Finals Flashcards
Pathogen, pathogenicity and virulence; determination of virulence
A pathogen is a microorganism (or virus) that is able to produce disease.
Pathogenicity is the ability of a microorganism to cause disease in a host organism.
Virulence is the degree of pathogenicity.
Dont forget the relationship of the host (degree of resistance to virulence factors) and the pathogen, which is dynamic.
Determination of virulence depends on the virulence factors of the pathogen: genetics, biochemical, or structures which enable it to produce a disease
Determination: lethal dose 50 or 90, meaning the dose/number it takes to kill 50 or 90% of the test subjects.
List up some virulence factors
Some virulence factors:
Capsule (K-antigene, anti-phagocytic: polysaccaride, poly-D-glutamate, hyaluronic acid)
Exotoxins
Pili ( adherance)
Flagella (H-antigene: movement)
O antigens (LPL)
Enzymes (coagulase, urease, IgA protease, M-protein (inhibit opsonization), protein A (binds to Fc-portion on Ig) ++)
Some special enzymes:
1: streptolysin O and hemolysin, these damage neutrophils and RBS, respectively, preventing destruction of the pathogen. This is common for S. pyogenes.
2: Leukocidin damage neutrophils. Common for staphylococci.
Define infection
inflammatory response to the presence of or invasion of normally sterile host tissue by microorganisms.
Molecular masking: what is it and give examples
Hide itself from phagocytes/immune system. Can do this by;
1: Coagulase on S. aureus coat itself with fibrin + protein A which binds to Fc portion on Ig.
2: Hyaluronic acid capsule in S. pyogenes
3: Treponema Pallidum binds fibronectin
Which organism have a capsule? What is its importance? which bacteria produces biofilms?
K-antigene
Importance:
1: prevent the phagocytosis of phagocytes
2: can be used as antigenes in vaccines
3: Quelling reaction or capsular swelling test
4: Latex agglutination + ELISA
5: Meningitis!
A common mnemonic used to remember some encapsulated pathogens is:
“Even Some Super Killers Have Pretty Nice Big Capsules”
Escherichia coli Streptococcus pneumoniae Salmonella Klebsiella pneumoniae Haemophilus influenzae Pseudomonas aeruginosa Neisseria meningitidis Bacteroides fragilis Cryptococcus neoformans (yeast)
Other encapsulated bacterias include: Bacillus anthracis (poly-D-glutamate) Streptococcus agalactiae Streptococcus pyogenes (hyaloronic acid) Staphylococcus epidermidis (not sure if it does have a real capsule, but makes a slime layer/biofilm)
Biofilms Strep mutans (dental plaques!) + Staph. epidermidis (catheters!)
Some bacteria are resistant to phagolysosome fusion or inhibit this formation: what are common for them and name some bacterias
This is common for intracellular bacterias: typical with granuloma formation!
Inhibit formation: Salmonella, M. tuberculosis, Legionella, Chlamydia
Can survive in phagolysosome: bacillus anthracis, M. tuberculosis, S. aureus
Rickettsia produces phospholipases that lyses the phagosomes and by doing this can escape the phagosomes.
Listeria escape before fusion
Structure of the peptidoglycan layer, function, what attaches to it, and what antibiotics act on its synthesis?
Some differences between gram + and - ?
Cell walls are present in most prokaryotes (except mycoplasma bacteria)
The sugar component consists of alternating residues of β-(1,4) linked NAG and NAM . Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer. The amount and type of peptide varies: in e.g. E.coli -> L-alanine, D-glutamate, DAP, and D-alanine
NAG: N-acetylglucosamine
NAM: N-acetylmuramic acid
Transpeptidase: inhibited by penicillin, cephalosporin.
Please note that the enzyme lysozyme act on this peptidoglycan layer
Function: maintein shape and prevent osmotic lysis
Fimbria, pilli and flagella can bind to the cell wall
Cell wall is also important for bacteriphages at they attach to it.
Gram +: much thicker. Contain teichoic acid (provide rigidity to the cell-wal)
Gram - : much thinner. They have a prominent periplasmic space in between the cytosolic membrane and the cell wall
Lipopolysaccharide: what is it, structure, where is it found, what function does it have? Does all bacteria have the same LPS?
LPS or endotoxin. Found on gram negative bacteria.
Consist of: Lipid A (endotoxin part), core polysaccaride, and an outer O-spesific polysaccharide (O-antigen)
LPS can:
1: activate macrophages
2: cause IL-1, TNFa, and IL-6 release
3: induce fever and shock
4: DIC (coagulation)
5: endothelial dysfunction
The outer O-antigen can differ. In neisseria meningitidis and H. influenzae this O-antigen is relative short (lipoologisaccharides). To be noted, these two bacterias can bind sialic acid to its LPS and by doing so makes it much more difficult for MAC complexes to lyse this bacterias
What ribosomal units does bacteria have and which antibiotics can act on it?
Prokaryotes have 30s + 50s forming 70s.
50s: macolides, chloramphenicols
30s: aminoglycosides, tetracyclins
What are the difference between pilli, fimbria and flagella?
