7.1 HOST-MICROORGANISM INTERACTIONS - PART 1 Flashcards
→ growth and multiplication of microorganisms that cause damage to the host
Infection
→bodily invasion of pathogenic microorganisms that reproduce, multiply and then cause disease through local injury, toxin secretion or An-Ab reaction to the host
Infection
→caused by microorganism from the microbiota of the host
Autogenous Infection
→ result of medical treatment or procedure
Iatrogenic infection
→affects immunocompromised host
Opportunistic Infection
→hospital-acquired infection
Nosocomal infection
Types of Infections
a. Autogenous
b. Iatrogenic
c. Opportunistic
d. Nosocomal
4 common types of INFECTION
- UTI
- Lung Infection (Pneumonia)
- Surgical site Infection
- Blood stream Infection
Predisposing factors
a. Wide variety of microbes in the hospital environment
b. Immunocompromised patient
c. Chain of transmission (direct or Indirect)
Chain of Transmission EXAMPLES
✓ Health worker to patient
✓ Patient to patient
✓ Use of fomites(catheters, needles, dressings, beds)
✓ Airborne transmission
✓ Vector-borne
Airborne transmission (TB & Pertussis)
TB: < 5um, Pertussis: > 5um
cornerstone of modern infection control program
Handwashing
TYPES OF INFECTION ACCORDING TO HOST DISTRIBUTION
- Local Infection
- Focal Infection
- Systemic Infection
signs and symptoms are confined in one area; wounds, boils, abscesses
Local Infection
starts as a focal infection before spreading to other parts of the body
Focal Infection
spread throughout the body through the blood or lymph
Systemic Infection
presence of bacteria in blood; highest concentration of bacteria in blood occurs before the fever spikes
Bacteremia
active multiplication of bacteria in blood
Septicemia
pus-producing organisms repeatedly invade the bloodstream and become localized at different parts of the body
Pyremia
presence of toxins in the blood
Toxemia
Classification of Disease According to Occurrence
- Sporadic
- Endemic
- Epidemic
- Outbreak
- Pandemic
disease that occurs occasionally
Sporadic
a disease constantly present at some rate of occurrence in a particular location
Endemic
a larger than normal number of diseased or
infected individuals in a particular location
Epidemic
a larger than normal number of diseased or infected individuals that occurs over a relatively short period
Outbreak
an epidemic that spans the world
Pandemic
a person who carries the etiologic agent but shows no apparent signs or symptoms of infection or disease
Carrier
harbors the microorganism temporarily for a few days or weeks
Causal/Acute/Transient Carrier
remain infected for a relatively long time, sometimes throughout its entire life (Typhoid Bacillus)
Chronic Carrier
recovered from infection but continuous to harbour larger numbers of the pathogen
Convalescent Carrier
overt clinical case of the disease
Active carrier
PHASES OF INFECTIOUS DISEASES
- Incubation Period
- Prodromal Period
- Clinical or Illness Period
- Decline Period
- Convalescence or the Period of Recovery
time between the exposure to a pathogenic organism and the onset of symptoms
Incubation Period
appearance of signs and symptoms period
Prodromal Period
peak of characteristic signs and symptoms
Clinical or Illness Period
signs and symptoms begin to subside as the host’s condition improves
Decline Period
host is recuperating towards full recovery
Convalescence or the Period of Recovery
a microorganism responsible for causing infection or infectious disease
Causative/Etiologic Agent
organism capable of producing disease
Pathogen
a quantitative measure of the degree of pathogenecity of a particular microorganism
Virulence
microorganism that does not cause disease; may be part of the normal flora
Nonpathogenic
an agent capable of causing disease only when the host’s resistance is impaired (PAE, Stenotrophomonas maltophilia)
Opportunistic pathogen
means by which etiologic agents are brought in contact with the human host (e.g. infected blood, contaminated water, insect bite)
Mode of Transmission
a non-living entity that is contaminated with
the etiologic agent and as such is the mode of
transmission for that agent
Vehicle/Fomite
a living entity (animal, insect, or plant) that transmits the etiologic agent
Vector
an animal or plant that harbors or nourishes another organism
Host
an organism which is dependent on another
organism for food and shelter
Parasite
any type of epidemiologic investigation that involves data collection for characterizing circumstances surrounding the incidence or prevalence of a particular disease or infection
Surveillance
the state of disease and its associated effects on the host
Morbidity
death resulting from disease
Mortality
laboratory-based characterization of etiologic agents designed to establish their relatedness to one another during a particular outbreak or epidemic
Strain typing
origin of the etiologic agent or location from which they disseminate (e.g., water, food, insects, animals, other humans)
Reservoir
the etiologic agent responsible for an epidemic or outbreak originates from a single source or reservoir
Common Source
association of two organisms living in close
proximity
Symbiosis
refers to a mutually beneficial relationship
between two species
Mutualism
a relationship wherein the parasite derives benefits from the host without causing injury or harm to the host
Commensalism
a relationship whereby one organism derives
benefits at the expense of another
Parasitism
ability of the organism to produce disease
Pathogenicity
large groups of genes that are associated with pathogenicity and are located on the bacterial chromosome
Pathogenicity Island
the ability of the organism to enter host tissues, multiply, and spread faster
Invasiveness
ability of the organism to produce toxins
Toxigenicity
non-poisonous forms of toxins which can be used for vaccination
Toxoid
Toxoid Preparation
✓ By aging
✓ By exposure to heat
✓ By exposure to 50% alcohol, formaldehyde, and dilute acids
General Stages of Microbial-Host Interaction
Physical encounter between host and microorganism → Microorganism colonization of host surface(s) → Microorganism entry, invasion, and dissemination → Outcome
microorganisms that are commonly found on or in body sites of healthy persons
Normal, Usual, or Indigenous Flora
microorganisms that colonize an area for months or years
Resident Microbial Flora
microorganisms that are present at a site temporarily represent
Transient Flora
Microorganism’s presence depends on:
✓physiologic factors of temperature
✓moisture
✓presence of certain nutrients and inhibitory substances
Microbial Flora ROLE!!!
