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Microbiology, Fifth Edition
Microbiology, 5/e
Lansing M Prescott, Augustana College
Donald A Klein, Colorado State University
John P Harley, Eastern Kentucky University
Human Diseases Caused by Bacteria

Study Outline

  1. Airborne Diseases
    1. Diphtheria-Corynebacterium diphtheriae
      1. Usually affects poor people living in crowded conditions
      2. Caused by an exotoxin (diphtheria toxin) produced by lysogenized bacteria
      3. Symptoms include nasal discharge, fever, cough, and the formation of a pseudomembrane in the throat
      4. Diagnosis is made by observation of pseudomembrane and bacterial culture; treatment is with antitoxin to remove exotoxins and with penicillin or erythromycin to eliminate the bacteria; prevention is by active immunization with the diphtheria-pertussis-tetanus vaccine (DPT)
      5. C. diphtheriae also causes skin infections called cutaneous diphtheria
    2. Legionnaires' disease and Pontiac fever-Legionella pneumophila
      1. Legionnaires' disease (legionellosis)
        1. Bacteria are normally found in soil and aquatic ecosystems; also found in air-conditioning systems and shower stalls
        2. Infection causes cytotoxic damage to lung alveoli; symptoms include fever, cough, headache, neuralgia, and bronchopneumonia
        3. Common-source spread
        4. Diagnosis is based on isolation of the bacterium and serological tests; treatment is supportive but also includes administration of erythromycin or rifampin
        5. Prevention is accomplished by elimination of environmental sources
      2. Pontiac fever-resembles an allergic disease more than an infection and is characterized by abrupt onset of fever, headache, dizziness and muscle pain; pneumonia does not occur; usually spontaneously resolves in two to five days
    3. Meningitis-inflammation of brain or spinal cord meninges caused by a variety of organisms and conditions
      1. Bacterial (septic) meningitis
        1. Diagnosed by the presence of bacteria in the cerebrospinal fluid; transmitted by inhalation of respiratory secretions from carriers or active cases
        2. Symptoms include initial respiratory illness or sore throat interrupted by one of the following: vomiting, headache, lethargy, confusion, and stiffness in the neck and back
        3. Cause is determined by Gram stain, isolation of bacterium from cerebrospinal fluid, or rapid tests; treated with various antibiotics, depending on the specific bacterium involved; disease caused by Haemophilus influenzae serotype b has been dramatically reduced by active immunization with the HIB vaccine
      2. Aseptic (nonbacterial) meningitis syndrome is more difficult to treat and prognosis is poor
    4. Mycobacterium avium-M. intracellulaire pneumonia
      1. Organisms are normal inhabitants in soil, water and home dust; these bacteria are closely related and referred to as M. avium complex (MAC)
      2. Both the respiratory and the gastrointestinal tracts have been proposed as portals of entry; the gastrointestinal tract is thought to be the most common site of colonization and dissemination in AIDS patients, in whom the disease can have debilitating effects; pulmonary infection is similar to tuberculosis and is most often seen in elderly patients with preexisting pulmonary disease
      3. MAC can be isolated from sputum and other specimens and identified by acid-fast stain and other methods; treatment is usually multiple drug therapy
    5. Pertussis-whooping cough caused by Bordetella pertussis
      1. Highly contagious disease that primarily affects children
      2. Transmission is by droplet inhalation; toxins are responsible for most of the symptoms
      3. Disease progresses in stages
        1. Catarrhal stage-inflamed mucous membranes; resembles a cold
        2. Paroxysmal stage-prolonged coughing sieges with inspiratory whoop
        3. Convalescent stage-may take months (some fatalities)
      4. Diagnosis is by culture of the bacterium, fluorescent antibody staining, and serological tests; treatment with erythromycin, tetracycline, or chloramphenicol; prevented by DPT vaccine
    6. Streptococcal diseases
      1. Streptococci are a heterogeneous group of gram-positive bacteria, and one of the most important is Streptococcus pyogenes; have a variety of virulence factors, including extracellular enzymes that break down host molecules, streptokinases (destruction of blood clots), cytolysins (kill leukocytes), and capsules and M protein (retard phagocytosis)
      2. S. pyogenes is widely distributed in humans and many are asymptomatic carriers; transmission can occur through respiratory droplets, direct contact, or indirect contact
      3. Diagnosis is based on clinical and lab findings; rapid tests are available; treatment is with penicillin or erythromycin; vaccines are not available, except for streptococcal pneumonia
      4. Best control measure is prevention of transmission by isolation and treatment of infected persons
