Antibiotic Classes & Modes of action

Question 1

Macrolides and examples. State Mechanism, What it’s active against. Bacteriostatic or sidal?

Answer 1

Bind to 50s subunit of ribosomes; inhibiting peptidyl transferase and so blocking peptide elongation.

Macrolides are generally good for respiratory infections and soft tissues as it can penetrate human tissues well. It’s an alternative to penicillin allergic patients.

e.g Erythromycin and Clarithromycin

Erythromycin: in particular and is also used for staphylococcal infections

Clarithromycin, a derivative of erythromycin, is used along the same lines but has additional activity e.g. against Legionellaspecies and chlamydiae.

Bacteriostatic. Can be Bactericidal at high concentrations.

Question 2

Chloramphenicol - Activity - Side effects - susceptible microorganisms. Static or Sidal?

Answer 2

Diffuses across cell membrane and Binds to 50s subunit of ribosomes inhibits protein synthesis inhibits peptidyl transferase, so no peptide elongation. In terms of activity - it has broad-spectrum range activity.

Penetrates the cerebrospinal fluid well, Therefore it’s used to treat meningitis.

It is Bacteriostatic, but when treating gram +ve cocci, it is bactericidal

Side effect: a bone marrow does not produce cells

Question 3

Tetracyclines. action - indication - examples and side effects. Static or Sidal?

Answer 3

Bind to 16s subunit of ribosomes but interefers with 30s ribosome subunit, inhibiting tRNA.

e.g doxycycline

Indicated for Acne Vulgaris,

Side Effects: Nausea, Diarrhoea and Renal Concern. It can accumulate in bones and teeth. Teratogenic.

Bacteriostatic

Question 4

Oxazolidinones

Answer 4

Bind to 50s subunit of ribosomes; inhibit tRNA binding

Question 5

Rifamycins MOA/Activity/Side effects

Answer 5

inhibit bacterial DNA-dependent RNA polymerase, preventing transcription of mRNA

Activity: Rifampicin crosses the BBB and is used to treat meningitis

It’s Broad Spectrum and can be used on both G+ve and G-ve Can also be used in combo with isoniazid for Mycobacterium Tuberculosos

Side Effects: Fever, Loss of Appetite, Malaise

Question 6

Quinolones

Answer 6

Inhibit topoisomerases

Question 7

Nitroimidazoles

Answer 7

Reduction in anaerobes produces radicals which cause oxidative damage to macromolecules e.g Metronidazole

Question 8

isoniazid

Answer 8

inhibits mycolic acid synthesis in Mycobacteria

Question 9

Bacitracin

Answer 9

inhibits regeneration of lipid barrier

Question 10

cycloserine

Answer 10

inhibits D-Ala-D-Ala formation

Question 11

Glycopeptides and an example. What are they only effective against? Indications?

Answer 11

prevention of incorporating subunits into growing peptidoglycan wall by binding to the D-ala D-ala of the short peptide chain on N-acetylmuramic acid

E.g Vancomycin

ONLY effective against Gram-positive (both anaerobes and aerobes) because they’re too bulky to penetrate outer membrane of the G-ve species

They’re reserved for seriously ill patients with G+ve species. e.g MRSA and C.difficule

Question 12

name 3 B-Lactams

Answer 12

Penicillin, Cephalosporin, Carbapenems

Question 13

Role of B-Lactams with an example

Answer 13

inhibit transpeptidase crosslinking of Peptidoglycan strands. Beta Lactam binds to penicillin-binding proteins.

This increases osmotic pressure, activating autolysins that degrade the cell wall.

There is a change in cell shape and size

Leads to the death of the bacterial cell

e.g Benzylpenicillin

Question 14

Polymixims

Answer 14

disrupt bacterial membranes

Question 15

Sulfonamides

Answer 15

DHTS (dihydropteroate synthetase) inhibitors

Question 16

Trimethoprim

Answer 16

DHFR (Dihydrofolate reductase) inhibitor

Question 17

Daptomycin

Answer 17

Disrupts Gram +ve plasma membrane

Question 18

Bind to 50s subunit of ribosomes; blocking peptide elongation

Answer 18

Macrolides

Question 19

Binds to 50s subunit of ribosomes; inhibits peptidyl transferase

Answer 19

Chloramphenicol

Question 20

Bind to 30s subunit of ribosomes, inhibiting tRNA binding

Answer 20

Tetracyclines

Question 21

Bind to 50s subunit of ribosomes; inhibit tRNA binding

Answer 21

Oxazolidinones

Question 22

inhibit bacterial RNA polymerase

Answer 22

Rifamycins

Question 23

inhibit topo-isomerases

Answer 23

Quinolones

Question 24

Reduction in anaerobes produces radicals which cause oxidative damage to macromolecules

