covered by a rigid cell wall, contains a DNA ge

nome with a molecular weight of 66 X 107 (about 600 genes, one-quarter of th

e genetic information present in the DNA of Escherichia coli).

A cryptic DNA plasmid (7,498 base pairs) is also found. It contains an open re

ading frame for a gene involved in DNA replication.

the elementary body contains an RNA polymerase responsible for the transcri

ption of the DNA genome after entry into the host cell cytoplasm and the initiati

on of the growth cycle.

Ribosomes and ribosomal subunits are present in the elementary bodies. Thro

ughout the developmental cycle, the DNA genome, proteins, and ribosomes ar

e retained in the membrane-bound reticulate body.


Developmental cycle

EBs attach to the microvilli of susceptive cells. Penetration into the host cell via endocytosis or pinocytosis and for

ming phagosomes Fusion of lysomes with the EB-containing phagosome are inhibited EBs reorganize into the metabolically active RBs. RBs synthesize their own DNA, RNA and protein but lack the neces

sary metabolic pathways to produce high-energy phosphate compounds.

Energy parasites. RBs replicate by binary fission and inclusion forms. RBs begin reorganizing into EBs. Cell ruptures and releasesthe infective Ebs. The developmental cycle takes 24～ 48 hours.


Developmental cycle


Staining properties

EBs stain purple with Giemsa stain—in contrast to the blue

of host cell cytoplasm.

RBs stain blue with Giemsa stain.

The Gram reaction of chlamydiae is negative or variable and

is not useful in identification.

Inclusions stain brightly by immunofluorescence ,with group-

specific,species-specific, or serovar-specific antibodies.


Antigens Group(fenus)-specific antigens:

– heat-stable LPS as an immunodominant component.– Antibody to these antigens can be detected by CF an

d immunofluorescence Species-specific or serovar-specific antigens

– Antigens are mainly outer membrane proteins(MOMP).

– Specific antigens can best be detected by immunofluorescence,particularly using monoclonal antibodies.


Growth and metabolism Unable to synthesize ATP and depend on the host cell for energy requirement

s.

Grow in cultures of a variety of eukaryotic cell lines

– McCoy cells are used to isolate chlamydiae

– C pneumoniae grows better in HL or Hep-2 cells.

– All types of chlamydiae proliferate in embryonated eggs,particularly in th

e yolk sac.

The replication of chlamydiae can be inhibited by many antibacterial drugs.

– Cell wall inhibitors (penicillins) result in the production of morphologicall

y defective forms but are not effective in clinical diseases.

– Inhibitors of protein synthesis (tetracyclines,erythromycins)are effective

in most clinical infections.

– C trachomatis strains synthesize folates and are susceptible to inhibition

by sulfonamides.


Classification

C trachomatis

– Biovar trachoma

– Biovar lymphogranuloma venereum

– Biovar mouse

C pneumoniae

C psittaci

C pecorum 兽类衣原体


Transmission


Pathogenicity

transmission Who is at risk Virulence factor Clinical syndromes Epidemiology immunity


Transmission

C. trachomatis

– Sexually transmitted;most frequent bacterial pathogen in

united states.

– Infected patients , who may be asymptomatic.

– Inoculation through break in skin or membranes.

– Passage to new born at birth.

– Trachoma spread to eye by means of contaminated hand,

droplets,clothing, and flies.


Transmission C. pneumoniae

– Person-to-person spread by inhalation of infectious aerosols.

– No animal reservoir

C. psittaci– Infection acquired by contact with infected bir

d or animal(may appear healthy).– Person-to-person infection very uncommon.


Who is at risk?

C. trachomatis– People with multiple sexual partners.– Homosexuals,who are more at risk for LGV.– Newborns born of infected mothers.– Reiter’s syndrome: young white men.– Trachoma:children,particularly those in crow

ded living conditions where sanitation and hygiene are poor.


Who is at risk?

C. pneumoniae– High prevalence of infections throughout life;m

ost infections asymptomatic.– Diease most common in adults.