Pili and fimbriae are cell surface appendages present in bacteria other than flagella. These are not for locomotion, which is the major function of flagella (flagellin proteins)
Flagella (H-antigen): one or several, and axial or terminal. Spirochetes have several axial flagellas. E.coli and Proteus mirabilis have flagella; important in UTI
There are som key differences between pili and fimbriae: Often, fimbriae are referred to as “common pili” involved in attachement, while pili are known as “sex-pili” which stabilizes mating bacteria durind DNA transfer by conjugation.
What are spores and what is is good for?
“Rest, and wait for better times”
Spores are highly resistant structures formed in response to adverse conditions, Bacillus and clostridium; both are gram positive spore forming bacterias.
Sporulation occurs when nutrients are depleted or the environment in general in not suitable. Spores form inside the cell.
Contains DNA, small amount of cytoplasm, cell membrane, peptidoglycan, very little water, and a thick keratinlike coat. The spore have no metabolic activity which allow it to remain dormant for years
Sporulate when the environment is good
Medical importance: highly resistant to heat, and chemicals. Can survive for years.
Bacterial genetics
DNA in the form on nucleotide. Only one chromosome. Haploid.
Plasmin: extrachromosomal DNA.
Methods of gene transfer
Transformation: Uptake of naked DNA from the environment by competent cells. Cells become competent under certain physiological conditions. DNA is taken up. DNA is linear HR (exchange of DNA). Need RecA
Conjugation (”bacterial mating”): Gene transfer from one bacteria to another involving direct cell-cell contact. Fertility factor control conjugation; Sex pili (genes of F) establish cell-cell contact. A single strand of donor DNA (male; have the F-factor) is transferred to recipient (female). Bacterial genes transferred by conjugation have to be stabilized by HR. Plasmid genes are stable without HR. Conjugation with recombination may produce new genetic combinations. All the recipient becomme F+ after conjugation with plasmids; does not become F+ with Hfr chromosome conjugation (use HR; exchange)!
Males: F+
Females: F-
Transduction: transfer of bacterial DNA by a phage vector. Phage picks up DNA through an error in phage production. Generalized and specialized types:
Generalized: Phage puts a piece of bacterial DNA into its head, and all genes have an equal chance of being transduced. “Phage mistake when packing”. Can occur in lytic and temperate infections.
Specialized: Dependent on integration of phage DNA into the bacterial chromosome at a specific site, and an excision error allows bacterial DNA to be excised and packaged with phage DNA. Only temperate phages (depend on excision errors)
Some information of Phage: bacterial viruses. Can be virulent, meaning it infects bacterial cells resulting in bacterial cell lysis, or temperate: often infects bacterial cells without lysing the cells. Integrates phage DNA into bacterium. Can also replicate lytically.
Mechanism of antibiotic resistance
Drug resistance
Intrinsic, plasmid or chromosomal.
Intrinsic: e.g. mycoplasma is resistant to penicillin as it does not have a cell wall.
Chromosomal-mediated: resistance located on bacterial chromosome. Most common modification of drug receptor so that the drug can no longer bind (PBP: MRSA). Transporters/pumps.
Plasmid-mediated: resistance located on the plasmid. R-factor (carry genes for drug resistance). One section of DNA mediated conjugation (F+), other section carries genes for drug resistance. Plasmid-mediated resistance is created by variety of mechanism, but often genes coding for enzymes that modify the drug (e.g. B-lactamase). One plasmid can code for several drug resistances
How do multiple drug resistance plasmids arise? Via gene cassettes/intergrons/transposons: mobile genetic elements that can move themselves or a copy from one molecule of DNA to another (jumping genes). Found in eukaryotes, bacteria and viruses. Have indirect repeats on each end. Carry transposase enzyme create mutation with their insertions. Insertion produces direct repeats on either side of the mobile segment.
Sterilization: what is it, and give some methods
Sterilization = the process of killing or removal of all microorganism in a preparation (including bacterial spores)
Sterile = treated objects are free of all living organisms
Methods
1: Physical methods - heat (dry* or moist**), gamma-radiation. Flames
2: Chemical methods - ethylene oxide, plasma (H2O2; in vacum -> ROS)
3: Membrane filtration - used for temperature-sensitive fluids. Viruses can pass :( variable pore size
- Dry heat: 3h with 140, 2 hour with 160, or 1 h with 180 degrees.
- Moist - Autoclave: 121 at 1 atm for 30 min or 134 at 2 atm for 10 min.
Disinfection: what is it, give some methods, and what is the importance of the phenol coefficiant?
Disinfection = treatment which reduces the number of potentially pathogenic microorganism in an environment (this process do not destroy all pathogens)
Disinfectant = a chemical substance used to kill micro-organism on non-living surfaces (too toxic to be applied directly to tissue)
Antiseptic agent = chemical used to reduce the number of potentially pathogenic microorganisms on living tissue (skin, mucous membrane) - Ignaz Semmelweis
Phenol coefficient is used to compare disinfective agents. Takes the “highest dilution factor that kills bacteria after 10 min, but nor after 5 min” relative to the dilution factor of phenol.
