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68 Cards in this Set
- Front
- Back
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Metagenome |
All the genes of the host, including those of its microbiota |
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Microbiome |
- All of the organisms in a biological system (e.g., organisms in and on a human) - Contains a lot of genes that we do not ourselves encode for. Contributes to plasticity |
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What are the four main phyla of the human skin? What three genera comprise 60% of the 200 different genera of the skin identified? |
Four Phyla: 1) Actinobacteria 2) Firmicutes 3) Proteobacteria 4) Bacteroidetes Three Main Genra: 1) Corynebacteria 2) Staphylococcus 3) Propionibacterium |
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What are the three microenvironments of the human skin? Describe the human skin's overall environment. |
Moist, dry, sebaceous The human skin is slightly acidic with high NaCl content. It is often dry and may contain agents to kill bacteria or limit their growth. |
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What two enzymes does saliva produce? |
Lysozyme and lactoperoxidase |
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Describe the microenvironment of the mouth. |
- Neutral pH - Moderate temperature - Available moisture - Available nutrients - Bacteria must resist breakdown by enzymes in the saliva and mechanical removal |
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What is the most abundant genera in the mouth |
- Firmicutes - Most microbes are facultatively aerobic - Anaerobic microbes live in areas like the gums |
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Which genera of bacteria produce adherence factors and form dental plaques, cavities, and gingivitis in the mouth? |
Streptococci |
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What are some common anaerobes present in the mouth? |
Bacteroidetes: Porphyromonas and Prevotella |
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The Stomach |
- Very acidic, hostile environment (2-3 pH) - Less than 10 microbes / mL |
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What microbes are commonly found in the stomach? |
Everyone has some gram positives: - Streptococcus - Staphylococcus - Lactobacillus May also have: - Proteobacteria - Bacteroidetes - Candida - Helicobacter (ulcer-causing) |
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What are the three parts of the small intestine? |
1) The duodenum 2) The jejunum 3) The ileum |
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The Duodenum |
- The first part of the small intestine - Acidic, so few bacteria |
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The Jejunum |
- Start to see some gram positives - Enterococcus faecalis - Lactobacilli - Diptheroids - Candida |
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The Ileum |
- More alkaline - Similar flora to the colon - Enterobacteriaceae (anaerobic gram negative) |
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The Large Intestine |
- Largest microbial community - 10^10 - 10^11 organisms / gram - Mostly anaerobic - Gram negative and gram positive rods - Yeasts and protozoans - Bacteroidetes, Firmicutes (including Clostridium), Proteobacteria, and Verrucuomicrobia - Sheds 3x10^13 microbes every day! |
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What species account for 99% of all bacteria in the large intestine? |
- Bacteroidetes - Gram positives |
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What is the nose commonly colonized by? |
- Staphylococcus aureus - Staphylococcus epidermidis - Corynebacteria - Lots of gram positives (similar to skin) |
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What are some potentially pathogenic organisms harboured in the nasopharynx? |
- Streptococcus pneumoniae - Neisseria meningitidis - Haemophilus influenza Neisseria meningitidis may live in 30% of the population |
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What bacteria occupy the oropharynx? |
- alpha-hemolytic streptococci - diphtheroids - Small, gram negative cocci |
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Is there microbial growth in the lower respiratory tract? |
No. Unless you have been infected or immunocompromised |
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Is there microbial growth in the upper tract of the genitourinary tract? |
- No, this area should be sterile. - Advancement of infection to the kidney can be serious, but it is difficult for the bacteria to take a hold |
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What are some microbes common to the female genital tract? |
- Lactobacillus acidophilus (Firmicutes): produces lactic acid and inhibits growth of other microbes - Candida (yeast) - Streptococci - E. coli Babies pass through the birth canal and pick up their first bacteria |
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Host |
Larger organism supporting the parasite |
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Infection |
When a host is supporting a parasite |
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Pathogen |
Organism that is capable of causing disease |
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Primary Pathogen |
Capable of infecting a healthy host |
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Opportunistic Pathogen |
Infects hosts with a compromised immune systems |
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Latent State |
Stage at which a parasitic organism is not infectious, therefore there are no symptoms |
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Virulence |
- Degree of pathogenicity - The more virulent it is, the more capable it is of causing disease |
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Attenuation |
- The decrease or loss of virulence of a pathogen - Viruses are attenuated to create a vaccine |
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What are the three stages of infection? |
1) Sticking to host cells 2) Invasion of host cells - penetrating into the deeper layers of the dermis 3) Infection: production of different virulence factors. Results in disease |
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Disease |
Tissue damage or injury that impairs host function |
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Lethal Dose50 |
The number of cells of a pathogen that kills 50% of the animals in a test group |
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Glycocalyx |
- Polysaccharide components outside of the bacterial cell wall; usually a loose network of polymer fibres extending outward from the cell - May include capsules and slime layers |
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Slime Layer |
A loose network of polymers extending outward from a cell |
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Capsule |
- A coat consisting of a dense, well-defined polymer layer surrounding the cell - Some bacteria have the ability to change sugars that make up the capsule to avoid detection by the host's immune system - Association with host cells allows for initial adherence |
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Non-covalent Adherence Factors |
These factors are associated with, but not covalently bound to the pathogen |
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Covalent Adherence Factors |
- Proteins that are covalently bound to the bacteria - Include fibre, pili, and flagella - e.g., Neisseria gonorrhoea first interacts via Type IV pili, allowing tighter binding via adhesions called Opa proteins |
