CHAPTER 10

1.      The main types of symbioses between microbes and human hosts are mutualism, commensalism, and parasitism.

2.      Most microbes in the human body reside in the gastrointestinal tract, particularly the large intestine.

3.      Staphylococcus is commonly found on the skin and in the nasal passages. Streptococcus is found in the oral cavity and upper respiratory tract. Escherichia, Proteus, and Bacteroides are primarily found in the gastrointestinal tract. Lactobacillus is found in the gastrointestinal tract and the female genitourinary tract.

4.      The relationship between resident microbiota and their human host is primarily mutualistic or commensalistic. Resident microbiota typically benefits the host by competing with pathogens, aiding in digestion, and producing essential vitamins, while the host provides a stable environment and nutrients.

5.      Transient microbiota cannot permanently colonize due to competition from resident microbiota, elimination by the host's immune system, and changes in environmental conditions (e.g., pH, temperature, nutrient availability) that are not conducive to their long-term survival.

6.      Infants start acquiring their normal microbiota at birth, primarily through contact with the mother's vaginal and fecal microbiota during a vaginal delivery, or from the environment and skin microbiota during a C-section.

7.      Factors influencing the composition of normal microbiota over a lifetime include diet, age, geographical location, hygiene practices, antibiotic use, stress, hormonal changes, and exposure to environmental microbes.

8.      Conditions that provide opportunities for pathogens to infect them include immunosuppression, breaches in physical barriers (e.g., wounds, burns), changes in normal microbiota (e.g., antibiotic use), malnutrition, stress, and exposure to a high dose of virulent pathogens.

9.      The three main reservoirs for pathogens are humans, animals (zoonoses), and non-living environments (e.g., soil, water).

10. The reservoir for HIV is humans. The primary reservoir for Lyme disease is small mammals (especially mice) and deer. The reservoir for tetanus is soil and animal feces.

11. Asymptomatic human carriers are individuals who harbor a pathogen and can transmit it to others without exhibiting any signs or symptoms of the disease themselves.

12. The three main portals of entry for human pathogens are the skin, mucous membranes, and the parenteral route. The skin can be breached by cuts, abrasions, or insect bites. Mucous membranes line the respiratory, gastrointestinal, urinary, and reproductive tracts, providing moist surfaces for pathogen entry. The parenteral route involves direct deposition of pathogens into tissues beneath the skin or mucous membranes, such as through injections, bites, or wounds.

13. The most common portal of entry for human pathogens is the respiratory tract, which is a type of mucous membrane.

14. Attachment proteins, or adhesins, are virulent factors found on the surface of pathogens that enable them to bind specifically to receptor molecules on the host cell surface. This attachment is crucial for colonization and initiating infection, preventing the pathogen from being washed away by host defenses.

15. Morbidity refers to the incidence of disease in a population, indicating the state of being diseased or unhealthy. Mortality refers to the incidence of death in a population, indicating the death rate from a specific disease or cause.

16. Contamination refers to the mere presence of microbes in or on the body or an inanimate object. Infection occurs when these microbes overcome the host's defenses, multiply, and cause damage to tissues, leading to disease.

17. Pathogenicity is the ability of a microorganism to cause disease. Virulence is the degree of pathogenicity, indicating the extent to which a pathogen can cause disease, often measured by factors like infectivity and severity of disease.

18. The etiology of disease is primarily established through Koch's Postulates, which provide a set of criteria to link a specific microorganism to a specific disease.

19. Koch's Postulates are four criteria used to establish a causal relationship between a microbe and a disease: 1. The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms. 2. The microorganism must be isolated from a diseased organism and grown in pure culture. 3. The cultured microorganism should cause disease when introduced into a healthy organism. 4. The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

20. Difficulties in establishing the etiology of disease include: some pathogens cannot be cultured in vitro; some diseases are caused by multiple pathogens; some pathogens cause multiple diseases; ethical considerations prevent infecting human volunteers; and asymptomatic carriers exist.

21. Five key virulence factors include adhesins (for attachment), exoenzymes (to invade tissues), toxins (to damage host cells), antiphagocytic factors (to evade host defenses), and mechanisms for evading the immune system (e.g., capsules, antigenic variation).

