Lecture 13 Haemophilus, Bordetella, Mycoplasma, Legionella Flashcards
What is Haemophilus influenzae?
Gram-negative coccobacillus, oxidase positive, facultative anaerobe, and non-motile. Frequently encapsulated (types a-f).
What are some susceptible hosts of H influenzae?
-High rate of healthy pediatric and adult carriers
-primarily pediatric pathogen,
initial protection by maternal antibody,
-peak incidence of infection 6 mo-18 mo of age
What are some virulence factors of H influenzae?
- pili and fimbriae for attachment
- capsule is antiphagocytic (Type b)
- IgA proteases
- can cross epithelial barrier, giving it capcity for vascular invasion.
How is H influenzae transmitted?
-transmission from person to person by respiratory droplets and direct contact with resp. secretions
How is H influenzae treated in pediatrics?
-vaccine: protein-linked PRP (invoke T cells!), very effective (given @ 2 months old)
What are some risk factors of H influenzae infection?
- complement deficiency, hypogammaglobulinemia, sickle cell anemia, functional asplenia, malignancy, HIV
- In adults, chronic pulmonary disease, smoking, HIV alcoholism, pregnancy, malignancy
- Socioeconomic factors: crowding, poor immunization, daycare attendance
What is non-typeable H influenzae?
- non-capsulated strains that are common constituents of nasopharyngeal microbiota
- cause localized disease: upper and lower respiratory tract infection, otitis media more
- severe disease in immunocompromised
How does H influenzae cause Otitis Media/sinusitis?
-likely displacement of normal microbiota by pathogen, strains involved are frequently non-typeable
What is Epiglottitis (H influenzae)?
- fever, sore throat, barking cough
- Rapid progression (24 h)
- dx by lateral neck X-ray or blood cx
How can H Influenzae cause Meningitis?
- previous respiratory infection or various vague symptoms prior to onset
- likely route = respiratory tract, gets into blood, gets into CNS
- significant mortality even with antibiotic therapy, 1/3 survivors have neurological problems
What diseases can also occur with URI by H influenzae?
Cellulitis/arthritis
How is H Influenzae diagnosed?
culture and identify organism:
- Requires X factor (hemin)
- V factor (NAD) for growth
- CO2 –enriched atmosphere
- can grow on chocolate agar
What is Haemophilus ducreyii?
- coccobacillus, often irregularly shaped with central indentation
- Common sexually STD in developing countries
- Enhances HIV transmission.
What are effect of Haemophilus ducreyii?
Chancroid - soft chancre, painful
- satellite lesions
- painful, unilateral lymphadenopathy common
How is H ducreyii diagnosed?
- gram stain from
- culture possible on chocolate + vancomycin (33°C, 5% CO2)
- Must rule out syphilis by dark field and serology
What is Bordetella perussis?
- Gram-negative coccobacillus
- specifically colonizes and destroys ciliated respiratory epithelium of large airways
What are some virulence factors of Bordetella perussis?
- Filamentous hemagluttinin (FHA) and pili for attachment
- Tracheal Cytotoxin (TCT)
- Pertussis toxin (PT)
- Adenylate cyclase toxin (ACT)
- FHA, PT, ACT expression controlled by two-component regulatory system
- spread via aerosolized droplets
What is TCT?
toxic PG-fragment destroys ciliated cells via NO and IL-1 pathway
What is PT?
AB subunit toxin, ADP-ribosylates G protein leading to increased host cell cAMP -> alters lymphocyte homing and function -> lymphocytosis (high lymphocyte counts)
What is ACT?
catalyzes ATP->cAMP also hemolysin
What is whopping cough or pertussis?
- Disease of Bordetella pertussis
- severe disease for children (95%)
- asymptomatic carriage by adolescents and adults
- frequent cause of persistent (>2 wks) cough among adults
What are ways to treat Whooping cough?
- immunization: “P” part of DTaP (aP=acellular pertussis); administered at 2, 4, 6, 15-18 months; 4-6 yrs old)
What are some complication to whooping cough?
- pneumonia,
- death secondary to dehydration, -malnourishment,
- brain damage secondary to anoxia
What is the dx of Bordetella pertussis?
- clinical symptoms,
- lymphocytosis
- culture is optimal in 5% CO2, on selective media
- PCR: nasal swab
What is mycoplasma pneumoniae?
- smallest free-living bacterium
- pleomorphic filaments
- no cell wall, cell membrane contains sterols -strict aerobe
What diseases can M. pneumoniae cause?
Tracheobronchitis and pneumonia
What group is susceptible to Tracheobronchitis and pneumonia?
- predominantly children/adolescents
- military recruits
- college students
What is the mechanism of infection for M. pneuomoniae in causing tracheobronchitis and pneumonia?
- adhesin protein P1, necessary for attachment to ciliated respiratory epithelium
- attaches to host glycolipid or glycoprotein on respiratory epithelial cells
- destruction of ciliated respiratory epithelium, mucociliary escalator
How large is M. pneumonaie genome?
- Just know small compared to H. influenza and E. Coli
- small genome: 689 encoded proteins
What is the attack rate of M. pneumonaie in the respiratory tract?
- 90% cases upper respiratory tract: low fever, headache, malaise, non-productive cough
- 10% cases lower respiratory tract:
- tracheobronchitis
- atypical pneumonia
- secondary infection/superinfection
How do you dx M. pneumonaie?
- culture (slow and insensitive)
- PCR (rapid and sensitive)
- Serology: lack of specificity
What is Legionella pneumophila?
- pleomorphic GNR stains poorly with Gram stain
- Environmental bacterium
- facultative
- intracellular pathogen (amoeba)
- interaction with macrophage essential
- virulence gene expression -> macrophage death
- transmitted via contaminated aerosols
- no documented human to human spread
What is legionnaires disease?
- headache, myalgia, rising fever, cough without much sputum, severe necrotizing pneumonia, high mortality
What is Legionnaires disease incidences dependent on?
depends on water contamination; exposure to contaminated water; susceptibility of host
What are some risk factors to Legionnaires disease?
smoking and chronic lung disease; increasing age, hematopoietic transplantation, other forms of immunosuppression [glucocorticoid administration] but not patients with neutropenia, acute leukemia or HIV.
What is pontiac fever?
- (Legionnella) acute febrile illness without pneumonia
- attack rate 90% (healthy and immunocompromised)
How is legionella pneumonia diagnosed?
- direct fluorescent antibody staining (DFA)
- Gram stain (often fails
- culture: often negative
How is legionella treated?
erythromycin .