C. psittaci– Disease most common in adults.– Occupations at increased risk include veterinari

ans,zookeepers,pet shop workers,and employees in poultry processing plants


Virulence factors

C. trachomatis– Intracellular replication,– prevention of phagolysosomal吞噬溶酶体 fusi

on, – survival of infectious EBs as a result of cross-li

nkage of membrane proteins.


Virulence factors

C. pneumoniae– Intracellular replication;– prevention of phagolysosome吞噬溶酶体 fusi

on;– ability to infect and destroy ciliated epithelial c

ells of respiratory tract,smooth muscle cells,endothelial cells,and macrophages;

– extracellular survival of infectious EBs.


Virulence factors

C. psittaci– Intracellular parasite,– prevention of phagolysosomal fusion,– survival of infectious EBs as result of cross-link

age of membrane proteins.


Clinical syndromes

C. trachomatis– Trachoma

– Adult inclusion conjunctivitis

– Neonatal conjunctivitis

– Infant pneumonia

– Ocular lymphogranuloma

venereum

– Urogenital infections

– Reiter’s syndrome

– Lymphogranuloma venereum


Clinical syndromes

C. pneumoniae– Bronchitis– Pneumonia– Sinusitis鼻窦炎– Pharyngitis– atherosclerosis动脉粥样硬化


Clinical syndromes

C. psittaci– psittacosis


Epidemiology Trachoma

– Trachoma is still prevalent in Africa and Asia, and sporadic cases occur all over the world.

– The disease flourishes in hot, dry areas where there is a shortage of water and where standards of hygiene are low.

– The agent is spread to the eyes by flies, dirty towels, fingers, or cosmetic eye pencils.

– The initial infection usually occurs in childhood, and the active disease eventually appears (mostly by 10 to 15 years of age). Trachoma may leave a residuum of permanent lesions that can lead to blindness.

– Chlamydia trachomatis also resides in the genital tract, cervix, and urethra of adults, and genital infection is spread sexually.


Epidemiology Lymphogranuloma venereum

– Lymphogranuloma venereum persists in the genital tract of infected persons.

– LGV is a chronic sexually transmitted disease caused by serotype L1,L2,and L3.

– Because C trachomatis is able to infect both the eyes and the urogenital tract, antitrachoma campaigns involving only ocular treatments are futile.

– It occurs sporadically in North America ,Australia ,and Europe but is highly prevalent in Africa, Asia and South America.

– Male homosexuals are the major reservoir of disease.– Acute LGV is seen more frequently in men,primarily because sym

ptomatic infection is less common in women.


Epidemiology

Chlamydia pneumoniae – Chlamydia pneumoniae spreads in human populations

by respiratory tract infections.

– It is the agent of atypical pneumonia in hospitalized patients as well as in young individuals with an acute respiratory disease.

– It has caused epidemics in Scandinavia.

– Studies of the prevalence of antibodies to C pneumoniae in humans around the world showed that it also prevails in Japan, Panama, and North America.


Epidemiology

Chlamydia psittaci– the cause of psittacosis in birds and occasionall

y in humans,– it is carried by wild and domestic birds, includi

ng poultry. – The severity of psittacosis in humans has been

considerably reduced by the susceptibility of C psittaci to antibiotics.


Immunity

C. trachomatis– Untreated infections tend to be chronic with per

sistence of the agent for many years.– Little is known about active immunity.– The coexistence of latent infection,antibodies,a

nd cell-mediated reactions is typical of many chlamydial infections.


Immunity

C. pneumoniae– Little is known about active or potentially prote

ctive immunity.– Prolonged infections can occur with C. pneumo

niae, and asymptomatic carriage may be common.


Immunity

C. psittacosis– Immunity in animals and humans is incomplete.– A carrier state in humans can persist for 10

years after recovery.– During this period, the agent may continue to

be excreted in the sputum.– Live or inactivated vaccines induce only partial

resistance in animals.– They have not been used in humans.


Diagnosis

Most diseases caused by the chlamydiae are diagnosed on the basis of their clinical manifestations.

Eye damage caused by C trachomatis is typical, as are the vesicles in the infected urogenital tract.

