Podcast
Questions and Answers
What defines prokaryotic microorganisms?
What defines prokaryotic microorganisms?
What is a prion?
What is a prion?
Which organism is known to cause Lyme disease?
Which organism is known to cause Lyme disease?
Which of the following are characteristics of viruses?
Which of the following are characteristics of viruses?
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What do viroids primarily affect?
What do viroids primarily affect?
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Which of the following describes the bacteria known as Campylobacter spp?
Which of the following describes the bacteria known as Campylobacter spp?
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Which classification of microorganisms are characterized by the presence of a nucleus?
Which classification of microorganisms are characterized by the presence of a nucleus?
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What distinguishes the methods of reproduction in microorganisms?
What distinguishes the methods of reproduction in microorganisms?
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What is a key factor in the transition of normal flora to opportunistic pathogens?
What is a key factor in the transition of normal flora to opportunistic pathogens?
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Which of the following is considered an endogenous source of infection?
Which of the following is considered an endogenous source of infection?
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What stage follows contamination in the process of infection?
What stage follows contamination in the process of infection?
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Which type of pathogen frequently uses the respiratory tract as a portal of entry?
Which type of pathogen frequently uses the respiratory tract as a portal of entry?
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What is a common effect of a compromised immune system?
What is a common effect of a compromised immune system?
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Through which portal do enteric bacteria typically enter the body?
Through which portal do enteric bacteria typically enter the body?
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Which factor is least likely to contribute to the opportunistic nature of pathogens?
Which factor is least likely to contribute to the opportunistic nature of pathogens?
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What type of microorganisms can act as opportunistic pathogens when normal flora balance is disrupted?
What type of microorganisms can act as opportunistic pathogens when normal flora balance is disrupted?
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What type of host do Rickettsiae require for replication?
What type of host do Rickettsiae require for replication?
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Which of the following is a characteristic of Gram-Positive Cocci?
Which of the following is a characteristic of Gram-Positive Cocci?
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Which of the following bacteria is known for causing food poisoning?
Which of the following bacteria is known for causing food poisoning?
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Which type of virus carries RNA as genetic material and does not replicate using DNA?
Which type of virus carries RNA as genetic material and does not replicate using DNA?
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What is a common mechanism of host cell damage caused by viral infections?
What is a common mechanism of host cell damage caused by viral infections?
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Which of the following describes an abortive viral infection?
Which of the following describes an abortive viral infection?
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Which of the following statements is true regarding mycobacteria?
Which of the following statements is true regarding mycobacteria?
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What is the main role of Lactobacilli in food production?
What is the main role of Lactobacilli in food production?
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Which of the following does NOT describe Chlamydiae?
Which of the following does NOT describe Chlamydiae?
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What distinguishes reverse transcribing viruses from other types of viruses?
What distinguishes reverse transcribing viruses from other types of viruses?
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What term describes the degree of pathogenicity or disease-provoking power of a microbe?
What term describes the degree of pathogenicity or disease-provoking power of a microbe?
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Which of the following is NOT a mechanism by which microbes evade host defenses?
Which of the following is NOT a mechanism by which microbes evade host defenses?
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What type of immunity does NOT result in apparent symptoms but can be carried for long periods?
What type of immunity does NOT result in apparent symptoms but can be carried for long periods?
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Which of the following best describes a systemic infection?
Which of the following best describes a systemic infection?
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Which type of toxin is characterized as being less potent and less specific than its counterpart?
Which type of toxin is characterized as being less potent and less specific than its counterpart?
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What is the main function of adhesins in the infection process?
What is the main function of adhesins in the infection process?
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Which pattern of infection is defined as having several infectious agents establish themselves at the same site?
Which pattern of infection is defined as having several infectious agents establish themselves at the same site?
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What is the term used to describe the permanent place where causative agents of infection reside?
What is the term used to describe the permanent place where causative agents of infection reside?
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Which type of infection has rapid onset and quickly resolves?
Which type of infection has rapid onset and quickly resolves?
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Where do pathogens typically colonize in the human body?
Where do pathogens typically colonize in the human body?
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Which organization serves as the central source of epidemiological information in the United States?
Which organization serves as the central source of epidemiological information in the United States?
