Treatment and prevention of bacteria Flashcards
1
Q
all antibiotics are
A
ANTIMICROBILAS BUT NOT ALL ANTIMICROBIALS ARE ANTIBIOTICS
2
Q
what is an antibiotic
A
- A natural antimicrobial substance produced by a microorganism that is effective against bacteria
3
Q
what are some examples of antibiotics
A
fungi
actinomycetes
4
Q
name some examples of fungi
A
- Penicillium spp – penicllin
- Cephalopsorium – cephalosporins
5
Q
name some examples to actinomycetes
A
- Streptomyces spp – streptomycin
6
Q
What is an antimicrobial
A
- Any substance of natural, semi-synthetic (chemically modified natural substances) or synthetic origin that kills or inhibits the group of microorganisms
7
Q
name some examples of antimicrobials
A
- Sulphonamides – from the dye prontosil in 1935 – synthetic
- Ampicillin – semi synthetic
- Quinolones – synthetic
8
Q
what are the characteristics of the ideal antimicrobial
A
• Selective toxicity: drug that kills or inhibits growth of the pathogen without harming the host
• Broad spectrum -menas that it is effective against a wide range of organsims
• Long half-life (maintain therapeutic concentrations)
• Easy to administer
• Good tissue distribution
• Does not interfere with other drugs and non-allergenic
• Resistance by microorganisms not easily acquired
• Reasonable cost
This doesn’t exsit
9
Q
How do you classify bacteria
A
- by spectrum broad spectrum or narrow spectrum
- by mode of action - bactericidal or bacteriostatic
10
Q
what is broad spectrum
A
wide range of coverage; used when susceptibility of pathogen to drug is not known
11
Q
what is narrow spectrum
A
small range of coverage – used when susceptibility to drug is known
12
Q
what is bactericidal
A
- Action; irreversible damages and kills bacteria
13
Q
What is bacteriostatic
A
- Action; inhibits bactieral growth and multiplication
14
Q
What is the drugs of bactericidal
A
Very Finely Proficient At Cell Murder
- Vacomysin – gycopeptide
- Fluroquinoles
- Pencillins
- Aminoglycosides
- Cephalosporins
- Monobactoms
15
Q
what are the drugs of bacteriostatic
A
- Tertacycline
- Trimethoprim
- Macrolides
- Clindamycin
- Chloramphenicol
16
Q
most drugs are described as
A
Most antibactieral are described as being potentially both bacteriostatic and bactericidal depending on the
- Dose
- Duration of exposure
- The state of invading bacteria
17
Q
what is a time kill assay
A
• Broth Microdilution method
– Range of antimicrobial concentations (1/4 to 2 x MIC)
– Tested alone and in combination with defined inoculum (1 x 105 cfu/ml)
– Aliquots removed at defined time points and plated for viable bacteria
– Synergy defined as > 2 log reduction
• Tests bactericidal concentrations
• Very labour intensive……
18
Q
what are examples of narrow spectrum bacteria
A
Aerobes examples – gram positive and gram negative
- Glycopeptides, Bacitracin, Penicillin - gram positive
- Polymyxins- gram negative
- Aminoglycosides, Sulfonamides, Actinomycin – both gram positive and gram negative
anaerobes
- Nitroimidazoles – both gram positive and gram negative
19
Q
What are examples of broad spectrum antibiotics
A
- These effects both aerobes and anaerobes
- Tetracyclines
- Phenicol’s
- Fluoroquinolones,
- Third-generation cephalosporins
- Fourth-generation cephalosporins
20
Q
what is selectivity toxicity
A
- This is the effectiveness against a pathogen with minimal toxicity against the host (effective against the microbial organism but not toxic to humans)
21
Q
how do you work out the therapeutic index
A
T1 = TD50/ED50
22
Q
what does a low Therapeutic Index mean
A
- A low TI means that there is a small safety margin between beneficial and toxic dose
23
Q
how does antibiotic selective toxicity work
A
- Exploits the differences in structure and biosynthetic pathways between bacteria and human cells
24
Q
what is the difference between bacteria and humans
A