      5. Cellulitis and erysipelas
        1. Cellulitis-diffuse, spreading infection of subcutaneous tissue characterized by redness and swelling
        2. Impetigo-superficial cutaneous infection commonly seen in children
        3. Erysipelas-acute infection of the dermis characterized by reddish patches
      6. Invasive Streptococcus A infections
        1. Dependent on specific strains and predisposing host factors; if bacterium penetrates a mucous membrane or takes up residence in a skin lesion, can cause necrotizing fasciitis (destruction of the sheath covering skeletal muscle) or myositis (inflammation and destruction of skeletal muscle and fat tissue)
        2. Rapid treatment with penicillin G reduces the risk of death
        3. Pyogenic exotoxins A and B are produced by 85% of the bacterial isolates; these evoke host defenses that destroy vascular tissues, and the surrounding tissues die from lack of oxygen; one of the toxins is a protease
        4. Can also trigger a toxic shock-like syndrome (TSLS) with a mortality rate over 30%
        5. Best preventative measures include covering food, washing hands, and cleansing and medicating wounds
      7. Poststreptococcal diseases-onset is one to four weeks after an acute streptococcal infection
        1. Glomerulonephritis (Bright's disease)-antibody-mediated inflammatory reaction (type III hypersensitivity); may spontaneously heal or may become chronic; for chronic illness a kidney transplant or lifelong renal dialysis may be necessary
        2. Rheumatic fever-autoimmune disease involving the heart valves, other parts of the heart, joints, subcutaneous tissues, and central nervous system; mechanism is unknown; occurs primarily in children ages 6 to 15 years old; therapy is directed at decreasing inflammation and fever, as well as controlling cardiac symptoms and damage
      8. Scarlet fever (scarlatina)-lysogenized S. pyogenes produces an erythrogenic toxin that causes skin-shedding as well as sore throat, chills, headache, and strawberry-colored tongue; treatment is with penicillin
      9. Streptococcal sore throat-inflammatory response with lysis of leukocytes and erythrocytes; diagnosis by rapid tests; treatment is with penicillin, primarily to minimize the possibility of subsequent rheumatic fever and glomerulonephritis; prevented by proper disposal and cleansing of contaminated objects
      10. Streptococcal pneumonia
        1. Endogenous (opportunistic) infection caused by S. pneumoniae, a member of normal microbiota; individuals usually have predisposing factors, such as viral infection of the respiratory tract, physical injury to the respiratory tract, alcoholism, or diabetes
        2. Bacterium's capsular polysaccharides and a toxin are important virulence factors; diagnosis is by chest X-ray, biochemical tests, and culture; treatment is with penicillin or erythromycin; a vaccine (Pneumovax) is available and preventative measures include vaccination and treatment of infectious persons
    7. Tuberculosis-Mycobacterium tuberculosis, M. bovis, and M. africanum
      1. Human-to-human transmission by droplet nuclei and food-borne transmission
      2. In lungs, bacterium forms nodules (tubercles) and the disease usually stops, but the bacterium remains alive; over time the tubercles can change into forms that lead to reactivation of the disease
      3. Infected individuals develop cell-mediated immunity that involves sensitized T cells; when exposed to tuberculosis antigens, these cells cause a delayed-type hypersensitivity; this reaction is the basis of skin tests that indicate prior exposure to M. tuberculosis
      4. Diagnosis is by isolation of organism, chest X-ray, skin test, or DNA probes; chemotherapeutic and prophylactic treatment is isoniazid and rifampin, and streptomycin and/or ethambutol
      5. Multidrug-resistant strains are appearing in the population
      6. Prevention and control is accomplished by treatment of infected individuals, vaccination, and better public health measures
  2. Arthropod-Borne Diseases
    1. Ehrlichiosis
      1. First case was diagnosed in the United States in 1986; caused by a new species of Rickettsiaceae, Ehrlichia chaffeensis, which is transmitted from unknown animal vectors to humans by ticks; bacterium infects circulating monocytes and causes a nonspecific febrile illness (human monocytic ehrlichiosis; HME) that resembles Rocky Mountain spotted fever; diagnosis is by serological tests; treatment is with tetracycline
      2. In 1994 a new form (human granulocytic ehrlichiosis; HGE) was discovered; caused by another species, as yet unidentified; has rapid onset of fever, headache, and muscle aches and is treated with antibiotics
    2. Epidemic (louse-borne) typhus-Rickettsia prowazekii
      1. Transmitted from person to person by the body louse (in the U.S., a reservoir is the southern flying squirrel); organism is found in insect feces, and feces are deposited when the insect takes a blood meal; as the person scratches, the bite becomes infected; the resulting vasculitis leads to headache, fever, muscle aches, and a characteristic rash; if untreated, recovery takes two weeks, but mortality rate is 50%; recovery gives a solid immunity that also cross-protects against endemic (murine) typhus
