Final answer:
The most common cause of infective endocarditis is bacteria (option 2) , particularly gram-positive cocci and the HACEK group. Individuals with heart damage or prosthetic valves are at higher risk, and the condition can manifest as either acute or subacute endocarditis.
Step-by-step explanation:
The most common cause of infective endocarditis is bacteria. This condition occurs when the endocardium, the tissue layer that lines the heart's muscles and valves, becomes infected. The most frequent bacterial culprits include gram-positive cocci such as Staphylococcus aureus, viridans streptococci, and Enterococcus faecalis, as well as the gram-negative HACEK group of bacteria. Infective endocarditis can be acute or subacute, with acute endocarditis often being more severe and rapid in the destruction of heart valves than subacute. Individuals at higher risk include those with previous heart damage, prosthetic valves, cardiac devices, and a history of rheumatic fever.
Streptococcus pyogenes, the bacterium responsible for rheumatic or scarlet fever, can also cause valvular disorders due to the autoimmune response it triggers. Such conditions can lead to carditis, or inflammation of the heart, compounding the risk of endocarditis. In cases of subacute bacterial endocarditis, vegetations form on the heart valves over time, leading to potential heart valve replacement due to damage caused by both the infection and the immune response.