Antibiotics: treating bacterial disease

what is the alternative to immunisation?

• to develop medicines to cure infectious diseases

• To do this we must destroy the pathogens that cause the disease

what are antibiotics?

antibiotics are medicines that either destroy microorganisms or prevent them from reproducing

why has death rate from communicable disease decreased by a lot?

• due to immunisation and because antibiotics mean we can cure many diseases which previously killed us

what is selective toxicity?

a substance that is toxic against some types of cells or organisms but not others

how antimicrobial drugs work against microorganisms?

• all antimicrobial drugs work against microorganisms by principle of selective toxicity

• they interfere with the growth or metabolism of function of the pathogen with minimal damage to the cells of the human host

• Best antimicrobial is antibiotics and can be used to a limited degree in treatment of some fungal infections

what is penicillin?

the first antibiotic discovered; it is bactericidal and affects the formation of bacterial cell walls. However doesn’t work against all pathogens.

how antibiotics work?

Antibiotics work by disrupting the biochemistry of the cells.

Different classes of drugs interrupt the cells in different ways.

The two main classes of antibiotics are bacteriostatic and bactericidal.

what are bacteriostatic drugs?

• Bacteriostatic drugs work by completely inhibiting the growth of the organism.

• This is usually sufficient for the majority of day to day infections

• The antibiotics, combined with our own immune system eradicate the pathogen.
  

what different types of bacteriostatic antibiotics do?

•  antimetabolites interrupt metabolic pathways; they block nucleic acid synthesis or the synthesis or the synthesis of vital nutrients such as folic acid in bacteria eg sulfomamides

• Protein synthsis inhibitors bind to ribosomes interrupt or prevent transcription and/or translation of microbial genes so protein production is affected eg tetracyclines, chloramphenicol

what are bactericidal antibiotics?

Bactericidal drugs destroy all of the pathogen present.

These are used in severe and dangerous infections.

These are also used when a patient has a suppressed immune system, e.g. for transplant patients, TB or HIV sufferers.

what are the different ways bactericidal antibiotics work?

• cell wall agents prevent formation of cross-linking in cell walls, so bacteria are killed by lysis (bursting) eg beta-lactams eg peincillins

• cell membrane agents damage the cell membrane, so metabolites can move out or water moves in, killing the bacteria eg eg some penicillins, cephalosporins

• DNA gyrase inhibitors stop bacterial DNA winding into rings so it no longer fits within the bacterium eg quinolene

effects of different doses of bactericidal and bacteriostatic?

• how they work depends on the dose given

• bacteriostatic antibiotics often kill a lot of bacteria and will usually kill them all at high enough doses

• bactericidal antibiotics do not kill all of the bacteria; they kill 99% within a given time frame

• lower doses of bactericidal antibiotics often bacteriostatic

Difference between broad-spectrum antibiotic and narrow-spectrum antibiotic?

• broad spectrum antibiotics destroy a wide range of harmful bacteria, pathogens, and neutral and good bacteria alike

• a narrow-spectrum antibiotic targets one or two specific pathogens

Factors which affect how effective an antibiotic are include

The concentration of the drug in the area of the body affected.

The local pH

Whether either the pathogen or host tissue destroy the antibiotic.

The susceptibility of the pathogen to the antibiotic used.

when is a pathogen said to be sensitive to that antibiotic?

• if standard dose of drug successfully destroys pathogen and cures the disease then pathogen sensitive to that antibiotic

• if disease cured by only using a dose of antibiotic that is much higher than standard dose, pathogen regarded as only moderately sensitive 

why mammalian cells not damaged by antibiotics?

• Since mammalian cells are eukaryotic, they will not be damaged by antibiotics

  • They do not have cell walls

  • They have different enzymes

  • They have different ribosomes

why viruses not affected by anitbiotics

• Viruses do not have cellular structures such as enzymes, ribosomes, and cell walls so they are not affected by antibiotics

describe an experiment to be carried out to determine a suitable antibiotic to use for treatment of an ear infection

1. idea of taking a swab from the ear ;

2. credit method of culturing the bacteria in the swab ;

3. credit appropriate method of adding a range of antibiotics ;

4. idea of culturing the bacteria with the antibiotics for a period of time at an appropriate temperature ; temp. range 25°C - 45°C incubation time 24 hours - 2 weeks

5. credit an indication of what is being looked for