Host-Pathogen interactions Flashcards
(33 cards)
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
