Prescott's Microbiology,4/e

		Microbiology, 4/e Prescott, Harley, Klein
		Instructor Resources

38 Human Diseases Caused by Other Bacteria (Chlamydiae, Mycoplasmas, Rickettsias); Dental and Nosocomial Infections

CHAPTER OVERVIEW

This chapter discusses some of the more important chlamydia, mycoplasmas, and rickettsia that are pathogenic to humans. Dental and nosocomial infections are also discussed.

CHAPTER OBJECTIVES

After reading this chapter you should be able to:

! describe diseases caused by Chlamydia trachomatis, C. psittaci, and C. pneumoniae

! describe the genitourinary diseases caused by Mycoplasma hominis and Ureaplasma urealyticum, and the respiratory disease caused by M. pneumonia

! discuss the typhus and spotted fever groups of rickettsias

! discuss the bacterial odontopathogens involved in tooth decay and periodontal disease

! discuss bacterial nosocomial infections, such as bacteremias, burn wound infections, respiratory tract infections, surgical wound infections, and urinary tract infections

CHAPTER OUTLINE

I. Chlamydial Diseases

A. Chlamydial PneumoniaCC. pneumoniae

1. Mild upper respiratory infection with some lower respiratory tract involvement

2. Infections are common but sporadic; about 50% of adults have antibodies to C. pneumoniae

3. Transmitted from human to human without a bird or animal reservoir

4. Diagnosis is based on symptoms and a microimmunofluorescence test

5. Treatment is with tetracycline and erythromycin

B. Inclusion conjunctivitisCC. trachomatis

1. Sensitive to sulfonamides; forms inclusions containing glycogen

2. Causes epithelial cell infections of the conjunctiva, pharynx, respiratory tract, urethra, cervix, and uterine tubes

3. Spreads primarily by sexual contact

4. Resolves spontaneously over several weeks or months

5. Diagnosed by direct immunofluorescence, Giemsa stain, or nucleic acid probes

6. Treatment is tetracycline or erythromycin

7. Inclusion conjunctivitis of newborns is established from contact with an infected birth canal

C. Lymphogranuloma venereumCC. trachomatis

1. Sexually transmitted disease (STD)

2. Occurs in phases

a. Primary phaseCulcer on genitals that heals with no scar

b. Secondary phaseCenlargement of lymph nodes (buboes); fever, chills, and anorexia are common

c. Late phaseCfibrotic 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

3. Treated by aspiration of buboes and by antibiotics in early phases; by surgery in late phase

4. Controlled by education, prophylaxis, and early diagnosis and treatment

D. Nongonococcal urethritis (NGU)Cinflammation of the urethra not caused by Neisseria gonorrhoeae

1. Caused by a variety of agents including C. trachomatis

2. Organisms are sexually transmittedC50% are caused by chlamydia; NGU is the most common STD in the U.S.

3. May be inapparent in many males, or may cause inflammation of genital tract

4. Asymptomatic in some females, but may cause pelvic inflammatory disease (PID), which can lead to sterility

5. Serious disease in pregnant females: leads to miscarriages, stillbirth, inclusion conjunctivitis, and infant pneumonia

6. Rapid diagnostic tests are now available

7. Treatment is with various antibiotics

E. Psittacosis (ornithosis)CC. psittaci

1. Resistant to sulfonamides; inclusions do not contain glycogen

2. Infectious disease in birds, which can be transmitted to humans

3. 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)

4. Infects respiratory tract, liver, spleen, and lungs, causing inflammation, hemorrhaging, and pneumonia

5. Diagnosis based on isolation of C. psittaci from blood or sputum or on serology

6. Treatment is with tetracycline, which decreases the mortality rate from 20 to 2%

F. TrachomaCC. trachomatis

1. Greatest single cause of blindness in the world, although uncommon in the U.S.

2. Transmitted by hand-to-hand contact or by contact with infected soaps and towels

3. First infection usually heals spontaneously with no lasting effects

4. Reinfection leads to vascularization of the cornea (pannus formation) and scarring of the conjunctiva

5. Treatment is the same as for inclusion conjunctivitis

6. Prevention and control is by health education, personal hygiene, and access to clean water for washing

II. Mycoplasmal Diseases

A. Genitourinary diseasesCMycoplasma homonis and Ureaplasma urealyticum

1. Colonization is related to sexual activity

2. Bacteria are difficult to recognize because they are not usually cultured in the clinical microbiology laboratory

3. Diagnosis is usually by recognition of clinical syndromes

4. Treatment is usually tetracycline or erythromycin

B. Primary atypical pneumoniaCM. pneumonia

1. Spread by close contact and/or airborne droplets

2. Common and mild in infants; more serious in older children and young adults

3. Symptoms vary from none to serious pneumonia

4. Diagnosis is considered if bacteria cannot be isolated and viruses cannot be detected; rapid antigenic detection kits are now available

5. Treatment is usually tetracycline or erythromycin

III. Rickettsial Diseases (Rickettsioses)

A. Ehrlichiosis

1. First case was diagnosed in the United States in 1986

2. Caused by a new species of Rickettsiaceae, Ehrlichia chaffeensis

3. Transmitted from unknown animal vectors to humans by Dermacentor andersoni and Amblyomma americanum ticks

4. Infects circulating monocytes causing a nonspecific febrile illness (human monocytic ehrlichiosis; HME) that resembles Rocky Mountain spotted fever

