host-microoganism interaction

infection

• growth and multiplication of microorganisms that cause damage to the host

• There is an invasion of pathogenic microorganisms, and in the body they reproduce; example by causing injury, toxin secretion, or initiate antigen-antibody reaction.

epitopes

surface antigens. portions of antigens that elicit immune response.

autogenous infection

caused by microorganism from form the microbiota of the host

iatrogenic infection

• result of medical treatment or procedure

• example: Health workers had an accidental prick from a needle that was used with patients with bloodborne disease, the tendency is we can also acquire these infections.

opportunistic infections

● affects immunocompromised host

● infections caused by pathogens that do not normally cause infections in healthy individuals, but when a person becomes immunocompromised (person with diabetes or cancer), the patients become susceptible with these kinds of microorganisms.

candida albicans

fungi like aspergillus

examples that causes opportunistic infections

nosocomial infections

hospital-acquired infections

urinary tract infections

lung infection (pneumonia)

surgical site infection

blood stream infection

4 common types of nosocomial infections

a. wide variety of microbes in the hospital environment

b. Immunocompromised patient

c. Chain of transmission

Predisposing factors of nosocomial infections

handwashing

cornerstone of modern infection control program

local infection

signs and symptoms are confined in one area; wounds, boils, abscesses

focal infection

start as a focal infection before spreading to the other parts of the body.

systemic infections

spread throughout the body through the blood or lymph

bacteremia

presence of bacteria in blood; highest concentration of bacteria in blood occurs before the fever spikes

septicemia

active multiplication of bacteria in blood

disseminated intravascular coagulation

intravascular coagulation

pyremia

pus-producing organisms repeatedly invade the bloodstream and become localized at different parts of the body

toxemia

presence of toxins in the blood

sporadic

endemic

epidemic

outbreak

pandemic

classification of disease according to occurrence

sporadic

occurs occasionally

endemic

a disease constantly present at some rate of occurrence in a particular location

epidemic

a large than normal number of diseased of infected individuals in a particular location

outbreak

a larger than normal number of diseased or infected individuals that occurs over a relatively short period.

pandemic

an epidemic that spans the world

carrier

a person who carries the etiologic agent but shows no apparent signs or symptoms of infection or disease.

Causal/Acute/Transient Carrier

harbors the microorganism temporarily for a few days or weeks

chronic carrier

remain infected for a relatively long time, sometimes throughout its entire life

Convalescent Carrier

recovered from infection but continuous to harbor larger numbers of pathogens.

active carrier

overt clinical case of the disease

incubation period

time between the exposure to a pathogenic organism and the onset of symptoms.

prodromal period

appearance of signs and symptoms

clinical or illness period

peak of characteristic signs and symptoms

decline period

signs and symptom begin to subside as the host’s condition improves

convalescence or the period of recovery

host is recuperating towards full recovery

Causative/Etiologic Agent

a microorganism responsible for causing infection or infectious disease.

pathogen

organism capable of producing disease

virulence

a quantitative measure of the degree of pathogenicity of a particular microorganism

nonpathogenic

microorganism that does not cause disease; may be part of the normal flora

opportunistic pathogen

an agent capable of causing disease only when the host’s resistance is impaired

mode of transmission

means by which etiologic agents are brought in contact with the human host

vehicle/fomite

a non-living entity that is contaminated with the etiologic agent and as such is the mode of transmission for that agent

vector

a living entity (animal, insect, or plant) that transmits the etiologic agent

host

an animal or plant that harbors or nourishes another organism

parasite

an organism which is dependent on another organism

surveillance

any type of epidemiologic investigation that involves data collection for characterizing circumstances surrounding the incidence or prevalence of particular disease or infection

morbidity

the state of disease and its associated effects on the hosts

mortality

death resulting from disease

strain typing

laboratory-based characterization of etiologic agents designed to establish their relatedness to one another during a particular outbreak or epidemic

reservoir

origin of the etiologic agent or location from which they disseminate (e.g. water, food, insects, animals, other humans)

common source

the etiologic agent responsible for an epidemic or outbreak originates from a single source or reservoir

symbiosis

association of two organisms living in close proximity

mutualism

refers to a mutually beneficial relationship between two species

commensalism

a relationship wherein the parasite derives benefits from the host without causing injury or harm to the host

parasitism

a relationship whereby one organism derives benefits at the expense of another

pathogenicity

ability of the organism to produce disease

pathogenicity island

large groups of genes that are associated with pathogenicity and are located on the bacterial chromosome

invasiveness

the ability of the organism to enter the host tissues, multiply, and spread faster.