Answer 24

Nitroimidazoles

Question 25

inhibits mycolic acid and synthesis in Mycobacteria

Answer 25

isoniazid

Question 26

inhibits regeneration of lipid barrier

Answer 26

Bacitracin

Question 27

inhibits D-Ala-D-Ala formation

Answer 27

cycloserine

Question 28

prevention of incorporating subunits into peptidoglycan wall

Answer 28

Glycopeptides

Question 29

Penicillin, Cephalosporin, Carbapenems

Answer 29

name 3 B-Lactams

Question 30

inhibit transpeptidase crosslinking of Peptidoglycan strands

Answer 30

Role of B-Lactams

Question 31

disrupt bacterial membranes

Answer 31

Polymixims

Question 32

DHTS (dihydropteroate synthetase) inhibitors

Answer 32

Sulfonamides

Question 33

DHFR (Dihydrofolate reductase) inhibitor

Answer 33

Trimethoprim

Question 34

Disrupts Gram +ve plasma membrane

Answer 34

Daptomycin

Question 35

state all the classes of antimicrobial agents

Answer 35

Aldehydes Oxygen species Halogens Phenoliccompounds Alcohols Biguanide-based compounds Quaternary ammonium-based compounds Organic acids

Question 36

what class is the most aggressive out of the Antimicrobial agents? give an example and how it works

Answer 36

Aldehydes, e.g Glutaraldehyde: It treats surfaces and temperature sensitive medical and dental equipment. Works by cross linking proteins, This therefore prevents protein synthesis of microbial macromolecules. It shows broad efficacy of action, and is rapidly **antibacterial, fungicidal, virucidal.** It is so active that it can be used as a *chemosterilant*. Pros: Effective at low temperature, highly active and low surface corrosiveness Cons: Can cause skin irritation

Question 37

name some broad spectrum antibiotics

Answer 37

(the three) B-Lactams, Tetracycline, Chloramphenicol, Quinolones, Macrolides

Question 38

name some narrow spectrum antibiotics

Answer 38

Glycopeptides, Aminoglycosides

Question 39

discuss an example of a biguanide based compound. comment on acivity, strengths and weaknesses

Answer 39

chlorhexidine. Antiseptic mouthwash used to treat a wound. It is rapidly absorbed through bacterial/yeast cells - acts primarily on cell membranes = leads to cytoplasm content leakage Thus - there is a loss of function and cell structure. Chlorhexidine **directly inserts into cell membrane bilayers** Activity: Broad spectrum antibacterial activity. Less effective against fungi. Strengths: relatively little irritation of skin or mucous membranes. Effective in preventing spread of pathogens in hospitals. Weaknesses: can cause eye problems and can damage the *inner* ear. It can also cause anaphylactic shock in extreme cases.

Question 40

what strategies emerged to deal with penicillinase producing strands? add examples

Answer 40

1. **design of penicillinase-tolerant penicillins** e.g flucloxacillin 2. **development of penicillinase inhibitors** e.g clavulanic acid, sulbactam and tazobactam the penicillinase inhibitors have little antibacterial activity alone, but bind and inactivate beta-lactamases/penicillinases. Allows a **combined** approach of penicillin (antibiotic) + tazobactam (inhibitor)

Question 41

can penicillins target only G-ve/G+ve or Both?

Answer 41

both

Question 42

give the structure for clavulanic acid

Answer 42

Question 43

what is co-amoxiclav?

