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Questions and Answers
Which of the following elements is considered a major essential element for life?
Which of the following elements is considered a major essential element for life?
What temperature range is optimal for mesophilic organisms?
What temperature range is optimal for mesophilic organisms?
Which term describes organisms that have complex nutritional requirements making their culture difficult?
Which term describes organisms that have complex nutritional requirements making their culture difficult?
What does the pH level measure in a solution?
What does the pH level measure in a solution?
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What is defined as the struggle for survival among organisms for a limited resource?
What is defined as the struggle for survival among organisms for a limited resource?
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What is the primary difference between an infection and a disease?
What is the primary difference between an infection and a disease?
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Which of the following describes a malignant condition?
Which of the following describes a malignant condition?
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Which of Koch's postulates states that a pathogen must be isolated and grown in pure culture?
Which of Koch's postulates states that a pathogen must be isolated and grown in pure culture?
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What is the purpose of colonization factors in bacterial pathogenicity?
What is the purpose of colonization factors in bacterial pathogenicity?
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Which of the following correctly defines 'infectious dose'?
Which of the following correctly defines 'infectious dose'?
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What is the process of a species successfully occupying a new habitat called?
What is the process of a species successfully occupying a new habitat called?
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Which of the following terms refers to a symptomless individual who carries a pathogenic microorganism?
Which of the following terms refers to a symptomless individual who carries a pathogenic microorganism?
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What facilitates adherence of bacterial cells to the host cells?
What facilitates adherence of bacterial cells to the host cells?
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Which of the following is NOT a mode of acquiring infectious agents?
Which of the following is NOT a mode of acquiring infectious agents?
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What is the main characteristic of invasins in relation to infection?
What is the main characteristic of invasins in relation to infection?
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Which factor does NOT influence the multiplication of microorganisms during an infection?
Which factor does NOT influence the multiplication of microorganisms during an infection?
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In acute care institutions, which site of nosocomial infections accounts for the highest percentage?
In acute care institutions, which site of nosocomial infections accounts for the highest percentage?
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What term is used to describe an organism's ability to reproduce during an infection?
What term is used to describe an organism's ability to reproduce during an infection?
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What biological process is characterized by an abnormal reduction in the number of leukocytes in the blood?
What biological process is characterized by an abnormal reduction in the number of leukocytes in the blood?
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Which condition is characterized by a vascular system failure and sequestration of large volumes of blood?
Which condition is characterized by a vascular system failure and sequestration of large volumes of blood?
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What is a key feature of two-component (bipartite) A-B exotoxins?
What is a key feature of two-component (bipartite) A-B exotoxins?
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Which of the following describes a disorder marked by a reduction in blood coagulation elements due to their utilization in widespread clotting?
Which of the following describes a disorder marked by a reduction in blood coagulation elements due to their utilization in widespread clotting?
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What is a primary effect of endotoxins on the body?
What is a primary effect of endotoxins on the body?
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What does Type I hypersensitivity lead to when triggered by a previously encountered antigen?
What does Type I hypersensitivity lead to when triggered by a previously encountered antigen?
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Which mechanism allows certain microorganisms to resist being engulfed by phagocytes?
Which mechanism allows certain microorganisms to resist being engulfed by phagocytes?
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What characterizes a Type II hypersensitivity reaction?
What characterizes a Type II hypersensitivity reaction?
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What is a common consequence of indirect damage due to the host immune response?
What is a common consequence of indirect damage due to the host immune response?
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Which of the following is a characteristic of a Type III hypersensitivity reaction?
Which of the following is a characteristic of a Type III hypersensitivity reaction?
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How does host tolerance differ from hypersensitivity?
How does host tolerance differ from hypersensitivity?
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What type of hypersensitivity is associated with a delayed-type immune response?
What type of hypersensitivity is associated with a delayed-type immune response?
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Which of the following components are part of the external host defense mechanisms?
Which of the following components are part of the external host defense mechanisms?
