Haemophilus aegyptius, Aggregatibacter aphorphilus, Haemophilus ducreyi.

Question 1

Haemophilus aegyptius: morphology and identification

Answer 1

Haemophilus aegyptius is a small, pleomorphic, Gram-negative coccobacillus. It closely resembles H. influenzae but is non-encapsulated. It requires both X (hemin) and V (NAD) factors for growth, so it grows on chocolate agar but not on blood agar. It is associated with purulent conjunctivitis and Brazilian purpuric fever.

Question 2

Haemophilus aegyptius: clinical significance

Answer 2

It causes acute, contagious conjunctivitis, especially in children, known as ‘pink eye.’ A more severe form called Brazilian purpuric fever (BPF) includes high fever, purpura, vomiting, septicemia, and shock, and can be fatal. BPF occurs in children and is caused by a specific clone of H. aegyptius.

Question 3

Aggregatibacter aphrophilus: morphology and classification

Answer 3

Previously classified as Haemophilus aphrophilus, it is now part of the HACEK group (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella). It is a facultatively anaerobic, Gram-negative coccobacillus that does not require X or V factor for growth. Colonies may have a musty odor due to production of indole and other metabolites.

Question 4

Aggregatibacter aphrophilus: clinical significance

Answer 4

It is part of the normal oral flora but can cause endocarditis, especially in patients with underlying heart disease or prosthetic valves. It is a rare but important cause of culture-negative endocarditis and may also cause brain abscesses or other head and neck infections. It grows slowly and may require enriched media for detection.

Question 5

Haemophilus ducreyi: morphology and identification

Answer 5

Haemophilus ducreyi is a small, Gram-negative coccobacillus arranged in ‘school of fish’ or ‘railroad track’ patterns on Gram stain. It is fastidious and grows on special enriched media (e.g., chocolate agar with vancomycin). Requires X factor but not V factor. It is non-motile, oxidase-negative, and catalase-negative.

Question 6

Haemophilus ducreyi: clinical significance

Answer 6

It is the causative agent of chancroid, a sexually transmitted infection characterized by painful genital ulcers with ragged edges and tender inguinal lymphadenopathy (buboes). The ulcers bleed easily and are soft (as opposed to the hard chancre of syphilis). It is more common in tropical areas with poor hygiene and is associated with increased risk of HIV transmission.

Question 7

Haemophilus ducreyi: diagnosis and treatment

Answer 7

Diagnosis is clinical and confirmed by culture of lesion swabs on specialized media, though culture is often difficult. PCR and immunologic tests may also be used. Treatment includes azithromycin (single dose), ceftriaxone (IM), ciprofloxacin, or erythromycin. Partner treatment and STI screening are also important.