WEEK 3: HOST-MICRO CONTROL Flashcards
Biological relationship between two or more organisms where both benefit from one another.
Symbiosis (Mutualism)
Organism benefits but there is no beneficial or harmful effects to the host
Commensalism
The microbe benefit at the expense of the
other (host).
Parasitism
Commonly found in body sites of healthy persons.
Microbial Flora
Microorganisms that colonize an area for months or years.
Resident microbial flora
➢ Present at a site temporarily, eliminated by host immune defense / competition with
resident flora.
➢ Carrier state may be acute (S. aureus) or
chronic (S. typhi)
Transient microbial flora
E.g: Diptheroids in moist areas
Nutritional and Environmental factors
E.g: P. acnes in hair follicles
Resistance to bile, lysozymes or fatty acids
E.g: Lactobacillusin Female genital tract
pH
E.g: Obligate anaerobes in the colon
Oxidation-reduction potential
Mouth, nasopharynx, oropharynx
and larynx
Upper Respiratory Tract
Viridans Strep. and Gram (-) anaerobes
Mouth
Diplococci and Diphtheroids * Oropharynx → Gram (-) anaerobes and Diphtheroids
Nose and Nasopharynx
Anaerobes makes up 90% of the microbial
flora
➢ Esophagus, stomach, small
intestine, and colon
Respiratory Tract
➢ G(+) staph and Enterococcus
➢ Anaerobic G(+) cocci and spore forming bacilli
➢ Enterobacteriaceae
Respiratory Tract
Example:
➢ Lactobacillus acidophilus
➢ Anaerobic Sporeformers
➢ G(+) cocci / Diphtheroids
Gastrointestinal Tract
Gastrointestinal Tract
➢ Sites – urethra and vagina
➢ Sterile – Kidneys, bladder and fallopian
tubes
➢ Activates or primes the immune system (e.g. cell mediated immunity)
➢ Blocks the colonization of extraneous pathogens.
Microbial Flora a in the Host Defense Against Infectious Disease
➢ Cause disease when their habitat is damaged, disturbed or changed by trauma or;
➢ When the host’s immune system is weakened or compromised
Microbial Flora in the Pathogenesis Infectious Disease
Is the ability of a microbe to produce disease in a susceptible individual.
Pathogenicity
➢ Organisms recognize to cause disease in healthy immune-competent individuals.
➢ B. anthracis and Y. pestis
True Pathogen
➢ Organisms that cause opportunistic or iatrogenic infections (medical treatment or procedures)
➢ H. influenzae and S. epidermidis
Opportunistic Pathogen
Is the relative ability of a microorganism to cause disease or the degree of pathogenicity
Virulence
➢ Allows pathogens to evade or overcome host defenses and cause disease
➢ E.g. Fimbriae, Capsules and Toxins
Microbial Virulence Factors
type of interference in staphylococcus and streptococcus
kill phagocyte
induces lysosomal discharge
leucocidin and streptolysin
type of interference in H. influenza, P. aeruginosa, E. coli, and S. typhi
resist phagocytosis
mechanism of E. coli
O and K antigen
mechanism of H. influenza
polysaccharide capsule
mechanism of P. aeruginosa
surface slime (polysaccharide)
e.g. Chlamydia, Mycobacterium, Brucella
and Listeria
Ability to Survive Intracellularly
➢ Cell surface structures that mediate attachment
➢ E.g. fimbriae and surface polysaccharides
Adhesins
mechanism of S typhi
Vi antigen
▪ e.g. lactoferrin – meningococci; IgA
protease – H. influenzae and Neisseria)
Ability to avoid or overcome local factors
these two contribute to low pH.
Microbial flora and Sebaceous gland
▪ e.g. Salmonella
Ability to Proliferate (Dissemination)
Poisonous substances produced by organisms that interact with host cells, disrupting normal metabolism and causing harm.
Toxins
➢ Secreted by the organism into the extracellular environment
➢ Toxin gene is commonly encoded by phages, plasmids or transposons.
Exotoxins
➢ A constituent Lipid A of the outer membrane of gram (-) bacteria
➢ Released upon lysis of the organism
Endotoxins
presents as mechanical barrier
Skin epithelium
(hydrolyzes peptidoglycan layer of bacterial cell walls) and β-lysin in serum and/or body fluids
Complement, Lysozyme
cellular protein that inhibit proliferation of viruses
Interferons
I. Desquamation of skin surfaces.
II. Flushing of tears and urine
III. Mucus production of membrane lining the
nasopharynx.
IV. Sweeping of particles by Ciliary epithelium
(trachea)
V. Low pH of the stomach
Cleansing Mechanisms
I. HCl in the stomach
II. Secretory IgA of the mucosa
III. Complement, Lysozyme (hydrolyzes
peptidoglycan layer of bacterial cell walls)
and β-lysin in serum and/or body fluids
IV. Interferons - cellular protein that inhibit
proliferation of viruses
Antimicrobial Substances
I. Compete with pathogens for nutrients and
space
II. Produce bacteriocins(inhibit the growth of
closely related bacteria)
III. Production of metabolic byproducts that
inhibits pathogens
IV. Synthesis of vitamins and other essential
nutrients
Indigenous Microbial Flora
- chemotaxis
- attachment
- ingestion
- killing
Phagocytosis
enhanced phagocytosis by PMNs due to coating of bacterium with antibody or complement
Opsonization (opsonins)
migration of PMNs into area of infection
Chemotaxis
movement of PMNs from blood vessel into tissues (surveillance)
Diapedesis
I. Body’s response to injury or foreign body
II. Hallmark is accumulation of phagocytic
cells
III. Leukocytes and other cells release
mediators to cause erythema, edema and
pus
IV. Enzymes digest foreign particles, injured
cell and cell debris
Inflammation
increase blood flow (R)
Redness
increase temperature of affected tissue (C)
Heat
vasodilation of blood vessels (T)
Swelling
tissue damage and pressure from increased (D) flow of fluid and cells
Pain
acts as mediator of infection
Blood Proteins
➢ Physical & Chemical barriers - skin and
mucous membranes
➢ Blood Proteins - acts as mediator of
infection
➢ Cellular Mechanisms - phagocytosis
(neutrophils, macrophages, natural killer
cells)
Innate or Natural Immunity
phagocytosis (neutrophils, macrophages, natural killer cells)
Cellular Mechanisms
after infection (natural)
Active
Vaccination-Abs dev’t
Active
Abs from mother to child
Passive (natural)
Anti-toxin/ Immune globulin ex. Anti-tetanus
Passive
what does humor mean in latin?
body fluid
able to remember each time it encounters a particular antigen
*Anamnestic immune response (rapid increase in IgG Abs)
Immunologic memory
- intact skin
- mucous membranes and their secretions
- normal microbiota
first line of defense
- phagocytic white blood cells
- inflammation
- antimicrobial substances
second line of defense
- specialized lymphocytes: B cells and T cells
- antibodies
third line of defense
Routes of Transmission
A. Airborne Transmission
B. Food and Water
C. Close Contact
D. Cuts and Bites
E. Arthropods
F. Zoonoses
