Antimicrobial Therapies

Question 1

What are the 4 types of antibiotic drugs?

Answer 1

1. Beta-Lactams - interfere with bacterial cell wall synthesis
2. Sulfonamides - interfere with folic acid synthesis
3. Aminoglycosides - target protein synthesis (30S ribosomal subunit), RNA proof-reading, damage cell membrane
4. Macrolides - targets protein synthesis (50s ribosomal subunit)
5. Quinolones - synthetic, targets cell replication

Question 2

What was the first anti-bacterial drug (antibiotic)?

Answer 2

Prontosil

Question 3

How does protonsil work?

Answer 3

It is bacteriostatic - it works by stopping the bacteria from growing, rather than directly killing it
Targets folate biosynthesis in bacteria

Question 4

Is protonsil still used today and if so, for what?

Answer 4

Yes, variants of the drug is still used to treat UTIs
2 variants - Trimethroprim and sulfonamides
Both stop same reaction pathway at different points - synergistic activity, and so are best effective together

Question 5

What are the 2 types of gram bacteria?

Answer 5

Gram positive and gram negative bacteria

Question 6

What are some features of gram positive bacteria?

Answer 6

Single membrane

Thick cell wall

Question 7

What are some features of gram negative bacteria?

Answer 7

Two membranes - inner membrane with phospholipids and outer membrane with phospholipids and lipopolysaccharides

Question 8

Why does prontosil only work on gram positive drugs?

Answer 8

Outer layer on gram negative is difficult for drugs to penetrate and pass through

Question 9

What properties should a drug typically have to work on gram negative bacteria?

Answer 9

A part that is hydrophillic to get thorugh the outer layer, and then a part that is hydrophobic to get through the inner layer
To find molecules with both those properties is difficult

Question 10

What were the issues with early penicillin?

Answer 10

Short half life - rapidly left the body - was quickly excreted via the urine
Often urine was collected from these patients and purified to recollect the penicillin (massive shortage)

Question 11

What category of antibiotics is penicillin an example of?

Answer 11

Beta-Lactams

Question 12

How do Beta-Lactams work?

Answer 12

All have the characteristic beta-lactam ring
The most commonly used antibiotic as they:
Interfere with the synthesis of the peptidoglycan component of the bacterial cell wall
Mimic molecules (precursors) involved in this process and bind to the enzymes, inactivating them - bacteria begin to grow, but soon after die

Question 13

What is an antibiotic?

Answer 13

An antimicrobial agent produced by a microorganism that kills or inhibits other microorganisms
Strictly speaking, a ‘natural product’ (taken from microbes) - although today, many are (semi-)synthetic versions

Question 14

What is an antimicrobial?

Answer 14

Chemical that selectively kills or inhibits certain microbes

Question 15

What is bactericidal?

Answer 15

Kills bacteria

Question 16

What is bacteriostatic?

Answer 16

Inhibits bacterial growth

Question 17

What is antiseptic?

Answer 17

Chemical that kills or inhibits microbes, usually used topically to prevent infection

Question 18

Define resistant bacteria?

Answer 18

Bacteria that are able to replicate in environments with high concentrations of the drug present (any concentration that is above what can be reasonably achieved therapeutically)

Question 19

What is a breakpoint?

Answer 19

An estimate of what could theoretically be given to / achieved in a patient - i.e. the strength of a dose that could realistically be given to a patient

Question 20

What can increase the speed of resistance arising towards a specific antibiotic and why?

Answer 20

Bacteria lie on a scale of sensitive to resistant towards the antibiotic
There are bacteria around the breakpoint that are neither susceptible, nor resistant
Hence over-prescription / or under-dosage can cause those bacteria to be able to survive the drug, and mutate to become more resistant

Question 21

How does the usage of antibiotics impact antibiotic resistance?

Answer 21

Using antibiotics more frequently causes higher rates of resistance - applies selective pressure on bacteria i.e. selects for resistance
Susceptible drugs killed, resistant left behind, increasing their prevalence
Loss of efficacy in drugs

Question 22

Why is it economically not profitable to invest in finding a new antibiotic?