      2. Diagnosis is by characteristic rash, symptoms, and a test called the Weil-Felix reaction; treatment is usually tetracycline and chloramphenicol; control of body louse is important preventive measure; a vaccine is also available
    3. Endemic (murine) typhus-R. typhi
      1. Occurs in isolated areas around the world, including southeastern and Gulf Coast states, especially Texas; transmitted from rats by fleas
      2. Similar to epidemic typhus, but milder with lower mortality rate (less than 5%); diagnosis and treatment are the same as for epidemic typhus; rat control and avoidance of rats are preventative measures
    4. Lyme disease-(LD, Lyme borreliosis) caused by Borrelia burgdorferi, B. garinii and B. afzelii
      1. Tick-borne, with deer, mice, or the woodrat as the natural reservoir
      2. Disease is complex and progressive; is divide into three stages
        1. Initial localized stage-characteristic bull's eye rash and flulike symptoms
        2. Disseminated stage-heart inflammation, arthritis, and neurological symptoms
        3. Final stage-symptoms resembling Alzheimer's disease and multiple sclerosis with behavioral changes as well
      3. Laboratory diagnosis is by isolation of the spirochete, PCR to detect DNA in the urine, or serological testing (ELISA or Western Blot); treatment with amoxicillin or tetracycline is effective if administered early; ceftriaxone is used if nervous system involvement is suspected
      4. Prevention and control involves environmental modification to destroy tick habitat and use of anti-tick compounds
    5. Plague-Yersinia pestis
      1. Transmitted from rodent by bite of flea, direct contact with animals or animal products, or inhalation of airborne droplets; bacteria survive and proliferate inside phagocytic cells
      2. Symptoms include subcutaneous hemorrhages, fever, and enlarged lymph nodes (buboes); mortality rate is 50 to 70% if untreated
      3. Diagnosis is by direct microscopic examination, culture of buboes, serological tests, PCR, and phage testing; treatment is with streptomycin or tetracycline
      4. Prevention and control involves ectoparasite and rodent control, isolation of human patients, prophylaxis, and vaccination of people at high risk
    6. Q fever-Coxiella burnetii
      1. Bacterium can survive outside host by forming endosporelike structures; transmitted by ticks between animals and by contaminated dust to humans; disease is an occupational hazard among slaughterhouse workers, farmers, and veterinarians
      2. Starts with mild respiratory symptoms and an acute onset of severe headache, muscle pain, and fever; rarely fatal, but some develop endocarditis and hepatitis; diagnosis is serological and treatment is usually tetracycline and chloramphenicol; prevention and control measures consist of vaccinating researchers and other of high occupational risk, as well as pasteurization of cow and sheep milk in areas of endemic Q fever
    7. Rocky Mountain spotted fever-R. rickettsii
      1. Transmitted by the wood tick or the dog tick; can also be passed from generation to generation of ticks by transovarian passage
      2. Disease is characterized by sudden onset of headache, high fever, chills, and a characteristic rash; if untreated, can destroy blood vessels in the heart, lungs, or kidneys, and lead to death; treatment is usually chloramphenicol and chlortetracycline; diagnosis is through observation of rash and serological tests; best prevention is by avoidance of ticks
  3. Direct Contact Diseases
    1. Anthrax-Bacillus anthracis
      1. Transmitted by direct contact with infected animals or their products; can take three forms
        1. Cutaneous anthrax results from contamination of cut or abrasion of the skin
        2. Pulmonary anthrax (woolsorter's disease) results from inhaling endospores
        3. Gastrointestinal anthrax occurs if endospores are ingested
      2. Causes ulcerated skin lesions or influenza-like symptoms; headache, fever, and nausea are major symptoms; if invades bloodstream can be fatal; symptoms are caused by toxins
      3. Diagnosis is by direct microscopic examination, culture of bacteria, and serology; treatment is with penicillin G or penicillin G plus streptomycin; vaccination, particularly of animals and persons with high occupational risks, is an important control measure
    2. Bacterial vaginosis
      1. Disease is sexually transmitted with polymicrobic etiology; may also be an autoinfection (rectum is inhabited by these organisms)
      2. Disease is mild but is a risk factor for obstetric infections, various adverse outcomes of pregnancy, and pelvic inflammatory disease
      3. Diagnosis is based on fishy odor and microscopic observation of clue cells (sloughed-off vaginal epithelial cells covered with bacteria) in the discharge; treatment is with metronidazole
