Intracellular Bacteria: Lecture Notes PDF

Intracellular Gram negative bacilli  Survival in phagocytes Listeria, Rickettsia S Typhi, Coxiella, M. leprae M. tuberculosis, chlamydia, legionella sp  Rickettsiaceae  Named after Howar...

Intracellular Gram negative bacilli  Survival in phagocytes Listeria, Rickettsia S Typhi, Coxiella, M. leprae M. tuberculosis, chlamydia, legionella sp  Rickettsiaceae  Named after Howard Taylor Ricketts (1871- 1910) who studied Rocky Mountain spotted fever.  He was dedicated to his research and injected himself several times with the pathogens.  In 1910 he injected himself once again, isolated the bacteria but died of the disease  Rickettsia Obligate intracellular Gram-negative bacilli Small, pleomorphic coccobacilli (0.3-0.4μ) Stain readily with Giemsa, Giminez Arthropod vectors: fleas, lice, ticks, mites No human-to-human transmission Spread: From portal of entry to regional lymph nodes to blood stream. Final target: Endothelial cells- degenerate, thrombosis-maculopapular rash & hmg Five medically important genera Rickettsia obligate intracytoplasmic parasites Orientia Ehrlichia Coxiella Bartonella Grow in cell lines or embryo cultures All, except Coxiella, are transmitted by arthropod vectors. Which cells do these bacteria parasitise? Rickettsia: Endothelial cells Coxiella: Macrophages Bartonella: Endothelial cells and RBCs Chlamydia: Squamous epithelial cells and macrophages Brucella: Macrophages/ RES Ehrlichia: WBCs, Monocytes, Granulocytes Mycobacterium Tuberculosis: Macrophages M. leprae: Macrophages Salmonella Typhi: Reticulo-endothelial cells (RES)  Location of bacteria Intracellular location: Bacteria are phagocytosed by endothelial cells and replicate in the following sites: Typhus group: Cytoplasm Spotted fever group: Cytoplasm and Nucleus Coxiella: Phago-lysosomes Ehrlichia: Phagosomes Characteristic feature: Endothelial damage and vasculitis Diseases caused by Rickettsia are all characterized by fever, headache, nausea, vomiting, abdominal pain, myalgias, and usually a rash. Disease, Reservoir, Vector: Typhus Group: Rickettsia prowazekii – Epidemic typhus; Reservoir-small mammals, vector- louse Spotted Fever Group: Rickettsia rickettsii – Rocky Mountain spotted fever; Reservoir: rodent, tick. vector- tick Rickettsial pox: Rickettsia akari, Reservoir: Mice, vector- mite Immunopathogenesis Rickettsia invade the endothelial cells, multiply and burst the cell, leading to cell death. Host defence: Cytotoxic T-cell lymphocytes, CD8 cells Interferon-gamma and tumor necrosis factor alpha activate the endothelial cells to kill the intracellular rickettsiae. Complications: Vascular damage leads to increased vascular permeability – can lead to hmgic rash, hypovolaemia, hypotensive shock, kidney damage, life threatening meningo-encephalitis and non-cardiogenic pulmonary oedema and respiratory distress, Rickettsia prowazekii (Epidemic typhus) Severe headache, chills, fever. Maculopapular rash: Subcutaneous hemorrhages - due to invasion of the blood vessels. Distribution of rash: Starts at upper trunk and spreads to involve the whole body except the face, palms of the hands, and the soles of the feet. Complications: Mental confusion, myocarditis R. prowazekii is known to cause latent infection (Brill Zinsser Disease). Rocky mountain spotted fever: R. rickettsii Potentially fatal disease Severe headache, chills, fever, myalgia, and nausea, rash Distribution of maculopapular rash: Starts on the extremities, including palms and soles, and spreads to the chest and abdomen. Progression of rash: Petechiae with hemorrhages in the skin and mucous membranes due to vascular damage as the organism invades the blood vessels. Complications: Pneumonitis, CNS involvement, myocarditis, renal failure, DIC Death may occur during the end of the second week due to kidney or heart failure.  Rickettsial pox – R. akari. Vector: mouse mite Reservoir: mouse Black painless eschar A papule followed by eschar develops at the entry site. with red halo Fever, malaise, and headache develop followed by a vesicular rash similar to chicken pox Regional lymphadenopathy The disease is mild and usually not fatal. Vesicular rash  Direct Microscopy Serology Laboratory Diagnosis Cell culture DNA amplification Serology: Indirect Immunofluorescence: Detects antibodies Discriminates between IgM & IgG antibodies which help in early diagnosis Direct Immunofluorescence: Detects antigen in biopsy tissues Most useful. Can diagnose disease in 3-4 days of illness. 