Download Rickettsia, Chlamydia, Mycoplasma, Legionella, and Gardnerella

Legionellaceae
Fastidious
Gram-Negative Bacilli
Legionellaceae: Genera
• Legionella pneumophilia
– Pontiac Fever – febile illness
• 1968, people working in Public Health Department,
Pontiac, Michigan
• Self-limited disease, no pulmonary involvement
– Legionnaires Disease – acute pneumonia
• 1976, outbreak American Legion convention,
Philadelphia
• 221 cases, 34 deaths (15%)
• Coxiella burnetii
– Q fever
– Intracelluar growth, originally classified with
Rickettsia
– Now shown related to Legionella
Legionella pneumophila: Gram
Stain and Characteristics
• G(-) small pleomorphic rods
• Stain poorly by Gram stain
• Ubiquitous aquatic saprophyte - lakes,
streams; air conditioning, water systems,
shower heads, hot tubs, humidifiers
• Facultative intracellular parasite
– Free-living amoebae in nature
– Human alveolar phagocyte, epithelial cell
• Sporadic, epidemic, nosocomial infection
L. pneumophilia: Lab Culture
• Fastidious - no growth ordinary lab media,
requires cysteine for growth
• Buffered charcoal yeast extract (BCYE) primary isolation, selective by antibiotics
• Growth enhanced in 3-5% CO2
• Colonies pinpoint, ground-glass appearance
observe under dissecting microscope
L. pneumophilia: Lab ID
• Previously not recognize – stains poorly, no growth on
common lab media
• BCYE culture - “gold standard” detection MO from
clinical specimen
• Rapid Urine Antigen Test – enzyme immunoassay
(EIA), lower specificity, sensitivity; test of choice
• Direct fluorescent antibody (IFA) test - specific
antibody tagged with dye to ID MO under UV
microscope; lower sensitivity
• Serology Test – specific Legionella antibody detected
by FA, EIA; require 4x rise antibody titer in paired
patient serum
• DNA amplification test – specific, sensitive; enzyme
inhibitors in RT secretions give false (-); currently
not available
L. pneumophilia: Virulence
Factors
• Endotoxin – LPS of Gram(-) cell wall
• Infect & replicate in macrophage
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–
–
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Enter cell by endocytosis
Inhibit phagolysosome fusion, not killed
Multiply in cell vacuole
Produce proteolytic enzymes, kill & lyse cell
• Proteolytic enzymes - hemolysin, protease,
nuclease, phosphatase, lipase
• Collagenase – spreading factor
L. pneumophilia: Pontiac
Fever
• Airborne transmission - inhale aerosols
from environment; no person-to-person
transmission; attack rate low (<5%)
• Acute, self-limited febrile illness
• Incubation 24-36 hours
• Fever, chills, malaise, myalgia, headache;
no pulmonary disease
• Persist 2-5 days, resolve spontaneously
without treatment
• Minimal morbidity, low mortality (<1%)
L. pneumophilia:
Legionnaires Disease
• Airborne transmission - inhale aerosols from
environment; no person-to-person transmission;
attack rate high (>90%)
• Incubation 2-10 days
• Abrupt fever, chills, malaise, myalgia, headache,
dry cough, vomiting, diarrhea, abdominal & chest
pain
• Primary manifestation – pneumonia, multilobar
consolidation
• Hospitalization usually required in 3-5 days
• Without antibiotics, fatality rate 15-20%, higher
in transplant patients
• Occurs more in males >60 years age, immune
compromised individual
• At risk are elderly, patients with compromised
pulmonary function (smokers), decreased CMI
(transplant patients)
L. pneumophilia: Treatment
and Prevention
• Use antibiotics able to penetrate
macrophages – macrolides (azithromycin),
fluoroquinolones (ciprofloxacin)
• Identify environmental source, then
reduce number of MO
• Water treatment – hyperchlorination,
heating, copper-silver ionization
• Elimination of all MO in water not possible,
reduce to low level not able to cause
infection
Coxiella burnetti: Gram
Stain and Characteristics
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•
•
•
•
Gram(-) small rod
Stain weakly
Infection of mammal, bird, tick
Facultative intracellular parasite
Extremely stable, survive in
environment long time
C. burnetti: Virulence
Factors
• Resistant to lysosomal enzymes –
survive and replicate in
phagolysosome of cell
• Intracellular growth – protected
from host immune defense
C. burnetii: Q Fever
• 1935 Australia - “query” unexplained
fever in cattle, slaughterhouse workers
• Disease worldwide, uncommon USA
• Human infection - contact infected
cattle, sheep, goats, dogs, cats
• Via inhalation, ingest contaminated milk
• Most infections AS, <5% acute disease
• Incubation 14-26 days, sudden onset
fever, chills, headache, no rash
• Atypical pneumonia 5-14 days, low
mortality
• Potential Bioterrorist weapon
– Extraordinarily infectious (~1 MO)
– Prolonged disease
– Difficult to diagnose
C. burnetti: Treatment
and Prevention
• Doxycycline for acute infection
• Vaccination of animal herd
Case Study 10 - Legionella
• A 73-year-old man was admitted to the
hospital because of breathing difficulties,
chest pain, chills, and fever of several
days’ duration. He had been well until 1
week before admission, when he noted the
onset of a persistent headache and a
productive cough. The patient smoked two
packs of cigarettes a day for more than
50 years and drank a six-pack of beer
daily; he also had a history of bronchitis.
Physical examination results revealed an
elderly man in severe respiratory distress
with a temperature of 39ºC,
Case Study 10 - Legionella
• pulse of 120 beats/minute, respiratory
rate of 36 breaths/minute, and blood
pressure of 145/95 mm Hg. Chest
radiograph revealed an infiltrate in the
middle and lower lobes of the right lung.
The white blood cell count was 14,000
cells/mm3 (80% polymorphonuclear
neutrophils). Gram stain of the sputum
showed neutrophils but no bacteria, and
routine bacterial cultures of sputum and
blood were negative for organisms.
Infection with Legionella pneumophilia was
suspected.
Case Study - Questions
• 1. What laboratory tests can be used to
confirm this diagnosis? Why were the
routine culture and Gram-stained specimen
negative for Legionella organisms?
• 2. How are Legionella species able to
survive phagocytosis by the alveolar
macrophages?
• 3. What environmental factors are
implicated in the spread of Legionella
infections? How can this risk be
eliminated or minimized?
Class Assignment
• Textbook Reading: Chapter 18
Haemophilus and Other Fastidious
Gram-Negative Rods
– B. Legionella
• Key Terms
• Learning Assessment Questions
Final Lecture Exam
Tue., March 20, 2012
8:30 – 10:30 am
• Mycobacterium thru Ureaplasma
• Lecture, Reading, Key Terms, Learning
Assessment Questions
• Case Study 7, 8, 9, 10 (Mycobacterium,
Clostridium, Chlamydia, Legionella)
• Exam Format:
– Multiple Choice
– Terms
– True/False Statements
– Short Essay
• Review, Review, Review!
• Repetition is the key to retention.