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Which category of disease occurs with greater frequency than usual in a given population?
Which category of disease occurs with greater frequency than usual in a given population?
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What is typically the portal of entry for microbes in vaginal yeast infections?
What is typically the portal of entry for microbes in vaginal yeast infections?
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Which of the following describes a phenomenon where pathogens are directly introduced to subcutaneous tissue?
Which of the following describes a phenomenon where pathogens are directly introduced to subcutaneous tissue?
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Which of the following viruses is known to cause smallpox?
Which of the following viruses is known to cause smallpox?
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What type of virus is primarily responsible for causing respiratory and enteric diseases, including SARS?
What type of virus is primarily responsible for causing respiratory and enteric diseases, including SARS?
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Which of the following groups includes the causative agent of hepatitis B?
Which of the following groups includes the causative agent of hepatitis B?
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What is the smallest known DNA virus that causes disease in humans?
What is the smallest known DNA virus that causes disease in humans?
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What type of organism is typically characterized as eukaryotic, unicellular, and lacking a cell wall?
What type of organism is typically characterized as eukaryotic, unicellular, and lacking a cell wall?
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Which of the following is a characteristic of nematodes?
Which of the following is a characteristic of nematodes?
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In which type of symbiotic relationship do both organisms benefit from the interaction?
In which type of symbiotic relationship do both organisms benefit from the interaction?
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Which fungi-associated structure plays a major role in symbiosis with plant roots?
Which fungi-associated structure plays a major role in symbiosis with plant roots?
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Which of the following viruses is highly pathogenic and belongs to the Paramyxovirus group?
Which of the following viruses is highly pathogenic and belongs to the Paramyxovirus group?
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What describes a parasite that causes disease?
What describes a parasite that causes disease?
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How do many protozoans ensure survival during unfavorable environmental conditions?
How do many protozoans ensure survival during unfavorable environmental conditions?
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Which of the following is a typical characteristic of resident flora in humans?
Which of the following is a typical characteristic of resident flora in humans?
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What role do fungi commonly play in the ecosystem?
What role do fungi commonly play in the ecosystem?
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Which of the following statements about transient flora is true?
Which of the following statements about transient flora is true?
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What are nonliving reservoirs that can harbor pathogens?
What are nonliving reservoirs that can harbor pathogens?
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What term is used to describe diseases primarily occurring in animals that can be transmitted to humans?
What term is used to describe diseases primarily occurring in animals that can be transmitted to humans?
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Which of the following is a mode of transmission for infectious diseases?
Which of the following is a mode of transmission for infectious diseases?
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What is the most effective form of droplet transmission?
What is the most effective form of droplet transmission?
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What is a biological vector?
What is a biological vector?
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What are healthcare-associated infections primarily caused by?
What are healthcare-associated infections primarily caused by?
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How can antimicrobial resistance in healthcare settings manifest?
How can antimicrobial resistance in healthcare settings manifest?
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What is a key feature of nosocomial infections?
What is a key feature of nosocomial infections?
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Which of the following is NOT a common route for zoonotic transmission?
Which of the following is NOT a common route for zoonotic transmission?
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What type of infection is caused by the patient's own microbial flora becoming pathogenic?
What type of infection is caused by the patient's own microbial flora becoming pathogenic?
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Which of the following is a characteristic of indirect contact transmission?
Which of the following is a characteristic of indirect contact transmission?
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Which mode of transmission includes pathogens traveling more than 1 meter?
Which mode of transmission includes pathogens traveling more than 1 meter?
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What is one primary prevention method for infectious diseases?
What is one primary prevention method for infectious diseases?
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What is a significant challenge posed by healthcare-associated infections?
What is a significant challenge posed by healthcare-associated infections?
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Study Notes
Microbiology
- The study of microorganisms, including their visualization, identification, and function.
- Originated with the invention of the microscope.
- Microorganisms can be classified as prokaryotes (lacking a membrane-bound nucleus) or eukaryotes (with membrane-bound organelles).
- Prokaryotes include archaea and bacteria.
- Eukaryotes include algae, fungi, and protozoans.
Shared Properties of Microorganisms
- Reproduce through cell division, including binary fission, mitosis, or meiosis.
