Chapter 15: Microbial Mechanisms of Pathogenicity Disease and Epidemiology

Pathology

The study of disease

Normal Resident Microbes

• Skin and its contiguous mucous membranes

• Upper respiratory tract (oral cavity, pharynx, nasal mucosa.)

• Gastrointestinal tract (mouth, colon, rectum, anus)

• Outer opening of urethra

• External genitalia

• Vagina

• External ear and canal

• External eye (lids, lash follicles)

Eitology

The study of the cause of a disease

Pathogenesis

Studies how disease develops

Pathogens

Microorganisms/infectious agents that can cause diseases.

• Cellular or Acellular

• <1% of microorganisms are pathogenic

Infection

The successful colonization of a host by a microorganism

• Penetrates host defenses → enter tissues → multiply

Disease

An abnormal state in which the body is not functioning normally.

Sign

A change in a body that can be measured or observed as a result of disease.

Symptoms

A change in body function that is felt by a patient as a result of disease.

Syndrome

A specific group of signs and symptoms that accompany a disease

Infectious Disease

Diseases caused by pathogens

Noninfectious Disease

Diseases not caused by pathogens

Communicable Disease

Spread directly or indirectly from one person to another.

• Tuberculosis, herpes, flu, AIDS, chickenpox, mumps, polio, etc.

• Contagious Disease

Noncommunicable Diseases

Not spread from one person to another.

• Tetanus, botulism, and yeast infections.

Iatrogenic Diseases

Diseases contracted as the result of a medical procedure.

• Surgical complications, blood transfusions.

Zoonotic Diseases

Diseases transmitted from animals to humans

• Rabies, COVID-19

incubation Period

No signs or symptoms

Prodromal Stage

Vague, general/nonspecific symptoms

Period of illness

More severe/specific signs and symptoms.

Period of decline

signs and symptoms decline

Convalescent Period

Recovers from the infection.

Acute Disease

Disease develop rapidly

Chronic Disease

Disease develops slowly

Latent Disease

The casual pathogen goes dormant for extended periods of time with no active replication.

Normal flora/Indigenous microbiota

Organisms that colonize the body’s surfaces without normally causing disease.

• Transient Flora

• Resident Flora

Transient Flora

microorganisms, sometimes pathogenic, that are only temporarily found in the human body

• Temporary flora; influenced by hygiene.

Resident Flora

microorganisms that constantly live in the human body

• Permanent flora; Not/Less influenced by hygiene.

Microbial Antagonism

Normal flora inhibits overgrowth of harmful microbes.

• Competition for nutrients and space

• Affecting the environmental factors such as pH, toxic substances, and oxygen availability.

Endogenous Infections

Occur when normal flora is introduced to a site that was previously sterile.

Primary/True pathogens

• Cause disease in healthy individuals

• Associated with specific and recognizable diseases

Opportunistic Pathogens

• Cause diseases in immune-compromised hosts

• Gain access to sterile regions.

  • Candida albicans

Pathogenicity

The ability of a microorganism to cause disease

Virulence

the degree of pathogenicity

Virulence factors

traits used to invade and establish themselves in the host, also determine the degree of tissue damage that occurs - the severity of disease.

Virulence factors

• Adhesions → Fimbriae pili, glycocalyx

• Resistance to host immunity → Antiphagocytic factors

• Invasion → Exoenzymes

• Secretion of toxins: Endotoxins and Exotoxins

Antiphagocytic Factors

Antiphagocytic Factors

Used to avoid phagocytosis

• Antiphagocytic chemicals

  • Leucocidins → Destroy phagocytic white blood cells

• Slime layer or capsule → Makes phagocytosis difficult

Ability to survive intracellular phagocytosis.

Exoenzymes

Dissolve extracellular barriers and penetrate through or between cells.

Infectious Dose

Minimum number of microbes required for infection to proceed

• Microbes with small IDs have greater virulence

• Lack of ID will not result in infection

Toxigenicity

Capacity of produce toxins at the site of multiplication

• Endotoxin

• Exotoxin

Endotoxin

Integral part of cell wall; released only when cell disrupts.

Eg: LPS → Outer membrane of Gram-negative cell walls.

• Lipids

Exotoxin

Actively secreted toxins by living cells into medium.

• Strong specificity for a target cell

• Proteins

Stages of pathogenesis

Exposure (contact ), Adhesion (colonization), Invasion, and Infection

Portals of Entry

Characteristic routes a microbe follows to enter the tissue of the body.

Exogenous agents

originates outside the body

Endogenous agents

originate within the body.

Adhesion

The capability of the pathogenic microbes to attach to the cells of the body using ____ factors

Invasion

• Once adhesion is successful, ______ can proceed.

• _______ involves the dissemination of a pathogen throughout local tissues of the body.

Localized infection

an infection that is confined to a specific area of the body

Ex: Boils

Systemic Infection

one that spreads throughout the body's systems

Ex: Influenza

Focal Infection

a localized infection that can spread bacteria or their toxins to other parts of the body

Mixed Infection

Several microbes grow simultaneously at the infection site - polymicrobial

Primary infection

An infection develops in an otherwise healthy individual

Secondary infection

An infection develops in an individual who is already infected with a different pathogen

Portals of exit

• Coughing

• Sneezing

• Skin cells (open lesions)

• Feces

• Urine

• Removal of blood

• Insect bite