1. action of antibiotics

ANTIMICROBIALS

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

• interfere with metabolism or function of pathogen, w/ minimal damage to cells of host

• most commonly used antimicrobials are antibiotics

  • primarily kill bacteria but can be used to a limited degree to treat some fungal infections

ANTIBIOTICS

• chemicals that kill or inhibit growth of microorganisms

• all work by disrupting biochemistry of bacterial cells

TYPES OF ANTIBIOTICS

• bacteriostatic

• bactericidal

BACTERIOSTATIC ANTIBIOTICS

• prevent bacteria growing

• this level of treatment usually enough for everyday infections as combined actions of the drug and immune system ensures pathogen is destroyed

• e.g. tetracycline

BACTERICIDAL ANTIBIOTICS

• kill bacteria

• used mainly in more severe and dangerous infections

• also used when immune system of patient is suppressed (e.g. in transplant recipients or cases of TB and HIV/AIDS)

• e.g. penicillin

BROAD VS NARROW

• broad spectrum antibiotics destroy wide range of bacteria

• narrow spectrum antibiotics target one or two specific pathogens

TETRACYCLINE

• prevents protein synthesis by attaching to 30s subunit of ribosomes

• so targets both gram pos and neg bacteria so is classed as broad spectrum

• as it stops production bacterial proteins it inhibits growth

• used to treat acne, respiratory tract infections and Chlamydia

PENICILLIN

• works only on gram pos bacteria as it prevents formation of cross links in thick peptidoglycan layer of cell wall

• when water enters cells by osmosis the cell wall breaks and cell lyses

• classed as narrow spectrum (no target gram neg)

• used to treat skin infections, chest infections and urinary tract infections

EFFECTIVENESS OF ANTIMICROBIAL DRUGS

• if standard dose of a drug successfully destroys pathogen and cures disease

  • pathogen is sensitive to that antibiotic

• if disease is cured only by a bigger dose than standard

  • pathogen is moderately sensitive

• but increasing numbers of microorganisms aren’t affected at all by some antibiotics, even when they have been effective in the past

  • microorganism has become resistant to drug

FACTORS AFFECTING EFFECTIVENESS OF ANTIMICROBIAL DRUGS

• conc of drug in area of body infected– affects how easily the drug can get to the tissue and how quickly it is excreted

• local pH

• whether pathogen or host tissue destroy the antibiotic

• susceptibility of pathogen to particular antibiotic used