Important to remember: the length of time the agent is applied and the concentration of the agent (think about scrubbing in surgery).
Methods:
1: Physical - pasteurization, boiling, UV-radiation
2: Chemical - isopropanol, alcohols (70%; bactericidal - disrups lipid membrane), phenols (protein denaturation), heavy metals (protein denaturation), oxidizing agents (iodine, chlorine (!)), alkylating agents (formaldehyde), detergents (surface active agent; cationic and anionic detergents)
What are the difference between antisepsis and asepsis?
Asepsis = is the state of being free from disease-causing micro-organisms (such as pathogenic bacteria, viruses, pathogenic fungi, and parasites). The term “asepsis” often refers to those practices used to promote or induce asepsis in an operative field in surgery or medicine to prevent infection
- Sterile is the absence of ALL microbs, Aseptic is just the absense of disease produceing microbs
Antisepsis = chemical used to reduce the number of potentially pathogenic microorganisms on living tissue (skin, mucous membrane) - Ignaz Semmelweis
Selective toxicity and chemotherapeutic index: give some examples
Selective toxicity = implies that a drug is harmful only to other organisms without harming the host: act on other biochemical structures not present on the host.
Chemotherapeutic index (Paul Ehrlich): the highest concentration of the antimicrobial agents that can be tolerated by the host, divided by the lowest concentration of the agent that inhibit or kills the microorganism Chemotherapeutic index = maximal tolerated dose / minimal effective dose - Penicillin have high range - Aminoglycosides have low range which means it need to be monitored much more closely to prevent adverse effects.
“The therapeutic index (TI) (also referred to as therapeutic ratio) is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxicity. The related terms therapeutic window or safety window refer to a range of doses which optimize between efficacy and toxicity, achieving the greatest therapeutic benefit without resulting in unacceptable side-effects or toxicity”
Principles of antibacterial chemotherapy
What are bacteriostatic and bactericidal effect?
Narrow vs. broad-spectrum antibiotics
Also explain what an antibiotic, semisynthetic antibiotic, and chemotherapeutic agent are.
Bacteriostatic effect: inhibit the growth of microorganisms but is unable to kill them within a short period, rely on host defenses to remove the pathogens.
- MIC = minimun inhibitory concentration: E-test, agar dilution or broth microdilution
Bactericidal effect: kill growing microorganisms within a short period. This is determined in vitro.
- The lowest concentration which kills 99.9% of the population is referred to as minimal bactericidal concentration (MBC)
Use narrow spectrum if possible; prevent side effects and large alterations in normal flora - dysbacteriosis (pseudomembranous colitis from C. difficile)
Dont forget - chemotherapeutic index and selective toxicity principle
Antibiotic = natural occurring agent produced by an organism to inhibit the growth or kill other microorganisms.
Semisynthetic antibiotic = natural synthetic agent which is modified chemically in order to have advantageous and pharmacokinetic properties
Chemotherapeutic agent = an antimicrobial synthesized chemically.
Antimicrobial drugs in combination: why is it sometimes useful?
Synergism: 1+1 = 3 (e.g. penicillin + aminoglycosides for enterococcus faecalis)
Antagonism: 1+1 = 0,1
Indifference: 1+1 = 1
Additive: 1+1 = 2
e.g. give penicillin together with a B-lacatamase inhibitor
You should always be aware of interactions with different drugs!
Antibiotics in combinations is used when:
- mixed infection is present with different antibiotic sensitivity
- pathogens hardly affected by drugs (M. tuberculosis)
- pathogen is multiple resistant (pseudomonas)
- it is difficult to achieve high enough dose at the infection site
- prevent emergence of resistant organism during therapy
- the immune system of the patient is week
Which tests can be used to determine antibiotics susceptibility?
Diffusion method: E-test, disc diffusion
Dilution method: agar, broth microdilution and tube dilution
Risks and side effects of antibacterial chemotherapy
Some risks and side effects
- Allergy: type 1 hypersensitivity -> anaphylaxis. E.g. to penicillin and cephalosporins (rash and urticaria)
- Dysbacteriosis: diarrhea and C. difficile (pseudomembranous colitis) from broad-spectrum antibiotics.
- Candidiases infection as normal flora is altered
- Direct toxic effect
1: Tetracyclins - because of depositions in developing teeth, its use should be avoided in children up to 8 years and in pregnant and lactating woman
2: Antifungal drugs are toxic to liver
3: Aminoglycosides are toxic to kidney and nerves
4: Chloramphenicol toxic to bone marrow
Antibiotics altering the peptidoglycan synthesis
Beta-lactams (inhibit peptidoglycan synthesis): penicillin, cephalosporins, carbapenems, and monobactams (used is someone has penicillin allergy)
Beta-lactams bind to PBP (penicillin binding proteins which is a transpeptidase) because they can be bound to beta-lactams. MRSA have altered PBP.
Beta-lactamase can destroy beta-lactams: this is why we can give beta-lactamase inhibitors to prevent this inactivation.
Bactericidal effect
Glycopeptides: Vancomycin (cross-linkage) and bacitracin (inhibit bacterial cell wall and movement of cell wall)
