Medical Microbiology
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What is the primary characteristic of the microbiota in the human body?

  • They are found only in the digestive tract.
  • They only exist in sick individuals.
  • All microbes are pathogenic.
  • They are regularly found at specific anatomical sites. (correct)

    • What is the typical ratio of bacteria and archaea to human cells in an average adult?

  • 10:1 (correct)
  • 10:100
  • 100:1
  • 1:1

    • Where are the majority of normal flora located in the human body?

  • In the mouth
  • On the skin
  • In the respiratory tract
  • In the gut (correct)

    • What can opportunistic pathogens do when a person is immunocompromised?

    <p>Take advantage of the weakened immune system</p> Signup and view all the answers

    Which of the following describes a relationship where both organisms benefit?

    <p>Mutualism</p> Signup and view all the answers

    What is primarily indicated when microorganisms are described as normal flora?

    <p>They do not typically cause diseases in healthy individuals.</p> Signup and view all the answers

    What is a common characteristic of the normal flora found on human body surfaces?

    <p>They can become harmful if the host’s health declines.</p> Signup and view all the answers

    Which anatomical site in the human body encompasses the largest area inhabited by normal flora?

    <p>Gut</p> Signup and view all the answers

    What is the primary mechanism by which botulinum toxin affects muscle tissue?

    <p>It blocks the release of acetylcholine.</p> Signup and view all the answers

    Which condition is most commonly associated with Campylobacter jejuni?

    <p>Bacterial gastroenteritis.</p> Signup and view all the answers

    What type of toxins are endotoxins typically found in?

    <p>Gram-negative bacteria.</p> Signup and view all the answers

    What effect do superantigen toxins have on the immune system?

    <p>Cause overdrive immune response.</p> Signup and view all the answers

    Which of the following food items can lead to outbreaks of infant botulism?

    <p>Chili sauce.</p> Signup and view all the answers

    What is a notable syndrome that can develop in 1 in 1000 cases of Campylobacter jejuni infections?

    <p>Guillain-Barré Syndrome.</p> Signup and view all the answers

    What characteristic differentiates exotoxins from endotoxins?

    <p>Exotoxins are generally more toxic than endotoxins.</p> Signup and view all the answers

    How do superantigens contribute to tissue damage?

    <p>By stimulating excessive immune cell activation.</p> Signup and view all the answers

    What immune response does the body display due to Campylobacter jejuni LPS components?

    <p>Produces antibodies against bacterial sugars</p> Signup and view all the answers

    What is a primary method of transmission for tuberculosis?

    <p>Via airborne droplets</p> Signup and view all the answers

    What critical role does cell-mediated immunity play in tuberculosis?

    <p>It prevents active disease after infection</p> Signup and view all the answers

    What characterizes multidrug-resistant tuberculosis (MDR TB)?

    <p>Resistant to both isoniazid and rifampin</p> Signup and view all the answers

    Which of the following is NOT a recommended method to prevent the spread of tuberculosis?

    <p>Immediate antibiotic treatment for everyone</p> Signup and view all the answers

    How is the treatment for tuberculosis typically characterized?

    <p>Requires combination therapies with multiple drugs</p> Signup and view all the answers

    What structural feature contributes to the acid-fastness of mycobacteria?

    <p>Their waxy mycolic acid content</p> Signup and view all the answers

    Which of the following factors differentiates the upper and lower respiratory tracts in terms of microbial colonization?

    <p>Differences in temperature and pH</p> Signup and view all the answers

    What condition is primarily caused by the accumulation of acid-producing bacteria on teeth?

    <p>Dental caries</p> Signup and view all the answers

    Which bacterium is most commonly associated with the formation of dental caries?

    <p>Streptococcus mutans</p> Signup and view all the answers

    What is the primary function of the bacteria colonizing the human gastrointestinal tract?

    <p>To enhance food digestion and energy extraction</p> Signup and view all the answers

    In which part of the digestive system is the microbial population largest?