- Biochemistry is different – for example bacteria synthesise essential vitamins
- Bacterial cell wall, animal cells do not have a bacteria cell wall
- Bacteria have a 70s ribosome whereas eukaryotes have an 80s ribosome
- Mitochondria have 70s ribosomes
- DNA directed RNA polymerases are different
25
what are the antibiotics that target cell wall synthesis
- Beta lactams - – penicillins, cephalosporins, carbapenems, monobactams, vancomycin, bacitracin
- Cell membrane – polymyxins
26
what are the antibiotics that target protein synthesis
- 30s subunit – tetracyclines and aminoglycosidases
| - 50s – streptogramnis, chloramphenicol, linezolid, clindamycin, macrolides
27
what are the antibiotics that target nucleic acid synthesis
- Folate synthesis – sulhanomides and trimethoprim
- DNA gyrase – quinolones
- RNA – polymerase rifampin
28
what are the selective bacteria targets for antibiotics
- cell wall synthesis
- protein synthesis
- nucleic acid synthesis
29
how does the peptidolygcan synthesis of the cell wall work
- Lattice structure of sugar residues that are formed of chains alternating NAM and NAG residues
- Each NAM contains 4-5 AA chains (Lalanine, D-glutamine, L-lysine (m-DAP), D-alanine,)
- Pentaglycine cross linking requires D-alanine-D-alanine, but the cross link itself is formed between D-alanine and L-lysine (m-DAP) catalysed by transpeptidase
- Terminal alanine is lost
30
what is the structure of beta lactams
- Made out of thiazolidine ring and B-lactam ring
31
what are the types of beta lactams
- Pencillins (Penicillin G, Amoxicillin, Ampicillin) – contains a peptide bond similar to transpeptidase dipeptide substrante
- Cephalosporins
- 1st Gen – Cephaphrin, Cephalexin
- 2nd Gen – Cefuroxime, Cefamandole, Cefotetan
- 3rd Gen – Ceftriaxone, Ceftazidime, Ceftizoxome
- 4th Gen – Cefepime
- Carbapenems (Imipenem)
- Monobactams (Azotreonam)
32
is beta lactam bacteriostatic or bacteriocidal
bactericidal
33
what do beta-lactams target
what is the action of beta lactams
what type of bacteria does betalactams target
is it bactericidal or bacteriostatic
- Target – transpeptidase (pencillin-biding protein) is inhibited
- Action; competitive inhibitor of transpeptidase, covalently activates serine in the active site of the enzyme
- What does it target – gram negative, gram positive
- bactericidal
34
what does transpeptidase catalyse
1. Formation of crosslinks between D-amino acids
2. Hydrolysis of peptide bonds
3. Hydrolyses peptide bond in penicillin
35
what are some examples of glycopeptides
- Vancomycin
| - Teicoplanin
36
what do glycopeptides target
what is the action of glycopeptides
what type of bacteria does glycopeptides target
is it bactericidal or bacteriostatic
- Target – D-Ala-D-Ala peptide
- Action – forms hydrogen bonds with D-Ala-D-Ala peptide thus preventing the transpeptidation of peptidoglycan layers, they bind to the things that should be cross-linked.
- What does it target – gram positive
- bactericidal
37
what is the clinical significance of glycopeptides and what is its uses
```
What is the clincia significance
- IV administration (Not absorbed orally)
Used to treat
• Septicaemia
• Lower Respiratory Tract Infections
• Skin Infections
• Bone Infections
```
38
why are glycopeptides not effective in gram negative bacteria
- They are twoo large so it cannot fit through porins
- Affective in gram positive but resistance is on the rise
- Only used as a last result
39
what is an example of polymyxins
* Polymyxin B
| * Polymyxin E (Colistin)
40
what do polymyxin target
what is the action of polymyxin
what type of bacteria does polymyxin target
is it bactericidal or bacteriostatic
Targets; LPS and phospholipids
Action
1. Binds to LPS or negatively charged phospholipids, displacing cations such as calcium and magnesium
2. Destabilises the outer plasma membrane of bacteria.
3. ↑ Permeability of membrane → leakage of ions.
