Although less than 1% of prokaryotic species are human pathogens, they cause a substantial number of human diseases by invading the body, producing toxins, or causing infections. This host-pathogen interaction represents a parasitic relationship, giving rise to diseases such as tetanus, diphtheria, pertussis, tuberculosis, and leprosy.

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Pathogenic bacteria are bacteria that can cause infectious disease.

Pathogenic Bacteria

Parasitism is a type of symbiosis where one organism or population benefits and the other is harmed.

Parasitism 

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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Virulence is the degree to which an organism is pathogenic. Highly virulent pathogens will almost always lead to a disease. Less virulent pathogens may cause an initial infection, but they do not always cause severe illness. Some individuals might even be asymptomatic. Two important indicators of virulence are:
- the median infectious dose (ID50) 
- the median lethal dose (LD50)

Virulence

There are four stages of pathogenesis. The pathogen must be able to gain entry to the host, travel to the location where it can establish an infection, evade or overcome the host’s immune response, and cause disease to the host.
- exposure (contact)
- adhesion (colonization)
- invasion
- infection.

Stages of Pathogenesis

A disease is any condition in which the normal structure or function of the body is damaged or impaired.

Disease

- Opportunistic pathogen
- Primary pathogen

Types of Pathogens

Which of the following statements correctly describes pathogenic bacteria?

Which of the following is a characteristic of pathogenic bacteria?

Which of the following is an example of a disease caused by pathogenic bacteria?

Which of the following methods can be used to prevent infections caused by pathogenic bacteria?

Prokaryotes as Human Pathogens

A pyogenic pathogen is a bacterium or microorganism that is associated with the production of pus during infections.

Pyogenic Pathogen

*Clostridium tetani* causes the disease tetanus. *C. tetani* makes a neurotoxin that can interact with the neurons in the central nervous system and inhibit nerves causing paralysis. This benefits the survival of the pathogen but is life threatening for the host. 

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