MLT-140: Chapter 2 – Host Parasite

The growth of microbiota in or on a body site without production of damage or notable symptoms

Microorganisms that are commonly found on or in body sites of healthy persons
Normal flora

Microorganisms that colonize an area for months or years

Present at site temporarily
"visit" but don't stay

Pathogenic organisms establish themselves in host without manifesting systems - no harm to the host
Can transmit to others and cause infection

The condition of the carrier host
Acute - short live or transient
Chronic - long lasting for months or years or permanently
EX: Salmonella typhi infection - excreted in stool for years. Staphylococcus aureus colonized in anterior nares of person - transmitted to hands and carried until hands washed.

Physical separation of bacteria from tissue.
Presence of fatty acids.
Excretion of lysozyme by sweat glands.
Desquamation of epithelium.

Staphylococcus epidermidis.
Propionibacterium spp.
Micrococcus spp.
Corynebacterium spp.

Mucosa.
Low oxidation-reduction potential

Staphylococcus epidermidis.
Streptococcus (viridians).
Peptostreptococcus spp.
Veillonella spp.
Actinomyces israelii.

Mucus.
Cilia

Viridans streptococci.
Moraxella catarrhails.
Neisseria spp.
Corynebacterium spp.

Cilia.
Mucus

None

Stomach - gastric juices - acidic.
Normal microbiota.

Bacteroides spp.
Closteridium spp.
Enterobacteriaceae.
Enterococcus.
Streptococcus spp.

Lactobacilli - produce lactic acid.
- Low pH of vagina

Viridians streptococcus

Do NOT normally have bacteria.
Blood, CSF, Bladder, Fallopian tubes, Cervix.

Area has normal microbiota.
GI tract, Skin, Mouth, Distal urethral.

Organisms recognized to cause disease in healthy immunocompetent individuals a high percentage of the time.
EX: Yersinia pestis, Bacillus anthracis.

Organisms that are found as normal biota are being seen with increasing frequency in clinical infections among immunosuppressed and immunocompromised individuals.

Infections caused by opportunistic pathogens
EX: Staphylococcus epidermidis

Infection that occurs as the result of medical treatment or procedures.
EX: patients with indwelling catheters develop UTI; patients taking immunosuppressant drugs to receive organ transplant.

Host immune system suppressed so not able to mount an effective immune response.
Susceptible to infections.

Aerosolization by coughing, sneezing, talking.
Droplet nuclei - remain airborne for long periods.
Nose/mouth to hand to object to nose.
EX: S. pneumonia, M. tuberculosis.

Ingestion of contaminated food or water.
Fecal-oral.
Toxins.
EX: Salmonella, Shigella, C. difficile, Campylobacter jejunii, S. aureus, Bacillus cereus.

Passage of organisms by salivary, skin, genital contact.
Direct transfer: Kissing, herpes simplex virus, Epstein-Barr virus.
Skin-to-skin: Human papillomavirus, syphilis, impetigo.
Sexually transmitted: Chlamydia trachomatis, Neisseria gonorrhoeae, Herpes simplex virus, syphilis, trichomonas, HIV.

Bite wound infection.
Rabies.
Dog and cat bites - Pasteurella multocida

Mosquito, tick, flea, or mite bite.
Diseases: malaria, relapsing fever, plague, Rocky Mountain spotted fever, Lyme disease, West Nile fever, hemorrhagic fevers.

Animal diseases that affect humans

Alcoholics, IV drug users, dialysis, AIDS/HIV, burn patients, diabetes chronic medical issues, foreign body implants (heart valves, prosthetic devices, indwelling catheters).

Streptococcus pneumoniae

The relative ability of a microorganism to cause disease or the degree of pathogenicity.
It is usually measured by the numbers of microorganisms necessary to cause infection in the host.
- Organisms that can establish infection with a relatively low infective dose are considered more virulent than organism that require high numbers for infection.

Bacteria avoid phagocytosis by:
- Polysaccharide capsule on bacteria surface.
- Protein A - interferes with binding of the host's antibodies to the surface of the organisms - binds to Fc portion of IgG.
- Releasing potent materials in tissues that kill phagocytes.

Host cells undergo mutation that changes the structure of adhesion or the host receptor.

Bacteria survive within the phagocytic cell after they have been engulfed.
- Prevent fusion of phagosomes and lysosomes.
- Resistance to the effects of lysosomal contents.
- Escape from phagosome into the cytoplasm.
- Produce IA protease that degrades the IgA found on mucosal surfaces.
- Circumvent host antibodies by shifting key surfaces antigens

Bacterial produce toxins that damage host cells.

Produced by: gram-positive and gram-negative bacteria.
Secreted by organisms into extracellular environment or released by lysis of organism.
Mediate direct spread of organism through matrix of connective tissue that cause cell and tissue damage.
Toxins specific for different bacteria: C difficile - Toxin A & B, C. diphtheria - diphtheria toxin, S. aureus - exfoliation.

Lipopolysaccharide portion gram-negative cell wall.
No enzyme activity.
Secreted in small amounts.
Do NOT have specificity in their activity.
Stimulate release of proinflammatory cytokines.
Lipid A - toxic activity
Causes: fever, hypotension, shock, intravascular coagulation, severe neutropenia followed by leukocytosis.
Stimulate proliferation of B-cells

Polysaccharide capsule on the surface.
- Many of the microorganisms possessing a capsule are highly virulent until removal of the capsule, at which point virulence becomes extremely low.

Compete with pathogens for nutrients and space.
- Competition lessens the change the pathogen will colonize host.
Production of bacteriocins - inhibit the growth of closely related bacteria.
Metabolic products result in a microenvironmental hostile to potential pathogens.
Vitamins and essential nutrients - synthesized by certain bacteria in intestine.
- Appear to contribute to overall health of host.