Microbiology: Chlamydiae, Mycoplasma, Listeria PDF

Facultative intracellular pathogen: the ability to have an intracellular phase in the host, which is required for pathogenicity, while capable of extracellular growth in vitro. In the host, L. monocytogenes can adhere to host cells, are internalized and then can travel throug...

Facultative intracellular pathogen: the ability to have an intracellular phase in the host, which is required for pathogenicity, while capable of extracellular growth in vitro. In the host, L. monocytogenes can adhere to host cells, are internalized and then can travel through host cells. Listeria monocytogenes moving inside a host cell https://www.youtube.com/watch?v=sF4BeU60yT8  Infection route and the disease L. monocytogenes is isolated from a variety of environmental sources and from the feces of mammals, birds, fish, and other animals. The primary source of infection with this organism is consumption of contaminated food; however, human to human transmission can occur primarily from mother to child in utero or at birth. Listeria infection is the leading cause of deaths attributed to foodborne illness in the United states.  Listeria monocytogenes caused diseases Cause fever, headache, and sometimes gastrointestinal symptoms such as nausea, vomiting and diarrhea. Some patients may develop severe complications such as meningoencephalitis or septicemia. L. monocytogenes can avoid antibody-mediated clearance because they are mainly intracellular.  16.9 Tenericutes: The Mycoplasmas Key genera: Mycoplasma, Spiroplasma – lack cell walls – some of the smallest organisms, pleomorphic cells – often called “mycoplasmas” because Mycoplasma is best-characterized – typically live in close association with animal and plant hosts – small genomes  Mycoplasma mycoides Metal-shadowed transmission electron micrograph. Note the coccoid and hyphae-like elements. The average diameter of cells in chains is about 0.5 m.  Mycoplasma and Ureaplasma Most clinically significant genera in the order Mycoplasmatales; the smallest free-living bacterium (able to pass through 0.45-µm pore filters); absence of cell wall and a cell membrane containing sterols that are unique among bacteria; grow slowly. The absence of the cell wall renders the mycoplasmas resistant to antibiotics that interfere with synthesis of the cell wall (e.g. penicillins, cephalosporins and vancomycin).  Mycoplasma pneumoniae Slow rate of growth (generation time, 6 hours), strict aerobe, small genome size (816,394 bp versus 4.6 million bp of E. coli), relatively AT rich (60%). Strict human pathogen and spread by close contact (inhalation of aerosolized droplet during coughing episodes). Key virulent factor, P1 adhesin protein, concentrated in the attachment tip that binds to base of cilia on epithelial cells, leading to eventual loss of ciliated epithelial cells. Colonies on SP4 agar Arrows indicate the attachment tip http://cmr.asm.org/content/17/4/697.full  IV. Chlamydiae, Planctomycetes, and Verrucomicrobia 16.15 Chlamydiae 16.16 Planctomycetes 16.17 Verrucomicrobia Chlamydia trachomatis  16.15 Chlamydiae Key genera: Chlamydia, Chlamydophila, Parachlamydia (Figure 16.43) Obligate intracellular parasites of eukaryotes Typically very small cocci with distinct developmental cycle Small genomes (0.55–1 Mbp) Well adapted to invading and colonizing eukaryotic cells Best-studied human pathogens include: – Chlamydophila psittaci (psittacosis in birds and humans, zoonotic disease) – Chlamydia trachomatis (blindness in humans and sexually transmitted disease), Chlamydophila pneumoniae  Chlamydia disease Genital chlamydia disease (a sexually transmitted disease) is caused by several strains (serotypes) of Chlamydia trachomatis, a group of Gram-negative, obligate intracellular bacteria of human. Obligate intracellular pathogens cannot reproduce outside their host cell, meaning that the pathogen's reproduction is entirely reliant on intracellular (inside the cells) resources. Lymphogranuloma venereum Chlamydia arthritis: the post- Neonatal conjunctivitis infectious chronic arthritis wikimedia.org https://pedclerk.bsd.uchicago.edu/page/ chlamydia-newborn  How to culture an obligate intracellular pathogen? Method 1: Inoculation and culture in yolk sac of embryonated hen eggs. Method 2: Inoculation on cultured mammalian cells. “McCoy” mouse www.slideshare.net fibroblast cells can be used to propagate Chlamydia spp. Chlamydial inclusions in infected yolk sac Ref. Chlamydia species in free-living Cattle Egret (Bubulcus ibis) and Hoopoe (Upupa Chlamydia trachomatis epops) in Egypt inclusion bodies (brown) in a McCoy cell culture Wikipedia  Life cycle of Chlamydia Chlamydia are transmitted in an extracellular nonreplicating form known as the elementary body (EB). a) The elementary body adheres to and is phagocytosed into a host epithelial cell. b) Once inside the epithelial cell, the elementary body transforms into the intracellular replicative form of the organism, the reticulate body. c) Reticulate bodies divide by binary fission within membrane-bound vacuoles called inclusions. The reticulate bodies then reorganize into elementary bodies. d) After 35 to 40 hours, the inclusion ruptures, and elementary bodies are Figure 16.44 released to infect adjacent epithelial cells or to be transmitted to other hosts. Cycle goes on.  Elementary body Very small - only about 0.3 m in diameter. It contains only small amounts of peptidoglycan. Instead it derives its strength, among other things, from cross links [-S-S- disulfide bridges] formed between the sulphur atoms of its sulphur amino acid (cysteine and methionine) rich proteins in the outer envelope. The EB is the only infectious stage of the chlamydial developmental cycle. It functions as a tough "spore-like" body whose purpose is to permit chlamydial (E) elementary bodies survival in the non-supportive (R) reticulate bodies (DR) dividing reticulate body environment outside the host cell. It is metabolically inert until it attaches to, and is endocytosed by, a susceptible host cell.