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94 Cards in this Set

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What are three G- rods associated with resporatory tract infections?
1) Haemophilus influenzae
2) Legionella pneumophilia
3) Bordetella pertussis
What virulence factor do these organisms have in common?
Lipopolysaccharide (LPS), which is common to all gram-negative bacteria.
What are their oxygen requirements?
Facultative anaerobes.
What are the structure of Haemophilus?
Pleomorphic; from coccobacillus to long slender rods
Why can Haemophilus be difficult to visualize on Gram stain?
The organisms are small
What are two pathogenic species of Haemophilus?
1) H. influenzae
2) H. ducreyi
How are serotypes of H. influenzae distinguished?
By their capsular polysaccharide
How many different serotypes exist?
6
There is another type which is denoted "nontypable" because it is unencapsulated.
What is the natural host of H. influenzae?
Humans are the only natural host
Where is H. influenzae commonly found?
Normal flora of the upper respiratory tract.
How is H. influenzae transmitted?
Respiratory droplets
What virulence factors enable H. influenzae to attach to respiratory mucosa?
IgA protease and several types of adhesins.
What are two general types of infections caused by H. influenzae?
1) Localized infections of the respiratory tract secondary to contiguous spread of bacteria (pneumonia)
2) Disseminated disease secondary to bacteremia (meningitis)
What part of H. influenzae enables it to cause disseminated disease?
The capsule
Do unencapsulated H. influenzae cause meningitis?
NO
Unencapsulated bacteria cannot survive in teh bloodstream or cause disseminated disease.
Which serotype of H. influenzae is associated with severre infections?
Type b
Why is type b H. influenzae associated with severe infections?
The capsule is composed of polyribose phosphate, facilitating tissue invasion.
What are four major infections caused by H. influenzae in children?
1) Sinusitis
2) Otitis media
3) Meningitis
4) Epiglottitis
SOME is an acronym for the infection caused by H. influenzae in children
What makes epiglottitis a life-threatening disease?
The swollen epiglottis may obstruct the airway.
What major adult infection is caused by H. influenzae?
Pneumonia
What population has an increased risk of infection with H. influenzae?
Patients with COPD who cannot effectively clear the organism.
What are other clinical manifestations of H. influenzae?
1) Septic arthritis
2) Purulent conjunctivitis
3) Brazilian purpuric fever
How is H. influenzae definitively diagnosed in the lab?
Culture on chocolate agar
Which two factors are required for growth of H. influenzae on laboratory media?
Factor V (NAD)
Factor X (heme)
How can meningitis be diagnosed?
1) Cerebrospinal fluid (CSF) Gram stain
2) Latex agglutination
3) Immunoelectrophoresis
4) Radioimmune assay of CSF
How are upper respiratory tract infections with H. influenzae treated?
Antibiotics including TMP-SMX
How are disseminated H. influenzae infections treated?
Third-generation cephalosporins such as ceftriaxone or cefotaxime
Why use third-generation cephalosporins for H. influenzae?
Many of the type b organisms produce Beta-lactamase, which destroys penicillin and ampicillin
What precent of H. influenzae type b isolates produce Beta-lactamase, thus requiring treatment with a cephalosporin?
20-30%
What is the mortality rate for untreated H. influenzae meningitis?
90%
How are H. influenzae infections prevented?
Adminitration of childhood conjugate vaccine.
What are the components of the conjugated H. influenzae vaccine?
Type b capsular polysaccharide conjugated to diptheria toxoid or another carrier protein.
Why is Type ba capsular polysaccharide conjugated to diphtheria toxoid in the H. influenzae vaccine?
The toxoid is antigenic, increasing the immunogenic response to the vaccine.
At what age is the H. influenzae administered?
2-15 months
How effective is the conjugated H. influenzae vaccine?
It has reduced the incidence of meningitis in immunized children by 90%.
How has the introduction of the H. influenzae vaccine affected teh prevalence of H. influenzae meningitis?
Until introduction of the vaccine in the early 1990s, H. influenzae was the number one cause of miningitis in children.
Which drug is used prophylactically for close contacts of H. influenzae-infected patients?
Rifampin
Why is Rifampin used prophylactically for H. influenzae contact?
Rifampin is secreted in saliva and therefore reduces respiratory carriage of organisms.
How is H. ducreyi transmitted?
Sexually
What does H. ducreyi cause?
Chancroid on the genitals and inguinal lymphadenopathy (buboes)
Who are H. ducreyi lesions distinguished from those of Treponema pallidum syphilitic lesions?
H. ducreyi chancres are very painful and tend to have ragged edges, whereas T. pallidum chancres are shallow, indurated, painless ulcers.
What is the sturcture of Legionella?
Unencapsulated slender rods that may appear coccobacillary.
How many different species of Legionella exist?
34
Which species is responsible for 90% of human disease caused by Legionella?
Legionella pneumophilia
What is the primary reservoir of Legionella?
Environmental water sources that contain stagnant water such as air conditioners.
How is Legionella transmitted?
Inhalation of aerosolized organisms.
Why is Legionella occasionally transmitted by swimming in pools?
It is chlorine tolerant
What type of immune response prevents Legionella infection?
Innate immunity
How does innate immunity prevent Legionella infection?
Alveolar macrophages phagocytose bacteria, normally killing the organism.
What allows Legionella to be pathogenic?