    3. Cat-scratch disease-probably caused by Bartonella henselae
      1. Diagnosis is based on the clinical history of a cat scratch or bite and subsequent swelling of the regional lymph nodes and by PCR
      2. It is typically self-limiting with abatement of symptoms over a period of days to weeks
    4. Chancroid-genital ulcer disease-caused by the gram-negative bacillus, Haemophilus ducreyi
      1. Bacterium enters the skin through a break in the epithelium; after 4 to 7 days a papular lesion develops with swelling and white blood cell infiltration; a pustule forms and ruptures leading to a painful ulcer on the penis or vagina; is a cofactor in the transmission of AIDS
      2. Diagnosis is by isolating the bacterium; treatment is with erythromycin or ceftriaxone; prevention is by use of condoms or abstinence
    5. Chlamydial Pneumonia-Chlamydia pneumoniae
      1. Mild upper respiratory infection (pharyngitis, bronchitis, sinusitis) with some lower respiratory tract involvement; symptoms include fever, productive cough, sore throat, hoarseness, and pain on swallowing
      2. Infections are common but sporadic; about 50% of adults have antibodies to C. pneumoniae; transmitted from human to human without a bird or animal reservoir
      3. Diagnosis is based on symptoms and a microimmunofluorescence test; treatment is with tetracycline and erythromycin
    6. Gas gangrene or clostridial myonecrosis-Clostridium perfringens, C. novyi, and C. septicum
      1. Found in soil and intestinal tract microbiota; contamination of injured tissues by endospores in soil or fecal material is usual route of transmission
      2. If endospores germinate in anaerobic tissues, bacteria grow and produce toxin and enzymes that cause necrosis (gangrene)
      3. Diagnosis is through recovery of bacterium; treatment involves extensive surgical wound debridement, administration of antitoxins and antibiotics, and the use of hyperbaric oxygen
      4. Prevention and control measures include debridement of contaminated wounds plus antimicrobial prophylaxis and prompt treatment of all wound infections; amputation may be necessary to prevent spread
    7. Genitourinary diseases-Mycoplasma urealyticum and Ureaplasma hominis
      1. Transmission is related to sexual activity
      2. Bacteria opportunistically cause inflammation of reproductive organs of males and females
      3. Bacteria are difficult to recognize because they are not usually cultured in the clinical microbiology laboratory; diagnosis is usually by recognition of clinical syndromes; treatment is usually tetracycline or erythromycin
    8. Gonorrhea-Neisseria gonorrhoeae (gonococci)
      1. Sexually transmitted disease of the genitourinary tract, eye, rectum, and throat
      2. Bacteria invade mucosal cells, causing inflammation and formation of pus
      3. In males there is urethral discharge and painful, burning urination; in females, disease can be asymptomatic, can cause some vaginal discharge, or may lead to pelvic inflammatory disease (PID); in both sexes, disseminated infection can occur; birth through infected vagina can result in neonatal eye infections (ophthalmia neonatorum, or conjunctivitis of the newborn) that can lead to blindness
      4. Diagnosis is by culture of the bacterium, oxidase reaction, Gram stain reaction, and colony and cell morphology; a DNA probe is also useful
      5. Treatment-several combination antibiotic treatment regimens have been found to be effective; silver nitrate is often used in the eyes of newborns to prevent infection
      6. Prevention and control by public education, diagnosis, treatment of symptomatic and asymptomatic individuals, and use of condoms
    9. Inclusion conjunctivitis-Chlamydia trachomatis
      1. Characterized by copious mucous discharge from eye, inflamed and swollen conjunctiva, and inclusion bodies in host cell cytoplasm; inclusion conjunctivitis of newborns is established from contact with an infected birth canal; in adults, disease spreads primarily by sexual contact
      2. Without treatment, recovery occurs spontaneously; therapy involves treatment with tetracycline, erythromycin, or a sulonamide; diagnosis is by direct immunofluorescence, Giemsa stain, nucleic acid probes, and culture; prevention depends upon diagnosis and treatment of all infected individuals
    10. Leprosy-severely disfiguring skin disease caused by Mycobacterium leprae
      1. Usually requires prolonged exposure to nasal secretion of heavy bacteria shedders
      2. The incubation period may be three to five years, or even longer; starts as skin lesion and progresses slowly; most lesions heal spontaneously, those that don't develop into one of two types of leprosy:
        1. Tuberculoid (neural) leprosy-mild, nonprogressive form associated with delayed-type hypersensitivity reaction
        2. Lepromatous (progressive) leprosy-relentlessly progressive disfigurement
      3. Diagnosis is by observation in biopsy specimens and by serodiagnostic tests
