Bacterial Infection and Human Microbiota Quiz

Study Notes

Bacterial infection occurs when the balance between bacterial virulence and host resistance is disrupted.
While bacteria's primary goal is to multiply, only 50 out of over 1000 bacterial species residing in humans typically cause disease.
Normal microbiota refers to the microorganisms inhabiting the skin and mucous membranes of healthy individuals.
Normal microbiota plays a crucial role in defending against pathogens, aiding digestion and contributing to immune system maturation.
Microbiota can be categorized as resident and transient.
Resident microbiota are fixed types of microorganisms normally found in a specific area, while transient microbiota are nonpathogenic or potentially pathogenic microorganisms that reside temporarily.

Pathogens can be classified as primary pathogens or opportunistic pathogens.
Primary pathogens can cause disease in healthy individuals, such as Mycobacterium tuberculosis causing tuberculosis.
Opportunistic pathogens cause disease only in immunocompromised individuals or when they leave their usual habitat.
Examples of opportunistic infections include Staphylococcus epidermidis causing infections in hospitalized patients, E. coli causing UTIs, and viridans Streptococci causing infective endocarditis.

The infectious process requires the pathogen to gain entry, reach the infection site, evade the immune system, and cause damage.
Adherence to host cells, usually epithelial cells, is the initial step in establishing infection.
Bacteria multiply and spread through tissues or the lymphatic system to the bloodstream, allowing for widespread infection.

These factors enable bacteria to invade the host, evade defense mechanisms, and cause disease.
Adherence factors like pili and teichoic acid aid bacteria attachment to host cells.
Invasion allows bacteria to penetrate and multiply within tissues.
Antiphagocytic factors help bacteria evade phagocytosis, such as surface protein A in Staphylococcus aureus and capsules in S. pneumoniae and N. meningitidis.
Toxin production involves endotoxins (LPS) in Gram-negative bacteria and exotoxins secreted by bacterial cells.
Extracellular enzymes, like coagulase in S. aureus and hyaluronidases, aid in tissue damage and spreading.
Bacterial biofilms provide a protective matrix for bacteria, making infection persistent and difficult to treat.
Intracellular survival enables bacteria like Mycobacterium tuberculosis to live and grow inside phagocytic cells.

Bacteria can adapt to various environments, including external reservoirs and host organisms.
Portals of entry, such as the respiratory tract, oral cavity, and skin, allow pathogens to enter the body.
Transmission modes include contact transmission (direct or indirect), vehicle transmission (water, food, air), and vector transmission (arthropods).
Contact transmission includes direct contact (horizontal, vertical, droplet) and indirect contact (fomites).
Vehicle transmission involves pathogens transmitted through vehicles like water, food, and air.
Vector transmission utilizes arthropod carriers to transmit pathogens from one host to another.
For infection persistence, bacteria need to exit the infected host through portals of exit, typically the skin and various tracts.