5. Diagnosis is by serological tests

6. Treatment is with tetracycline

7. In 1994 a new form (human granulocytic ehrlichiosis; HGE) was discovered

B. Epidemic (louse-borne) typhusCRickettsia prowazekii

1. Transmitted from person to person by the body louse (in the U.S., a reservoir is the southern flying squirrel)

2. 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

3. Causes vasculitis (infection of blood vessel endothelial cells); leads to headache, fever, muscle aches, and a characteristic rash

4. If untreated, recovery takes two weeks, but mortality rate is 50%

5. Recovery gives a solid immunity that also cross-protects against endemic (murine) typhus

6. Treatment is usually tetracycline and chloramphenicol

C. Endemic (murine) typhusCR. typhi

1. Transmitted from rats by fleas

2. Occurs in isolated areas around the world, including southeastern and Gulf coast states, especially Texas

3. Similar to epidemic typhus, but milder with lower mortality rate (less than 5%)

4. Treatment is the same as for epidemic typhus

D. Q feverCCoxiella burnetii

1. Can survive outside host by forming endosporelike structures

2. Transmitted by ticks between animals, and by contaminated dust to humans; an acute zoonotic disease

3. Occupational hazard among slaughterhouse workers, farmers, and veterinarians

4. Starts with mild respiratory symptoms, but an acute onset of severe headache, muscle pain, and fever

5. Rarely fatal, but 10% of cases develop endocarditis in 5 to 10 yrs

6. Treatment is usually tetracycline and chloramphenicol

7. Prevention and control consists of vaccination researchers and other of high occupational risk as well as pasteurization of cow and sheep milk in areas of endemic Q fever

D. Rocky Mountain spotted feverCR. rickettsii

1. Transmitted by the wood tick or the dog tick

2. Can destroy blood vessels in the heart, lungs, or kidneys, and lead to death; causes a characteristic rash

3. Treatment is usually chloramphenicol and chlortetracycline

IV. Dental InfectionsCcaused by various odontopathogens

A. Dental plaque

1. Enamel adsorbs acidic glycoproteinsCacquired enamel pellicle

2. Colonized by S. gordonii, S. mitis and S. oralis

3. This environment provides binding surface for other microorganisms, such as S. mutans and S. sobrinus via intergeneric bacterial adherence (coaggregation)

4. The latter two organisms hydrolyze sucrose to glucose and fructose, and polymerize the glucose into polymers (glucans) that act like a cement which forms a dental plaque ecosystem

B. Dental caries (tooth decay)

1. Dental plaque allows growth of anaerobes

2. Anaerobes produce lactic acid and acetic acid, which remain at that site undiluted because of the impermeability of the dental plaque

3. Lactic and acetic acids cause demineralization of the enamel (repair or remineralization occurs, except when diet is too rich in fermentable substrates); leads to cavitation (dental caries)

4. If enamel is breached and bacteria reach dentin and pulp, the tooth can die

5. Drugs are not available to prevent dental caries

6. Good dental hygiene (brushing, flossing, fluoride) and minimal ingestion of sucrose are the main strategies for the prevention of dental caries

C. Periodontal diseaseCinitiated by formation of subgingival plaque

1. Main species involved is Porphyromonas gingivalis

2. Can be mild inflammationCgingivitis

3. Can lead to loss of teeth if unchecked

4. Controlled by plaque removal and good dental hygiene; oral surgery and antibiotics may be necessary in some cases

V. Nosocomial Infections

A. BacteremiaCtransient presence of bacteria in the blood (6% of all nosocomial infections)

1. Bacteria can be introduced via intravenous infusion, respiratory devices, catheters, and other procedures and devices that penetrate the body=s normal defense mechanisms (primary bacteremia)

2. Infection may also result from infections at another body site (secondary bacteremia)

3. Occurs primarily in newborns and the elderly, whose natural defense mechanisms are compromised

4. Organisms commonly found are coagulage negative staphylococci (CONS), S. aureus, and E. coli

B. Burn wounds are frequently infected by Pseudomonas aeruginosa and Staphylococcus aureus and account for about 8% of all nosocomial infections

C. Respiratory tract diseases (18%) involve pneumonias and other infections related to the use of respiratory devices that are used to aid breathing or administer medications; the microorganisms most often found are S. aureus, P. aeruginosa, and Enterabacter spp.

D. Surgical site infections (SSI; 17%) are a particular problem when surgery is on the gastrointestinal, respiratory, or genitourinary tracts; frequent bacterial isolates are S. aureus CoNS, and Enterococcus spp.

E. Urinary tract infection (UTI) are the most common of all nosocomial infections (39%) and generally result from catheterization; frequent isolates are E. coli, Enterococcus spp. and P. aeruginosa

F. Miscellaneous infections include skin and eye infections that are common in newborns but not in adults; infections often occur in immunosuppressed patients and cancer patients; organ transplant patients receiving immunosuppressive therapy are also highly susceptible

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