Targets – gram negative bacteria
- bactericidal
41
what does chloramphenicol target
protein synthesis
42
what do chloramphenicol target
what is the action of chloramphenicol
what type of bacteria does chloramphenicol target
is it bactericidal or bacteriostatic
- Targets; 50S ribsome subunit
- Action; inhibits the formation of peptide bonds in the growing polypeptide chains
- Bacteira that it effects include gram positive, gram negative,
- bacteriostatic
43
what is the clinical signficance of chloramphenicol
- Cheap and broad spectrum
- Adverse effect – bone marrow suppression which can lead to aplastic anaemia
- Not to be used trivially
- Can be chemically synthesized or isolated from streptomcyes
- Low but serious risk of bone marrow suppression
44
what do macrolides target
protein synthesis
45
what are the examples of macrolides
- Erythromycin and clarithromycin
46
what do macrolides target
what is the action of macrolides
is it bactericidal or bacteriostatic
- Target 50s ribosome subunit (P site)
- Action – inhibits the translocation of the growing polypeptide chain
- bacteriostatic
47
what do linocosamdies target
protein synthesis
48
what are the examples of linocosamdies
clindamycin, lincomycin
49
what do linocosamdies target
what is the action of linocosamdies
what type of bacteria does linocosamdies target
is it bactericidal or bacteriostatic
Target – 50s ribsooem subunit (23S portion)
Action – leads to premature dissociation of peptidyl-tRNA from ribosome
Targets – gram negative and gram positive
can be both bactericidal or bacteriostatic
Achieve a high concentration in host tissue so it is good for intracellular pathogens
50
what do tetracyclines target
protein synthesis
51
what are the types of tetracyclines
doxycycline and minocycline
52
what do tetracyclines target
what is the action of tetracyclines
what type of bacteria does tetracyclines target
is it bactericidal or bacteriostatic
- Tagert – 30s ribosome subunit
- Action - Prevents aminoacyl-tRNA attaching to A site on ribosome → formation of non-functional proteins.
- Targets – gram negative and gram positive
- bacteriostatic
53
what does aminoglycosdies target
- protein synthesis
54
what are examples of aminoglycosides
gentamicin, tobramycin, amikacin, streptomycin (active against M.tuberculosis)
55
what do aminoglycosides target
what is the action of aminoglycosides
what type of bacteria does aminoglycosides target
is it bactericidal or bacteriostatic
- Target- 30s subunit
- Action - Change shape of 30S subunit → incorrect reading of mRNA code → inaccurate mRNA translation
- Targets – gram negative and gram positive
- bactericidal
56
what is the clinical significance of aminoglycosides
* Use: mostly against gram-negative bacteria, but Streptomycin may be used against M. tuberculosis.
* Administration: typically IV.
* Adverse Effect:
* Hearing loss
* Renal impairment
57
what is the winding problem
During DNA replication and transcription, DNA becomes overwound ahead of a replication fork.
This torsion would eventually stop the ability of DNA or RNA polymerases involved in these processes to continue down the DNA strand.
Topoisomerases create nicks in supercoiled DNA and then repair.
58
what does quinolone target
nucleic acid synthesis
59
what are the types of quinolones
Ciprofloxacin, Gatifloxacin, Levofloxacin, Moxifloxacin
60
what do Quinolones/fluoroquinolones target
what is the action of Quinolones/fluoroquinolones
what type of bacteria does Quinolones/fluoroquinolones target
is it bactericidal or bacteriostatic
Target: Topoisomerase II (DNA Gyrase) + Topoisomerase IV
Action:
Prevents preventing bacterial DNA from unwinding and duplicating
Target bacteria – gram positive and gram negative
In gram negative bacteria what is the target
- DNA gyrase
In gram positive what is the target
- Topoisomerase iV is the target for many
- bactericidal
61
what are the clinical significance of quinolones
* Use: active against intracellular bacteria (Chlamydia spp., Legionella spp., Mycoplasma spp.)
* Widely used drug.
62
what does rifampicin target
nucleic acid synthesis
63
what do rifampicin target
what is the action of rifampicin
what type of bacteria does rifampicin target
is it bactericidal or bacteriostatic
Target: DNA-dependent RNA Polymerase
Action:
Suppresses RNA synthesis (transcription).
Target bacteria – gram negative and gram positive
In gram negative bacteria DNA gyrase is the target
In gram positive bacteria – topoisomerase IV is the target for many
- bactericidal
64
what is the clinical significance of rifampicin
• Use: treatment of tuberculosis.
| Lipophillic drug → can cross BBB to treat TB meningitis
65
Describe how the DHFR pathway works and what inhibits it
Bacteria synthesis their own folic acid, PABA is a precursor of folic acid
Sulphonamides are structurally the same to PABA
Sulpanomides are competitive inhibitors of dihydropteroate synthase so inhibit the synthesis of dihydropteroic acid
Human DHFR is resistant to trimethoprim which is a sulphanomide therefore it can still form DNA pruines
66
what do sulphonamides target
nucleic acid synthesis
67
what are the types of sulphonamides
Sulfamethoxazole, Sulfasalazine, Sulfadoxine
68
what do sulphonamides target
what is the action of sulphonamides
is it bactericidal or bacteriostatic
Target: Dihydropteroate Synthase
Action:
Competitive inhibitor of dihydropteroate synthase (drug structure resembles PABA substrate) → preventing synthesis of dihydropteroic acid with downstream consequences of decreasing purines.