Answer 22

Already many antibiotics available that work effectively in most cases
Money/funding required
If a new antibiotic is found, it must be used sparingly, as greater usage is linked with greater loss in efficacy - cannot be distributed to many patients, lack of profit (little financial return to the companies / market)
Therefore almost total lack of investment

Question 23

By which mechanism does antibiotic resistant resistance arise?

Answer 23

Evolution by natural selection

Question 24

What were the major misconceptions of antibiotic resistance at the start of the era?

Answer 24

1. Resistance to more than one class of antibiotics could occur in a single organism
2. Bacteria can swap genetic information - horizontal gene transfer
3. Resistant bacteria that would emerge would be significantly ‘less fit’ to survive (sometimes true, but often those with infections already have weakened immune systems so bacteria do not need to be aggressive)

Question 25

When does resistance emerge against an antibiotic?

Answer 25

Soon after it is introduced into the wider population

Question 26

Why is resistance different in different countries, and why is it important to acknowledge that?

Answer 26

The frequency of the usage of that specific antibiotic in that area / country impacts resistance i.e. greater usage = greater selection = greater resistance If a patient has been abroad, looking at statistics for that country can help determine which antibiotic is best to prescribe

Question 27

How does antibiotic resistance impact society / populations?

Answer 27

Greater mortality - greater morbidity - and so leads to more cost Increased time for effective therapy - may need to come back for higher dosages / stronger antibiotics Requirement for additional approaches – e.g. surgery (surgical drainage) Use of expensive therapy (newer drugs) Use of more toxic drugs e.g. vancomycin Use of less effective ‘second choice’ antibiotics

Question 28

How are antibiotics given to patients? (i.e. following which diagnostic tool?)

Answer 28

Often, no diagnostic tool, given blindly on an educated guess

Question 29

Why are antibiotics often given blindly?

Answer 29

Because infection can take hold rapidly - by the time results from the diagnostic tool come back, it may be too late

Question 30

What are some examples of majorly resistant gram positive bacteria?

Answer 30

``` Staphylococcus aureus (MRSA, VISA) - wound and skin infected, pneumonia, septicaemia, infective endocarditis Streptococcus pneumoniae - pneumonia, septicaemia Clostridium difficle - pseudomembranous colitis, antibiotic-associated diarrhoea Enterococcus spp (VRE) - UTI, bacteraemia, infective endocarditis Mycobacterium tuberculosis (MDRTB, XDRTB) - tuberculosis ```

Question 31

What are some examples of majorly resistant gram negative bacteria?

Answer 31

Pseudomonas aeruginosa - cystic fibrosis, burn wound infections, survives on abiotic surfaces. E. Coli (ESBL) - GI infection, neonatal meningitis, septicaemia, UTI Salmonella spp. (MDR) - GI infection , typhoid fever. Acinetobacter baumannii (MDRAB) - opportunistic, wounds, UTI, pneumonia (VAP), survives on abiotic surfaces. Neisseria gonorrhoeae - gonorrhoea

Question 32

Gentamycin and Streptomycin are examples of which type of antibiotics, and how do they work?

Answer 32

Aminoglycosides Bactericidal - kill the bacteria Target protein synthesis (30S ribosomal subunit), RNA proofreading and cause damage to cell membrane Toxicity has limited use, but resistance to other antibiotics has led to increasing use

Question 33

What properties of Rifampicin may discourage patients to discontinue its use?

Answer 33

Bactericidal - targets RNA polymerase Subject to spontaneous resistance frequently Causes fluid secretions to turn orange / red e.g. tears, urine, faeces

Question 34

How does vancomycin work?

Answer 34

Bactericidal Targets Lipid II component of cell wall biosynthesis Toxicity has limited use, but resistance to other antibiotics has led to increasing use e.g. against MRSA

Question 35

How does linezolid work?

Answer 35

Bacteriostatic Inhibits the initiation of by binding to the 50S rRNA subunit. Only targets gram-positives

Question 36

How does dactomycin work?

Answer 36

Bactericidal Targets bacterial cell membrane. Only targets gram-positives Toxicity limits dose

Question 37

Which major principle do antibiotics work on?

Answer 37

Selective toxicity - bacteria have many different characteristics unique to them (and not present in humans), and processes that occur with a sufficiently different mechanism to mammals, which are targeted by antibiotics e.g. cell replication cycle, bacterial cell wall synthesis, protein synthesis etc

Question 38

What are the 4 distinct mechanisms by which resistance occurs?

Answer 38

1. Altered target site 2. Inactivation of antibiotic 3. Change metabolic profile 4. Decreased drug accumulation (i.e. pump out the antibiotic)

Question 39

How does altering the target site work?

Answer 39

Can arise via acquisition of alternative gene or a gene that encodes a target-modifying enzyme e.g. MRSA encodes an alternative PBP (PBP2a) with low affinity for beta-lactams Antibiotic can no longer bind to the specific protein structure it needs to, to inhibit / kill bacteria

Question 40

How is the antibiotic inactivated?

Answer 40