➢Provide a first line of defense against microbial pathogens
➢Assist in digestion and absorption of nutrients; also synthesis of Vitamin K
➢Play a role in toxin-degradation
➢Contribute to maturation of the immune system
How does MICROBIAL FLORA provides first line of defense?
✓competition for receptors or binding sites on host cells
✓competition for nutrients
✓mutual inhibition by metabolic or toxic products
✓mutual inhibition by antibiotic materials or bacteriocins
Different Body Site of Microbial Flora
a. Usual Flora of the Skin
b. Usual Flora of the Mouth
c. Usual Flora of the Respiratory Tract
d. Usual Flora of the GIT
e. Usual Flora of the Genitourinary Tract
**_____________ in vagina is a part of the normal flora but are important colonizers
Escherichia coli
ability of a microbe to produce disease in a
susceptible individual
Pathogenicity
→are organisms recognized to cause disease in healthy immunocompetent individuals
True pathogens
Example of True Pathogens
Yersinia pestis
Bacillus anthracis
→cause disease if the host is immunocompromised
Opportunistic pathogens
Example of Opportunistic Pathogen
E. coli
Conditions Compromising Host Defenses
Foreign bodies
Alcoholism
Burns
Hematoproliferative disorders
Cystic fibrosis
Immunosuppression
Examples of Foreign Bodies that can compromise host defenses
catheters, shunts, prosthetic heart valves
Foreign bodies - Organisms
Staphylococcus epidermidis
Propionibacterium acnes
Aspergillus spp.
Candida albicans
Viridans streptococci
Serratia marcescens
Pseudomonas aeruginosa
Alcoholism - Organisms
Streptococcus pneumoniae
Klebsiella pneumoniae
Burns - Organisms
Pseudomonas aeruginosa
Hematoproliferative disorders - Organisms
Cryptococcus neoformans
Varicella-zoster virus
Cystic fibrosis - Organisms
Pseudomonas aeruginosa
Burkholderia cepacia
Immunosuppression (drugs, congenital disease) - Organisms
Candida albicans
Pneumocystis jirovecii (carinii)
Herpes simplex virus
Aspergillus
Diphtheroids
Cytomegalovirus
Staphylococcus spp.
Pseudomonas spp.
→relative ability of a microorganism to cause disease or the degree of pathogenicity
→measured by the numbers of microorganisms necessary to cause infection in the host
Virulence
Microbial Virulence Factors
a. inhibiting phagocytosis
b. Facilitating adhesion to host cells or tissues
c. enhancing intracellular survival after phagocytosis
d. damaging tissue through the
e. production of toxins and extracellular enzymes
→highly virulent
→mask the cell surface structures that are recognized by receptors on the surface of the phagocytic cell
→inhibits the activation of complement by masking structures to which complement proteins bind
Capsule
Example of Microorganisms that uses Capsule to resist Phagocytosis
Streptococcus pneumoniae
Haemophilus influenzae
Neisseria meningitidis
Klebsiella pneumonia
Salmonella typhi
Pseudomonas aeruginosa
Bacillus anthracis
Yersinia pestis
→interfering with the binding of the host’s antibodies to the surface of the organism
→ binds to the Fc portion of IgG preventing opsonization and phagocytosis by turning the antibody around on the surface
Protein A
Protein A is found in the cell wall of
Staphylococcus aureus
CELL WALL PROTEINS
- M protein
- Fimbriae and Outer Membrane Protein
- Mycolic Acid
- Antigenic variation
→heat resistant and acid resistant protein, mediates attachment to host epithelial cell and helps resist phagocytosis; overcome by antibodies produced this protein
M protein
Neisseria gonorrhoeae - Cell Wall Proteins
Fimbriae and Outer Membrane Protein
Antigenic variation
→M. tuberculosis; resist digestion during phagocytosis; the bacteria can even multiply inside macrophages
Mycolic acid
→produced by Streptococci
→lyse red blood cells and induce toxic effects on WBC
Hemolysins
→realesed by pathogenic staphylococci
→cause lysosomal discharge into cell cytoplasm
Leukocidins
→ Staphylococcal leukocidin
→lethal to leukocytes and contributes to the
invasiveness of the organism
Panton-Valentine
→cell surface structures that mediate
attachment
Adhesins
Main Adhesins in Bacteria:
- Fimbriae (pili)
- Surface polysaccharides
→enable bacteria to adhere to host cell surfaces, offering resistance by attachment to target cells, increasing the organism’s colonizing ability
Fimbriae (pili)
→ use lactoferrin as a source of iron
Meningococci
→produce an IgA protease that degrades the IgA found at mucosal surfaces
H. influenzae, N. gonorrhoeae, and N. meningitides
→circumvent host antibodies by shifting key cell surface antigens
Borrelia spp.
