Rickettsia, Chlamydia and Mycoplasmas

Comparative study Rickettsiae, Chlamydiae, Mycoplasmas Features Rickettsiae Clamydiae Mycoplasmas DNA + RNA in cell + Size of cells 5OOnm 3OOnm 1OOnm Intracellular parasite - Growth in living cell Inclusion body Gorwth on media Antibiotic sensivity Transmission by vector

Rickettsia

General Characteristics Small obligate intracellular coccobacilli Gram negative (poorly), better stained with Giemsa (Blue) Have cell wall, bigger than virus but smaller than bacteria Have DNA and RNA Have an ATP transport system that allows them to use host ATP Arthropod reservoirs and vectors ( e.g., ticks, mites, lice or fleas). Sensitive to antibiotics

Structure: Similar with Gram negative bacteria Cell wall: outer membrane peptidoglycan lipopolysaccharide (LPS) Microcapsule and polysaccharide Two antigenically distinct groups: LPS: heat-stable, cross-reactive with somatic antigens of non-motile Proteus species (Weil-Felix test) Outer membrane protein: heat-unstable, species-specific

Endothelial cells, micro blood vessels Pathogenic Mechanism Materials： Endotoxin and Phospholipase A Mechanism： Bites or faeces of arthropod Local lymph or micro blood vessels (1st bacteremia) Endothelial cells, micro blood vessels in whole body (2nd bacteremia) Fever, rash, headache, etc Targets: Endothelial cells, micro blood vessels

Replication

Five genera in this class cause human diseases: Rickettsia Bartonella Coxiella (does NOT cause skin rash) Ehrlichia Orientia

Diseases Caused by the Rickettsia Organism Vector Reservoir Rocky Mountain spotted fever R. Rickettsii Tick Tick, wild rodents Scrub typhus R. Tsutsugamushi Laval Mite (chiggers) Mites, wild rodents Epidemic typhus R. Prowazekii Louse Humans, squirrel fleas, flying squirrels Murine typhus R. Thphi Flea Wild rodents Q fever Coxiella Burnetii None Cattle, sheep, goats, cats

Rickettsia rickettsii in endothelial cells of a blood vessel from a patient

Orientia tsutsugamushi growing in mouse abdominal macrophages (Giemsa)

R. Prowazekii Louse   Human Human Epidemic typhus

(much milder than epidemic typhus) R. Typhi Rodent   Flea Rat Tick Flea Human Murine typhus (much milder than epidemic typhus)

Eggs Adult stage Nymphal stage R. Tsutsugamushi Eggs Adult stage Nymphal stage Chigger Rats Nymphal stage Nymphal stage Human Nymphal stage Adult stage Eggs Scrub typhus

Coxiella Burnetii Q fever（query fever ） Self-limiting flu-like syndrome with high fever (40℃) Primary reservoirs are wild (cattle, sheep, goat etc.) Non-cross reactive antigen with non-motile Proteus (Weil-Felix reaction negative) Live in macrophages of vertebrate host

Bartonella Henselae Cat scratch disease (CSD) Weil-Felix reaction negative Infection by cats or dogs “Parinaud” Eye-Lymph node syndrome The eye looks red, irritated, and painful, similar to conjunctivitis.

Immunity Cellular immunity is important, and humoral immunity is helpful. Persons become immune to further infection following recovery from the disease.

Diagnosis and Prevention Microscopy Serological Test (Weil-Felix reaction, ELISA, IF, PCR) Breaking the infection chain ( controlling and killing the intermediate hosts and reservoir hosts) Inactivated vaccine has protective effect Chloromycetin, tetracycline are helpful for therapy, sulphonamides are not administered (increasing the penetrating of the vessel).

Chlamydia

Characteristics Small obligate intracellular parasites Contain DNA, RNA and ribosome and make their own proteins and nucleic acids, unable to make their own ATP Have special growth cycle and replicate by binary fission Possess a rigid cell wall similar to gram-negative bacteria Sensitive to antibiotic

A. Elementary bodies (EB) Special Growth Cycle A. Elementary bodies (EB) small (0.3～0.4 µm) infectious form a rigid outer membrane resistant to harsh environmental conditions outside of eukaryotic host cells bind to receptors on host cells initiate infection.