      4. Treatment-long-term use of sulfa drugs (diacetyl/dapsone) and rifampin, sometimes in conjunction with clofazimine; use of vaccine in conjunction with the drugs shortens the duration of therapy
      5. Control by identification and treatment of patients; children of contagious parents should be given prophylactic drug therapy until their parents are treated and have become noninfectious
    11. Lymphogranuloma venereum-sexually transmitted disease caused by Chlamydia trachomatis
      1. Occurs in phases
        1. Primary phase-ulcer on genitals that heals with no scar
        2. Secondary phase-enlargement of lymph nodes (buboes); fever, chills, and anorexia are common
        3. Late phase-fibrotic changes and abnormal lymphatic drainage leading to fistulas and/or urethral or rectal strictures; leads to untreatable fluid accumulation in the penis, scrotum, or vaginal area
      2. Diagnosis by staining infected cells with iodine to observe inclusions, culture, nucleic acid probes, and serological tests; treated by aspiration of buboes and by antibiotics in early phases; by surgery in late phase; controlled by education, prophylaxis, and early diagnosis and treatment
    12. Mycoplasmal pneumonia-Mycoplasms pneumoniae
      1. Spread by close contact and/or airborne droplets; common and mild in infants; more serious in older children and young adults
      2. Symptoms vary from none to serious pneumonia
      3. Diagnosis is considered if other bacteria cannot be isolated and viruses cannot be detected; rapid antigenic detection kits are now available; colony morphology is also helpful; treatment is usually tetracycline or erythromycin; no preventative measures
    13. Nongonococcal urethritis (NGU)-an inflammation of the urethra not caused by Neisseria gonorrhoeae
      1. Caused by a variety of agents including C. trachomatis; organisms are sexually transmitted-50% are caused by chlamydia; NGU caused by chlamydia is the most common STD in the U.S.
      2. Infection may be asymptomatic in many males or may cause urethral discharge, itching, and inflammation of genital tract; females may be asymptomatic or may develop pelvic inflammatory disease (PID), which can lead to sterility; disease is serious in pregnant females, where it may lead to miscarriage, stillbirth, inclusion conjunctivitis, and infant pneumonia
      3. Diagnosis is by observation of leukocyte exudates, Gram stain reaction, and culture; rapid diagnostic tests are now available; treatment is with various antibiotics
    14. Peptic ulcer disease and gastritis-Helicobacter pylori
      1. Bacterium colonizes gastric mucus-secreting cells, alters gastric pH to favor its own growth, and releases toxins that damage epithelial mucosal cells
      2. Transmission is probably person-to-person, but common source has not been definitively ruled out
      3. Diagnosis is by culture of gastric biopsy specimens, serological testing, and tests for urease production
      4. Treatment includes bismuth subsalicylate (Pepto-Bismol) and antibiotics
    15. Psittacosis (ornithosis)-Chlamydia psittaci
      1. Spread by handling infected birds or by inhalation of dried bird excreta; occupational hazard in the poultry industry (particularly to workers in turkey processing plants)
      2. Infects respiratory tract, liver, spleen, and lungs, causing inflammation, hemorrhaging, and pneumonia
      3. Diagnosis based on isolation of C. psittaci from blood or sputum, or by serology; treatment is with tetracycline; prevention is by chemoprophylaxis for pet birds and poultry (this practice can lead to antibiotic resistance and so is discouraged)
    16. Staphylococcal diseases
      1. Staphylococci are gram-positive, facultative anaerobes and are usually catalase positive
      2. Staphylocci are very important human pathogens and are also part of normal human microbiota
      3. Staphylococci can be divided into pathogenic species and relatively nonpathogenic species by the coagulase test
        1. S. aureus-coagulase positive, pathogenic; causes severe chronic infections
        2. S. epidermidis-coagulase negative, less invasive, opportunistic pathogens associated with nosocomial infections
      4. Many of the pathogenic strains are slime producers; slime is a viscous extracellular glycoconjugate that allows the bacteria to adhere to smooth surfaces, such as medical prostheses and catheters, and form biofilms; slime also inhibits neutrophil chemotaxis, phagocytosis and the antimicrobial agents vancomycin and teicoplanin
      5. Can be spread by hands, expelled from respiratory tract, or transported in or on inanimate objects; staphylococci cause disease in any organ of the body; disease is most likely to occur in individuals whose defenses have been compromised
      6. Staphylococci produce exotoxins and substances that promote invasiveness
      7. They produce toxins that can cause disease ranging from food poisoning to bacteremia
