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Questions and Answers
Which mechanism allows pathogens to attach to host cells effectively?
Which mechanism allows pathogens to attach to host cells effectively?
- Inhibition of immune response through toxins
- Random engagement with cellular membranes
- Production of cryptic proteins
- Adherence through flagella and fimbriae by Gram - bacteria (correct)
What is a significant feature of exogenous sources of infectious diseases?
What is a significant feature of exogenous sources of infectious diseases?
- Only caused by viral infections
- Transmission solely through the respiratory system
- Involves vectors such as animals and insects (correct)
- Results from the host's normal flora
Which property is characteristic of Gram negative organisms regarding their toxins?
Which property is characteristic of Gram negative organisms regarding their toxins?
- Their toxins are primarily neurotoxins
- Endotoxic activity is due to LPS found in their cell wall (correct)
- They produce exclusively A-B toxins
- They do not elicit fever or septic shock
How do some pathogens evade the host immune response effectively?
How do some pathogens evade the host immune response effectively?
What is a common consequence of toxin production by certain bacteria such as Clostridium difficile?
What is a common consequence of toxin production by certain bacteria such as Clostridium difficile?
Which of the following correctly describes antibiotic resistance mechanisms?
Which of the following correctly describes antibiotic resistance mechanisms?
What role does the LPS in Gram negative bacteria play during infection?
What role does the LPS in Gram negative bacteria play during infection?
Which bacterial structure is responsible for the adherence of Gram positive bacteria?
Which bacterial structure is responsible for the adherence of Gram positive bacteria?
What is a primary method by which HIV enters host cells?
What is a primary method by which HIV enters host cells?
How do certain pathogens like Staphylococcus aureus kill phagocytes effectively?
How do certain pathogens like Staphylococcus aureus kill phagocytes effectively?
Flashcards
Bacterial Adherence Mechanisms
Bacterial Adherence Mechanisms
Gram-positive bacteria adhere to cells via peptidoglycans, while gram-negative bacteria use antigens on flagella, pili, or fimbriae.
Viral Adherence
Viral Adherence
Viruses attach to specific host cell receptors or proteins on the cell surface, using their capsid, like HIV with CD4 cells or Covid-19 with ACE2.
Exogenous Infections
Exogenous Infections
Infections transmitted from an external source, such as contaminated surfaces (fomites), animals & insects, or other humans.
Endogenous Infections
Endogenous Infections
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Toxin Production in Bacteria
Toxin Production in Bacteria
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Immune Evasion Mechanisms
Immune Evasion Mechanisms
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Antibiotic Resistance
Antibiotic Resistance
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Bacterial Multiplication
Bacterial Multiplication
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Transmission
Transmission
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Pathogen Survival within Phagocytes
Pathogen Survival within Phagocytes
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Study Notes
Infectious Diseases: Transmission and Virulence
- Infectious diseases are transmitted through various mechanisms
- Key mechanisms include encounter, adherence, evasion of the immune system, multiplication and spread, cell/tissue damage, and shedding
- Sources of infection can be exogenous (external) or endogenous (internal)
- Exogenous sources include fomites (inanimate objects), animal and insect vectors (like Lyme disease), and other humans (influenza, tuberculosis)
- Endogenous sources include commensal organisms in the body (skin, intestines, nasal passages)
- Most organisms have a defined survival time outside a host, except some fungi and bacteria (like anthrax) which can form spores for extended survival
Adherence
- Viruses typically adhere to specific receptors on host cells; examples include COVID-19 (ACE2 receptor) and HIV (CD4 receptor)
- Gram-positive bacteria adhere via peptidoglycans in their cell wall
- Gram-negative bacteria adhere through antigens on structures like flagella, pili, or fimbriae.
Spread/Multiplication
- Some bacteria produce toxins (e.g., E. coli, C. difficile, superantigens-Staph)
- Others secrete enzymes that contribute to spread and multiplication (e.g., streptolysin, proteases, lipoproteins)
Toxin Production
- Gram-negative bacteria produce endotoxins (LPS) which cause fever, permeability changes, and septic shock
- A-B toxins are another type of toxin, including those from C. tetani (synaptic transmission) and Vibrio cholerae (ADP ribosylation)
Evading Host Immune Response
- Some pathogens inhibit chemotaxis, kill phagocytes (A-toxin), or avoid ingestion (LPS, capsule of Strep)
- Others avoid complement lysis by coating themselves with IgA antibodies (Nisseria) or survive within phagocytes (inhibiting endosome-lysosome fusion in Chlamydia, NADPH oxidase in Salmonella, H+-ATPase in tuberculosis)
Survival Within Host Phagocyte
- Some pathogens inhibit endosome-lysosome fusion in order to prevent degradation inside phagocytes (Chlamydia)
- Others inhibit NADPH oxidase (Salmonella) or endosomal H+-ATPase (Tuberculosis).
Antibiotic Resistance
- Mechanisms of antibiotic resistance include inducing or modifying enzymes that inactivate drugs (penicillinase)
- Other resistance mechanisms include multidrug resistant transporters and altered metabolic function. Horizontal gene transfer (phage transfer) also plays a role in resistance
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