toxigenicity

ability of the microorganism to produce toxins

toxoid

non-poisonous forms of toxins which can be used for vaccination

1. Physical encounter between host and microorganism.

2. Microorganism colonization of host surface(s)

3. Microorganism entry, invasion, and dissemination

4. Outcome

general stages of microbial-host interaction

normal/usual/ indigenous flora

• microorganisms that are commonly found on or in body sites of healthy persons

• present in gut, vagina, or mouth;

resident microbial flora

microorganisms that colonize an area for months or years

transient flora

microorganisms that are present at a site temporarily represent

● 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

roles of microbial flora

streptococcus

predominant genus in usual flora of the mouth

viridans streptococci

usual flora of the respiratory tract

• found in the mouth, nasopharynx, oropharynx

escherichia coli

bacteria in vagina that is a part of the normal flora but are important colonizers

pathogenicity

ability of a microbe to produce disease in a susceptible individual

true pathogens

are organisms recognized to cause disease in a healthy immunocompetent individuals

Yersinia pestis, Bacillus anthracis

examples of true pathogens

E.coli

example of opportunistic pathogens

• Inhibiting phagocytosis

• Facilitating adhesion to host cells or tissues

• Enhancing intracellular survival after phagocytosis

• Damaging tissue through the

• Production of toxins and extracellular enzymes

microbial virulence factors

capsule

• 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

protein A

• Found in the cell wall of Staphylococcus aureus

• 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

m protein

Heat resistant and acid resistant protein, mediates attachment to host epithelial cell and helps resist phagocytosis

fimbriae and outer membrane protein

antigenic variation

cell wall protein of N. gonorrhoeae

mycolic acid

resist digestion during phagocytosis; the bacteria can even multiply inside macrophages

hemolysins

• ● Produced by Streptococci

• Lyse red blood cells and induce toxic effects on WBC

leukocidins

• Released by pathogenic staphylococci

• Cause lysosomal discharge into cell cytoplasm

panton-valentine

• Staphylococcal leukocidin

• Lethal to leukocytes and contributes to the invasiveness of the organism

adhesins

Cell surface structures that mediate attachment

fimbriae

Enable bacteria to adhere to host cell surface, offering resistance by attachment to target cells, increasing the organism’s colonizing ability

fimbriae, surface polysaccharides

main adhesins in bacteria

ability to survive intracellularly and proliferate

• Prevent fusion of phagosomes and lysosomes

• Resistance to the effects of the lysosomal contents

• Escape from the phagosome into the cytoplasm

meningococci

Use lactoferrin as a source of iron

H. influenzae, N. gonorrhoeae, and N. meningitides

Produce an IgA protease that degrades the IgA found at mucosal surfaces

borellia spp.

Circumvent host antibodies by shifting key cell surface antigens

Chlamydia, Mycobacterium, Brucella, and Listeria

Ability to multiply intracellularly

invasion

Ability to penetrate and grow in tissues

dissemination

Disease or organisms spread to distant sites Example: Salmonella spp.

Clostridium perfringens

Highly invasive organism that may not disseminate

collagenase

Breaks down collagen, which forms the connective tissue of muscles and other body organs and tissues

hyaluronidase

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

coagulase

Produced by S. aureus and accelerated the conversion of fibrinogen to a fibrin clot

kinases

enzymes of Streptokinase, Staphylokinase

Immunoglobulin A protease (IgA protease)

Destroy IgA antibodies found on secretions

Leukocidin

Destroy neutrophilic leukocytes and macrophages

exotoxins

• Composed of two subunits: nontoxic (binds the toxin to the host cells) and toxic

• Produced by both gram-negative and gram-positive bacteria

• 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

toxin gene

• Encoded by phages, plasmids, or transposons

• Most toxic substance

antitoxins

Good antigens and induce the production of antibodies called