"Pathogenic" refers to organisms, particularly microorganisms like bacteria, viruses, fungi, and parasites, that can cause disease in a host. These pathogens invade the body, multiply, and disrupt normal bodily functions, leading to various health issues. Common examples of pathogenic bacteria include Staphylococcus aureus and Escherichia coli, while viruses like influenza and HIV are also well-known pathogens. The study of pathogenic organisms is crucial in fields like microbiology and medicine, as it helps in understanding how diseases spread and how to prevent or treat infections. Vaccines and antibiotics are essential tools developed to combat pathogenic threats and protect public health.