    <p>Large intestine</p> Signup and view all the answers

    What is a major factor contributing to the formation of dental plaque?

    <p>Saliva's glycoproteins facilitating bacterial adhesion</p> Signup and view all the answers

    Which of the following best describes anaerobic bacterial species in the oral cavity?

    <p>They grow extensively in thick dental plaque.</p> Signup and view all the answers

    What role do mucous membranes play in bacterial infection risk?

    <p>They provide a favorable environment for bacterial growth.</p> Signup and view all the answers

    How do bacteria influence the human body beyond digestion?

    <p>By contributing to nutrient absorption and immune function.</p> Signup and view all the answers

    What happens to microbes when they pass quickly through the stomach?

    <p>Some may survive if they are in food particles.</p> Signup and view all the answers

    What is dental plaque primarily composed of?

    <p>Living bacteria and their byproducts in a matrix</p> Signup and view all the answers

    Which process eliminates microbes from the large intestine?

    <p>Desquamation and peristalsis</p> Signup and view all the answers

    What is the primary source of microorganisms in the oral cavity after birth?

    <p>Colonization from the surrounding environment</p> Signup and view all the answers

    Which of the following statements about sugar and bacteria is accurate?

    <p>Sugar is fermented to produce lactic acid.</p> Signup and view all the answers

    How does the body counteract the microbial population within the large intestine?

    <p>Through mechanisms like peristalsis and mucus movement.</p> Signup and view all the answers

    What is the primary role of virulence factors in pathogens?

    <p>To assist in pathogen survival and promote pathogenicity.</p> Signup and view all the answers

    What does LD50 represent in the context of virulence?

    <p>The lethal dose that kills 50% of test subjects.</p> Signup and view all the answers

    Which enzyme breaks down hyaluronic acid and aids bacterial invasion?

    <p>Hyaluronidase</p> Signup and view all the answers

    How does coagulase function in terms of pathogen protection?

    <p>By forming a protective fibrin coating.</p> Signup and view all the answers

    Which toxin directly damages the integrity of host cell membranes?

    <p>Cytolytic toxins</p> Signup and view all the answers

    What is the function of siderophores in bacterial pathogens?

    <p>To grab iron and assist in bacterial growth.</p> Signup and view all the answers

    Which characteristic differentiates highly virulent pathogens from less virulent ones in terms of LD50?

    <p>Lower LD50 indicates higher virulence.</p> Signup and view all the answers

    How does the Diphtheria toxin impact host cells?

    <p>It prevents transfer of amino acids necessary for protein synthesis.</p> Signup and view all the answers

    Which of the following best describes the role of fimbriae in bacterial pathogens?

    <p>To facilitate adherence to host tissues.</p> Signup and view all the answers

    Which type of exotoxin is characterized by its ability to stimulate excessive immune responses?

    <p>Superantigen toxins</p> Signup and view all the answers

    What component of the Gram-negative cell wall is considered a virulence factor?

    <p>Lipopolysaccharide (LPS)</p> Signup and view all the answers

    What process allows bacteria to acquire virulence factors via genetic exchange?

    <p>All of the above</p> Signup and view all the answers

    How do hemolysins affect red blood cells?

    <p>They degrade the integrity of red blood cells.</p> Signup and view all the answers

    What is a key function of enterotoxins specifically in food-borne pathogens?

    <p>They promote growth of the bacteria in the gut.</p> Signup and view all the answers

    What characterizes extensively drug resistant tuberculosis (XDR TB)?

    <p>Resistant to isoniazid, rifampin, fluoroquinolone, and at least one injectable second-line drug.</p> Signup and view all the answers

    Which age groups are more susceptible to infectious diseases?

    <p>Very young individuals and the elderly.</p> Signup and view all the answers

    What is the role of the immune memory in the immune system?

    <p>To enhance the body's ability to recognize and respond to specific antigens.</p> Signup and view all the answers

    Which factor does NOT contribute to a compromised host's susceptibility to infection?

