Which of the following is an example of a pathogen?

A pathogen is defined as any organism or agent that can cause disease in a host, and bacteria fit this definition perfectly. Bacteria are single-celled microorganisms that can be found in various environments and can lead to various infections and diseases in humans, animals, and plants. Pathogens include a range of organisms such as viruses, fungi, and parasites, but bacteria are one of the most commonly recognized groups in the context of infectious disease.

The other options do not fit the definition of a pathogen. Chemical agents refer to substances that can cause harm through chemical means, but they do not classify as living organisms. Explosive materials are substances designed to cause explosions and do not lead to disease. Nerve agents are a type of chemical weapon that disrupts the nervous system, but they are not classified as pathogens since they do not multiply or evolve as living organisms do. Therefore, the identification of bacteria as a pathogen is accurate in the context of this question.