        1. Abscesses-related to coagulase production, which leads to formation of abscess; at core, tissue necrosis occurs
        2. Impetigo-a superficial skin infection often observed in children
        3. Toxic shock syndrome (TSS)-serous disease characterize by low blood pressure, fever, diarrhea, skin rash, and shedding of the skin
        4. Staphylococcal scalded skin syndrome-caused by strains of S. aureus that carry a plasmid-borne gene for exfoliative toxin; common in infants and children
      8. Diagnosis is by culture identification, catalase and coagulase tests, serology, DNA fingerprinting, and phage typing; no specific prevention; several antibiotics can be used for treatment, but isolates should be tested for sensitivity because of the existence of many drug-resistant strains; cleanliness, hygiene, and aseptic management of lesions are best control measures
    17. Syphilis-Treponema pallidum
      1. Sexually transmitted or congenitally acquired in utero
      2. Disease progresses in stages
        1. Primary stage-lesion (chancre) at infection site that can transmit organism during sexual intercourse
        2. Secondary stage-skin rash and other more general symptoms
        3. Latent stage-not communicable after two to four years except possibly congenitally
        4. Tertiary stage-degenerative lesions (gummas) in the skin, bone, and nervous system
      3. Diagnosed by clinical history, physical examination, microscopic examination of fluids from lesions, and serology
      4. Treatment-penicillin in early stages, tertiary stage is highly resistant to treatment; immunity is incomplete and subsequent infections can occur
      5. Prevention and control is by public education, treatment, follow-up on sources and contacts, sexual hygiene, and prophylaxis (use of condoms)
    18. Tetanus-Clostridium tetani
      1. Found in soil, dust, hospital environments, and mammalian feces
      2. Transmission is associated with skin wounds; bacterium exhibits low invasiveness, but in deep tissues with low oxygen tension, its endospores germinate; when the vegetative cells lyse, they release tetanospasmin (an exotoxin)
      3. Toxin causes prolonged muscle spasms; a hemolysin (tetanolysin) is also produced and aids in tissue destruction
      4. Prevention is important and involves:
        1. Active immunization with toxoid (DPT)
        2. Proper care of wounds contaminated with soil
        3. Prophylactic use of antitoxin
        4. Administration of penicillin
    19. Trachoma-Chlamydia trachomatis
      1. Greatest single cause of blindness in the world, although uncommon in the U.S.
      2. Transmitted by hand-to-hand contact, by contact with infected fomites, and by flies; first infection usually heals spontaneously with no lasting effects; with reinfection, vascularization of the cornea (pannus formation) and scarring of the conjunctiva occur
      3. Diagnosis and treatment is the same as for inclusion conjunctivitis; prevention and control is by health education, personal hygiene, and access to clean water for washing
    20. Tularemia-Francisella tularensis
      1. Is spread from animal reservoirs by a variety of mechanisms, including biting arthropods, direct contact with infected tissue, inhalation of aerosolized bacteria, and ingestion
      2. Characterized by ulcerative lesions, enlarged lymph nodes, and fever
      3. Diagnosis by PCR or culture and serological tests; treated with antibiotics; prevention and control involves public education, protective clothing, and vector control; a vaccine is available for high-risk laboratory workers
    21. Sexually transmitted diseases
      1. A global health problem caused by viruses, bacteria, yeasts, and protozoa
      2. Spread of sexually transmitted diseases (STDs) is currently out of control
      3. STDs are most frequent in the most sexually active group (15-30 years of age); the more sexual partners, the more likely that a person will acquire an STD
  4. Food-Borne and Waterborne Diseases
    1. Food poisoning-gasterenteritis that can arise in two ways
      1. Food-borne infection-microorganism is transferred to host in food and then colonizes host
      2. Food intoxication-toxin is ingested in food; the toxins are called enterotoxins
    2. Botulism-Clostridium botulinum
      1. Frequently caused by canned foods that contain endospores, which germinate and produce an exotoxin (neurotoxin) within the food; if food is eaten without adequate cooking, the toxin remains active
      2. Can cause death by respiratory or cardiac failure
      3. Diagnosis is by hemagglutination testing or toxigenicity testing in animals using the patient's serum, stools, or vomitus; treatment is supportive and also involves antitoxin administration
      4. Infant botulism is a disease of infants under 1 year of age; endospores germinate in infant's intestines and then produce toxin
      5. Prevention and control involves safe food processing practices in the food industry and in home canning; not feeding honey to babies under one year of age helps prevents infant botulism