22. Extracellular enzymes contribute to the disease process as follows: Hyaluronidase breaks down hyaluronic acid, a component of the extracellular matrix, allowing pathogens to spread through tissues. Coagulase causes plasma to clot blood, forming a protective barrier around bacteria. Collagenase breaks down collagen, the main protein of connective tissue, facilitating pathogen spread. Kinase breaks down blood clots, allowing pathogens to escape from a localized infection.

23. Exotoxins are proteins secreted by living bacteria (gram-positive and some gram-negative), highly toxic, specific in their effect, heat-labile, and generally do not produce fever. Endotoxins are lipid A components of the outer membrane of gram-negative bacteria, less toxic, produce general systemic effects (e.g., fever, inflammation), are heat-stable, and are potent fever-producing agents (pyrogens).

24. Endotoxins primarily produce general systemic physiological effects such as fever, inflammation, diarrhea, hemorrhage, and in severe cases, septic shock and disseminated intravascular coagulation (DIC).

25. Bacterial capsules are composed of polysaccharides and make the bacterial surface slippery, preventing phagocytes from adhering and engulfing the bacteria. Anti-phagocytic chemicals, such as leukocidins, can directly kill phagocytic cells, while others inhibit the fusion of lysosomes with phagosomes, allowing bacteria to survive and multiply within phagocytes.

26. Signs are objective manifestations of disease that can be observed or measured by others (e.g., fever, rash, swelling). Symptoms are subjective characteristics of disease felt by the patient (e.g., pain, nausea, headache). Disease syndrome is a group of signs and symptoms that collectively characterize a particular disease or abnormal condition.

27. The 5 stages of infectious disease are: 1. Incubation period: The time between infection and the onset of signs and symptoms. 2. Prodromal period: A short period of generalized, mild symptoms (e.g., malaise, muscle aches). 3. Illness: The most severe stage, where signs and symptoms are most evident. 4. Decline: The body gradually returns to normal as the immune system or medical treatment overcomes the pathogen. 5. Convalescence: The patient recovers, and tissues are repaired, though some damage may be permanent.

28. Direct disease transmission involves immediate physical contact between an infected host and a susceptible host (e.g., touching, kissing, sexual intercourse). Indirect disease transmission occurs when pathogens are transmitted via an inanimate object (fomite), airborne particles, or vectors, without direct host-to-host contact.

29. Contact transmission involves direct or indirect physical contact (e.g., touching, fomites). Vehicle transmission occurs via inanimate reservoirs like air, water, or food. Vector transmission involves living organisms (e.g., insects, ticks) that transmit pathogens between hosts.

30. Direct contact transmission involves physical contact between hosts. Indirect contact transmission involves a fomite. Droplet transmission involves respiratory droplets traveling short distances. Airborne transmission (vehicle) involves aerosols traveling long distances. Waterborne transmission (vehicle) involves pathogens in water. Foodborne transmission (vehicle) involves pathogens in food. Bodily fluid transmission (vehicle) involves pathogens in bodily fluids.

31. Biological vectors are arthropods that transmit pathogens and also serve as hosts for the pathogen's multiplication or development (e.g., mosquitoes transmitting malaria). Mechanical vectors are arthropods that passively carry pathogens on their body parts from one host to another without being infected themselves (e.g., flies carrying bacteria on their legs).

32. The vector for malaria, dengue fever, and viral encephalitis is the mosquito.

33. The vector for Lyme disease is the tick, specifically the deer tick (Ixodes scapularis).

34. Nosocomial infections, also known as healthcare-associated infections (HAIs), are infections acquired by patients during a stay in a hospital or other healthcare facility.

35. The three factors playing a role in nosocomial infections are: 1. Presence of microorganisms in the hospital environment. 2. Immunocompromised patients. 3. Transmission of pathogens between staff and patients, and among patients. The single most effective way to minimize the risk for nosocomial infections is proper hand hygiene.

36. Exogenous HAIs are caused by pathogens acquired from the healthcare environment (e.g., contaminated surfaces, healthcare workers). Endogenous HAIs are caused by the patient's own microbiota becoming opportunistic pathogens due to changes in host defenses. Iatrogenic HAIs are a direct result of medical procedures (e.g., surgery, catheterization). Superinfections are secondary infections that occur when the normal microbiota is disrupted, often by broad-spectrum antibiotics, allowing opportunistic pathogens to proliferate.