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Which type of mechanism primarily facilitates direct damage to host tissues during infection?
Which type of mechanism primarily facilitates direct damage to host tissues during infection?
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What type of hypersensitivity reaction is often seen in autoimmune diseases?
What type of hypersensitivity reaction is often seen in autoimmune diseases?
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What is the primary function of mononuclear phagocytes in host defense mechanisms?
What is the primary function of mononuclear phagocytes in host defense mechanisms?
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Which feature characterizes the inflammatory response?
Which feature characterizes the inflammatory response?
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What enhances the efficiency of phagocytosis by phagocytes?
What enhances the efficiency of phagocytosis by phagocytes?
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What role do B-lymphocytes play in the immune response?
What role do B-lymphocytes play in the immune response?
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Which of the following best describes the complement protective system?
Which of the following best describes the complement protective system?
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What is a characteristic of the humoral immune response?
What is a characteristic of the humoral immune response?
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Which substance is part of the non-specific host defense mechanisms?
Which substance is part of the non-specific host defense mechanisms?
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Which immune response is associated with cell-mediated defense mechanisms?
Which immune response is associated with cell-mediated defense mechanisms?
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Study Notes
Microbial Pathogenesis and Host-Pathogen Interactions
- Microbial pathogenesis involves the ways microorganisms cause disease.
- Host-pathogen interactions encompass the interplay between the host and the pathogen.
Ecological Relationships
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Microbial interactions encompass various relationships among microorganisms.
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Host-parasite interactions include symbiosis, mutualism, commensalism, and parasitism.
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The environment also plays a key role in microbial pathogenesis.
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Symbiosis: includes neutral, antagonistic, or synergistic relationships between microorganisms
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Mutualism: mutually beneficial relationship between two species
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Commensalism: one species benefits while the other is unaffected.
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Parasitism: one species benefits while the other is harmed.
Basic Ecological Definitions
- Flora/Microbiota: microorganisms present in a location. Flora usually refers to plants, while fauna refers to animals.
- Indigenous microbiota (resident flora): microorganisms that permanently occupy a niche
- Transient flora: microorganisms that temporarily occupy a niche.
- Niche: the role and position of an organism in its environment or ecosystem
- Natural Microbial Habitats: Soil, Water, Air, Animals and Animal Products
Microbial Flora of the Normal Human Body
- Skin: Respiratory Tract, Nose and Nasopharynx; Mouth and Oropharynx
- Eye (Conjunctivae) and Outer Ear
- Intestinal Tract: Stomach and Small Intestine, Large Intestine, Newborn Intestinal Tract, Antibiotic Alteration of Flora and Significance of Intestinal Flora
- Genitourinary Tract: External Genitalia & Anterior Urethra, Vagina
- Blood and Tissues
Normally Sterile Sites in the Human Body
- Brain, Central nervous system, Blood, Tissues, Organ systems, Sinuses, Inner and Middle Ear
- Lower Respiratory Tract (larynx, trachea, bronchioles, lungs, alveoli)
- Kidneys, Ureters, Urinary Bladder, Posterior Urethra
- Uterus, Endometrium, Fallopian Tubes, Cervix, Endocervix
Factors Controlling Growth of Microorganisms
- Nutrient Availability: accessibility of necessary resources for nourishment and structural building blocks.
- Fastidious organisms: require complex nutritional requirements, making isolation and culture difficult.
- Essential Elements: Major (C, O, H, N, S, P, K, Mg, Ca, Fe, Na, Cl) and Minor (Zn, Mn, Mo, Se, Co, Cu, Ni, W)
- Physico/Environmental Parameters: (i) Water activity/osmotic pressure, (ii) Oxygen metabolic requirements (obligate or facultative, anaerobic or aerobic, or in between [microaerophilic]), (iii) pH (power of hydrogen; measurement of hydrogen ion concentration in a solution—0 to 14), and (iv) Temperature (psychrophiles [15-20°C], mesophiles [20-45°C] and thermophiles [50-70°C]).