- Contain DNA and RNA for protein synthesis.
- Possess plasma membranes.
Viruses
- Noncellular, submicroscopic particles consisting of nucleic acid surrounded by a protein coat.
- Obligate intracellular parasites that infect both eukaryotes and prokaryotes.
- Can be classified based on their genome type: dsDNA, ssDNA, dsRNA, or ssRNA.
Prions
- Not cellular or viral, lacking nucleic acids.
- Misfolded proteins that act as infectious agents, leading to transmissible spongiform encephalopathies (e.g., mad cow disease, kuru).
Viroids
- Plant pathogens lacking a protein coat.
Microbial Ecology
- Often involves biofilms, which are communities of microorganisms attached to a surface.
- Microorganisms can interact in various ways, including:
- Mutualism: Both organisms benefit.
- Commensalism: One organism benefits, and the other is unaffected.
- Synergism: Both organisms benefit from the interaction but can survive independently.
- Parasitism: One organism benefits at the expense of the other.
- Amensalism: One organism inhibits the growth of another without being affected itself.
Bacteria
- A diverse group of prokaryotes with various shapes, sizes, and metabolic capabilities.
- Classified based on their morphology, staining properties (Gram-positive or Gram-negative), and oxygen requirements (aerobic, anaerobic, or facultative anaerobic).
Spirochetes
- Helical, motile bacteria with twisting motions due to axial fibrils.
- Found in aquatic environments and associated with human or animal hosts.
- Important pathogens include:
- Treponema pallidum (syphilis)
- Borrelia burgdorferi (Lyme disease)
- Leptospira interrogans (Leptospirosis)
Aerobic/Microaerophilic Helical Vibrioid Gram-Negative Bacteria
- Slightly curved or have multiple helical turns.
- Motile with flagella.
- Live in aquatic environments.
- Medically important examples include:
- Campylobacter spp.
- Helicobacter pylori
Gram-Negative Aerobic Rods and Cocci
- Diverse group, widely distributed in nature.
- Many are human and animal pathogens.
- Medically important examples include:
- Legionella pneumophila
- Neisseria gonorrhoeae
- Neisseria meningitidis
- Bordetella pertussis
- Francisella tularensis
- Pseudomonas aeruginosa
Facultative Anaerobic Gram-Negative Rods
- Large group with simple nutritional requirements.
- Found in soil, water, and the intestinal tract of animals and humans.
- E. coli is a key organism in molecular biology.
- Most strains are harmless, but some can cause gastroenteritis, UTIs, and hemorrhagic gastritis.
Rickettsias and Chlamydias
- Very small, gram-negative bacteria that require a host for replication.
- Generally rod-shaped but can be coccoidal.
- Often cause disease.
- Rickettsiae need a vertebrate and an arthropod host (e.g., Rickettsia rickettsii causes Rocky Mountain spotted fever transmitted by ticks).
- Chlamydias do not infect invertebrates (e.g., Chlamydia trachomatis causes urogenital infections).
Gram-Positive Cocci
- Include aerobic and anaerobic bacteria.
- Range from harmless to very virulent.
- Includes Micrococcus, Staphylococcus, Streptococcus, and Peptococcus.
- Medically important examples include:
- Staphylococcus aureus
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Peptostreptococcus
Endospore-Forming Gram-Positive Rods and Cocci
- Include Bacillus and Clostridium.
- Important in medicine and the food industry.
- Spores are resistant to heat and disinfectants.
- Widespread in the soil.
- Clostridium perfringens is found in decaying matter, marine sediment, and the intestinal tract of humans and other animals.
- Bacillus species are either obligate aerobes or facultative anaerobes.
- Clostridium species are mainly obligate anaerobes.
- Medically important examples include:
- Bacillus anthracis
- Bacillus cereus
- Clostridium botulinum
- Clostridium difficile
- Clostridium perfringens
- Clostridium tetani
Regular Nonsporulating Gram-Positive Rods
- Obligate or facultative anaerobes.
- Complex nutritional requirements.
- Includes Carnobacterium, Lactobacillus, and Listeria.
- Lactobacilli convert sugars to lactic acid, used in the production of yogurt, cheese, sauerkraut, and pickles.