``` Bacteria develop enzymes that digest molecules of the antibiotic Particularly important for beta-lactams - target beta-lactam rings e,g, beta-lactamase or chloramphenicol acetyl-transferase (cat) Renders huge class of antibiotics as ineffective ```

Question 41

How does altering the mechanism work?

Answer 41

By increasing the number of enzyme substrate / enzyme so it out-competes the effect of the antibiotic as an inhibitor Or by switching the metabolic pathway to require less of the original enzyme substrate / enzyme e.g. prontosil inhibited folate biosynthesis, but resistant bacteria developed the ability to acquire folate from surroundings

Question 42

How does decreased drug accumulation work?

Answer 42

Bacteria have selective pumps in their membranes that can recognise abd eject certain drugs / toxic chemicals Or reduced penetration of antibiotic into bacterial cell (permeability) Therefore the drug does not reach the concentration required to be effective

Question 43

How have bacteria, such as gonococcus (gram-negative), acquired resistance?

Answer 43

1. Point mutations - single nucleotide is changed/deleted/added to the DNA or RNA typically causing a target site modification 2. Plasmid transformation - take up pieces of DNA directly from the environment around the cell 3. Plasmid conjugation - two bacteria can pair up and connect through structures in the cell membranes and then transfer DNA from one bacterial cell to another 4. Transduction - viruses called bacteriophages can infect bacteria, these viruses sometimes bring along genes that they picked up during infection of another bacterium. These genes may then be incorporated into the DNA of the new bacterial host

Question 44

Erythromycin and azithromycin are examples of which type of antibiotic and how do they work?

Answer 44

Macrolides Targets protein synthesis - 50s ribosomal subunit Works on gram positive and some gram negative bacteria

Question 45

What is another type of antibiotic that is entirely synthetic and how do they work?

Answer 45

Quinolones Entirely synthetic, broad spectrum, bactericidal Target DNA replication cycle (specifically the winding / unwinding) by targeting DNA gyrase in gram positive and topoisomerase in gram negative bacteria

Question 46

What are the sources of antibiotic resistance genes in bacteria?

Answer 46

1. Plasmids - extra, chromosomal, circular piece of DNA, often multiple copies, that frequently carry antibiotic resistance genes. Sometimes a single plasmids contains genes that confer resistance to multiple antibiotics. Applied selective pressure (e.g. the use of antibiotics) selects to keep that particular plasmid, as there is an energy cost to maintain the plasmid 2. Transposons - molecular shuttles transfer genes from plasmid to chromosome or vice versa to enable transmission to daughter cells 3. Naked DNA - dead bacteria release DNA into the environment

Question 47

What is an advantage of plasmids?

Answer 47

Can be swapped between bacteria via horizontal gene transfer (to those that are not their offspring)

Question 48

How can the selection of a single plasmid confer to multi-drug resistance?

Answer 48

A single plasmid may contain several genes of antibiotic resistance, but applying just one antibiotic, means at least one of those genes in the entire plasmid is useful / selected for, so the whole plasmid is retained within the bacterium, hence retaining the other antibiotic resistance genes

Question 49

What are the mechanisms for the transmission of plasmids?

