Host-Pathogen interactions Flashcards
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 of a bacterium to cause infection
Virulence factor?
Bacterial product or strategy that contributes to virulence
Primary pathogens?
Not normally associated with the host and cause infection
• E.g. Yersinia pestis (Plague), Influenza virus
Opportunistic pathogens?
Cause disease under some circumstances
• E.g. Pseudomonas aeruginosa (associated with burns)
Sometimes the pathogen is part of the normal flora?
E.g. Staphylococcus epidermidis causing catheter-related diseases
The normal microbial flora?
In healthy individuals
• The internal tissue (blood, brain, lungs, muscle etc.) are normally free of microorganisms
However
• Surface tissue (i.e. the skin and mucous membranes) are constantly colonized/infected by
various microbial species
Many members of the normal flora are either pathogens or opportunistic pathogens
Vaginal child-birth?
Vagina-bacteria such as • Lactobacillus spp. • Prevotella spp. • Sneathia spp. • et.al.
Lactobacillus produce?
Hydrogen-peroxide
• Lactic acid
• Toxic molecules
These inhibit the growth of more pathogenic bacteria
Sitisms?
Parasitism Beneficial for one part but at the expense of the other • Protozoa • Helmints Mutualism Beneficial for both parts • Normal-flora Commensalism Beneficial for one part but ether help or hurt the other • Decomposers
The skin?
The skin is not hostile to bacteria • Dry • Acidic • Salty • “Cool” • Lytic enzymes • Antimicrobial peptides • Shedding
Resident and transient flora?
Resident flora
Mostly Gram-positive bacteria
• Staphylococcus epidermidis
Transient flora Varying flora • Alfa-hemolytic streptococci • Spore-forming bacteria • Intestinal-bacteria • Gram-negative environmental-bacteria • Yeast
Function
• Consume nutrient
• Occupies space
• Alters the pH
Flora of the mucous membranes?
Eyes • Normally few bacteria due to lysozyme • Can be: o Coagulase-negative staphylococci (KNS) o Alfa-hemolytic streptococci
Ears
• Common skin-flora
• Intestinal-bacteria
Nose
• KNS
• Staphylococcus aureus
Life in mouth?
There are lots of nutrients in saliva
• Nutrients are present at low concentrations
• Food particles and cell debris thus provide high
concentrations of nutrients near surfaces (teeth and gum)
Saliva contains
• Lysozyme (cleaves peptidoglycan)
• Lactoperoxidase
Before and after teeth
• Before: aerotolerant bugs, e.g. streptococci and lactobacilli
• After: anaerobes that usually grow as biofilm
Dental plaque?
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)
Hemolysis?
Streptococci produce hemolysins • α-hemolysis o Results in a greenish color • β-hemolysis o Total-hemolysis • γ-hemolysis o No hemolysis
Normalflora of the mouth?
Consists of viridans streptococci (viridis, Lat. ”green) • α-hemolytic streptococci • Low-pathogenic Diseases • Plaque • Caries • Gingivitis • Bacteremia • Subacute endocarditis
Intestinal normal-flora?
Bacterial life in the gut
The stomach fluids are very acidic
• Prevents entry of microorganisms into the intestinal tract
Helicobacter pylori
• May result in ulcers and gastric cancer
• Produces urease, which transforms urea → ammonium (increase in pH)
Intestinal normal-flora?
300-1000 different species • A mass between 1.5 and 2.5 kg • Most of them are anaerobic The number differs between parts of gastrointestinal tract • Most bacteria are found in colon • Constitute 50-60 % of feces
The function of intestinal flora?
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
Bacterial life in the lungs?
Most pathogens are trapped by secretions from the mucous membranes and expelled The upper respiratory tract • Staphylococcus aureus • Streptococcus pneumoniae The lower respiratory tract • No resident microflora
Life 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.
Harmful microbial interactions?
E A I CG TI D
Exposure?
Bacteria mostly infects via • Skin • Respiratory tracts • Gastrointestinal tracts • Urogenital tracts
Adherence?
Adherence proteins Slime (polysaccharides) • Important for binding to host-cells and other bacteria Capsule • Also prevents phagocytosis Fimbriae and pili • Adherence surface protein-structures
Invasion?
Bacteria generally need access to underlying tissues
Generally a break or a wound is required
• Can be caused by toxins?
Growth?
Growth is affected by: • 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)
Invasiveness?
• The ability of an organism to grow in host-tissue in such large numbers that the pathogen
inhibits host-function
Toxicity?
The ability of an organism to cause disease by means of a toxin that inhibits host-cell function
or kills host-cells
Measuring virulence ?
ID50
• The dose of an agent required to infect 50 % of the animals in a test group
LD50
• The dose of an agent that kills 50 % of the animals in a test group