    <p>Regular exercise.</p> Signup and view all the answers

    What is the main purpose of vaccination?

    <p>To prepare the immune system to recognize specific pathogens.</p> Signup and view all the answers

    What is required for herd immunity to be effective?

    <p>Vaccination of a significant portion of the population to protect vulnerable groups.</p> Signup and view all the answers

    What is a key challenge in creating new flu vaccines each year?

    <p>Flu viruses can mutate, requiring updated vaccines.</p> Signup and view all the answers

    Which of the following is NOT a component of specific immunity?

    <p>Phagocyte-driven innate immunity.</p> Signup and view all the answers

    What condition is associated with a higher risk of TB infection?

    <p>Compromised immune function due to other conditions.</p> Signup and view all the answers

    What is a common misconception about herd immunity?

    <p>The entire population must be vaccinated for herd immunity.</p> Signup and view all the answers

    Study Notes

    Medical Microbiology BS2002 Lecture 9

    • Lecture presented by A/Prof Yann Boucher, SCELSE, Public Health, NUS
    • Email address: [email protected]

    Pippi and Scientific Pedigree

    • Carl Woese, just shy of Nobel, Father of Archaea
    • Norm Pace, NAS member, Father of 16S
    • Ford Doolittle, NAS member, Father of LGT
    • Yann Boucher, Dog owner, Father of new Vibrio species,

    Meet your Prof

    • Images depicting various locations and activities

    Medical Microbiology - Human Body Diversity

    • Human body is a diverse environment
    • Specific niches exist
    • Most microbes are benign
    • Application of ecological principles is important
    • Many interactions between humans and normal microbial flora
    • Microbiota: microbes regularly found at a given anatomical site

    Normal Flora

    • Microorganisms living on body surfaces of healthy individuals
    • ~10^14 bacteria and archaea in average adult (about 10^13 human cells)
    • Most in the gut (400 m² surface)
    • Skin (2 m²)
    • Mouth
    • Respiratory tract
    • Urogenital tract
    • Many normal flora are opportunistic pathogens
    • Commensalism or mutualism

    Mouth

    • Microbes adhere to gums and teeth
    • Not removed by brushing
    • Acid contributes to dental plaque, caries, gingivitis, and periodontal disease
    • Oral cavity is colonized by microorganisms from the surrounding environment within hours following birth

    Oral Microbes and Bacteria

    • Bacteria colonize tooth surfaces by attaching to glycoproteins deposited by saliva
    • Extensive growth of oral microbes results in a thick bacterial layer (dental plaque)
    • Anaerobic species produce high concentrations of acid that decalcifies tooth enamel (dental caries): Streptococcus mutans

    Gastrointestinal Tract

    • Stomach: most microbes are killed by acidic conditions
    • Some survive if pass through quickly
    • Some survive in food particles
    • Small intestine: few organisms
    • Large intestine: largest microbial population of body (10^13 to 10^14 microbial cells) eliminated by peristalsis, desquamation, and movement of mucus
    • Replaced rapidly due to rapid doubling times
    • Most microbes are anaerobes

    Bacteria Associated with Mucous Membranes

    • Mucous membranes are frequent sites of infection due to a favorable environment for bacterial growth

    Major Bacteria Present (Table 28.2)

    • Data presented in the shown table

    Bacteroides

    • Colonizes exfoliated host cells, food particles, and sloughed mucus
    • Rapidly eliminated if not attached
    • Adheres to particles in the gut, not the gut itself
    • Degrades complex carbohydrates along with methanogens for energy

    Bacteroides and Obesity

    • Human gut: has 10-100 trillion bacteria that break down food (sugar polymers)
    • Obese people have less Bacteroides and more Firmicutes
    • Bacteroides populations increase as obese people lose weight
    • Bacteria-free mice infected with microbial population from guts of obese mice become obese
    • Microbes determine how many calories can be extracted and absorbed

    Why?

    • Firmicutes have numerous enzymes that break down "indigestible" carbohydrates.