- bacteriostatic
69
what do DHFR target
nucleotide synthesis
70
what are the types of DHFR inhibitors
trimethoprim
71
what do DHFR inhibitors target
what is the action of DHFR inhibitors
what type of bacteria does DHFR inhibitors target
is it bactericidal or bacteriostatic
Target: Dihydrofolate Reductase
Action:
Competitive inhibitor of dihydrofolate reductase → preventing synthesis of THF with downstream consequences of decreasing purines.
Targets – gram negative and gram postiie
It is nearly always used in combination with sulfamethoxazole for syngestic effects
Has anti-malarial properites
- bacteriostatic
72
what are the types of antibiotic resistance
inherent (intrinsic) resistance
| acquired resistance
73
what is intrinsic resistance due to
due to inherent structural/functional characteristics
| - passed from mother to daughter cells
74
what is acquired resistance due to
mutations and horizontal gene transfer.
| - may spread between clones, may spread between species
75
what are examples of intrinsic resistance
• Outer Membrane of Gram Negative bacteria.
- Vancomycin cannot cross outer membrane to reach target side (peptidoglycan).
• Efflux Pumps that actively transport drug out of bacteria.
- Tet proteins in E. coli.
76
what drugs are inactivated by hydrolysis
- Beta-lactamases these are enzymes that hydrolyse the beta-lactam ring preventing it from working
- Transmission by clones and plasmids that are mobile
77
how is beta lactmase inactive by hydrolysis
- Early beta – lactamase; action against first generation beta-lactams – the beta-lactam ring is destroyed which means it does not bind to targets in the cell wall
78
what are the other types of drugs inactivated by hydrolysis
- Extended spectrum beta lactamases (ESBLs); action against cephalosporins with oxyimino side chain (ceftriaxone, ceftazidime)
- Carbapenemases; action against carbapenems
79
how do you treat extended spectrum beta lactamases (ESBLs)
- Beta – lactam/ beta lactamase inhibitors (BLBI)
- Combination drug
- Examples; Amoxicillin and clavulanic acid for resistant strains of S.aureus, E.coli and H.influenzae
80
describe how activation of efflux pumps are over expressed
- Actively pump antibiotics out of bacterial cell
- Example AcrB in E.coli
- Some pumps have 2 binding pockets (of variable size and properties) this leads them to having a wide range of antibiotic transport
81
what is a target site mutation and what is an example of one
- Mutation of the target site – prevent the antibiotic from binding but allow the target protein to function, this leads to antibiotic resistance
- For example, quinolone resistance (qnr) – mutation to topoisomerases
82
what are the two target modifications that lead to antibiotic resistance
target site mutation
| target site protection
83
what is target site protection and give example of one
- Addition of chemical group that prevents antibiotics binding to the target site,
- Example; erythromycin ribosome methylase (erm) methylates 30s subunit and this prevents macrolides from binding to 50s
84
where is plasmid encoded resistance
this is resistance passed from mother to daughter cells
85
what is alternative enzymes
this is production of alternative enzymes
- Example trimethoprim resistance – resistant chromosomal DHFR due to spontaneous mutations in intrinsic DHFR
- Resistant plasmid mediated DHRF – due to acquisition of resistance genes via plasmids or transporter
- Gene duplication – same susceptible enzyme but over production of it
86
what is plasmid addiction
* Genes located on the plasmid produce a toxin and the antidote – the antitoxin
* The antitoxin is rapidly degraded by intracellular enzymes
* The toxin is not degraded
* If a daughter cell does not inherit the plasmid it will be unable to synthesise antitoxin
* All cells without the plasmid are self poisoned by the remaining toxin
* Plasmid addiction systems are now on the same plasmids as the resistance genes
87
what are solutions to antibiotic resistance
- More effective prevention in antibiotic use
- Targeted treatments – use narrow spectrum instead of broad spectrum
- More informed clinical decisions
- Public education
88
what are the ideal characteristics of an bacterial vaccine
1. Produces immune protection which usually follows a natural infection coruse without causing disease
2. Long lasting immunity
3. Interrupts the spread of infection
89
what are the problems with vaccines
Primary failure; inadequate response to 1st vaccination
Secondary failure – initial immune decreases overtime and boosters are required
Some people do not produce an immune response such as HIV or cancer patients
90
what are the causes of vaccine failure
Different serotype from challenged virus.