- Listeria monocytogenes causes listeriosis.
Irregular Nonsporing Gram-Positive Rods
- Unusual shape.
- Mostly facultative anaerobes, few obligate aerobes.
- Medically important examples include:
- Actinomyces (opportunistic)
- Corynebacterium diphtheria (diphtheria)
- Propionibacterium acnes (acne)
- Actinomyces israelii (periodontal disease, lung infections)
Mycobacteria
- Gram-positive, aerobic, acid-fast rods.
- Found in water, soil, and food sources.
- Some are obligate intracellular parasites in humans and animals.
- Difficult to treat infections.
- Naturally resistant to many antibiotics.
- Medically important examples include:
- Mycobacterium tuberculosis
- Mycobacterium leprae
Viruses
- Microscopic particles that infect cells or other organisms.
- Contain either DNA or RNA but cannot reproduce on their own.
- Obligate intracellular parasites.
- Bacteriophages are viruses that infect bacteria.
Viral Infections
- Abortive: No viral production.
- Lytic or cytocidal: Kills the host cell.
- Persistent: Chronic (not lytic but productive) or latent (limited synthesis, virus remains in asymptomatic host).
- Slow infections: Prolonged incubation, damage might take years, followed by disease.
- Transforming infections: Viral nucleic acid may remain indefinitely without virus production, possible oncogenic changes.
Major Groups of Viruses in Vertebrates
- Cause disease after breaking protective barriers and gaining access to underlying tissues.
- Most viruses are specific to a particular cell or tissue type.
- Viral genomes consist of either DNA or RNA.
DNA Viruses
- Adenoviruses: Cause respiratory illness, gastroenteritis, conjunctivitis, cystitis, and rashes.
- Hepadnaviruses: Cause hepatitis in humans and animals (e.g., Hepatitis B).
- Herpesviruses: Include Herpes simplex 1 and 2, Varicella-zoster.
- Papillomaviruses and polyomaviruses: Cause warts and possibly cervical carcinomas.
- Parvoviruses: The smallest DNA viruses, B19 causes human disease, others infect animals.
- Poxviruses: The largest viruses, cause smallpox.
RNA Viruses
- Bunyaviridae: Arthropod-borne viruses.
- Coronaviruses: Cause respiratory and enteric disease, including SARS-CoV-2.
- Hepatitis viruses: Cause hepatitis (A through E) and can lead to cirrhosis and hepatocellular carcinomas.
- Orthomyxoviruses: Include influenza A, B, and C viruses.
- Paramyxoviruses: Include Morbillivirus, Paramyxovirus (highly pathogenic), Pneumovirus, Nipah and Hendra viruses (zoonosis-causing).
- Picornaviruses: Important pathogens, include Enterovirus, Rhinovirus, Hepatovirus, Aphthovirus, Parechovirus, Erbovirus, Kobuvirus, Teschovirus.
- Rhabdoviruses: Infect plants, insects, fish, birds, mammals, including humans (e.g., rabies virus).
- Reoviruses: Not associated with a specific disease but include Rotavirus, which causes gastroenteritis in children.
- Retroviruses: Include Oncovirinae, Lentivirinae, Spumavirinae (e.g., HIV).
- Togaviruses: Include Alphavirus (infectious arthritis, encephalitis, fever) and Rubivirus (rubella virus).
- Flaviviruses: Cause yellow fever, encephalitis, dengue fever, hepatitis C, and West Nile virus.
Eukaryotic Microorganisms
Fungi
- The study of fungi is called mycology.
- Few fungi are pathogenic and virulent.
- Immune system usually fights fungal invasion.
- Have important symbiotic relationships with other organisms.
- Play a major role in decomposition.
- Mycorrhizae are fungi that live on plant roots.
- Fungal colonies are vegetative and appear as yeast, molds, or fleshy fungi.
- Have cell walls composed of chitin.
Yeast
- Unicellular fungi that reproduce by budding.
Molds
- Multicellular fungi that grow as filamentous hyphae.
Protozoans
- Eukaryotes, unicellular, and lack a cell wall.
- Most are free-living, but some are parasites of humans and other animals.