Failure of fusion between the phagosome and lysosome allows bacteria to multiply with the protected environment of the phagosome until it ruptures, releasing bacteria.
What two infections are caused by Legionella?
1) Legionnaire's disease
2) Pontiac fever
What is Legionnaires' disease?
An atypical pneumonia with a lobar distribution
What percentage of patients exposed to Legionella develop Legionnaires' disease?
1-5%
Which populations are most susceptible to Legionella infection?
Elderly,
Smokers
Alcoholics
Immune-suppressed individuals
What type of sputum is seen in Legionella pneumonia?
Scant and nonpurulent
What does Gram stain of sputum from a person with Legionella pneumonia demonstrate?
Neutrophils without bacteria
What nonrespiratory clinical findings accompany Legionella infection?
Confusion
Fever
Malaise
Myalgias
Anorexia
Diarrhea
Proteinuria
Hematuria
Death
What metabolic abnormality is commonly associated with Legionella pneumonia?
Hyponatremia
What is the fatality rate for Legionnaires' disease?
5-30%
What is Pontiac fever?
An influenza-like illness
How is Legionella diagnosed?
1) Culture
2) Serology
Which method is the gold standard for diagnosis of Legionella?
Culture
What are the culture requirements for Legionella?
Special medium containing buffered charcoal yeast extract with iron and L-cysteine.
How is Legionella diagnosed by serology?
Antibody titers or urine antigen detection.
What role does Gram stain have in the diagnosis of Legionella?
A minor one because Legionella stains poorly with Gram stain.
What is the treatment for Legionella?
Legionnaires' disease is treated with erythromycin or azithomycin and supportive therapy; Pontiac fever is treated symptomatically.
What is the structure of Bordetella?
Small, encapsulated coccobacillus that grows singly or in pairs.
How are serotypes of Bordetella distinguished?
Cell-surface molecules called agglutinogens.
What does bortetella pertussis cause?
Whooping cough
How is B. pertussis transmitted?
Respiratory droplets (highly contagious)
What populaation is most susceptible to B. pertussis infection?
Infants and children
How does B. pertussis interact with the respiratory epithelium?
Attaches to cilia without invading the tissue, producing toxins and virulence factors that eventually cause cilia to die.
What is the major toxin produced by B. pertussis?
Pertussis toxin
What is the structure of pertussis toxin?
Two subunits, including an enzymatically active A subunit and a B subunit that bind host cells.
What is the function of the A subunit of B. pertussis?
Stimulates adenylate cyclase resulting in increase camp by adenosine diphosphate (ADP) ribosylating (and therefore inactivating) Gi, the inhibitory subunit of the G protein.
What makes pertussis toxin pathogenic?
1) Lymphocytosis
2) Increased histamine sensitivity
3) Insulin secretion secondary to pancreatic Beta-islet cell activation resulting in hypoglycemia.
What are five other virulence factors produced by B. pertussis?
1) Filamentous hemagglutinin
2) Adenylate cyclase toxin
3) Dermonecrotic toxin
4) Tracheal toxin (peptidoglycan)
5) Agglutinogens
What is the mechanism of Filamentous hemagglutinin in B. pertussis?
Allows bacteria to attach to ciliated epithelial cells.
What is the mechanism of Adenylate cyclase toxin of B. pertussis?
Taken up by leukoctes, causing excessive accumulation of intracellular cyclic adenosine monophosphate (cAMP), resulting in decreased chemotaxis and phagocytosis of bacteria.
What is the mechanism of Dermonecrotic toxin of B. pertussis?
Vasoconstriction and ischemic necrosis.
What is the mechanism of Tracheal cytotoxin of B. pertussis?
Inhibits cillia movement and regeneration of damaged cells.
What is the mechanism of Agglutinogens of B. pertussis?
Facilitates attachment of bacteria to host cells.
What part of the respiratory tract does B. pertussis infect?
Tracheobronchioles.
What is the incubation period for pertussis?
1-3 weeks
What are the three stages of whooping cough?
1) Catarrhal phase
2) Paroxysmal phase
3) Convalescent phase
What are the symptoms of the catarrhal phase of pertussis?
Nonspecific symptoms, including copious rhinorrhea, conjunctival infection, malaise, fever,and nonproductive cough.
What are the symptoms of the paroxysmal phase fo pertussis?
Paroxysmal, productive hacking cough which often ends with an inspiratory "whoop" and ma last up to 4 weeks.
What are the symptoms of the convalescent phase?
Less-frequent and less-severe coughing episodes with gradual resolution after 1-3 months.
How is B. pertussis infection diagnosed?
Clinical suspicion with marked lymphocytosis.
How is pertussis confirmed?
Culture of B. pertussis from nasopharynx of symptomatic patient or direct fluorescent antibody test.
Blood cultures will always be negative.
What type of medium is required for growth of B. pertussis?
Selective agar medium containing blood and charcoal supplemented with antibiotics to inhibit growth of other normal flora of the nasopharynx.
What is the treatment for B. pertussis?
Erythromycin and supportive therapy.
What two vaccines are available for B. pertussis?
1) Acellular vaccine containing proteins from inactivated pertussis toxin
2) Killed whole cells
Which vaccine for B. pertussis is approved for use in the US?
Acellular vaccine usually given with diptheria and tetanus toxoids in 3 doses beginning at 2 months of age.
(DTaP)