Answer 43

Amoxicillin - similar and often combined with clavulanic acid. It is active against **certain gram negatives e.g** *H.influenzae.* The addition of the B-lactamase inhibitor clauvulanic acid increases the **spectrum** of antimicrobial activity

Question 44

state the three locations on a bacterial ribosome for attack

Answer 44

APE: A (aminoacyl) site - where after initiation each 'new' aminoacyl- tRNA attaches P (Peptidyl) site - where the the peptide bonds are formed E (Exit) site - where tRNA leaves the ribosome

Question 45

Aminoglycosides - Mode of action - Suseptible organisms - Side effects - drug examples

Answer 45

Aminoglycosides are actively transported into bacterial cells **growing aerobically.** They bind irreversibly to 30S subunit, Inhibiting protein synthesis. Interruption of translation results in misreading of mRNA. This leads to NO proteins or **DEFECTIVE** proteins. They are active against staphylococci and mycobacteria. However they're innefective against anaerobically respiring bacteria which have **innate resistance**. *indicated for Pseudomonas Aeruginosa* Examples are gentamicin, and streptomycin. Side effects: Renal Toxicity, Dizziness, Hearing loss, Nausea and Vomiting.

Question 46

What is a side effect of penicillins? suggest a drug class (and examples in that) to give to a patient with a penicillin allergy.

Answer 46

_S/E_ rash, diarrhoea, abdominal pain, nausea, vomiting, hypersensitivity. _Alternatives_ Macrolides - erythromycin and clarithromycin

Question 47

Antibiotics inhibiting nucleic acid synthesis have three main interrupting strategies. What are they?

Answer 47

1. Binding to **DNA Topoisomerases** 2. Preventing transcription by binding **DNA-dependent *RNA polymerase*** 3. Distupting bacterial DNA through **cytotoxicity**

Question 48

what are the four overall strategies of bacteria activity. Give examples

Answer 48

1. Disrupt bacterial cell walls - e.g **Beta Lactams,** **Glycopeptides** 2. Inhibit protein synthesis e.g **Aminoglycosides**, **Tetracyclines**, **Chloramphenicol**, **Macrolides**, **Clindamycin** 3. Inhibit nucleic acid synthesis e.g **Quinolones**, **Rifampicin**, **Methonidazole** 4. antimetabolite activity e.g **Trimethoprim, Sulfenamide**

Question 49

Metronidazole indication - mode of action. Static or Sidal?

Answer 49

Indicated for C.Difficile and B. Fragilis. It is only active in **anaerobic bacteria** and the drug is cytotoxic. It converts **oxidoreductase** into a **mutagenic** product which binds to DNA and destbilises the DNA Helix, causing it to break. Bactericidal.

Question 50

Give an overview of the mechanisms of antibiotic resistance

Answer 50

1. Metabolic bypass-resistance (alters the enzyme in a metabolic pathway targeted by the abx) 2. Over production ( the bacteria produces more of what is being targeted, so the abx is **overwhelmed**) 3. Reduced uptake (e.g Beta-lactams reduced uptake) 4. Efflux pumps (e.g S.Aureus has efflux pumps for fluoroquinolones) 5. Alteration (e.g of the receptor or target site) 6. Destroy the Abx (Beta-lactamases) 7. Modify the Abx - e.g aminoglycosides made less able to produce oxidative radicals)

Question 51

name two elements of a bacteria that can be transferred by **horizontal gene transfer**

Answer 51

**Plasmid** **_Transposons_**

Question 52

what are the pros and cons of multiple horizontal gene transfer?

Answer 52

There is an increased metabolic cost to the cell, this can affect cell fitness. However there is an increased ability for the cell to resist more than one of a particular number of antibiotic challenges

Question 53

State 4 ways we can maintain the effectiveness of antibiotics

Answer 53

1. Make them less generally available (e.g prevent agricultural use) 2. Antibiotic rotation 3. Resistance surveillance 4. stop innapropriate use of antibiotics

Question 54

name two Quinolones, Mode of action, activity, side effects

Answer 54

e.g **Ciprofloxicin** - Broad Spectrum **Fluoroquinolones -** Narrow Spectrum (Gram Negative Enterobacteria, UTI) In Gram -ve cells = DNA Gyrase is the target In Gram +ve cells = Binds to DNA Toposiomerases to trap them. This affects supercoiling processes: **Bacteriostatic.** if it breaks bacterial DNA this can result in cell death. **Bactericidal** nausea, vomiting, diarrhoea, abdominal pain, headache, **lethargy**, **insomnia**

Question 55

What is Amphtotericin B and what's it indicated for. State MOA

Answer 55

Broad Spectrum Antifungal. It exhibits selective toxicity Binding to the **ergosterol** in fungal **cell wall membranes, not cholesterol in human cell walls**. It damages the fungal membrane, causing pores. This **compromises** the **membrane integrity**, leading to **leakage of fungal metabolites** Indicated for *Candida Albicans*

Question 56

Give an example of an azole drug, stating how they work

Answer 56

Terbinafine - Inhibits egosterol synthesis

Question 57

how does the malaria parasite operate and how are qunine and chloroquine throught to work?

