Host-Pathogen Interactions Flashcards
Define colonization, infection, disease, asymptomatic carrier, virulence/pathogenesis and virulence factor.
Colonization:A bacterium occupies and multiplies in a particular
area of the human body
Infection: Colonization of the body by a bacterium capable of
causing disease
Disease:Infection that produces symptoms
Asymptomatic carrier:Infected person that do not have detectable symptoms
Virulence/Pathogenesis: The ability for a bacterium to cause disease
Virulence factor: Bacterial product or strategy that contributes to virulence
What is the difference between a primary pathogen and an opportunistic pathogen?
primary pathogen: not normally associated with the host and causes disease e.g yersina pestis (plague), influenza
opportunistic pathogen: causes disease under circumstances Pseudomonas aeruginosa (associated with burns)
What is the normal microbial flora? What tissues in healthy individuals are normally free of any microorganisms?
Microorganisms that live on another organism, without causing disease.
brain, lungs, blood, muscles are free, if the person is healthy.
What is the function of the normal microbial flora on the skin?
preventing transient pathogenic organisms from colonizing the skin surface, either by competing for nutrients, secreting chemicals against them, or stimulating the skin’s immune system.
Why is it difficult for bacteria to colonize the skin? What bacterial species can we still find there?
Dry • Acidic • Salty • “Cool” • Lytic enzymes • Antimicrobial peptides • Shedding
we can still find Enterobacter, Klebsiella, Escherichia coli, and Proteus spp
How is the bacterial flora in the mouth? What is dental plaque? Why do people get caries?
biofilm of microorganisms (mostly bacteria, but also fungi) that grows on surfaces within the mouth.
Glycoproteins from the saliva adhere to tooth surface
• To these proteins, bacterial cells can attach
o Streptococcus sanguis
o Streptococcus sobrinus
o Streptococcus mutans
As dental plaque accumulates, the bacteria produce organic acids
that decalcify the tooth enamel (caries)
How is the bacterial flora in the stomach? Are there any bacteria that can survive this acidic environment?
Many bacterial pathogens, such as Escherichia coli, Salmonella Typhimurium, and H. pylori, can circumvent the acid conditions of the stomach by developing adaptive mechanisms that allow these bacteria to survive in acid environments.
What is the function of the normal microbial intestinal flora? What kind of diseases afflict us after antibiotic treatments and why?
Metabolic function • Break-down of sugar o Cellulose o Starch • Break-down of protein o Elastin o Collagen Vitamin-synthesis • Vitamin K • Vitamin B12 Protective-effect • Protect epithelial cells • Consume nutrients Bacteriocine-production
How is the bacterial flora in the respiratory tract?
The upper respiratory tract • Staphylococcus aureus • Streptococcus pneumoniae The lower respiratory tract • No resident microflora
How is the bacterial flora in the urogenital tracts?
The bladder is typically sterile but the epithelial cells of the urethra is often colonized
Anatomical differences predispose women to get urinary tract infections
• Escherichia coli
• Staphylococcus saprophyticus
• Klebsiella spp.
• Proteus mirabilis
• Enterococcus spp.
In what ways do bacteria usually infect humans?
Skin
Respiratory tracts
Gastrointestinal tracts
Urogenital tracts
Describe the general principles utilized by bacteria to adhere to skin or mucosa-membranes.
Adherence proteins Slime (polysaccharides) • Important for binding to host-cells and other bacteria Capsule • Also prevents phagocytosis Fimbriae and pili • Adherence surface protein-structures
What affects bacterial growth in the body?
Temperature • pH • Oxygen • Normal flora • Nutrients/trace elements The bacteria must be able to handle • Stomach acids • Bile • Skin secretions • IgA (present on mucosal membranes)
What is invasiveness and toxicity?
Invasiveness: the ability of a pathogen to grow in such large numbers that it inhibits host function.
Toxicity: the ability of a pathogen to infect via toxin that inhibits host cell function or kills host cells
What are ID50 and LD50? How do you measure these?
ID50: the dose of an agent required to infect 50% of animals in a test group, determined by measuring active infection
LD50: the does of an agent required to kill 50% of animals in a test group, determined by measuring death.