    Innate Resistance to Infection

    • Nonspecific barriers prevent colonization of the host by most pathogens
    • Lysozyme in tears and other secretions dissolve cell walls
    • Normal flora compete with pathogens
    • Rapid pH change inhibits microbial growth
    • Flushing of urinary tract prevents colonization
    • Blood proteins inhibit microbial growth
    • Mucus and phagocytes prevent colonization
    • Stomach acidity inhibits microbial growth
    • Normal flora compete with pathogens

    Deaths by Cause, Circa 2017

    • Worldwide mortality data from 2017 presented (see chart)

    Worldwide Deaths Due to Infectious Diseases, 2002

    • Worldwide mortality data from 2002 presented (see chart) and various causative agents are detailed. This data is used to demonstrate the importance of disease data

    Transmission Routes

    • Person-to-person: airborne, direct contact, sexually transmitted
    • Zoonotic and vector-borne
    • Soil-borne
    • Waterborne
    • Foodborne

    Terms of Pathogenicity

    • Attenuation: the decrease or loss of virulence
    • Toxicity: ability of an organism to cause disease through toxin production; toxins can travel to the host's sites
    • Invasiveness: ability of pathogen to grow in host tissue inhibiting host function; causes damage without producing toxin.
    • Many pathogens use a combination of toxins, invasiveness, and virulence factors to enhance pathogenicity

    Pathogenesis

    • Pathogens use various strategies to establish virulence
    • Exposure to pathogens
    • Adherence to skin or mucosa
    • Invasion through epithelium
    • Colonization and growth
    • Produce virulence factors
    • Toxicity (local or systemic)
    • Invasiveness (original site and distant sites)
    • Tissue damage and disease

    Adherence of Pathogen

    • Pathogen gains access to host tissues and multiplies before damage can be done
    • Infectious bacteria and viruses often adhere specifically to epithelial cells
    • Interactions between pathogen surfaces and host cell surfaces facilitate adherence

    Major Adherence Factors

    • Factors such as capsules/slime layers, adherence proteins, lipoteichoic acid, fimbriae (pili) facilitate the attachment of microbial pathogens

    Invasion

    • Starts at the site of adherence
    • May spread throughout the host via the circulatory or lymphatic systems
    • Availability of nutrients is important to pathogen growth
    • Pathogens may grow locally at site of invasion or throughout the body

    Virulence

    • Estimated from experiments using LD50 (lethal dose 50): dose of agent that kills 50% of animals in test group

    Virulence

    • Highly virulent pathogens: little difference in number of cells between LD50 and LD100
    • Moderately virulent pathogens may show greater difference in number of cells between LD50 and LD100.

    Virulence Factors

    • Enzymes enhance virulence by breaking down or altering host tissue for nutrient access
    • Hyaluronidase breaks down hyaluronic acid, protecting pathogens from host defense mechanisms
    • Coagulase allows bacteria to be coated with fibrin
    • Virulence factors can be encoded by bacteriophages, plasmids, and transposons

    Virulence Factors: Salmonella

    • LPS (Lipopolysaccharide) is found in gram-negative cell walls and is present in food-borne pathogens
    • O-specific polysaccharide
    • Iron uptake using siderophores
    • Virulence plasmid only in pathogenic strains
    • Fimbriae for adherence
    • Enterotoxin affects the small intestine

    Exotoxins

    • Proteins released from pathogenic organism as it grows
    • Categories include:
      • Cytolytic toxins
      • AB toxins
      • Superantigen toxins

    Cytolytic Toxins

    • Work by degrading cytoplasmic membrane integrity
    • Causing host cell lysis and death
    • Hemolysins

    Example; Staphylococcal α-toxin

    • Makes a pore in cell membranes for cell death by causing leakage of intracellular components

    AB Toxins

    • Consist of A and B subunits
    • Work by binding to host cell receptor (B subunit) and transfer a damaging agent (A subunit) across the cell membrane

    Diphtheria Toxin

    • Catalyzes ADP-ribosylation of elongation factor 2 (EF-2)
    • Prevents transfer of amino acids to growing peptide chain in ribosome

    Botulism (Clostridium botulinum)

    • Botulinum toxin blocks the release of acetylcholine to muscle tissue resulting in a permanent relaxed state
    • The toxins can be from food and cause paralysis and death

    Botulism cases (graph)

    • Time-series data showing outbreaks, mostly food-borne, and especially infant botulism.

