CLLS 202 - Introduction to Microbes Flashcards

Overview of Microorganisms and Infectious Diseases

  • Microorganisms (Microbes): Organisms that are too small to be seen with the unaided eye. Microbes include bacteria, fungi, protozoa, microscopic algae, and viruses.

  • Infectious Disease Definition: As defined by the Centers for Disease Control and Prevention (CDC), infectious diseases are illnesses caused by germs (such as bacteria, viruses, and fungi) that enter the body, multiply, and can cause an infection.

  • Modes of Transmission: Infectious diseases can be acquired through several vectors and pathways, including:

    • Direct contact with other infected people.

    • Exposure to environmental sources.

    • Direct or indirect animal contact.

    • Insect bites.

  • Examples of Infectious Diseases:

    • Chickenpox

    • Common cold

    • Diphtheria

    • E. coli infection

    • Giardiasis

    • HIV/AIDS

    • Infectious mononucleosis

    • Influenza (flu)

    • Lyme disease

    • Malaria

    • Measles

    • Meningitis

    • Mumps

    • Poliomyelitis (polio)

    • Pneumonia

    • Rocky Mountain spotted fever

    • Rubella (German measles)

    • Salmonella infections

    • Severe acute respiratory syndrome (SARS)

    • Sexually transmitted diseases

    • Shingles (herpes zoster)

    • Tetanus

    • Toxic shock syndrome

    • Tuberculosis

    • Viral hepatitis

    • West Nile virus

    • Whooping cough (pertussis)

Major Groups of Microorganisms

  • Bacteria:

    • Prokaryotes ("prenucleus"), lacking membrane-bound organelles and a true organized nucleus.

    • Unicellular microorganisms.

    • Cell walls are composed of peptidoglycan.

    • Reproductive method: Divide via binary fission.

    • Functional roles: Some species are capable of causing disease, whereas others are highly beneficial.

  • Archaea:

    • Prokaryotes.

    • Cell wall composition: Lack peptidoglycan cell walls, or may lack a cell wall entirely.

    • Habitat: Frequently inhabit extreme environments.

    • Major ecological sub-groups:

      • Methanogens

      • Extreme halophiles

      • Extreme thermophiles

    • Pathogenicity: Generally not known to cause disease in humans.

  • Viruses:

    • Acellular structures (non-cellular).

    • Structural core: Consist of a DNA or RNA nucleic acid core.

    • Coating: Core is encased in a protective protein coat, which may additionally be enclosed in a lipid envelope.

    • Replication cycle: Replicated exclusively when located inside a living host cell; entirely inert outside living hosts.

  • Fungi:

    • Eukaryotes, possessing a distinct cell nucleus surrounding their DNA genetic material.

    • Cell walls are composed of chitin.

    • Energy acquisition: Absorb organic chemicals from their environment.

    • Unicellular forms: Yeasts.

    • Multicellular forms: Molds and mushrooms. Molds characteristically consist of visible masses of mycelia, which are composed of long filaments termed hyphae.

  • Protozoa:

    • Unicellular eukaryotic organisms.

    • Nutritional strategies: Absorb or ingest organic chemicals; some species are photosynthetic.

    • Motility: May be motile using specialized structures such as pseudopods, cilia, or flagella.

    • Lifestyle: Free-living or parasitic (deriving nourishment directly from a living host).

    • Reproduction: Capable of reproducing either sexually or asexually.

Parasites and Environmental Epidemiology

  • Parasite Terminology:

    • Parasite: An organism that lives in or on another organism and takes its nourishment from that host; it cannot live independently.

    • Obligate Parasites: Microorganisms that must be parasitic and cannot exist without the aid of another host.

    • Facultative Parasites: Organisms capable of functioning with both parasitic and free-living abilities (e.g., Naegleria fowleri).

  • Factors Driving Increased Frequency and Awareness of Parasitic Infections:

    • An increasing overall number of immunocompromised patients.

    • Elevated levels of global travel.

    • A growing global population of immigrants.

    • Ongoing global climate change.

First Golden Age of Microbiology: Germ Theory and Early Vaccines

  • The Germ Theory of Disease:

    • Replaced historical beliefs that disease was caused by divine punishment for misdeeds or moral crimes with the scientific principle that microorganisms might cause disease.

    • 1865: Louis Pasteur established that a silkworm disease was caused by a protozoan parasite.

    • 1860s: Joseph Lister implemented phenol (carbolic acid) to treat surgical wounds. This intervention caused a significant decrease in post-surgical infections and deaths, directly proving that microorganisms caused wound infections.

  • Robert Koch and Anthrax Investigations:

    • Robert Koch was a German physician who sought to establish the specific cause of anthrax.

    • Discovered rod-shaped bacteria (Bacillus anthracis) in the blood of cattle that died from anthrax.

    • Cultured the bacteria in pure culture and injected the cultured isolates into healthy animals, which subsequently contracted and died of the disease.

    • Re-isolated the bacteria from the blood of those experimental animals and confirmed it matched the original isolate.

  • Koch's Postulates:

    • A standardized sequence of experimental procedures used to directly link a specific microorganism to a specific disease:

      1. The exact same pathogen must be present in every case of the disease.

      2. The pathogen must be isolated from the diseased host and grown in pure culture (and identified).

      3. The pathogen isolated from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.

      4. The pathogen must be re-isolated from the inoculated experimental animal and shown to be identical to the original organism.