    3. Campylobacter jejuni gastroenteritis
      1. Transmitted by contaminated food or water, contact with infected animals, or anal-oral sexual activity
      2. Causes diarrhea, fever, intestinal inflammation and ulceration, and bloody stools
      3. Diagnosis is by culture in reduced oxygen environment; disease is self-limited; treatment is supportive, with fluid and electrolyte replacement; erythromycin is used in severe cases
    4. Cholera-Vibrio cholerae
      1. Acquired by ingesting food or water contaminated with fecal material; shellfish and copepods are natural reservoirs;
      2. Bacteria adhere to the intestinal mucosa of the small intestine; are not invasive, but secrete cholera enterotoxin (choleragen), which stimulates hypersecretion of water and chloride ions, while inhibiting adsorption of sodium ions; leads to fluid loss; death may result from increased protein concentrations in blood, causing circulatory shock and collapse
      3. Diagnosis is by culture of the bacterium from feces and by serotyping; treatment is rehydration therapy (fluid and electrolyte replacement) and administration of antibiotics; control is based on proper sanitation
    5. Listeriosis-Listeria monocytogenes
      1. L. monocytogenes is isolated from soil, vegetation, and many animal reservoirs; disease generally occurs in pregnant women or in immunosuppressed individuals; causes meningitis, sepsis, and stillbirth; does not cause gastrointestinal illness
      2. Bacterium is an intracellular pathogen; can be part of normal gastrointestinal microbiota; pathogenicity is due to production of hemolysins and other enzymes
      3. Diagnosis is by culture; treatment is intravenous administration of ampicillin or penicillin; the USDA and food manufacturers are developing food safety measures
    6. Salmonellosis-Salmonella typhimurium and other serovars
      1. Food-borne, particularly in poultry, eggs, and egg products; also in contaminated water
      2. Food infection; bacteria must multiply and invade the intestinal mucosa; as they reproduce they produce enterotoxin and cytotoxin, which destroy intestinal epithelial cells; this causes abdominal pain, cramps, diarrhea, and fever; fluid loss can be a problem, particularly for children and elderly people; treatment is fluid and electrolyte replacement; prevention depends on good food processing practices, proper refrigeration, and adequate cooking
    7. Shigellosis-Shigella spp.
      1. Shigellosis or bacterial dysentery is transmitted by fecal-oral route and is most prevalent in children 1 to 4 years old; bacterium has small infectious dose (10 to 100 bacteria); in U.S. shigellosis is a particular problem in day care centers and custodial institutions where there is crowding
      2. Bacteria are facultative intracellular parasites, but do not usually spread beyond the colon epithelium; endotoxins and exotoxins cause watery stools that often contain blood, mucus, and pus; in some cases colon becomes ulcerated
      3. Identification is based on biochemical characteristics and serology; disease is self-limiting in adults but may be fatal in children; treatment is fluid and electrolyte replacement; antibiotics may be used in severe cases; prevention is a matter of personal hygiene and maintenance of a clean water supply
    8. Staphylococcal food poisoning-Staphylococcus aureus
      1. Caused by ingestion of improperly stored or prepared food in which the organism has grown
      2. Organism produces several enterotoxins that are heat stable
      3. Symptoms include severe abdominal pain, diarrhea, vomiting, and nausea; symptoms come quickly (one to six hours) and leave quickly (24 hour)
      4. Diagnosis is based on symptoms or identification of bacteria or enterotoxins in food; treatment is fluid and electrolyte replacement; prevention and control involves avoidance of contaminated food and control of personnel responsible for food preparation and distribution
    9. Traveler's Diarrhea and Escherichia coli Infections
      1. Traveler's diarrhea is a rapidly acting, dehydrating condition caused by certain viruses, bacteria or protozoa normally absent from the traveler's environment; E. coli is one of the major causative agents
      2. Six categories or strains of diarrheagenic E. coli are now recognized
        1. Enterotoxigenic E. coli (ETEC) produces two enterotoxins that are responsible for symptoms including hypersecretion of electrolytes and water into the intestinal lumen
        2. Enteroinvasive E. coli (EIEC) multiplies within the intestinal epithelial cells; may also produce a cytotoxin and an enterotoxin
        3. Enteropathogenic E. coli (EPEC) causes effacing lesions, destruction of brush border microvilli on intestinal epithelial cells
        4. Enterohemorrhagic E. coli (EHEC) causes attaching-effacing lesions leading to hemorrhagic colitis; it also releases toxins that kill vascular epithelial cells; E. coli 0517:H7 is a major form of BHEC and has caused many outbreaks of hemorrhagic colitis in the U.S.
