What characterizes an infection?

An infection is fundamentally characterized by the growth and proliferation of harmful pathogens, particularly bacteria, viruses, fungi, or parasites, within the body. This growth often leads to a variety of symptoms as the body responds to the invaders, indicating that the normal functioning of tissues is being disrupted. The presence of harmful bacteria is central to the definition of an infection, as they can cause damage to the host's tissues and trigger immune responses that manifest through various symptoms such as fever, inflammation, or localized pain.

Other choices highlight aspects that do not define an infection. For example, the growth of healthy tissue generally indicates healing rather than infection, while an absence of symptoms could imply that there is no active infection or that it is asymptomatic. Likewise, the healing of wounds suggests that an injury is being repaired, not that an infection is present. Therefore, the correct answer revolves around the detrimental effects and clinical manifestations arising from harmful bacteria's presence during an infection.