Answer 49

1. Transformation - uptake of naked DNA in the environment 2. Conjugation - using a pillus, horizontal gene transfer 3. Transduction - phages move DNA from organism to another

Question 50

What are some non-genetic factors that contribute to resistance?

Answer 50

1. Can grow in biofilms - growth or increase by the gradual accumulation of additional layers (accretions) 2. Intra-cellular locations - hide within cells 3. Grow slowly - antibiotics target biosynthetic prcoesses, which in slow-growing bacteria are used less frequently 4. Spores - e.g. C. difficile 5. Persisters - bacteria that do not replicate

Question 51

What are some non-genetic factors that contribute to treatment failure?

Answer 51

1. Inappropriate choice for organism - not all antibiotics kill all bacteria 2. Poor penetration of antibiotic into target site - penetrate different areas in varying amounts e.g. penetrate liver better than lungs 3. Inappropriate dose / poor half life so the antibiotic is excreted too quickly before it can work 4. Inappropriate administration (oral vs IV) 5. Presence of antibiotic resistance within commensal flora , so the commensal microbiota in the gut e.g. via the secretion of beta-lactamase

Question 52

How or why do hospital acquired infections have greater antibiotic resistance?

Answer 52

1. Crowded 2. Many immuno-compromised - old, young, chemotherapy, transplants etc 3. Many wounds / broken skin - from surgery, catheterisation etc. 4. Indwelling devices - e.g. intubation 5. Transmission by staff Therefore majority patients on several different antibiotics - environment with high selective pressure for resistant bacteria Many bacteria strongly linked to drug resistance and hospital acquired infections

Question 53

How can antibiotic therapy impair commensal microbiota (i.e. on guts and skin)?

Answer 53

Antibiotics can also kill good bacteria on our guts and skin Those 'good' bacteria are an important defence against pathogenic bacteria, so when they die, selects for resistant bacteria and less competition for resistant bacteria to grow

Question 54

With which infection is gut microbiota important and how does the infection work?

Answer 54

C. difficile - lives in the gut amongst resident microbiota, completely harmless as it is kept in check by resident microbiota If a patient undergoes antibiotic therapy that kills the resident microbiota, only C. difficile is left behind Reduced competiton and increased space allows for C. difficile to grow and produce toxins, causing infection and harm Causes diarrhoea, produces spores (which are hard to kill)

Question 55

How to address resistance?

Answer 55

Use new and existing drugs sparingly Better diagnostics so antibiotics are prescribed less blindly Prescribing strategies – tighter controls, temporary withdrawal of certain classes. Restriction of antibiotics for certain serious infections Reduce use of broad-spectrum antibiotics Quicker identification of infections caused by resistant strains Combination therapy Knowledge of local strains/resistance patterns

Question 56

How to overcome resistance?

Answer 56

Modify existing drugs - enhance efficacy Use combinations of antibiotics and inhibitors e.g. beta-lactams with inhibitors of beta-lactamase Infection control - works well with some infections e.g. MRSA (though others are endogenous - e.g. bloodstream infections from E. coli come from gut)

Question 57

What are fungi?

Answer 57

Eukaryotic organisms that digest their food outside of the cell by secreting hydrolytic enzymes - break down biopolymers to be absorbed for nutrition

Question 58

What are the 3 ways fungi affect humans (medically)?

Answer 58

1. Allergy – allergic reactions to fungal products e.g. allergic bronchopulmonary aspergillosis (ABPA) 2. Mycotoxicoses – ingestion of fungi and their toxic products e. g. aflatoxin 3. Mycoses – superficial, subcutaneous or systemic colonisation, invasion and destruction of human tissue

Question 59

How are mycoses classified?

Answer 59

By the level of tissue affected: Superficial - skin Cutaneous - deeper into the skin Subcutaneous - deeper, e.g. roots of hair Systemic - deep, organs i.e. brain, lungs, kidney, spleen etc.

Question 60

What do anti-fungal therapies target?

Answer 60

1. Cell membrane - fungi primarily use ergosterol instead of cholesterol 2. DNA synthesis - some compounds may be selectively activated by fungi, therefore stopping synthesis 3. Cell wall - unlike mammalian cells, fungi have cell walls