Interference from maternal antibodies in neonates.
Vaccine manufacturing problem → insufficient antigen/live virus.
Storage/Administration problem → vaccines becomes denatured or inactivated.
91
what are the different types of vaccines
live attenuated vaccines
inactivated vaccines
subunit vaccine
92
what is the method of live attenuated vaccines
how is the immunity of live attenuated vaccines achieved
what are examples of live attenuated vaccines
– achieved by passage through a foreign host
Method: bacteria is cultured and attenuated (not killed) over a period of time.
Immunity: cell-mediated + humoral.
Bacterial Vaccines:
• BCG → for M. tuberculosis.
• Ty21a → for Salmonella typhi.
• CVD 103-HgR → for Vibrio cholera (LAV + Subunit Vaccine).
93
what is the method of Inactivated vaccines
how is the immunity of Inactivated vaccines achieved
what are examples of Inactivated vaccines
```
- Chemical inactivation can be achieved using formalin, heat or ß-propriolactone, and purification of protein or polysaccharide components
Method: bacteria is inactivated by treatment with a heat or chemical.
Immunity: humoral only.
Bacterial Vaccines:
• Pertussis vaccine
• Anthrax vaccine
• Plague vaccine.
• Toxoid – tetanus and diphtheria
```
94
what is the problem with inactivated vaccines
- Frequency of adverse events increase with number of disease therefore if there is a good secondary immune response then this can cause inflammation
95
what is the method of Subunit vaccines
how is the immunity of Subunit vaccines achieved
what are examples of Subunit vaccines
Difference between subunit and inactivated vaccines is that the subunit vaccine only contains the antigenic part of the pathogen
Method: a certain antigenic component (protein/polysaccharide) of bacteria is purified and used in vaccine.
Immunity: humoral only.
Bacterial Vaccines:
• Polysaccharide vaccines → Meningicoccal A, C, W and Y.
• Conjugate vaccine (linked to bacterial protein carrier) → PCV, HiB
96
why is sensitivity testing performed
– to see whether the therapy is likely to be effective
– to enable ‘narrow’ spectrum therapy to be give to reduce side effects
– to obtain data on local prevalence of resistance
– to enable antimicrobial policies to be formed
– to provide surveillance for national databases
97
what are the methods of susceptibility testing
```
– Disc diffusion – BSAC / Kirby-Bauer
– Agar dilution
– Broth microdilution
– Gradient methods - Etest
– Automated systems – VITEK, Microscan
– Molecular detection of resistance mechanisms
```
98
how is agar dilution performed
- Double dilutions off antibiotic into series of agar plates,
- Organism is then spotted on and there is either growth or no growth
99
how are broth micro dilution tests perfumed
- Same as agar but uses liquid culture media
| - Assessed for turbidity
100
how are Broth microtitre dilution performed
- Performed in microtitre plates
- Broth methods enable the minimal bactericidal concentration (MBC) to be determined by plating out the tubes which don’t grow
101
how does a disc diffusion test work
* A standard inoculum of the organism is plated on to sensitivity testing agar
* Antibiotic discs are added and the antibiotics diffuse into the agar
* Plate is incubated overnight and zones of inhibition are measured and compared either to a sensitive control or ‘zone diameter breakpoints’
102
what are the automated methods and what are they based of
- Micro scan walkaway
- Vitek
- Phenoix
What are the automated methods based on
- Broth microdilution, but it has a higher resolution optical scanning for microbial growth
103
what is the definition of susepctible
A bacterial strain inhibited in-vitro by a concentration of an antimicrobial agent that is associated with a high likelihood of therapeutic success
104
what is the definition of intermediate
: A bacterial strain inhibited in-vitro by a concentration of an antimicrobial agent that is associated with uncertain therapeutic effect.
105
what is the definition of resistant
A bacterial strain inhibited in-vitro by a concentration of an antimicrobial agent that is associated with a high likelihood of therapeutic failure
106
what are pharmacodynamic indices
Concentration-dependent killing with prolonged antibiotic effect (PAE)
• Cmax / MIC ratio most important
• Characteristic of aminoglycoside, some fluoroquinolones
Time-dependent killing with minimal PAE
• T> MIC is most important parameter
• Characteristic of β-lactams
Time-dependent killing with prolonged PAE
• AUC24 / MIC ratio most important
• Characteristic of glycopeptides, tetracyclines and macrolides