Answer 57

As part of their cell cycle, malaria infects blood cells. They'll use haemoglobin as a source of amino acids. **Haem remains intact. The haem is toxic and they'll detoxify it.** Both quinine and chloroquine are thought to act to **prevent detoxification of haeme** in the parasite \> this means the haeme remains and as such is toxic ultimately through cell lysis.

Question 58

Clindamycin mode of action and what is it active against?

Answer 58

Binds to 50s subunit and inhibits protein elongation. Active against Staphylococcus (a G+ve) and Anaerobic G-ve

Question 59

How does Metabolic bypass give bacteria resistance? - Give an example

Answer 59

_How?_ Bacteria alters enzyme in the metabolic pathway targeted by the abx _Example?_ **Mutagens give** bacteria -\> trimethoprim-resistant variants of dihydrofolate reductase **genes** ∴ bacteria bypasses the block trimethoprim causes on the non-mutated version

Question 60

How does Overporduction give bacteria resistance? What example

Answer 60

_How?_ Bacterial cell makes more of what an abx is targeting: Hence abx gets used up faster _Example?_ Overproduction of a specific penicillin-binding protein (PBP-4) e.g increases beta-lactam resistance in S. auereus by “mopping up’ the bacteria

Question 61

How does reduced uptake give bacteria resistance?

Answer 61

Bacterial cell takes LESS Abx - abx causes LESS damage to the bacteria

Question 62

How des efflux pumps give bacteria resistance? E.g?

Answer 62

_How?_ Efflux pumps to get rid of as much drug entering the bacterial cytoplasm as possible _Example_ P.aeruginosa has multi-drug efflux pumps to efflux out many different types of abx (Pseudomodas infections are hard to treat!)

Question 63

How does Alteration give bacteria resistance

Answer 63

_How?_ Bacteria alters the target site of abx _Example?_ Mutations in chromosomal genes coding for ribosomal subunits can alter the abx target

Question 64

Give an example of how modifying the antibiotic give bacteria resistance

Answer 64

Aminoglycoside abx resistance is due to modification of Abx structure as a result of 3 classes of enzymes

Question 65

How do patients make antibiotic resistance worse?

Answer 65

* Patient non-compliance can lead to -\> resistance * By not completing their course -\> suboptimal therapy, it makes bacteria sensitive to the Abx ∴ allows bacteria to emerge as resistant.

Question 66

Where on the bacterial genome has resistance arisen? How does this fit in the bacterial survival.

Answer 66

Firstly, Antibiotics are needed to give selective pressure and favour resistant strains in survivng. * ***Chromosome*** -\> contains all genes required for cellular maintenance + growth * Only the specific bacteria will become resistant * ***Plasmid*** -\> DNA molecule that replicates independently from the chromosome * Can move between cells -\> **_CONJUGATION_** * of the same or **_DIFFERENT_** species!! \> leads to **acquired resistance** * can be multi-drug resistant = **THREATHENING**! Thrives in hospitals where lots of Abx is used

Question 67

How do I maintain the effectiveness of currently available agents? What factor do we consider when choosing an antibiotic to use?

Answer 67

_Maintain effectiveness_ 1. Make Abx generally less available 2. Abx rotations 3. Resistance surveillance 4. Stop inappropriate use of Abx use _Choosing an Antibiotic is based on_ 1. Pathogen susceptibility 2. Cost 3. Side effects 4. Impact on host microbiota

Question 69

Give a whistle stop tour on how to select an Antibiotic for an infection

Answer 69

_Selecting an Abx to Treat an Infection_ First = **Identify the pathogen** -\> via undertaking tests in the Diagnostic Microbiology Lab * Sample is received * The specimen is look under the microscope to see what pathogens are likely in the sample * This indicates what: * Growth condition should be used * Growth media should be used * After incubation -\> colonies of pathogen are recognised by their **phenotype,** identifying the pathogen * Microscopy confirms OR denies this identify based on cell shapes + staining * Staining -\> Gram +ve OR Gram –ve * Shapes -\> Bacillus(rods) or Coccus (spherical) * Often a mixed culture. Next step = derive a pure culture