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Questions and Answers
What defines prokaryotic microorganisms?
What is a prion?
Which organism is known to cause Lyme disease?
Which of the following are characteristics of viruses?
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What do viroids primarily affect?
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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?
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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?
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Which of the following is considered an endogenous source of infection?
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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?
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What is a common effect of a compromised immune system?
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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?
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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?
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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?
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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?
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Which of the following describes an abortive viral infection?
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Which of the following statements is true regarding mycobacteria?
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What is the main role of Lactobacilli in food production?
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Which of the following does NOT describe Chlamydiae?
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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?
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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?
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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?
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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?
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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?
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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?
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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?
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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?
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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?
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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?
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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?
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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?
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What describes a parasite that causes disease?
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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?
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What role do fungi commonly play in the ecosystem?
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Which of the following statements about transient flora is true?
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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?
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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?
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What is a biological vector?
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What are healthcare-associated infections primarily caused by?
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How can antimicrobial resistance in healthcare settings manifest?
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What is a key feature of nosocomial infections?
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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?
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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?
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What is one primary prevention method for infectious diseases?
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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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