Bacterial Infections Flashcards
What happens in Parasitic Host-Microbe interaction
One partner (the human host) is harmed
“harm” = “damage”
Other partner (the microbe) probably derives benefit.
Not always obvious what the benefit is
what is a parasitic organism
A Parasitic organism causes damage to its host
Viruses
Bacteria
Fungi
Protists*
Nematodes*
Helminths*
what does damage to host cause
disease
what is a pathogen
an organism participating in a parasitic interaction i.e. an organism that causes disease.
What is colonisation
growth of any microorganism within a host.
What is infection
growth of a pathogen within a host with concomitant damage to the host.
What turns a microorganism into a pathogen?
Two properties are needed
Ability to overcome non-specific defence (Innate immunity) mechanisms of the body
i.e. the ability to colonise and the Ability to cause damage
Can We can have colonisation without damage?
Yes, Damage without colonisation is relatively rare
Exception would be foodborne intoxication
Clostridium botulinum
What are some non-specific host defences?
- Rapid pH change inhibits microbial growth at the bottom of stomach
- Removal of particles including microbes by rapid passage of air over cilia in nasopharynx
- Mucus, cillia lining the trachea suspended and move microbes out of the body
- blood proteins inhibit microbal growth
- Flushing of urinary tract prevents colonisation
What is non-specific host defences
innate immunity
what are non-specific defenses always?
always active- instant response to infectious agent
What happens in innate immunity?
Individual components are not very powerful= collectively they exert a very powerful effect.
Each of the systems will be considered separately= no system works in isolation and physical, chemical, and biological barriers are closely integrated.
What barriers does innate immunity have
Physical Barriers
Chemical Barriers
Biological Barriers
General Barriers
What are physical barieers
Body surfaces need to provide a physical barrier
Skin
Thick layer of dead cells covered with keratin
Cannot be penetrated directly by microbes
How do pathogenic microbes cross skin?- after some form of direct trauma
How do micorbes overcome physical barriers?skin
Physical processes that damage skin integrity promote infection:
Wounds
Accidental trauma
Surgery
Biting insects
Ensure you can name some specific infections spread by biting insects
what are mucus membranes and how are they related to physical barriers
Mucus Membranes
Layer of epithelial cells covered with mucus
Vulnerable to penetration
Normally lining areas exposed to a flow of material
Examples??- nositals, mouth, anus, ears
How do pathogenic microbes overcome such a barrier?- they collect on mucosal surfaces in large numbers that overcome the mucus or cilia
where do most infections begin
in the mucus membrane- The most common infections are gastrointestinal or respiratory infections.
How do microbes overcome physical barriers in mucus membranes?
Direct damage of mucus membranes is not normally encountered:
Adhesion of pathogens to mucus membranes-invasion of the epithelial layer and a deeper penetration into the body.
Anchoring pathogens in Gut, respiratory tract etc.
What are alternative physical barriers
respiratory cilia, nasal baffle plates, gut peristalsis and urine flow
What is respiratory cilia
On epithelial cells of the respiratory tract
Trap particles (pathogens) in mucus and beating moves them upwards to be swallowed or coughed up
Interference with cilia increases respiratory infection
SMOKING
Medical ventilation
What are nasal baffle plates
acts as a filter for larger particles
what are gut peristalsis
Constant movement of longitudinal and circular muscles in the GI tract. Makes it difficult for pathogens to attach to these mucus membranes
what is urine flow
Regular flow of liquid removes pathogens
Interference with urine flow predisposes to Urinary Tract Infection. UTI a major complication of the use of catheters
what are the chemical barriers on the skin?
high salt
pH 5-6
low water availability
what are the chemical barriers on the mucus membranes?
lysozyme
iron binding proteins=
transferrin
lactoferrin
what is lactopreoxidase
an effective antimicrobial agent- Gram-positive bacteria such as Streptococci and Lactobacilli are only inhibited and are not killed by the LPS
what are antimicrobial proteins
Soluble in blood serum, Activated by
Microbial polymers
Mannose residues
Immunoglobulin binding
what are biological barriers
Phagocytosis (professional phagocytes)
Polymorphonuclear leucocytes (PMNs)=
short lived cells, monitor tissues and vascular system
Macrophages (MOs)= long lived cells and monitor tissues
what are the biological barriers for normal microbiota
Propionibacterium acnes on skin releases Oleic acid- product of fatty acid metabolism and inhibitory to gram positive organisms
Lactobacillus spp. in vagina release various acids (mostly lactic)= products of glycogen metabolism
and pH 3-5 is inhibitory to most microorganisms especially bacteria
GI microflora: Lactobacillus, Bifidobacterium - probiotics
how is inflammation a biological barrier
A complex and tightly regulated set of responses= triggered by tissue damage and infection.
Essential features:
1. vasodilation- an increase in blood flow in the capillaries
2. swelling of local tissues (edema)-
escape of fluid and phagocytic cells from the capillaries
3. recruitment of phagocytes - chemotaxis
4. fibrin clot- formed to stop bleeding
what are the general factors
age, nutrition and genetic factors
How is nutrtion a general barrier
Malnutrition increases the frequency of all infection especially among younger age groups.
Integrity of connective tissue challenged
Inefficient functioning of phagocytic system
how is age a general barrier
Individuals at both age extremes are very vulnerable to infection
Inefficient immune systems
how are genetic factors general barriers
Different human populations are inherently different in their disease responses.
Malaria is less severe in individuals who are heterozygous for sickle cell anaemia that for individuals that do not even harbour even one copy of the altered gene.
what is the CCR5 gene
cell surface receptor with reduced HIV binding and knockout frquency is 1% of Northern Europeans
what is the CASP12 gene
immune response to bacteria and resistance to sepsis and knockout frquency is most non-Africans
what is direct damage
Production of toxins that kill/damage cells
growth within cells and competition for essential nutrients etc. e.g tetanus toxin - When these bacteria enter the body, they produce a toxin that causes painful muscle contractions
What is indirect damage
action of host to eliminate microbial invader results in self-damage
indirect is us
What is tetanus toxin
released by clostridium tetani- soil bacterium
its a protein- 150KD
Behaves as an enzyme protease
Blocks nerve signalling
what is haemolysin- direct damage
Streptococcus
β-haemolysis
Protein released by bacteria
Streptolysin O
69 KD
forms pores in RCB membrane
Detected on Blood Agar.
what is cystic fibrosis- indirect damage
CF is a genetic disease
Inherited defect
Mucus buildup in lungs
Bacterial infections, difficult to cure
Repeated infections
Repeated inflammation
Irreparable lung damage
what is chlamydia trachomatis?
C. trachomatis
Obligate intracellular pathogen
STD- no survival outside of the human body
No agar cultivation
examples of insect bites causing infections
impetigo – a highly contagious bacterial infection that causes sores or blisters. cellulitis – an infection that makes your skin red, swollen and painful
