Microbe/Host Relationships Quiz

Microbe/Host Relationships

• Terminology:

  • Symbiosis: Living together
  • Mutualism: Both benefit
  • Commensalism: One benefits, the other is unaffected
  • Parasitism: One benefits, the other is harmed
  • Pathogen: Organism that causes disease

• Normal Microbiota (Normal Flora):

  • Indigenous microorganisms
  • Can become harmful in unusual circumstances
  • Factors: Introduction into abnormal sites, immune suppression, elimination of microbial antagonism

• Opportunistic Pathogens:

  • Normal flora that cause harm in certain situations
  • Require a chance or opportunity to cause disease

Infectious/Disease Processes

• Infection:

  • Growth of microorganisms in host
  • Does not always lead to disease

• Disease:

  • Significant injury to body, hindering regular functioning

• Reservoirs of Infection:

  • Animal Reservoirs: Animals carry pathogens
  • Human Carriers: Individuals harboring pathogens
  • Nonliving Reservoirs: Environments that harbor pathogens.

• Stages of Infection:

  • Entry
  • Adhesion (binding to surface)
  • Colonization and Growth (survive and spread)

Manifestations of Disease

• Symptoms:

  • Subjective characteristics (felt by patient)

• Signs:

  • Objective characteristics (observed by others)

• Syndromes:

  • Combination of symptoms and signs characterizing a disease

Virulence Factors of Infectious Agents

• Extracellular Enzymes:
  • Breakdown tissues
  • Examples: Collagenase, Hyaluronidase, Coagulase, Kinases

Folliculitis

• Usually caused by Staphylococcus aureus (gram-positive coccus)
• Highly resistant to drying
• Spread by contact with infected individuals or fomites.
• Infection of hair follicle.

Toxins

• Exotoxins:
  • Proteins released by some bacteria
  • Highly toxic
  • Specific target cells (e.g., neurotoxins, enterotoxins, nephrotoxins)
  • Can be inactivated into toxoids for immunization

Staphylococcal Diseases

• Scalded Skin Syndrome:

  • Exfoliative toxin causes skin to peel off

• Food Poisoning:

  • Heat-stable enterotoxin causes nausea, vomiting, diarrhea

• Toxic Shock Syndrome:

  • Toxin release causing fever, low blood pressure

Scarlet Fever

• Caused by lysogenized strains of Streptococcus pyogenes
• Gram positive, catalase negative coccus

Diphtheria

• Caused by lysogenized strains of Corynebacterium diphtheriae
• Gram positive pleomorphic rods
• Diphtheria toxin interferes with protein synthesis

Pertussis/Whooping Cough

• Caused by Bordetella pertussis
• Gram-negative coccobacillus
• Initial symptoms resemble common cold
• Recurrent, violent coughing

Cholera

• Caused by Vibrio cholerae
• Gram-negative, curved rod
• Endemic in areas with poor sanitation
• "Rice-water stool" - major symptom

Rocky Mountain Spotted Fever

• Caused by Rickettsia rickettsii
• Gram-negative rod-shaped intracellular parasite
• Transmitted by various species of ticks
• Fever, chills, headache, and muscular pain followed by rash.

Plague

• Caused by Yersinia pestis
• Gram negative rod
• Endemic in rodents, spread to humans by flea bite
• Bubonic Plague and Pneumonic Plague

Lyme Disease

• Caused by Borellia burgdorferi
• Gram negative spirochete
• Most prevalent tick-borne disease in the U.S.
• "Bull's-eye" rash, may progress to chronic symptoms

Malaria

• Caused by Plasmodium protozoa
• Endemic in areas with mosquito breeding sites
• Characterized by recurrent fever, chills, and other symptoms

Epidemiology

• Study of incidence, frequency and transmission of disease

• Definitions:

  • Incidence: Number of new cases
  • Prevalence: Total number of cases
  • Endemic: Constantly present disease
  • Sporadic: Occurs infrequently
  • Epidemic: Outbreak in a particular population
  • Pandemic: Worldwide outbreak

• Healthcare-Associated Infections (Noscomial Infections):

  • Exogenous: Acquired from environment
  • Endogenous: Normal flora
  • Iatrogenic: Resulting from treatment
  • Superinfections: Result of antimicrobial treatment