- Diverse group of microbes, most are motile by cilia, flagella, or pseudopodia.
- Require a moist environment.
- Most live in ponds, streams, lakes, and oceans.
- Most are chemoheterotrophs and obtain nutrients from bacteria, decaying organic matter, other protozoans, or host tissue.
- Many enter a dormant stage (cyst) when the environment becomes unfavorable, which can be distributed by air.
Helminths
- Multicellular parasitic worms that produce microscopic infective and diagnostic stages in their life cycle.
- Often found in blood, feces, and urine.
- Spend much of their life cycle in a mammalian host.
- Most are either flatworms (platyhelminths) or roundworms (nematodes).
- Adult animals are typically large enough to be seen with the naked eye.
- Eggs and larvae are microscopic.
Platyhelminths (Flatworms)
- Trematodes (lung fluke, liver fluke, blood fluke), named by their host tissue.
- Cestodes or tapeworms, intestinal parasites.
Nematodes (Roundworms)
- Enterobius vermicularis (pinworm), spends its life in the human host, eggs transmitted by fomites.
- Ascaris lumbricoides (human parasite without an intermediate host).
- Necator americanus and Ancylostoma duodenale (hookworm), found in the small intestine of humans.
Symbiosis
- A close relationship between two different types of organisms in a community.
Mutualism
- Both members benefit from the interaction.
Commensalism
- One organism benefits, and the other is neither harmed nor helped.
Parasitism
- One organism benefits while the other is harmed.
- Pathogen: A parasite that causes disease.
Amensalism
- One organism can hamper or prevent the growth/survival of another without being affected by the other organism.
Normal Flora
- Microorganisms that establish residency in mucous membranes open to the environment.
- Resident flora remain part of the normal flora throughout life.
- Transient flora are found in the same locations as resident flora, but only remain for a short period.
Opportunistic Pathogens
- Pathogens are microorganisms capable of causing disease.
- Opportunistic pathogens do not cause disease in their normal habitat in a healthy person.
- Causes of opportunistic infections include a compromised immune system, changes in normal flora, and entrance of normal flora into areas where it is not normally present.
Stages of Infection
- Contamination: Presence of microbes in or on the body.
- Infection: Presence and growth of a microorganism in the body (excluding normal flora).
- The microorganism must gain entry into the host and its tissues.
- Not all infections cause disease.
Portals of Entry
- Sites where pathogens enter the body.
- Source of infection can be exogenous (from outside the body) or endogenous (organism is already in the body).
- Majority of pathogens have preferred portals of entry.
Skin
- A thick layer of keratinized dead cells.
- Pathogens can enter through natural openings or damaged skin.
Mucous Membranes
- Gastrointestinal tract: Portal of entry for pathogens present in food, liquids, and ingested substances.
- Respiratory tract: The most frequent portal of entry for pathogens in air, dust, moisture, and respiratory droplets.
- Urogenital tract: Pathogens usually contracted by sexual contact.
Additional Notes
- E. coli is often referred to as the ‘workhouse’ of molecular biology, due to its use in numerous studies and applications.
- Clostridium difficile is commonly associated with antibiotic-associated diarrhea and colitis.
- Bacillus anthracis is associated with anthrax, which can be fatal if untreated.
- Corynebacterium diphtheriae causes diphtheria, a potentially severe illness.
Vaginal Yeast Infections
- Caused by overgrowth of Candida albicans
- Opportunistic infection
Barriers of the Body Against Infectious Agents
- Conjunctiva: Usually a good barrier, but some bacteria can attach easily.
- Placenta: Usually effective in preventing microbes, however, some can cross and infect the embryo or fetus, leading to spontaneous abortions, birth defects, or premature births.
Parenteral Route
- Not a true portal of entry, more a bypassing of portals of entry.
- Introduces pathogens directly into subcutaneous tissue.
- Examples: Punctures by nail, thorn, contaminated needles, cuts, bites, stab wounds, deep abrasions, surgery.
Virulence and Pathogenicity
- Virulence: The degree of pathogenicity or disease-provoking power of a specific microbe.
- Virulence factors contribute to virulence.
- Pathogenicity: The ability of a microbe to cause disease.
