Gram Negative: Haemophilus, Bordetella, & Legionella Flashcards
What do species of Haemophilus, Bordetella, and Legionella have in common? What diseases does each major species cause?
- these are all Gram negative rods that are acquired via the respiratory tract
- H. influenzae causes septic arthritis and meningitis in children, pneumonia, epiglottitis
- H. ducreyi causes chancroid
- B. pertussis causes whooping cough
- L. pneumophila causes Pontiac fever and Legionnaire’s disease/pneumonia
What does Haemophilus influenzae require for culture/growth? Which patients are usually affected? What is its major virulence factor?
- Haemophilus: “blood loving”; requires blood-containing medium for growth
- this is an obligate human parasite that often attacks the lungs of people debilitated by an underlying viral influenza infection; also affects children
- major VF: polysaccharide capsule (allows for invasion); 6 serotypes (a through f)
What do we mean by “non-typeable” Haemophilus influenzae? What diseases it is associated with?
- these species lack the polysaccharide capsule and are therefore unable to be serotyped via this virulence factor
- they cause otitis media in children as well as COPD exacerbations
Why are children at an increased risk for infection with Haemophilus influenzae?
- (particularly it is for H. influenzae serotype b)
- because the antibodies to the polysaccharide capsule are lacking between 6 months and 3 years of age
Hib
- H. influenzae serotype b
- causes meningitis, epiglottitis, septic arthritis, and sepsis in children
- Hib is inhaled, invades local lymph nodes and bloodstream, can then penetrate meninges, joints, etc.
- Hib meningitis is the most serious disease presentation of this organism
- Hib is the most common cause of septic arthritis in infants
How do patients with Hib induced meningitis present?
- these are usually children (between ages of 6 months and 3 years)
- they usually do NOT present with the classic stiff neck
- look for fever, vomiting, and altered mental status
What percentage of patients with Hib meningitis will have residual deficits? What causes this? How can we prevent this?
- 50% will have residual deficits (deafness, epilepsy, etc.)
- this is because when the bacteria die, they release cellular antigens (the LPS endotoxin), causing a violent, damaging immune reaction
- help prevent by giving prophylactic corticosteroids 15-20 minutes before IV antibiotics are given
Which organisms are largely responsible for meningitis in children (between 6 months and 3 years)? What about in neonates?
- children: Hib and Neisseria meningitides
- neonates: E. coli, group B Strep (Strep. agalactiae), Listeria monocytogenes
What disease does Hameophilus ducreyi cause? What does the disease entail? What are some major differentials?
- H. ducreyi causes chancroid; this is a painful genital ulcer that can rapidly progress to coexisting unilateral painful swollen inguinal lymph nodes (suppurative; risk of rupture)
- DDx: syphilis via Treponoma pallidum (genital ulcer is painless; lymph involvement is bilateral, painless, non-suppurative); lymphogranuloma venerum via Chlamydia trachomatis (LGV; lymph involvement is slower and painless, ulcer disappears before the lymph involvement); herpes via HSV (lesions are initially vesicles; systemic signs are common)
What percentage of endocarditis is attributed to Haemophilus infection?
- 5%
- this is one of the HACEK organisms (slow growing bacteria that can cause endocarditis)
- (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, Kingella)
What disease does Gardnerella vaginalis cause? How do we treat it?
- causes bacterial vaginitis (burning/pruritis of labia, dysuria, copious fishy foul-smelling vaginal discharge)
- treat with metronidazole
What organism causes whooping cough? What are the major virulence factors of this organism?
- Bordetella pertussis
- pertussis toxin: increases cAMP to cause histamine sensitization
- extra adenylate cyclase: increases cAMP to inhibit WBC chemotaxis and phagocytosis
- FHA (filamentous hemagglutinin): attaches to ciliated epithelial cells in bronchi
- tracheal cytotoxin: destroys ciliated cells (results in loss of airway defenses)
What is whooping cough? What are the three stages of this disease?
- whooping cough is a highly contagious infectious disease; 1 week incubation/prodrome followed by 3 stages
- 1) catarrhal stage: 1-2 weeks; a mild upper resp tract infection, this is the most contagious stage
- 2) paroxysmal stage: at least 1 month; fever subsides, rapid onset of bursts of nonproductive cough w/ inspiratory gasps (the “whoops”) due to narrowed glottis
- 3) convalescent stage: about 1 month; coughing attacks decrease in frequency, patient is no longer contagious
In a patient with whooping cough, what are some complications that can occur with each bout of coughing?
- these bouts are extremely intense and lead to temporary developments of hypoxemia and cyanosis
- during the cough, the patient’s eyes bulge and neck veins enlarge
- vomiting after a bout is common
How do we collect and culture Bordetella pertussis?
- (B. pertussis causes whooping cough)
- this organism does not grow on cotton, so instead of the normal cotton swab, use a calcium alginate swab
- culture on Bordet-Gengou medium (contains potato, blood, and glycerol agar)
