STEPTRACKERMICROBIOLOGY + PEDIATRICS | GRAM-NEGATIVE COCCOBACILLI | HIGH-YIELD REVIEW

Haemophilus, Bordetella & Moraxella

Small gram-negative coccobacilli of the airway — the capsule that vaccines conquered, the toxin behind whooping cough, and a common otitis cause.

FOCUS ON
H influenzae: needs factors V (NAD⁺) and X (hematin) (chocolate agar). Type b capsule (polyribosylribitol phosphate) → epiglottitis, meningitis, septic arthritis in unvaccinated children; nontypeable → otitis, sinusitis, COPD exacerbations. Hib conjugate vaccine at 2–18 months. H ducreyi → painful chancroid ulcer. B pertussis: catarrhal → paroxysmal (whoop, post-tussive vomiting) → convalescent; lymphocytosis; macrolides. Moraxella catarrhalis → otitis, sinusitis, COPD.
ORGANISM · DISEASE
FEATURES · VIRULENCE
CLINICAL PICTURE
CLUE · TREATMENT
Hib — epiglottitis
Capsule (PRP), IgA protease
Unvaccinated child: high fever, drooling, tripod position, muffled voice, stridor
"Thumbprint sign" · secure airway, ceftriaxone
Hib — meningitis
Was #1 in children before vaccine
Fever, irritability, bulging fontanelle
Ceftriaxone · rifampin for contacts
Nontypeable H influenzae
No capsule; mucosal
Otitis media, sinusitis, conjunctivitis, bronchitis, COPD exacerbations
Amoxicillin-clavulanate (β-lactamase common)
Hib vaccine
PRP conjugated to a protein (diphtheria/tetanus toxoid)
T-cell–dependent response in infants
Given 2–18 months
H ducreyi — chancroid
Sexual transmission
Painful ragged ulcer with gray base + painful suppurative inguinal nodes
Painful, unlike syphilis · azithromycin or ceftriaxone
Pertussis — catarrhal stage
Filamentous hemagglutinin, pertussis toxin (Gi off), tracheal cytotoxin
1–2 weeks of cold-like symptoms; most contagious
Treat now (azithromycin) to cut spread
Pertussis — paroxysmal stage
Ciliary damage
Coughing fits, inspiratory whoop, post-tussive vomiting, cyanosis; infants may have apnea
Marked lymphocytosis · PCR of nasopharynx
Pertussis — convalescent
Recovery
Cough fades over weeks ("100-day cough")
Antibiotics don't shorten this stage
Pertussis prevention
Acellular vaccine (DTaP children, Tdap adults)
Waning immunity → adolescent/adult cases
Tdap each pregnancy (27–36 weeks) protects newborns
Moraxella catarrhalis
Gram ⁻ diplococcus, β-lactamase ⁺
Otitis media, sinusitis, COPD exacerbation
Amoxicillin-clavulanate
Haemophilus in HACEK
Haemophilus (parainfluenzae) is part of HACEK
Culture-negative endocarditis
See 4.09

Mechanism — why lymphocytosis in pertussis

Pertussis toxin
→
ADP-ribosylates GiInhibitory signal lost
→
↑ cAMP in leukocytes
→
Lymphocytes can't leave bloodMarked lymphocytosis

Otitis media organisms

ORGANISM
FEATURE
NOTE
S pneumoniae
Most common
Gram ⁺ diplococci
Nontypeable H influenzae
2nd
β-lactamase
Moraxella catarrhalis
3rd
β-lactamase

How it's tested

COMMON CONFUSIONEpiglottitis (Hib; toxic, drooling, thumbprint) vs croup (parainfluenza; barking cough, steeple sign, well-appearing).
THE TRAPNever examine the throat of a child with suspected epiglottitis outside the OR — it can trigger complete obstruction.
YOUR APPROACHCoccobacillus + airway setting → vaccinated? → capsule type → age and stage → macrolide or β-lactam.

If you see… think…

Unvaccinated drooling child, tripod position, thumbprint sign → Hib epiglottitis
Needs both V and X factors → H influenzae
COPD exacerbation organism (besides pneumococcus) → nontypeable H flu, Moraxella
Painful genital ulcer with painful nodes → chancroid (H ducreyi)
Coughing fits with whoop and vomiting, lymphocytosis → pertussis
Pertussis treatment and contact prophylaxis → azithromycin
Toxin disabling Gi → pertussis toxin
Vaccine given in each pregnancy to protect newborns → Tdap
β-lactamase ⁺ gram ⁻ diplococcus causing otitis → Moraxella
Conjugate vaccine turning a polysaccharide T-dependent → Hib (PRP)