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Opa Proteins |
Covalent adherence factor of Neisseria gonorrhoea that binds specifically to a host protein called CD66 found only on the surface of mucosal epithelial cells in the genitourinary tract |
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Invasion |
- The ability of a pathogen to enter into host cells or tissues, spread, and cause disease - Usually begins at breaks or wounds in the skin or on the mucous membranes of the respiratory, digestive, or genitourinary tract this is because wounds provide easy access while mucous membranes have a direct pathway to the environment |
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Bacteremia |
The presence of bacteria in the bloodstream, from where they can travel to distant parts of the body |
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Septicaemia |
- A blood borne systemic infection that may lead to massive inflammation and death - "Blood poisoning" |
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What are the two microbial species implicated in tooth decay? How do they decay teeth? |
Streptococcus sobrinus: has an affinity for salivary glycoproteins secreted onto smooth tooth surfaces Streptococcus mutans: resides in crevices and small fissures where it produces dextran, a strongly adhesive polysaccharide that it used to attach to tooth surfaces Streptococci ferment glucose to lactic acid, destroying enamel over time. Over time, decalcification results in dental cavities Dental cavities are therefore an infectious disease |
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Dextran |
A strongly adhesive polysaccharide produced by Streptococcus mutants to attach to tooth surfaces |
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What allows bacteria to bind to the smooth surface of teeth? |
Acidic glycoproteins from saliva form a film on the tooth surface |
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What bacteria colonize the thick biofilm formed over the surface of teeth? |
- Fusobacterium (filamentous) - Borrelia - Actinomyces (filamentous) |
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Virulence Factors |
- Physical and chemical characteristics that contribute to pathogenicity - May be features of the bacteria themselves or be secreted proteins - May relate to ability to survive in external environments or be involved in invasiveness - Are often enzymes |
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Pathogenicity Island |
- Genes that encode major virulence factors - Transferred by horizontal gene transfer - 3' and 5' ends have IS-like elements, suggesting they are mobile - G+C content of pathogenicity island may differ considerably from that of the rest of the genome - Contain several putative open reading frame - Can be encoded on plasmids |
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Toxicity |
- The ability of an organism to cause disease by means of a preformed toxin that inhibits host cell function or kills host cells - Alter the normal metabolism of the host - Once bacteria have been cleared, toxins can remain in the system |
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Exotoxins |
- Toxic proteins released from the pathogen as it grows - Soluble - Heat-labile - Mainly produced by gram positive bacteria - Measure in ng/kg - Travel from the site of infection and cause damage at distant sites - Host may protect itself by raising antibodies against the toxin - A host may build up immunity to released toxins, because of low-level exposure in the past |
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Intoxication |
Diseases that result from exposure to toxins |
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Cytolytic Toxins |
- Work by degrading cytoplasmic membrane integrity, causing lysis - Soluble - Also called 'cytotoxins' - Type II exotoxin (damages the membrane) - Form membrane-spanning pore to release cytoplasmic contents and allow the influx of extracellular material, killing the cell |
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AB Toxins |
- Consist of two subunits - The B component binds to a host cell surface molecule, facilitating the transfer of the A subunit across the cytoplasmic membrane, where it damages the cell |
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Superantigen Toxins |
- Work by stimulating large numbers of immune cells (T cells), resulting in extensive inflammation and tissue damage - Commonly associated with Staphylococcus aureus and Streptococcus pyogenes - T cell and APC interact in the absence of corresponding antigen - May lead to the activation of 5-25% of T cells, instead of the 0.01% activated during a regular immune response - May result in toxic shock and death - 'Cytochine storm" |
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Type I Toxins |
- Act from cell surface - Toxin binds to host receptor to initiate signal |
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Type II Toxins |
-Membrane-damaging or cytolytic |
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Type III Toxins |
Intracellular: toxin enters into the cell and exerts its effect |
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Enterotoxins |
- Exotoxins whose activity affects the small intestine, generally causing secretion of fluid into the intestinal lumen resulting in vomiting and diarrhea - Usually acquired by ingestion of contaminated food or water |
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Endotoxins |
The toxic lipopolysaccharides (LPS) found in most gram-negative bacteria - Structural components of the gram-negative outer membrane and are thus not soluble products of growing bacteria (like exotoxins) - Are released when the organism is lysed - Lipid A is the toxic component - May lead to septic shock |
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Lipid A |
The toxic component of endotoxins (LPS) |
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What are some human barriers to infection? |
1) The Presence of the Normal Microflora (especially on the skin and in the gut) 2) Natural Host Resistance (some animals are more susceptible than others) 3) Infection Site (the organism cannot infect the host if the site is not compatible with the pathogen's nutritional and metabolic needs) 4) Physical and Chemical Barriers: the structural integrity of tissue surfaces |
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What are some examples of direct contact person-to-person transmission? |
- Horizontal Contact (e.g., kissing, sex) - Airborne Droplets - Vertical Contact - Vector-transmitted |
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What are some examples of indirect contact pathogen transmission? |
- Contact with an object - Through food, water, or biological products - Airborne in dust particles |
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Fomites |
Inanimate objects that, when contaminated with a viable pathogen, can transfer the pathogen to a host |
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External Vector-Borne Transmission |
When the organism is carried on the vector (on legs) |
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Internal (Harbourage) Vector Transmission |
When the organism is carried within the vector and does not undergo a change |
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Internal (Biological) Vector Transmission |
The organism is changed biologically during its passage through the vector |