100% specific and 70% sensitive Molecular tools: PCR Culture: Tissue culture systems and hen’s eggs Animal model: Guinea pigs & mice Emerging Disease: Human Ehrlichiosis In April 1986, a medical intern scanning the peripheral blood smear of a severely ill man with an unexplained illness observed peculiar intracytoplasmic inclusions in several of the patient's monocytes. The patient described multiple tick bites sustained approximately 2 weeks earlier during a visit to a rural area in northern Arkansas, and a presumptive diagnosis of Rocky Mountain spotted fever had been made. Clinicians and scientists subsequently identified these inclusions as clusters of bacteria belonging to the genus Ehrlichia, previously known in the United States solely as veterinary pathogens Ehrlichia Small, Gram negative obligate intracellular parasites Anaplasma phagocytophilum: human granulocytic Ehrlichiosis Vector: Ixodes ticks. Reservoir: Deer, cattle and sheep. E. chaffeensis: human monocytic ehrlichiosis Vector: Amblyomma ticks. Reservoir -deer Multiply to form mulberry shaped aggregates- morulae Characterised by: Lymphadenopathy, Hepatosplenomegaly Leucopenia and thrombocytopenia, DIC Pathogenesis Cytokine mediated immunopathogenesis A. phagocytophilum evades host immune system by antigenic variation. E. chaffeensis: Modulates host defence. Block phagosome- lysosome fusion inside macrophages. To accommodate slow generation time, they prolong the host cells life span by inhibiting apoptosis  Lab Dx ? Q fever – Coxiella burnetii. Isolation in cell lines Zoonosis (Cattle, sheep and goat) Animals Route of infection: inhalation of infectious material Antibody detection Molecular tools ingestion of contaminated milk Intracellular parasite in macrophages. Resistant to lysosomal enzymes Sudden onset of fever, chills, and headache, but no rash. Disease: Atypical pneumonia, CNS involvement, Endocarditis Bartonella quintana First isolated by Vinson in 1960 Used to self inoculate the bacteria To prove Koch’s postulates Recruited human volunteers Luckily disease is usually not fatal. Diseases: Trench fever Bacillary angiomatosis: neovascularization, often occludes blood flow. [Also caused by Bartonella henselae: involve spleen and liver- peliosis] Endocarditis Trench fever – Bartonella Quintana. Transmitted by body lice. Was a major problem during WW I and WW II. Bartonella: Fastidious, slow growing (12-45 days), facultative intracellular Gram-negative bacilli. Invades RBCs and other cells. Bacteremia Headache, exhaustion, leg pains, and a high, relapsing fever. A roseolar rash occurs and the patient usually recovers. Complication: endocarditis Can be grown on artificial media Bartonella on BA Chlamydia: Energy parasites Classification : order Chlamydiales : genus – Chlamydia Obligate intracellular parasites. ATP parasites Cell walls are similar to Gram negative bacteria but lack muramic acid Have a complex developmental cycle Infective form: elementary body (EB). It induces phagocytosis. Replicative form: Reticulate body multiplies inside the phagocytic vesicle  Over 6-8 hours, the EB reorganizes into the noninfectious, metabolically active reticulate body (RB). The RB divides by binary division to form inclusion bodies that reorganize and condense into EBs. The cell lyses and releases the EB which begin the cycle again.  Serotypes A-K and L1,2,3; Sexually transmitted infections Non gonococcal urethritis: D-K Lymphogranuloma venereum: L1,2,3 Eye Infections: Trachoma: A-C Serotypes and Neonatal Infections: Disease Neonatal inclusion conjunctivitis: D-K Neonatal pneumonia Adults: Atypical pneumonia Chlamydia pneumoniae, C psitacci Direct microscopy Iodine stain Giemsa stain Direct Immuno-fluorescent Fluorescence antibody Culture Yolk sac of 6-8 day old chick embryo Tissue culture- Irradiated McCoy, HeLa cell lines  Legionella pneumophila 1976 outbreak of atypical pneumonia at Philadelphia convention of American Legion “Legionnaires’ disease” Thrives in slow moving / stagnant water 20-500C Intracellular pathogen (macrophages, alveolar epithelial cells) Inhibits phagosome lysosome fusion Disease caused Pontiac fever Atypical pneumonia Fatality rate: 15% in healthy Multi-organ involvement 75% in immunocompromised. GIT, CNS, liver, kidneys  Epidemiology Opportunistic Disease: underlying illness/weak immune system. Middle-aged, elderly, COPD, smokers Reservoir of infection: cooling towers of air conditioning systems, hot water lines as well as in soil and water Nosocomial infections are major concerns.  Virulence factors Inhibit phagosome- lysosome fusion allowing intracellular growth Endotoxin: Inhibit generation of peroxide in phagocytic cells Morphology/cultural characteristics Small, motile Gram-negative pleomorphic rods that stain poorly Direct fluorescent antibody Urinary antigen: Rapid, easy, cheap Media: buffered charcoal yeast extract (BCYE) agar in CO2 Selective agent: antibiotics Molecular tools  Brucella spp Brucella abortus Br. melitensis Small Gram negative coccobacilli Br. suis Non-motile, aerobic, capnophilic, Diseases: Pathogenesis: Zoonosis Non specific Facultative intracellular pathogen: RES symptoms: Fatigue, wt loss,weakness, Survives within macrophages Fever, chills & rigors Inhibits phagosome lysosome fusion Abdominal pain, diarrhea, vomiting Culture and Biochemicals Undulant fever Growth on complex media: Brucella BA Typhoid like fever Musculoskeletal Oxidase and catalase positive, H2S & urease production symptoms Notifiable category 3 zoonosis CNS: Depression CVS:Endocarditis  Blood culture Serology Standard agglutination test: IgM IgG: ELISA Molecular tools Animals: Antibody detection: Rose Bengal card test  Treatment Rickettsia: Chlamydia: Legionella: Brucella: Doxycycline, Doxycycline, Erythromycin, Streptomycin, chloramphenicol Erythromycin tetracycline Doxycycline