B. Initial body or Reticulate bodies (RB) non-infectious intracellular form metabolically active replicating form Have fragile membrane, easy to broken

Chlamydia inclusion body

Comparison of chlamydial elementary bodies and reticulate bodies Characteristic Elementary body Reticulate body Size Morphology Infectivity to host RNA:DNA ratio Metabolic activity Trypsin digestion Projections and rosettes 0.2～0.3μM Electron-dense core, rigid Infectious 1:1 Relatively inactive Resistant Few 1 μM Fragile, pleomorphic Non-infectious 3:1 (increased ribosomes) Active, replicating stage Sensitive More

Chlamydia trachomatis Only infects human epithelial cells (Except Biovar mouse) Three biovars (biological variants): Biovar Trachoma (14 Serologic types) Biovar lymphogranuloma venereum, LGV (4 serologic types) Biovar mouse

Pathogenesis and Immunity Infects non-ciliated columnar epithelial cells Stimulate the infiltration of polymorphonuclear cells and lymphocytes which leads to lymphoid follicle formation and fibrotic changes Cells destruction / host inflammatory response Infection does not stimulate long lasting immunity Reinfection results in a inflammatory response and subsequent tissue damage

Ocular infections worldwide primarily in areas of poverty and overcrowding 500 million people are infected worldwide and 7 - 9 million people are blind as a consequence Infections occur most commonly in children The organism can be transmitted by droplets, hands, contaminated clothing, flies, and by passage through an infected birth canal

Genital tract infections C. trachomatis (Biovar trachoma) The most common sexually transmitted bacterial disease C. trachomatis (Biovar: LGV) Humans are the only natural host

Clinical Syndromes 1. Trachoma Chronic infection or repeated infection inflammation and follicle formation involving the entire conjunctiva Chlamydial kerato-conjunctivitis

Clinical Syndromes 2. Inclusion conjunctivitis 3. Infant pneumonia 4. Urogenital infections cervicitis, salpingitis urethritis 5. Reiter's syndrome 6. Lymphogranuloma (LVG)

Laboratory diagnosis 1. Cytology 2. Culture 3. Serology Examination of stained cell scrapings for the presence of inclusion bodies 2. Culture the most specific method for diagnosis cultures of susceptible cells iodine-staining inclusion bodies 3. Serology Detection of high titer IgM antibodies is indicative of a recent infection

Treatment and prevention Tetracycline Erythromycin Sulfonamides Vaccines are of little value and are not used. Treatment coupled with improved sanitation to prevent reinfection is the best way to control infection.

Mycoplasmas

Morphology and Physiology The smallest free-living organisms Pass through some filters used to remove bacteria Lack of a cell wall Multiple shapes including round, pear shaped and even filamentous

Require complex media Require sterols for growth and for membrane synthesis Grow slowly (3 weeks) by binary fission and produce "fried egg" or “T strain” (tiny strain) colonies on agar plates

Structure Three layer membranes Outer and inner: proteins and saccharide Middle: 1/3 cholesterol dsDNA, has ribosomes, no endoplasmic reticulum (ER)

Pathogenesis Adherence factors Adherence proteins are one of the major virulence factors Adhesin localizes at tips of the cells and binds to sialic acid residues on host epithelial cells

Specialized tip organelle

Pathogenesis Toxic Metabolic Products The intimate association provides an environment in which toxic metabolic products accumulate and damage host tissues Products of metabolism : hydrogen peroxide and superoxide -- oxidize host lipids Inhibit host cell catalase

Pathogenesis Immunopathogenesis M. pneumoniae is a superantigen Activate macrophages and stimulate cytokine production and lymphocyte activation Host factors contribute to pathogenesis

Organism Disease M. pneumoniae Upper respiratory tract disease, Tracheobronchitis, atypical pneumonia M. hominis Pyelonephritis, pelvic inflammatory disease, postpartum fever M. genitalium Nongonococcl urethritis (NGU) U. urealyticum Nongonococcl urethritis (NGU)

M. Pneumoniae Need 10-20% Serum to culture in pH 7.8-8.0 Pathogenesis: P1 protein, capsule and saccharide Spread  by close contact via aerosolized droplets Cause tracheobronchitis Cause “primary atypical pneumonia” long duration Antibodies play a role in controlling infection, particularly sIgA Delayed type hypersensitivity spread in confined populations

M. Pneumoniae Laboratory Diagnosis Organisms can be cultured from sputum before symptoms occur and throughout the course of the disease. Serology Complement fixation test :A fourfold rise in titer is indicative of a recent infection. Cold agglutinins are IgM antibodies that agglutinate human “O” erythrocytes at 4℃ but not at 37℃ not specific/a presumptive diagnosis ELISA

M. pneumoniae Treatment and Prevention The antibiotics of choice are tetracycline (adults only) and erythromycin. Long duration of the disease, hard to isolate patients to avoid close contact for a long period of time. No vaccines are currently available

U. Urealyticum Isolation pathogen cultured in pH 6.0 media Metabolism of urea in infectious site and damage cells Associated with urogenital infections, can cause NGU (Nongonococcl urethritis)

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