        5. Enteroaggregative E. coli (EAggEC) forms clumps adhering to epithelial cells, toxins have not been identified but are suspected from the type of damage done
        6. Diffusely adhering E. coli (DAEC) adheres in a uniform pattern to epithelial cells and is particularly problematic in immunologically naive or malnourished children
      3. Diagnosis is based on past travel history and symptoms; lab diagnosis is by isolation of the specific type of E. coli from feces and identification using DNA probes, determination of virulence factors, and the polymerase chain reaction; treatment is electrolyte replacement plus antibiotics; prevention and control involve avoiding contaminated food and water
    10. Typhoid fever-Salmonella typhi
      1. Caused by ingestion of food or water contaminated with human or animal feces
      2. Symptoms are fever, headache, abdominal pain, and malaise, which last several weeks
      3. Diagnosis is by demonstration of bacterium in blood, urine, or stools and by serology; treatment is with antibiotics
      4. Prevention and control involves purification of drinking water, pasteurization of milk, preventing carriers from handling food, and complete patient isolation; a vaccine is available for high-risk individuals
  5. Sepsis and Septic Shock
    1. Cannot be categorized under a specific mode of transmission
    2. Sepsis
      1. Systemic response to a microbial infection
      2. Manifested by fever or retrograde fever, heart rate is greater than 90 beats per minute, respiratory rate is greater than 20 breaths per minute, a pCO2is less than 32 mmHg, a leukocyte count is greater than 12,000 cells per ml or less than 4,000 cells per ml
    3. Septic shock
      1. Sepsis associated with severe hypotension (low blood pressure)
      2. Gram-positive bacteria, fungi, and endotoxin-containing gram-negative bacteria can initiate the pathogenic cascade of sepsis leading to septic shock
      3. Lipopolysaccharide (LPS), an integral component of the outer membrane of gram-negative bacteria, has been implicated
    4. Pathogenesis begins with localized proliferation of the microorganism
      1. Bacteria may invade the bloodstream or may proliferate locally and release various products into the bloodstream
      2. Products include structural components (endotoxins) and secreted exotoxins
      3. These products stimulate the release of endogenous mediators of shock from plasma cells, monocytes, macrophages, endothelial cells, neutrophils, and their precursors
      4. The endogenous mediators have profound effects on the heart, vasculature, and other body organs
      5. Death ensues if one or more organ systems fail completely
  6. Dental Infections-caused by various odontopathogens
    1. Dental plaque
      1. Acquired enamel pellicle-a membranous layer produced by the selective absorption of saliva glycoproteins to the hard enamel surface of tooth: its net negative charge helps repel bacteria
      2. Dental plaque is initiated by the colonization of the acquired enamel pellicle by streptococci; this is followed by coaggregation due to cell-to-cell recognition between genetically distinct species; eventually an environment develops that allows Streptococcus mutans and S. sobrinus to colonize the tooth surface
      3. S. mutans and S. sobrinus produce glucans that cement plaque bacteria together and create anaerobic microenvironments; these are colonized by anaerobes
      4. After the plaque ecosystem develops, bacteria produce acids that can demineralize the enamel and initiate tooth decay
    2. Dental decay (caries)
      1. Production of fermentation acids after eating and the subsequent return to a neutral pH leads to a demineralization-remineralization cycle
      2. When diet is too rich in fermentable substrates, demineralization exceeds remineralization and leads to dental caries
      3. Drugs are not available to treat dental caries; prevention includes minimal ingestion of sucrose; daily brushing, flossing, and mouth washes; and professional application of fluoride
    3. Periodontal disease-diseases of the periodontum
      1. Peridontum-supporting structure of tooth; includes the centum, the periodontal membrane, the bones of the jaw, and the gingivae; disease begins by formation of subgingival plaque and leads to inflammatory reaction (periodontitis; periodontitis leads to formation of periodontal pockets that are colonized by bacteria, causing more inflammation; eventually bone destruction (periodontosis), inflammation of gingiva (gingivitis), and general tissue necrosis occur
      2. Can be controlled by plaque removal; by brushing, flossing, and mouthwashes; and at times by oral surgery








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