Introduction to Infectious Diseases (IP4: Exam 1)

A virus is defined as...

A non-living, obligate parasite that contains DNA/RNA genomes and are the smallest infectious agents that require life-cycle inhibiting treatment.

A bacteria is defined as...

• A living organism that can have gram negative, positive, and atypical cell walls but do not have a nucleus.

• Treatment is bacteriostatic or bactericidal.

• Bacteria can exhibit drug resistance.

What type of toxins do gram-negative bacteria produce?

endotoxins

What type of toxins do gram-positive bacteria produce?

exotoxins

Fungus is defined as...

Eukaryotic cells with a nucleus and cell wall that can be transmitted via inhalation or person-person spread. They may cause systemic infections and can display drug resistance.

Parasites are defined as…

Eukaryotic microorganisms that require a host for survival and are spread by contamination or ingestion. Treatment focuses on killing the parasite.

Learning Objectives 1:

Describe the morphology of the gram-positive cell wall and the gram-negative cell wall.

Gram-positive cell walls:

• thick peptidoglycan layer

• no outer membrane.

Gram-negative cell walls:

• thin peptidoglycan layer,

• an outer membrane (made of lipopolysaccharides)

• periplasmic space → drug resistance enzymes may reside

• porins to transport nutrients.

Learning Objective 2:

Explain the mechanism behind the gram-stain and describe the steps of the gram-staining procedure.

Gram-positive cells are stained by crystal violet/iodide and will appear blue as the crystal violet is taken up by their thick peptidoglycan layer.

Gram-negative cells are stained by safranin following an ethyl wash as they have the outer membrane and only a thin peptidoglycan layer.

Describe in detail the components of a gram-positive cell wall.

Gram-positive cell wall is composed of:

• inner plasma membrane

• thick peptidoglycan cell wall layer.

Describe in detail the components of a gram-negative cell wall.

Gram-negative cell wall is composed:

• inner plasma membrane,

• thin peptidoglycan cell wall layer

• periplasmic space

• outer membrane → serve as permeability barrier.

What are gram-positive cocci anaerobes?

Oral anaerobes that ferment sugars after eating and are often relavant to dental practice. Some examples include:

• peptostreptococcus spp.,

• peptococcus spp.,

• streptococcus intermedius.

What are gram-positive bacilli anaerobes?

Some examples include:

• lactobacillus spp.

• propionibacterium spp.

• actinomyces

• clostridium perfringes

• clostridium difficile

  • C. difficile causes severe infection of the intestinal tract.

What are gram-positive aerobic cocci?

Organisms that appear in clusters or pairs/chains and may be either:

• catalase positive → staph

• catalase negative → strept or enterococcus

  • They may also exhibit hemolysis.

Define hemolysis:

Clearing around colonies on blood agar plates

What are catalase-positive aerobic cocci?

Bacteria that produce catalase can detoxify the opsonization process. Examples include:

• staphylococcus aureus,

• staphylococcus epidermidis,

• staphylococcus lugdunensis

• staylococcus saprophyticus.

Catalase is defined as...

An enzyme that converts hydrogen peroxide to water and oxygen.

Opsonization is defined as...?

A process that allows the body to tag foreign pathogens for elimination by phagocytosis.

What are catalase-negative cocci?

Some examples include:

• streptococcus pneumoniae,

• streptococcus pyogenes

• streptococcus agalactiae

Streptococcus pneumoniae is the most common cause of...

Community acquired pneumonia (CAP)

Coagulase is defined as...

An enzyme that converts fibrinogen to fibrin.

A positive coagulase test confirms what?

The presence of staphylococcus aureus.

• coagulase results in a fibrin coat around S. aureus that helps it evade phagocytosis.

• other species of staphylococcus are coagulase negative.

Define IgA antibodies:

• Found in fluid secretions (mucous, tears, respiratory secretions, and GI secretions)

• prevent pathogens from adhering to and infecting epithelial cells.

Define IgM antibodies:

• secreted EARLY in the immune response after the FIRST ENCOUNTER with a pathogen.

• they disappear within three months and give way to IgG.

• they’re pentameric and do not have exposed Fc regions, therefore can’t opsonize pathogens.

• they can activate complement.

Define IgG antibodies:

• compose 80% of the antibodies in the body

• body's LONG TERM responders after additional encounters with a pathogen.

Define IgD antibodies:

• not well understood

• found in B-lymphocytes

• may help with differentiation.

Define IgE antibodies:

• found on mast cells

• help facilitate inflammation and allergic reactions (like histamine)

• it also assists with fighting parasitic infections alongside eosinophils.

When present in a CBC, what do high numbers of neutrophils most likely mean?

Bacterial infection

When present in a CBC, what do high numbers of bands (developing neutrophils) most likely mean?

Sepsis/chemotherapy

When present in a CBC, what do low numbers of neutrophils most likely mean?

Sepsis/drug reactions

When present in a CBC, what do high numbers of lymphocytes most likely mean?

Viral infecitons

When present in a CBC, what do low numbers of lymphocytes most likely mean?

HIV/AIDS

When present in a CBC, what do atypical lymphocytes most likely mean?

• CMV

• EBV

• (Mono)

• Toxoplasmoisis

When present in a CBC, what do high numbers of eosinophils most likely mean?

• Parasites

• Drug reactions

• Vasculitis

What are basophils?

They are essential white blood cells found in bone marrow that secrete inflammatory mediators.

What is bone marrow's role in immunology?

Bone marrow is the major immune system organ and is responsible for manufacturing hematopoietic pluripotent stem cells.

What is the thymus's role in immunology?

The thymus produces mature T cells (thymus-dependent lymphocytes), which are required for cell-mediated immunity.

What is the spleen's role in immunology?

• The spleen is a clearinghouse for filtration of blood and destruction of lymphocytes.

• It also helps to clear out encapsulated microorganisms.

What are lymph node's role in immunology?

• They are tiny organs that are filters for lymphatic fluid.

• The lymph nodes also sequester activated immune cells.

Define innate immunity:

Immunity that is always present such as:

1. physical and chemical barriers (skin, respiratory tract, mucous, and cilia).

2. phagocytosis (involving monocytes/macrophages, neutrophils, mast cells, and eosinophils) are able to recognize and eat pathogens.

3. Interferons also aid in immunity by causing cellular changes that fight off viral infections.

Interferons are much like...

Warning signals that announce the presence of a virus to prepare an immune response

Define opsonin-dependent phagocytosis:

• Requires opsonins (like antibodies, complement C3b, or lectins) to bind to receptors on the pathogen.

• Then the opsonin will bind to receptors on the phagocyte which will activate and begin the phagocytosis process.

Define opsonin-independent phagocytosis:

Occurs via leukocyte pattern recognition receptors that bind to highly conserved structures on pathogens.

Name an example of a pattern recognition receptor (PRR).

Toll-like receptors: they recognize and bind to a variety of receptors on fungi and bacteria.