Diagnosis of pneumonitis requires laboratory testing


Diagnosis Chlamydia trachomatis can be identified microscopically i

n scrapings from the eyes or the urogenital tract. Inclusion bodies in scraped tissue cells are identified by iodine staining of glycogen present in the cytoplasmic vacuoles in infected cells.

To isolate the agent, cell homogenates that contain the chlamydial elementary bodies are centrifuged onto the cultured cells (e.g., irradiated McCoy cells).

After incubation, typical cytoplasmic inclusions are seen in the cells stained with Giemsa stain or iodine.


Diagnosis Staining with iodine can distinguish between inclusion bod

ies of C trachomatis and C psittaci, as only the former contain glycogen.

Each chlamydial agent can also be identified by using specific immunofluorescent antibodies prepared against either C trachomatis or C psittaci.

Homogenates or exudates of infected tissues also have been used to isolate the agent in the yolk sac of embryonated eggs.


Diagnosis

Sera and tears from infected humans are used to detect anti-Chlamydia antibodies by the complement fixation or microimmunofluorescence tests.

The latter is useful for identifying specific serotypes of C trachomatis.

Fluorescent monoclonal antibodies are used to stain C trachomatis elementary bodies in urethral and cervical exudates.


Diagnosis It is possible to diagnose C trachomatis in tissue biopsy sp

ecimens by in situ DNA hybridization with cloned C trachomatis DNA probes.

DNA from C trachomatis isolates can be examined by restriction endonuclease analysis.

The DNA cleavage pattern of C trachomatis isolates differs greatly from that of DNA from C psittaci isolates.

DNAs of the agents of trachoma and lymphogranuloma venereum differ in their cleavage patterns, and this allows identification of the biovars


Diagnosis Chlamydia pneumoniae DNA has 10 percent homology

with C trachomatis or C psittaci; C pneumoniae isolates have 100 percent homology. Chl

amydia pneumoniae isolates can be diagnosed by hybridization with a specific DNA probe that does not hybridize to other chlamydiae.

Two additional serologic tests are in use: the microimmunofluorescence test with C pneumoniae-

specific elementary body antigen, and the complement fixation test, which measures Chlamydia antibodies.


Prevention and control C. trachomatis

– It is difficult to prevent C. trachomatis infections because the population with endemic disease frequently has limited access to medical care.

– It is difficult to eradicate the disease within a population and to prevent reinfections.

– Chlamydia conjunctivitis and genital infections are prevented through the use of safe sexual practices and the prompt treatment of symptomatic patients and their sexual partners.


Prevention and control

C. pneumoniae– Treatment is with tetracycline or erythromycin.– Failures are common.– Retreament maybe required.


Prevention and control

C. psittaci– Tetracycline or erythromycin is used for treatm

ent.– Infections should be controlled in domestic and

imported pet birds using chlortetracycline.


Treatment C. trachomatis

– Ocular,genital & respiratory infections– In endemic areas,sulfonamides,erythromycins,and tetracyclines have

been used to suppress chlamydiae and bacteria that cause eye infections.

– Genital infections & inclusion conjunctivitis– It is essential that chlamydial infections be treated simultaneously in b

oth sex partners and in offspring to prevent reinfection.– tetracyclines are commonly used in non pregnant in fected females.– Erythromycin is given to pregnant women.

– LGV– The sulfonamides and tetracyclines have been used with food results

especially in the early stages.– Little is known about active immunity.


Treatment

C. pneumoniae– It is susceptible to the macrolides and tetracyclines and

to some fluoroquinolones.

– Treatment with doxycycline, azithromycin,or clarithromycin appears to benefit patients with the infection.

– The symptoms may continue after routine courses of therapy with erythromycin,doxycyclinbe, or tetracycline.

– These drugs should be given for 10- to 14-day courses.


Treatment C. psittacosis

– tetracyclines. Are the drugs of choice and should be continued for 10 days.

– It may not free the patient from the agent.– Intensive antiviotic treament may also delay the

normal course of antibody development.– Strains may become drug-resistant.– With antibiotic therapy the mortality rate is 2 ﹪

or less.

Chlamydiae

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