Miscellaneous Bacterial Agents of Disease

Transcription

1 Chapter 21 Miscellaneous Bacterial Agents of Disease Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 21.1 The Spirochetes Gram-negative human pathogens Free living saprobes, or commensals of animals, not primary pathogens Treponema Leptospira Borrelia Figure 21.1 Typical spirochete Endoflagellum Periplasmic space Endoflagellum (a) Outer membrane Cell body (b) a. General spirochete morphology Science VU/Charles W. Stratton/Visuals Unlimited b. Borrelia 2

3 Treponemes: Members of the Genus Treponema Thin, regular, coiled cells Live in the oral cavity, intestinal tract, and perigenital regions of humans and animals Pathogens are strict parasites with complex growth requirements Require live cells for cultivation 3

4 Treponema pallidum: The spirochete of syphilis Causes Syphilis Human is the natural host Extremely fastidious and sensitive; cannot survive long outside of the host Sexually transmitted and transplacental Figure 21.6 T. pallidum viewed with dark field illumination CDC 4

5 Primary Syphilis Spirochete binds to the epithelium, multiplies, and forms a chancre Fluid from the chancre is highly contagious Chancre spontaneously heals as the spirochete moves into the blood Dr. Gavin Hart, Dr. N. J. Fiumara/CDC Figure 21.2 Primary syphilis lesion: chancre 5

6 Secondary Syphilis Spirochete is multiplying in the bloodstream Rash forms on the skin, palms and soles with fever, headache and sore throat The rash disappears spontaneously Figure 21.3 symptom of secondary syphilis 6

7 Tertiary Syphilis If left untreated, tertiary syphilis forms Damage to multiple tissues and organs Gummas may develop (a) CDC/J. Pledger Figure 21.4 Pathology of late, or tertiary syphilis a. A gumma on the nose b. Irregular shaped pupil Pupil with an (b) irregular shape Kathy Park Talaro 7

8 Congenital Syphilis T. pallidum can pass through the placenta to the fetus Symptoms include nasal discharge, skin eruptions, bone deformation and nervous system abnormalities Figure

9 Syphilis Diagnosis and Testing Stages of syphilis can mimic other diseases, such as various bacterial and fungal infections Consider symptoms, history, microscopic, and serological testing RPR, VDRL, FTA-ABS: tests for antibodies against syphilis Treatment: penicillin G 9

10 Borrelia: Arthropod-Borne Spirochetes Large spirochetes with 3-10 coils irregularly spaced Borrelioses are transmitted by an arthropod vector, usually ticks or lice B. hermsii relapsing fever B. burgdorferi Lyme disease 10

11 B. burgdorferi Lyme Disease Complex lifecycle involving mice and deer and transmission by ticks Figure 21.9 the cycle of Lyme disease 2 2. In the second year the larvae molt into the nymph, an aggressive feeding stage. Infected nymph 3 Infected larval tick First year Second year Human (accidental host) Mouse infected with Borrelia burgdorferi Borrelia spirochetes Deer 3. The nymph takes blood from a number of hosts, including deer and humans. 1 Larval tick 1. Newly hatched larvae become infected when they feed on small animals such as mice, which harbor the spirochete. The larvae continue development through this year. (a) 4 Adult ticks 4. On deer, the nymph matures into adult male and female ticks, which mate. The female lays eggs in plant litter, where they hatch and once again begin the cycle. 11

12 B. burgdorferi Lyme Disease Acquired by tick bites Nonfatal, slowly progressive syndrome that mimics neuromuscular and rheumatoid conditions 50-70% get bull s eye rash Fever, headache, stiff neck, and dizziness If untreated can progress to cardiac and neurological symptoms, polyarthritis Treated with tetracycline or amoxicillin (b) CDC (c) CDC 12

13 21.2 Curviform Gram-Negative Bacteria and Enteric Diseases Gram-Negative Generally cause enteric diseases Vibrio comma-shaped rods, single polar flagellum Campylobacter short spirals or curved rods; one flagellum Helicobacter spirochete with tight spirals and several polar flagella

14 Intestinal lumen Intestinal lumen The Biology of Vibrio Cholera Comma-shaped bacteria is ingested in food or water El Tor biotype: survives longer, more infectious Infects mucous barrier of small intestine, noninvasive Releases cholera toxin that causes electrolyte and water loss through secretory diarrhea, rice water stool ; resulting dehydration leads to muscle, circulatory, and neurological symptoms Rehydrate and treat with Tetracycline Cl 2 HCO 2 3 Na 1 K 1 H 2 O Cl 2 HCO 2 3 Na 1 K 1 H 2 O H 2 O H 2 O (a) Intestinal cell a. Normal action of intestinal absorption (b) b. General actions of cholera toxin on electrolytes and water 14

15 Figure magnified view of Cholera Toxin Activity 1 The Vibrio cholerae cell comes to rest in the protective mucous coating near the cell surface and secretes its toxin, which is a complex protein. 2 The toxin has an affinity for specialized receptors on the glycocalyx and binds there. Vibrio cholerae Cell membrane 3 The active portion of the toxin is released, is transported through the membrane, and enters the cytoplasm. Glycocalyx 4 It becomes a signal in a system that converts inactive adenyl cyclase into an active state. 1 Adenyl cyclase, inactive 5 This enzyme converts ATP into a molecule called cyclic AMP (camp). The camp is needed by the cell to control a major membrane pump for negative ions. ions. Cholera toxin molecules Adenyl cyclase, active The result is that the membrane begins to actively pump Cl 2, and HCO 3 into the intestinal lumen. One additional effect of the toxin is that it overrides the usual controls for the adenyl cyclase/camp system so that the cell continues to pump out these ions for an extended time. Positive ions (Na + and K + ) follow the anions and are also lost into the intestinal fluid, along with large amounts of water, causing secretory diarrhea and dehydration. HCO 3 Cl 2 Na +, K + H 2 O Membrane pump HCO 3 6 Cl Na +, K + H 2 O 7 Cyclic AMP 5 15 (c)

