Microbial Pathogens

Learning Objective 1: Explain the different taxonomic categories of microbial agents

What are the two major cellular categories of organisms?

Prokaryotes and eukaryotes.

What distinguishes prokaryotes from eukaryotes?

Prokaryotes do not have a membrane-bound nucleus.

Which major microbial pathogen group consists of prokaryotes?

Bacteria.

What are the three bacterial shapes?

Coccus, bacillus, and spiral.

What is the shape of a coccus?

Round.

What is the shape of a bacillus?

Rod-shaped.

How are spiral bacteria shaped?

Spiral or corkscrew-shaped.

How can bacteria be classified by staining characteristics?

Gram-positive or Gram-negative.

What percentage of bacteria have a cell wall?

More than 90%.

What does Gram staining differentiate?

Types of bacterial cell walls.

What bacterial cell-wall component is associated with Gram-positive bacteria?

Lipoteichoic acid.

Which Toll-like receptor recognizes lipoteichoic acid?

Toll-like receptor 2.

What bacterial cell-wall component is associated with Gram-negative bacteria?

Lipopolysaccharides.

Which Toll-like receptor recognizes lipopolysaccharides?

Toll-like receptor 4.

What are endotoxins?

Components of bacterial cells.

What are exotoxins?

Substances secreted by bacteria.

What types of exotoxins are there?

intracellular toxins

neurotoxins

Enzymes

superantigens.

What are spirochetes?

Long corkscrew-shaped Gram-negative bacteria.

Which bacterium causes syphilis?

Treponema pallidum.

Which bacterium causes diphtheria?

Corynebacterium diphtheriae.

Which bacterium causes pertussis?

Bordetella pertussis.

Which bacterium causes tuberculosis?

Mycobacterium tuberculosis.

Which bacterium causes pseudomembranous colitis?

Clostridium difficile.

What type of organism is a virus?

obligatory intracellular parasite.

What type of nucleic acid can a virus contain?

DNA or RNA.

What protects viral nucleic acid?

protein coat called a capsid.

What may surround the viral capsid?

A lipid membrane called an envelope.

What is viral tropism?

tendency of a virus to infect certain cells.

What determines which cells a virus can infect?

Receptors for viral glycoproteins.

How do viruses gain entry into cells?

Through membrane interactions.

What do viruses use to replicate once inside a cell?

Cellular machinery.

What are fungi?

Eukaryotes with cell walls.

What are the two forms in which fungi grow?

Multicenter filaments called mold

chains called yeast.

What causes candidiasis?

Candida albicans.

What type of organism is Candida albicans?

A yeast.

What are parasites?

Eukaryotic organisms that infect humans and cause pathology.

What are the two categories of parasites?

Protozoan and metazoan.

What is a protozoan?

A single-cell parasite.

What is a metazoan?

A multiple-cell parasite.

Which organism causes malaria?

Plasmodium falciparum.

Learning Objective 2: Explain how pathogens gain entry, disseminate, and cause injury to the host

What is an infectious microbial disease?

Colonization of a human host by a microbe that results in pathology.

What is a pathogen?

A biological agent or microbe that can cause disease in its host.

Do all colonizations of a human host cause disease pathology?

No.

What are commensal bacteria?

Bacteria that establish a beneficial and mostly harmless relationship with the host.

What is virulence?

The relative capacity of a pathogen to cause disease.

What factor involving the pathogen can influence virulence?

The number of infecting microbes.

What factor involving entry can influence virulence?

The route of entry into the body.

What host-related factor can influence virulence?

The effects of host defense mechanisms.

What are virulence factors?

Components of a pathogen that damage the host.

What are the major portals of entry for pathogens?

Respiratory tract,

gastrointestinal tract,

urogenital tract,

skin and mucous membranes,

vertical transmission, and

bloodborne entry.

How can pathogens enter through the respiratory tract?

By inhaling droplets or dust containing germs.

Which pathogens are examples of respiratory entry?