  • Early Inoculations and Vaccination Development:

    • Smallpox Inoculation:

      • Smallpox is a highly contagious viral disease that causes fever, rash, vomiting, and death in approximately 30% of infected individuals.

      • Early historical antecedents: Chinese physicians attempted smallpox prevention methods in the 1500s.

      • 1796: Edward Jenner observed that individuals infected with cowpox (a milder infection) were immune to smallpox.

      • Jenner collected scrapings from cowpox blisters and inoculated a healthy volunteer child by scratching the material into the child's arm.

      • The child developed a mild cowpox infection, recovered fully, and subsequently demonstrated complete immunity to smallpox.

      • Etymology: The word vaccination originates from the Latin word vacca, meaning cow. The resulting protection is defined as immunity.

    • Pasteur and Cholera Attenuation:

      • Louis Pasteur observed that bacterial cultures left to dry out lost their capability to cause disease, becoming avirulent.

      • Demonstrated that organisms with decreased virulence could be administered safely for immunization.

      • Modern vaccine modalities based on this principle:

        • Attenuated Vaccines: Formulated using live, avirulent microbial strains with reduced virulence (e.g., Measles, Mumps, Rubella [MMR] vaccine).

        • Killed Vaccines: Formulated using completely killed microbial strains (e.g., Influenza flu vaccine).

Second Golden Age of Microbiology: Chemotherapy and Antimicrobial Development

  • Chemotherapeutic Terminology:

    • Chemotherapy: The medical treatment of disease using chemical substances.

    • Antibiotics: Chemicals produced naturally by bacteria and fungi that act to inhibit or kill other microorganisms.

    • Synthetic Drugs: Chemotherapeutic agents synthesized artificially from chemical compounds in a laboratory.

  • First Synthetic Drugs:

    • Salvarsan: An arsenic-derived synthetic compound developed by Paul Ehrlich in 1910, effective at treating syphilis.

    • Quinine: A plant extract derived from the bark of a South American tree, used to treat malaria.

    • Sulfa Drugs: Synthetic agents and dye derivatives developed with potent antimicrobial properties.

  • Discovery of Penicillin:

    • Alexander Fleming observed that mold contaminating his bacterial culture plates created a clear zone that inhibited bacterial growth.

    • The active mold was identified as Penicillium chrysogenum, and its inhibitory secretion was named penicillin.

  • Complications of Antibiotic Usage:

    • Host tissue damage and adverse drug toxicity (e.g., side effects associated with Ciprofloxacin).

    • Development of antibiotic resistance among pathogens (e.g., Vancomycin-resistant Enterococcus faecalis [VRE]).

  • Target Mechanisms of Antimicrobial Action:

    • Cell wall biosynthesis

    • Folate synthesis

    • DNA replication

    • RNA transcription

    • mRNA translation

Third Golden Age of Microbiology: Genomics and Modern Applications

  • Genomic Analysis: Technological tools such as DNA sequencing and computer-assisted bioinformatic systems facilitate detailed DNA analysis, identification of novel genes, and exact determination of gene functions.

  • Clinical Identification: Microorganisms can now be identified clinically directly by their gene sequences rather than depending solely on phenotypic traits (e.g., clinical identification of Clostridium difficile).

  • Genetic Engineering: Microorganisms can be genetically modified to synthesize large quantities of human hormones and essential pharmaceutical preparations (e.g., production of human insulin using modified E. coli).

Branches of Microbiology

  • Bacteriology:

    • The study of bacteria.

    • Historical origin: Initiated through the microscopic examination of human tooth scrapings.

    • Ongoing research: New bacterial species are continuously discovered.

  • Mycology:

    • The study of fungi.

    • Clinical impact: Fungal infections have risen steadily, now accounting for 10% of hospitalizations.

    • Epidemiological shifts: Infections caused by Coccidioides immitis have increased tenfold in California, likely influenced by environmental shifts.

  • Parasitology:

    • The study of protozoa and parasitic worms.

    • Historical awareness: Many parasitic worms have been known for thousands of years because they are macroscopic.

    • Prevalence: Protozoan infections are rare in the United States, but still occur.

  • Immunology:

    • The study of the immune system.

    • Scope: Includes vaccinations, cytokine research, antibody production, and diagnostic testing for infectious diseases.

    • Clinical example - Hepatitis B:

      • Hepatitis B causes severe inflammation of the liver, which can progress to chronic infection and liver cirrhosis.

      • Preventative control: A Hepatitis B vaccine is available.

      • Diagnostics: Standard diagnostic tests rely on detecting specific antibodies produced in response to infection.

  • Virology:

    • The study of viruses.

    • Historical milestones:

      • 1892: Dmitri Iwanowski reported that the infectious agent causing mosaic disease in tobacco was small enough to pass completely through a bacteria-retaining filter.

      • 1935: Wendell Stanley demonstrated that this infectious agent was tobacco mosaic virus (TMV).

    • Structural analysis: The development of the electron microscope permitted microbiologists to visualize the precise physical structure of viruses.