- Factors influencing pathogenicity include:
- Number of microorganisms
- Portal of entry
- Host defense mechanisms
- Intrinsic characteristics of the organism
- Virulence factors
Adhesion
- First and most crucial step in infection.
- Without adhesion, the organism will be removed by natural mechanisms like ciliary motion, sneezing, coughing, swallowing, urine flow, tears, and intestinal peristalsis.
- Bacteria must bind to host cells using pili, fimbriae, or specific membrane receptor sites.
- Adhesion can be specific or nonspecific.
- Specific: Involves a lock-and-key interaction between molecules on pathogen and host cells.
- Nonspecific: Based on electrostatic forces and atomic & molecular vibrations.
Colonization and Invasion
- Human pathogens usually colonize tissues that are in contact with the external environment:
- Urogenital tract
- Digestive tract
- Respiratory tract
- Conjunctiva
- Invasion: May be facilitated by extracellular substances that disrupt host cell membranes, breaking down the body's primary and secondary barriers.
- Invasins are substances produced by pathogens that help them grow and spread.
Evasion of Host Defense
- Pathogens have strategies to evade host defenses:
- Capsules: Prevent phagocytosis by immune cells.
- Production of proteins that bind to host antibodies, disguising the pathogen from the immune system.
- Mutation of surface antigens, changing the pathogen's appearance to evade recognition by the immune system.
- Avoiding contact with phagocytes.
- Inhibiting phagocytic engulfment.
- Surviving inside phagocytes.
- Production of products that kill or damage phagocytes before or after ingestion.
Toxins
- Toxigenic: Organism produces toxins.
- Toxins are the underlying mechanism by which microorganisms cause disease.
- Bacterial toxins can be endotoxins or exotoxins.
- Endotoxins: Found within the bacterial cell wall (lipopolysaccharides).
- Exotoxins: Secreted by bacteria (proteins).
Exotoxins
- Released by bacteria during the exponential growth phase.
- Can act at sites different from the site of infection.
- Often species specific and associated with a particular disease.
Endotoxins
- Lipopolysaccharides of Gram-negative bacterial cell walls.
- Released during lysis (breakdown) of the bacteria, initiated by host defenses or antibiotics.
- Less potent and less specific than exotoxins.
- Can act on sites remote from the original site of infection.
Portal of Exit
- The site where the pathogen leaves the infected person.
- Often the same as the portal of entry.
- Pathogens can also leave the host through excretion or secretion.
Etiology of Infectious Disease
- The study of the cause of disease when an infectious agent causes pathological changes and interferes with normal body functions.
Patterns of Infection
- Local infections: Organism enters the body and remains confined to a specific tissue.
- Focal infections: Pathogen spreads from a local infection to other tissues.
- Systemic infections: Infection spreads to several sites and tissue fluids, usually by the way of the circulatory system.
- Septicemia
- Bacteremia
- Toxemia
- Viremia
- Mixed infections: Several infectious agents concurrently establish themselves at the same site.
Patterns of Infection (Continued)
- Acute infections: Appear rapidly with severe symptoms and vanish quickly.
- Chronic infections: Usually less severe symptoms, but they persist for long periods.
- Primary infections: The initial infection.
- Secondary infections: Follows a primary infection, typically caused by a different microbe.
- Subclinical infections: Don't cause any apparent symptoms.
- Carriers: Infected individuals without symptoms, who can infect others.
Epidemiology and Public Health
- Epidemiology: The study of the distribution and cause of disease in populations.
- Serves as the foundation for public health interventions and preventive medicine.
- Investigates:
- Number of people affected
- Location of the disease
- Outcome of the disease (recovery, death, disability)
Major Public Health Organizations
- Public Health Agency of Canada: Central source for epidemiological information in Canada.
- Centers for Disease Control and Prevention (CDC): Central source of epidemiological information in the United States.
Morbidity and Mortality Weekly Report (MMWR)
- Published by the CDC.
- Contains data on morbidity (incidence of specific notifiable diseases) and mortality.
Diseases in the Population
- Prevalence: The total number of existing cases in the entire population.
- Incidence: The number of new cases over a certain period compared to the general healthy population.
Disease Categories
- Endemic diseases: Repeatedly present in a given population or geographical area.