    Superantigens

    • Stimulate large numbers of immune cells
    • Result in extensive inflammation and tissue damage.
    • Antigens mediate interaction with over 5% of lymphocyte pool

    Endotoxins

    • Lipopolysaccharide (LPS) portion of cell wall of certain gram-negative bacteria
    • Generally less toxic than exotoxins

    Campylobacter jejuni endotoxins

    • Food-borne pathogen of poultry
    • Most common cause of bacterial gastroenteritis
    • 1 in 1,000 people develop Guillain-Barré Syndrome
    • Paralytic disorder

    C. jejuni LPS components

    • Mimic human gangliosides (host sugars) causing immune system to attack own sugars

    Airborne Pathogens

    • Aerosols are important for person-to-person transmission
    • Most pathogens survive poorly in air
    • Respiratory infections, Different pathogens

    Respiratory Tract Colonization

    • Upper and lower respiratory tracts differ in their environments (temperature, air flow, pH).
    • This favors different microbes to colonize the respiratory tract

    Tuberculosis

    • Caused by Mycobacterium tuberculosis
    • Hansen's disease (leprosy) caused by Mycobacterium leprae
    • Acid-fast because of the waxy mycolic acid content of their cell walls.

    Tuberculosis (Incidence and Transmission)

    • Worldwide infectious disease of humans
    • Incidence is increasing.
    • Transmitted by airborne droplets
    • Cell-mediated immunity plays critical role

    Tuberculosis (Treatment)

    • Prevent by hospitalization of patients, face masks of healthcare workers
    • Treatment usually requires a nine-month regimen of isoniazid or rifampin to affect mycolic acid in mycobacteria
    • Direct observed therapy is popular to assure compliance and reduce risk

    Tuberculosis (MDR and XDR)

    • Multidrug-resistant (MDR-TB): resistant to isoniazid and rifampin
    • Extensively drug-resistant (XDR-TB): MDR-TB resistant to isoniazid, rifampin, fluoroquinolones, and injectable drugs

    Risk Factors of Infection

    • Compromised Host: one or more resistance mechanisms are inactive
    • Age: factor for determining susceptibility to infectious diseases
    • Stress: predisposes healthy individuals
    • Diet and lifestyle choices
    • Genetic Conditions can compromise a host

    Specific Immunity

    • Complex, multi-pathway systems; innate immunity (phagocytes), T-cell immunity, and antibody-mediated immunity
    • Immune system recognizes organism, person becomes immune, resulting in immune memory

    The Immune System

    • Complex and diverse to cover

    Immunization

    • Inoculation with attenuated or killed pathogens or chemically modified exotoxin-vaccination
    • Immune system recognizes specific antigens - may mutate
    • Why we need new flu vaccine each year: more likely with viral than bacterial diseases

    Herd Immunity

    • In a context of vaccines, it protects vulnerable individuals that cannot be vaccinated; blocking transmission
    • In a context of illness, a sufficient number of population is immunized

    Disease Eradication (Polio and Measles)

    • Polio and measles need to be eradicated in populations with vaccination, but vaccination campaigns may be compromised.

    Reported Cases (Measles)

    • Data plotted in time series to show reported cases of measles.

    Reported Cases (Polio)

    • Data provides a graph showing the prevalence of polio cases.

    Polio Virus in Wastewater

    • Discovery extending virus's presence in NYC

    Additional Information (Table 33.9)

    • Table of factors encoded by bacteriophages, plasmids, and transposons

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