Dr. Bailey Study Guide 1 Flashcards
6 Steps in the infectious disease process
1) Encounter
2) Entry
3) Spread
4) Multiplication
5) Damage
6) Outcome
Encounter with microbe
The different natural reservoirs of infectious microbes
Does not necessarily mean infection
Entry
Pathogens going into the body
Spread
Pathogens must adhere to the host, multiply, and spread
Different mechanisms for microbe spreading
Lateral propogation
Dissemination
Lateral propogation
Microbes multiply then spread to distant sites
Dissemination
Microbes spread then multiply
Damage
How a host responds
Processes for entering into a host
1) Ingress of microorganisms into body that are contiguous with the outside capsule
2) Penetration of a microorganism into deeper tissues after crossing an epithelial barrier (insect bites, cuts, transplants, etc)
Body parts that are “external”
Nose Mouth Respiratory tract Alimentary canal Anus Female genital tract Urinary Tract
Steps for bacteria to enter epithelia
Attachment
Internalization
Strict aerobes
Must have oxygen to grow
Obligate anaerobes
Cannot tolerate oxygen
Facultative anaerobes
Can grow with or without oxygen
Most medically important bacteria
Oligotrophs
Can grow with limited nutrients
What must microbes overcome in order to spread
Host defenses
Microaerophiles
Require some oxygen, but lower levels of oxygen
Mesophils
Grow in mild temperatures (15-45 degrees C)
Inoculum size
The number of organisms it takes to cause disease
Important in establishing an infection
4 Possible outcomes of a host-parasite interaction
1) Host wins and clears infection
2) Parasite overcomes the host
3) The hist and parasite adapt to eachother
4) Neither host or parasite win
How long can a chronic infection last
Indefinately
Damage to the host can be caused by…
The infectious agent or immune response or both
The great majority of microorganisms are..
Commensal
Gram positive bacteria
Have a thick cell wall made up of muerin
Muerin
A peptidoglycan made up of long chains of N-acetylmuramic acid and N-acetylglucosamine linked together by short polypeptides
Gram negative bacteria
Have a thin layer of muerin between two membranes
Outer membrane of Gram-negative bacteria
Made up of Lipopolysaccharide (LPS) that is species-specific
Lipopolysaccharide
On outer membrane of Gram- cell walls. Toxic in even in purified form. Made up of a lipid region that faces towards the cell, and a polysaccharide that faces out.
Bactericidal agents
Kill bacteria
Bacteriostatic agents
Inhibit bacteria growth
How do Penicillins and other beta-lactams work?
Bactericidal agents that affect the cell wall
How do antibiotics often work
By targeting bacterial ribosomes. Can target either the 30S or 50S subunits
2 subunits to bacterial ribosomes
30S
50S
30S ribosomal subunit
Primarily responsible for the translation of mRNA
Teichoic acid
Surface structure found on both Gram+ and Gram- bacteria not embedded in cell membrane (Lipoteichoic acid when it is)
Thicker in Gram+
Importance of bacteria cell surface structures
Cells of the immune system recognize them
Toll-like receptor 4 recognizes
LPS
Toll-like receptor 2 recodnizes
Peptidoglycan
Toll-like receptor 2 and 4 together reecognizes
Teichoic acids
50S ribosomal subunit
Resonsibel for joining amino acids together and moving the complex along the mRNA molecule
Sulfonamides and trimethoprim inhibit…
Folic acid metabolism
Aminoglycosides, tetracyclines, and erythromycin inhibit
Protein syntesis
Metronidazole inhibits
DNA synthesis
Pili or fimbriae
Specialized structures on the surface of bacteria that are involved in adhesion to cells or other surfaces
Sex pili
Specialized pili that link a donor cell to a recipient during transfer of DNA
Flagella
Surface structures used for locomotion.
Flagella counterclockwise movement
Locomotion of a cell
Flagella clockwise movement
Tumbling
Flagellar movement is used by bacteria for..
Chemotaxis - the movement towards a substance that attract and away from substances that repel
Obligate intracellular parasites
Can only grow inside host cells
Theraputic index
The ratio between the effective dose and toxic use of the antibiotic
Antibiotics tend to target structures that…
are unique in bacteria compared to structures found in host cells
Sulfa drugs
Interact with an enzyme to prevent the production of a metabolite
Mechanisms of antibiotic resistance
- Synthesizing enzymes that inactivate a drug
- Inhibiting uptake of a drug
- Increasing secretion of the drug (pumping it out of the cell)
- Modifying the target of the drug
Drug resistant genes
Often found on plasmids that can readily be transferred from one bacteria to another
In order to survive as an infectious agent, bacteria must…
1) Avoid being washed away
2) Find a nutritionally compatible niche
3) Survive host defenses
4) Transfer to a new host
Damage to a host as a result of an infection can be caused by….
- cell death
- pharmacological alteration of metabolism
- mechanical causes
- host responses
- bacterial toxins
Many structures on the microbial surface consists of…
Repeated molecules - referred to as pathogen associated molecular patterns
Pattern recognition receptors
Recognize pathogen associated molecular patterns
Bacteria are often classified by…
Their surface antigens (aka serotype)
O refers to LPS
H refers to flagella
K refers to a capsule