18 Questions
What is a common way for microbes to gain access to the body?
Through openings in the skin, such as hair follicles and sweat gland ducts
Which of the following can establish a parenteral route of entry?
Punctures, injections, or wounds
Why is the portal of entry important for microbes?
Because it affects the type of disease that will occur
Which of the following mucous membranes is most susceptible to microbial penetration due to its delicacy?
Conjunctiva
What determines the likelihood of disease when microbes enter the body?
The number of microbes that enter
What is the primary mechanism by which microorganisms bypass host defenses in the skin?
Through cuts and wounds
How can microbes infect the skin?
By infecting the keratin in skin
Which of the following routes of infection is also known as the parenteral route?
Direct deposition beneath the skin or membranes
What is required for microbes to cause disease?
A large number of microbes must enter the body
Which portal of entry is specific to sexually transmitted infections?
Genitourinary tract
What is the primary mechanism by which microorganisms damage host cells?
Production of toxins that disrupt cellular function
Which of the following is a characteristic of mucous membranes that makes them prone to microbial penetration?
Delicate membrane structure
What is the primary function of the M protein produced by Streptococcus pyogenes?
To mediate attachment and resist phagocytosis
Which of the following mechanisms is used by some pathogens to obtain free iron from the host?
Secretion of siderophores to bind iron
What is the primary function of capsules in bacterial pathogens?
To impair phagocytosis and resist host defenses
Which of the following enzymes is involved in the breakdown of fibrin and facilitation of bacterial movement?
Kinase
What is the primary function of mycolic acid in Mycobacterium tuberculosis?
To resist digestion by phagocytes
Which of the following mechanisms is used by some pathogens to damage host cells?
Direct damage through the production of toxins
Study Notes
Portals of Entry
- Microorganisms can enter the body through: mucous membranes, skin, and direct deposition beneath the skin or membranes (parenteral route)
- Mucous membranes are a common portal of entry, including: respiratory tract, gastrointestinal tract, genitourinary tract, and conjunctiva
- Skin is the largest organ in terms of surface area and weight, and can be penetrated by microorganisms
Protecting Against the Host's Defenses
- Bacterial capsules can resist phagocytosis, a process by which certain cells engulf and destroy microorganisms
- Examples of bacteria with capsules include: Streptococcus pneumoniae
- Cell wall components can also contribute to virulence, such as:
- Streptococcus pyogenes producing M protein, which mediates attachment and resists phagocytosis
- Mycobacterium tuberculosis producing waxy lipid (mycolic acid), which resists digestion by phagocytes
Enzymes and Toxins
- Some bacteria produce extracellular enzymes (exoenzymes) that aid in virulence
- Examples of enzymes include:
- Coagulases, which coagulate fibrinogen into fibrin to protect the bacterium from phagocytosis
- Kinases, which break down fibrin and allow bacteria to move further
How Pathogens Damage Host Cells
- Pathogens can damage host cells by:
- Using the host's nutrients, such as iron, by producing siderophores
- Directly damaging host cells
- Producing toxins
Number of Invading Microbes
- The likelihood of disease increases as the number of pathogens increases
- A small number of microbes may be overcome by the host's defenses, but a large number can set the stage for disease
This quiz covers the mechanisms of bacterial pathogenesis, including the role of capsules in resisting host defenses and cell wall components that contribute to virulence.
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