- Competition: simultaneous demand for limited resources and physical space by multiple organisms
- Host Immune System: cells and tissues involved in recognizing and eliminating foreign substances.
Acquiring Infectious Agents
- Portal of Entry/Exit: Ingestion, Inhalation, Direct Penetration (trauma, surgical procedure, needlestick, arthropod bite, sexual transmission, transplacental)
- Colonization: successful occupation of a new habitat by a species
- Adherence (attachment) of bacterial to host cells is dependent on receptors on target sites. Adhesins are structures on the bacterial cell that promote attachment
- Invasion: entering and spreading throughout host tissues. Invasins are structures that facilitate invasion.
- Multiplication: the organism's ability to reproduce during an infection. This is influenced by factors like the underlying disease state, immune response, antibiotic treatment, and nutrient availability.
Transmission of Disease
- Entrance, Colonization, Penetration: factors like age, sex, nutrition, host's immunologic state and general health, and bacterial virulence factors.
- Vector: an animal that transfers an infectious agent from one host to another (e.g., arthropod).
- Carrier: a symptomless host to a pathogenic microorganism, who can transmit it to others.
- Nosocomial Infections: hospital-acquired infection typically occurring within 72 hours of admission
Epidemiology
- Epidemic: disease occurring suddenly in numbers clearly exceeding the normal expectancy
- Endemic: disease present or usually prevalent in a geographic area
- Pandemic: widespread epidemic distributed or occurring widely throughout regions, countries, or globally
Emerging Infectious Diseases
- Emerging infectious diseases (EIDs): new or re-emerging diseases with increasing incidences.
- Causes of EIDs: antibiotic/pesticide use, climate change, travel, lack of vaccination, insufficient case reporting
- Surveillance and disease responses are crucial for emerging infectious diseases, and the CDC, NIH, and WHO play this role
Pathogenicity vs. Virulence
- Pathogenicity: ability to cause disease and produce pathologic changes
- Virulence: a measure of pathogenicity, assessed by the severity of disease caused or by determining the dosage required to cause a specific degree of pathogenicity (e.g., LD50 or lethal dose 50%)
- Dosage: number of pathogenic microorganisms entering the host
- True Pathogen: any microorganism capable of causing disease
- Opportunistic Pathogen: usually harmless microorganism that becomes pathogenic under favorable conditions
Infection vs. Disease
- Infection: colonization and/or invasion and multiplication of pathogenic microorganisms with or without the manifestation of disease
- Disease: abnormal condition of body function(s) or structure that harms the host.
Benign vs. Malignant
- Benign: non-life or non-health threatening condition
- Malignant: disease tending to become progressively worse and potentially result in death
- Morbidity: illness
- Mortality: death
Koch's Postulates
- Four criteria for identifying the causative agent of a specific disease
- Presence in all cases, isolation, replication/growth in pure culture and re-isolation from an animal model with resultant disease
- Four steps for determining causation of disease
Bacterial Virulence Mechanisms
- Adherence (Colonization): invasion, degradative enzymes, exotoxins, endotoxins, induction of inflammation, evasion of immune clearance, byproducts of growth (e.g., gas, acid), superantigen, resistance to antibiotics
Microbial Pathogenicity- Virulence Factors
- Colonization Factors: specific recognition of receptor sites
- Capsule, Surface Receptors/Target Sites
Microbial Pathogen- Adhesins and Receptors
- Tables of specific bacterial pathogens, adhesins, and receptors used to classify them
Virulence Factors (cont.)
