Which type of pathogen is more likely to cause disease in a healthy individual?

Pathogenic bacteria are typically well-adapted to invade host tissues, overcome the host's immune defenses, and cause disease. They possess specific virulence factors that enhance their ability to infect and cause harm in healthy individuals. These factors may include toxins, adherence factors, and mechanisms to evade immune responses.

In comparison, commensals usually exist in a mutualistic relationship with the host and typically do not cause disease. Opportunistic pathogens usually only cause infections in individuals with compromised immune systems or underlying health issues, rather than in healthy individuals. Non-pathogenic viruses do not typically cause disease, as they have not evolved mechanisms to harm a host organism.

Thus, pathogenic bacteria are the most likely to elicit disease symptoms in healthy individuals due to their evolved characteristics and capabilities for causing infections.