Haemophilus aphrophilus

Haemophilus aphrophilus is a species of bacteria that is part of the normal flora of the human oral cavity and pharynx. It is a small, pleomorphic, Gram-negative coccobacillus. This bacterium is considered to be an opportunistic pathogen, meaning that while it is normally harmless, it can cause disease in individuals with weakened immune systems or with underlying health conditions. Haemophilus aphrophilus is associated with endocarditis, an infection of the inner lining of the heart chambers and heart valves, and has also been implicated in other infections such as brain abscesses and periodontal diseases.

Characteristics

Haemophilus aphrophilus is characterized by its requirement for the V factor (nicotinamide adenine dinucleotide or NAD) for growth, but unlike some other members of the Haemophilus genus, it does not require the X factor (hemin). It grows best at 35-37°C in a carbon dioxide-enriched atmosphere, which is similar to conditions found in the human respiratory tract. On blood agar, it may produce small, translucent colonies.

Pathogenesis

The pathogenic mechanism of Haemophilus aphrophilus involves colonization of the oral and pharyngeal mucosa, from which it can enter the bloodstream, especially in individuals with dental infections or those undergoing dental procedures. Once in the bloodstream, it can disseminate to various parts of the body, including the heart, where it can contribute to the formation of vegetations on heart valves, leading to infective endocarditis. The bacterium's ability to adhere to surfaces and form biofilms contributes to its pathogenicity and resistance to the host's immune responses.

Clinical Significance

Haemophilus aphrophilus is a notable cause of infective endocarditis, particularly in individuals with pre-existing heart conditions or those who have undergone dental procedures without appropriate antibiotic prophylaxis. Diagnosis of infections caused by this bacterium involves culturing from blood or tissue samples and identifying the organism based on its growth characteristics and biochemical properties. Treatment typically involves prolonged courses of antibiotics, and in cases of endocarditis, surgery may be required to repair or replace damaged heart valves.

Prevention

Preventive measures against infections caused by Haemophilus aphrophilus include maintaining good oral hygiene and ensuring appropriate antibiotic prophylaxis before dental procedures in individuals at high risk of infective endocarditis. Public health initiatives aimed at improving oral health can also contribute to reducing the incidence of infections caused by this bacterium.

See Also

• Endocarditis
• Opportunistic infection
• Oral microbiology
• Biofilm