- Sporadic diseases: Break out only occasionally.
- Epidemic diseases: Occur with greater frequency than usual in a population of a given area.
- Pandemic diseases: Worldwide epidemics.
Reservoirs
- For an infection to continue, its causative agent must have a permanent place to reside.
- Reservoirs of infection maintain pathogens and are sources of infection:
- Nonliving reservoirs: Soil, water, food.
- Animal reservoirs: Zoonoses - diseases that occur primarily in animals and can be transmitted to humans.
- Human carriers: Main reservoir for human infectious agents; infected individuals without symptoms.
Routes of Zoonoses
- Direct contact with infected animals.
- Contact with animal waste.
- Contaminated food or water.
- Dust from contaminated hides, fur, or feathers.
- Consuming infected animal products.
- Insect vectors.
Modes of Transmission
- For infectious diseases to spread, they must move from a reservoir or portal of exit to a portal of entry of another host.
- Contact transmission
- Vehicle transmission
- Vector transmission
Contact Transmission
- Direct contact: Direct physical contact between hosts without an intermediate object. - Examples: Respiratory tract infections, staphylococcal infections, measles, scarlet fever, sexually transmitted diseases.
- Indirect contact: Pathogen is transmitted by a fomite (nonliving object). - Examples: Tissues, handkerchiefs, towels, bedding, toys, clothes, diapers, eating utensils, drinking cups, medical equipment.
- Droplet transmission: Via respiratory droplets released by exhaling, laughing, coughing, or sneezing.
Vehicle Transmission
- Airborne transmission: Via droplet nuclei or aerosols.
- Droplet nuclei: Droplets of mucous.
- Other aerosols: Dust.
- Airborne transmission requires travel of more than 1 meter.
- Bodily fluid transmission: Especially relevant for healthcare workers. - Precautions are necessary when handling fluids that may be contaminated with pathogens. - Examples: Blood, urine, saliva, and other bodily fluids.
- Waterborne transmission: Through untreated or poorly treated sewage. - Examples: Giardiasis, amebic dysentery, cholera, water-borne shigellosis, leptospirosis.
- Foodborne transmission: Incompletely cooked, poorly processed, or unsanitary foods. - Contamination by normal flora, zoonotic pathogens, or parasitic worms.
Vector Transmission
- Animals, especially arthropods, serving as vectors.
- Biological vectors: Transmit pathogens and also serve as a host for a part of the pathogen's life cycle. - Example: Mosquitoes, ticks, lice, fleas, blood-sucking flies or bugs, mites.
- Mechanical vectors: Passively carry agents to a new host. - Example: Flies.
Vaccinations
- Most effective method of preventing infectious diseases.
- Public health agencies provide information on vaccine-preventable diseases.
- Examples: Health Canada, CDC's Global Immunization Division (GID).
- Vaccinations have eradicated smallpox and polio.
Healthcare-Associated (Nosocomial) Infections
- Acquired as a result of treatments in a hospital or hospital-like setting.
- Secondary to the patient’s original condition.
- Among the top 10 leading causes of death in the United States.
- Incidence of MRSA and VRE bloodstream infections in Canadian hospitals has increased significantly.
Types of Nosocomial Infections
- Exogenous: Caused by pathogens in the healthcare environment.
- Endogenous: Caused by microbes in the normal flora of the patient, becoming pathogenic due to weakened immune systems, antimicrobial drugs, or overgrowth.
- Iatrogenic: Result from medical procedures such as the use of catheters, invasive diagnostic procedures, and surgery.
Transmission of HAIs
- Direct contact transmission: From hospital staff to patient, visitors, and patient to patient.
- Indirect contact transmission: Through fomites.
- Airborne transmission: Through ventilation systems.
Antimicrobial Resistance in Healthcare Settings
- Drug-resistant pathogens are a growing threat.
- More than 70% of bacteria causing infections are resistant to at least one commonly used drug.
Control and Prevention of HAIs
- Safety programs, policies, and procedures: Implemented by healthcare facilities to prevent transmission of pathogens.
- Blood-borne pathogen training.
- Proper handwashing and good housekeeping.
- Infection control committees: Established in accredited hospitals.
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