→microorganisms able to multiply intracellularly
Chlamydia, Mycobacterium, Brucella, and Listeria
→ ability to penetrate and grow in tissues
Invasion
→ disease or organisms spread to distant sites Example: Salmonella spp.
Dissemination
highly invasive organism that may not disseminate
Clostridium perfringens
→poisonous substances produced by organisms that interact with host cells, disrupting normal metabolism and causing harm
Toxins
→soluble substances that liquefy the hyaluronic acid of the connective tissue matrix, helping to spread bacteria in tissues, promoting the dissemination of infection
Proteases and Hyaluronidases
→breaks down collagen, which forms the connective tissue of muscles and other body organs and tissues
Collagenase
→hydrolyzes hyaluronic acid, a type of
polysaccharide that holds together certain cells of the body, particularly cells of the connective tissue helping the organism spread from its initial site of infection
Hyaluronidase
can cause cellulitis
Streptococcus pyogenes
can cause gas gangrene
Clostridium perfringens
→produced by S. aureus and accelerates the
conversion of fibrinogen to a fibrin clot
Coagulase
Kinases
Streptokinase
Staphylokinase
→ destroy IgA antibodies found on secretions
Immunoglobulin A protease (IgA protease)
→ destroy neutrophilic leukocytes and macrophages
Leukocidin
→composed of two subunits: nontoxic (binds the toxin to the host cells) and toxic
→produced by both gram-negative and gram-positive bacteria
Exotoxins
→secreted by the organism into the extracellular environment, or they are released on lysis of the organism
→mediate direct spread of the microorganisms through the matrix of connective tissues and can cause cell and tissue damage
Exotoxins
→encoded by phages, plasmids, or transposons
Toxic Gene
→good antigens and induce the production of antibodies called
ANTITOXINS
When treated with formaldehyde (or acid or heat), the exotoxin polypeptides are converted into _____________, which are used in protective vaccines
TOXOIDS
Examples of EXOTOXINS
✓Diphtheria toxin
✓Tetanospamin
✓Botulism toxin
✓Heat labile enterotoxin by E. coli, Vibrio, Bacillus
✓Verotoxin
✓Erythrogenic toxin
✓Three toxins of B. anthracis (EF, PA, LF)
✓TSST-1
3 principal types on the basis of Exotoxin structure and function:
- A-B Toxin
- Membrane-Disrupting Toxins
- Superantigens
→composed of the LPS portion of the outer membrane
on the cell wall of gram-negative bacteria
→do not have enzyme activity
→secreted in only very small amounts
→do not have specificity in their activity on host cells
ENDOTOXINS
→not very potent
→not destroyed by heating
→less antigenic and induce antibody production in a poor manner
→no toxoid have been produced from enough
endotoxin
ENDOTOXINS
Effects of Endotoxin
✓Stimulates the fever centers in the hypothalamus (1 hour after exposure)
✓Hypotension (30 minutes after exposure)→Shock
✓Initiates coagulation→DIC
✓Severe neutropenia
✓Activates macrophages, activates complement, and has an adjuvant effect with protein antigens
✓stimulates interferon production and causes changes in carbohydrates, lipids, iron, and sensitivity to epinephrine
→ test to detect endotoxins in drugs, medical devices, and body fluid
Limulus Lysate Test
Limulus Lysate Test
Reagent used:
Limulus polyphemus (horse shoe crab)
Principle of the Limulus Lysate test:
in the presence of endotoxin, the horse shoe crab will release amoebocytes which results to positive result of clumping
Positive Result of Limulus Lysate Test:
Clumping (there is endotoxin in the body fluid or bacterial instrument)
