Chlamydiae and Zoonotic Intracellular Bacteria

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Chlamydiae and Zoonotic Intracellular Bacteria

I Chlamydia species

• Three chlamydial species are pathogenic for humans: C. trachomatis, C. psittaci, and C. pneumoniae (Table 17-1).

TABLE 17-1

Comparison of Chlamydia Species

A Shared chlamydial properties

Chlamydia cannot make adenosine triphosphate (ATP) and lack peptidoglycan.

1. Chlamydiae are very small, obligate intracellular bacteria.

2. They possess a cytoplasmic membrane and outer membrane but lack peptidoglycan layer (unlike gram-negative bacteria) and thus are insensitive to β-lactam antibiotics.

• Chlamydiae are energy parasites.

3. Morphologic forms

• Elementary body (EB)

a. Smaller, extracellular infectious form that is metabolically inert and resistant to harsh conditions

• Reticulate body (RB)

a. Larger intracellular form that is metabolically active and replicates within target cells

b. RBs cannot produce ATP and thus depend on target cells for energy production.

Chlamydia species: small, obligate intracellular bacteria existing in two forms: Elementary body Enters cells; Reticulate body Replicates within cells.

4. Growth cycle (Fig. 17-1)

17-1 Growth cycle of Chlamydia trachomatis. For each elementary body (EB) that enters a susceptible cell, replication and reorganization yield an inclusion body containing 100 to 500 EBs, which are released from the cell. RB, replication body.

• Ingested EB is converted to RB within a cytoplasmic phagosome.

• RB replication by binary fission produces a large inclusion body containing numerous RBs, most of which are reorganized into EBs.

• Extrusion of the inclusion body releases infectious EBs into extracellular environment and ruptures the cell.

B C. trachomatis

Trigger words:

C. trachomatis: elementary bodies, iodine stain, intracellular inclusion bodies, LGV, PID, reticulate bodies, STD, trachoma, UTI

• Three major groups of serotypes are associated with different diseases.

1. Identification

• Cytologic examination for iodine-staining inclusion bodies

• Growth and isolation in cell culture

• Polymerase chain reaction (PCR)

• Detection of chlamydial antigens or nucleic acid sequences in clinical specimens

• Serologic tests for antichlamydial antibodies

2. Pathogenesis

Virulence factors: adhesion, intracellular growth

• Types A through K infect nonciliated epithelial cells of mucous membranes, which have EB-binding receptors on their surface.

a. These target cells are found in the urethra, vagina, fallopian tubes, anorectal tract, respiratory tract, and conjunctiva.

• Types L1, L2, and L3 infect macrophages.

• Destruction of target cells due to bacterial replication and severe host inflammatory reactions cause disease manifestations.

Inflammatory reactions are major cause of chlamydial pathogenesis.

3. Chlamydial infections caused by types D through K (Box 17-1)

BOX 17-1 Infections Caused by Chlamydia Trachomatis, Types D through K

Urogenital Infections

In women: cervicitis, urethritis, salpingitis, pelvic inflammatory disease

In men: urethritis, epididymitis, proctitis

Systemic Infections

In women: arthritis, dermatitis

In men: Reiter syndrome (nongonococcal urethritis; triad of arthritis, urethritis, uveitis-conjunctivitis)

Ocular and Neonatal Infections

Adult inclusion conjunctivitis: mucopurulent discharge, keratitis, inflammation, potential scarring; spread by autoinoculation or ocular-genital contact

Neonatal conjunctivitis: swelling of eyelids, hyperemia, and purulent discharge beginning 2 to 30 days after birth to infected mother. Conjunctival scarring and corneal vascularization develop in untreated infections. Topical erythromycin, which is administered routinely to neonates, prevents eye infection.

Infant pneumonia: rhinitis beginning 2 to 3 weeks after birth followed by distinctive staccato cough; no fever. Without treatment, infection may develop into diffuse interstitial pneumonia.

C. trachomatis: types D through K = most common cause of sexually transmitted diseases (STDs) in the United States.

• Transmitted by sexual contact or during passage through infected birth canal

• Urogenital infections

Reiter syndrome triad: arthritis, urethritis, uveitis-conjunctivitis

a. Asymptomatic infections are more common in women than in men.

b. Symptomatic infections produce mucopurulent discharge, with dysuria or pyuria.

• Systemic infections

• Ocular and neonatal infections

C. trachomatis: most common cause of neonatal blindness worldwide

4. Lymphogranuloma venereum

Lymphogranuloma venereum initially causes small painless lesion at infection site with possible fever, headache, and myalgia but can progress to swollen draining lymph nodes.

• Caused by types L1 through L3 and transmitted by sexual contact

• Initial stage

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