- Invasive Factors/Invasins: enabling entry and spread of microorganisms through tissues; specific recognition of receptor sites on target cells
- Degradative Enzymes: class of proteins capable of catalytic reactions - Bacterial & host enzymes involved
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Toxigenicity: ability of a microorganism to cause diseases determined by toxin
- Endotoxin: complex bacterial toxin (LPS) released upon cell lysis; protein, lipid, and polysaccharide components
- Exotoxins: potent toxic substances formed and secreted by certain bacterial species
Basic Effects of Endotoxin
- Fever
- Leukopenia/Leukocytosis
- Metabolic Effects
- Release of Lymphocyte Factors
Basic Effects of Endotoxin- Severe Cases
- Cellular death & Septic Shock
- Disseminated Intravascular Coagulation (DIC)
- Organ Necrosis
Exotoxins (cont.)
- Two-Component (Bipartite) A-B Toxins
- Binding domain (B subunit) associated with absorption
- Enzymatic/active domain (A subunit) disrupts cell function
- Bacterial cytolysins (with cell membrane targets): hemolysis, tissue necrosis, and intravenous administration may be lethal depending on concentration and route
Examples of Bipartite A-B Toxins with Intracellular Targets
- Diphtheria toxin, Pseudomonas toxin, Cholera toxin, Enterotoxigenic E. coli toxin, Tetanus neurotoxin, Botulinum neurotoxin
Bacterial Cytolysins with Cell Membrane Targets
- Hydrolyze membrane phospholipids (e.g., phospholipases), thiol-activated cytolysins (e.g., oxygen-labile), detergent-like activity on cell membranes
Endotoxins vs. Exotoxins
- Integral part of cell wall vs. released from the cell
- Lipid A (toxic) vs. Protein
- Heat stable vs. Heat labile
- Questionable immunogenicity vs. Antigenic and immunogenic
- No toxoids produced vs. Toxoids produced
- Multiple effects on host vs. Effects specific to the target
- Produced by gram-negative only vs. Produced by gram- positive and gram-negative
Microbial Pathogenicity (cont.) - Resistance to Host Defenses
- Encapsulation, Antigenic Mimicry, Masking or Shift
- Evasion or Incapacitation of Phagocytosis
- Resistance to Humoral and Cellular Factors
Microbial Pathogenicity (cont.) - Damage to Host
- Direct damage (tissue damage from toxins, enzymes)
- Indirect damage (responses to immune system reaction- hypersensitivity reactions)
Host Resistance
- Tolerance: Suppression of symptoms or endurance to large doses of a drug, toxin, or protein
- Hypersensitivity: Increased or specific susceptibility to an antigen—leading to allergic reactions
- Immunity: the body's ability to resist an infection—by immunological factors or a biological condition
Hypersensitivity Reactions
- Type I (Anaphylactic): life-threatening, immediate hypersensitivity reaction to antigen
- Type II (Cytotoxic): specific destructive action against cells by the invading agent—mostly antibody mediated
- Type III (Immune Complex): deposition of circulating immune complexes in small vessels with complement activation
- Type IV (Cell-mediated): delayed-type hypersensitivity through T-cell mediated responses
Immunopathological Response with Tissue Reactions (cont.)
- Type I, Type II, Type III, Type IV Hypersensitivity Reactions and a breakdown of tissue reactions from each
- Example details for each type of hypersensitivity
Host Defense Mechanisms
- External (Primary): physical barriers, mechanical factors, and physical factors (sweat, fatty acids, pH, indigenous competitive flora, peristalsis, hair, cilia, flushing, mucus, tears, nasal secretions, saliva, semen, mucosal antibody (IgA))
- Internal (Secondary): immune response to pathogens that penetrated the external barriers, including phagocytosis and inflammation, mononuclear phagocytes, Reticular Endothelial System with phagocytic cells.
- Other: Non-specific (oxygen metabolites, host-generated proteins— lysosomes, lipid mediators, prostaglandins, histamine, and heat shock proteins), and cellular and humoral responses (phagocytosis, T-lymphocytes, cytokines, complement protective system, B-lymphocytes, antibody production).
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Test your knowledge on microbial pathogenesis and host-pathogen interactions. Explore the ecological relationships that govern these processes, including symbiosis, mutualism, commensalism, and parasitism. Understand the role of the environment in these interactions.