16 Other Vibrio Pathogens Salt-tolerant inhabitants of coastal waters, associate with marine invertebrates Vibrio parahaemolyticus gastroenteritis from raw seafood; symptoms similar to cholera Vibrio vulnificus gastroenteritis from raw oysters; serious complications in persons with diabetes or liver disease Treatment fluid and electrolyte replacement; occasionally antimicrobials 16

17 Diseases of the Campylobacter Vibrios Slender, curved, or spiral bacilli, often S-shaped or gull-winged pairs S Comma Polar flagella Spiral Common residents of the intestinal tract, genitourinary tract, the oral cavity of birds and mammals Most important: Campylobacter jejuni Campylobacter fetus From R.R. Colwell and D. M. Rollins, ÒViable but Nonculturable Stage of Campylobacter jejuni and its Role in Survival in the Natural Aquatic Environment, Ó /it/applied and Environmental Microbiology, /xit/ 52(3): , Reprinted by permission of American Society for Microbiology; Figure Campylobacter jejuni 17

18 Campylobacter jejuni Important cause of bacterial gastroenteritis Transmitted by beverages and food Reach mucosa at the last segment of small intestine near colon; adhere, burrow through mucus and multiply Heat-labile enterotoxin CJT stimulates a secretory diarrhea like that of cholera Symptoms of headache, fever, abdominal pain, bloody or watery diarrhea Treatment with rehydration and electrolyte balance therapy 18

19 Campylobacter fetus An opportunistic pathogen that infects debilitated persons or women late in pregnancy Meningitis, pneumonia, arthritis, septicemia in the newborn 19

20 Helicobacter pylori: Gastric Pathogen A gastric pathogen Curved cells discovered in 1979 in stomach biopsied specimens Causes 90% of stomach and duodenal ulcers; apparent cofactor in stomach cancer Stomach mucosa Helicobacter cells Figure The causative agent of stomach ulcers People with type O blood have a 1.5-2X higher rate of ulcers Produces urease which converts urea into ammonium and bicarbonate 20

21 21.3 Medically Important Bacteria of Unique Morphology and Biology Unrelated to each other but similar in morphology, pathogenicity and all are atypical Atypical bacterial pathogens: Family Rickettsiaceae - intracellular pathogens that rely on an arthropod vector Family Chlamydiaceae - intracellular pathogens that alternate between elementary and reticulate bodies Mycoplasmas - lack a cell wall and are highly pleomorphic 21

22 Order Rickettsia Small obligate intracellular parasites Gram-negative cell wall Nonmotile pleomorphic rods or coccobacilli Ticks, fleas, and lice are involved in their life cycle Bacteria enter endothelial cells and cause necrosis of the vascular lining vasculitis, vascular leakage, and thrombosis Cell morphology Budding from a cell 22

23 Specific Rickettsioses 1. Epidemic typhus R. prowazekii carried by lice; starts with a high fever, chills, headache, rash; Brill-Zinsser is a chronic, recurrent form 2. Endemic typhus R. typhi, harbored by mice and rats; occurs sporadically in areas of high flea infestation; milder symptoms 3. Rocky Mountain spotted fever R. rickettsii zoonosis carried by dog and wood ticks; most cases in Southeast and on eastern seaboard; distinct spotted rash; may damage heart and CNS 4. Ehrlichia genus contains 2 species of rickettsias; tickborne bacteria cause human monocytic and granulocytic ehrlichiosis 23

24 Rocky Mountain Spotted Fever Rickettsia rickettsii is transmitted to humans through a tick bite and is the most common rickettsial infection in North America tick with eggs CNS damage, coma DC (b) Egg Rash Figure trends of Rocky Mountain Spotted Fever Incidence rates (per 1,000,000 persons) Tick/Dog Infection (a) Figure transmission cycle Human Infection (c) (d) 24 Vascular damage

25 Rocky Mountain Spotted Fever First symptoms are fever, chills, headache and a spotted rash appears in days Figure a rash of RMSF CDC Central nervous system can become involved and fatality rates are 20% if untreated

26 Other Obligate Parasitic Bacteria: The Chlamydiaceae Family Small, gram-negative, obligate intracellular parasites Alternates between: Elementary body: small metabolically inactive, extracellular, infectious form released by the infected host (1) Reticulate body: noninfectious, actively dividing form, grows within host cell vacuoles (2 5) 6 New host cell EB 3 Binary fission RB RB 4 EB R David M. Phillips / Photo Researchers, Inc 2 5 EB E EB Host cell Nucleus 1 2 mm Phagosomes with EB Phagosome Figure life cycle 26 Enlarged view of cycle in phagosome

27 Diseases of Chlamydia trachomatis Human reservoir and 2 strains can infect humans: Trachoma attacks the mucous membranes of the eyes, genitourinary tract, and lungs Ocular trachoma: severe infection, deforms eyelid and cornea, may cause blindness Inclusion conjunctivitis: occurs as baby passes through birth canal; prevented by prophylaxis STD: second most prevalent STD; urethritis, cervicitis, salpingitis (PID), infertility, scarring Figure primary ocular chlamydial infection 27

28 Diseases of Chlamydia trachomatis Human reservoir and 2 strains can infect humans: Trachoma attacks the mucous membranes of the eyes, genitourinary tract, and lungs Lymphogranuloma venereum disfiguring disease of the external genitalia and pelvic lymphatics Figure Clinical appearance of advanced lymphogranuloma venereum in a man 28 CDC