Influenza and tuberculosis.

How can pathogens enter through the gastrointestinal tract?

By ingesting contaminated food or water.

Which pathogen is an example of gastrointestinal entry?

Salmonella.

How can bacteria enter through the urogenital tract?

Through the urethra or mucous membranes.

What infections can result from urogenital entry?

Urinary or sexually transmitted infections.

How can pathogens enter through skin and mucous membranes?

Through cuts, burns, animal bites, or needle sticks.

What is vertical transmission?

Transmission from mother to fetus via the placenta, birth, or milk.

What is bloodborne transmission?

Transmission involving microorganisms present in human blood or body fluids.

What is direct contact transmission?

Transmission through touching or kissing an infected person.

What is indirect contact transmission?

Transmission through touching contaminated objects called fomites.

What are fomites?

Contaminated objects that can transmit infection.

What is airborne and droplet transmission?

Transmission by breathing in large respiratory drops or tiny suspended aerosols.

What is vector-borne transmission?

Transmission through bites from infected insects such as mosquitoes and ticks.

What are examples of ways microbes can be shed from an infected host?

Skin shedding, coughing, sneezing, urine, and feces.

What type of contact can transmit microbes sexually?

Sexual contact.

What are zoonotic infections?

Infections transmitted from animals to humans.

What are nosocomial infections?

Infections acquired in a hospital.

How can pathogens disseminate locally?

By spreading locally through tissues.

What three body systems can pathogens use for dissemination?

Lymph, blood, or nerves.

What are two maternal routes of microbial dissemination?

Placental transfer and maternal milk.

What is an important example of transmission through maternal milk?

HIV.

What three abilities determine bacterial damage to host tissues?

The ability to adhere to host cells, invade cells and tissues, or deliver toxins.

What are adhesins?

Surface molecules on bacteria that bind to host cells.

What can happen when bacteria enter host cells?

They can replicate, inhibit host protein synthesis, or lyse host cells.

What is bacterial entry into host cells associated with?

Opsonization and phagocytosis into macrophages.

What is an endotoxin associated with Gram-negative bacteria?

Lipopolysaccharide.

What can endotoxin activate?

Protective immunity.

What serious condition can endotoxin contribute to?

Septic shock.

What is an exotoxin?

A toxin secreted by bacteria.

What is an example of immune-mediated tissue damage caused by infection?

Granuloma formation in tuberculosis.

Learning Objective 3: Discuss the transmission, dissemination, disease presentation, and diagnosis of bacterial, viral, fungal, and parasitic infections

What disease is caused by Corynebacterium diphtheriae?

Diphtheria.

What type of infection is diphtheria?

A Gram-positive vaccine-preventable disease.

What is a major throat manifestation of diphtheria?

Pharyngotonsillitis.

What respiratory complication can occur with diphtheria?

Airway obstruction.

What lymphatic manifestation can occur with diphtheria?

Bulk neck lymphadenopathy.

What is a skin manifestation of cutaneous diphtheria?

Blisters.

What other skin manifestations can occur with cutaneous diphtheria?

Scaling rash and open sores.

What cardiac complication can occur with diphtheria?

Myocarditis.

What neurological complication can occur with diphtheria?

Polyneuritis.

What renal complication can occur with diphtheria?

Kidney failure.

What disease is caused by Bordetella pertussis?

Pertussis.

What is pertussis commonly called?

Whooping cough or the 100-day cough.

What characterizes the cough of pertussis?

Severe, uncontrollable coughing fits followed by a high-pitched intake of breath.

Why is pertussis particularly dangerous?

It can be potentially fatal for infants.

What vaccine is given to young children against pertussis?

DTaP.

How many DTaP doses are listed?

Five doses.

At what ages are the five DTaP doses administered?

2, 4, 6, and 15-18 months, and 4-6 years.

What booster protects adolescents against pertussis?

Tdap.

At what age is the adolescent Tdap booster given?

11 or 12 years.