Control of Microorganisms: sterilisation and disinfection

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Control of Microorganismssterilisation and
disinfection

• HISTORICAL BACKGROUND
• disease prevention food preservation
• CONTROL OF MICROORGANISM
• destruction of microbial pathogens
• elimination of sources, routes and agents
• protect human host

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Patient risk -

• ASSESSING RISK OF TRANSMISSION OF INFECTION AND
  SUSCEPTIBLE PATIENTS
• CRITICAL
• enter sterile tissues and blood, e.g. IV fluids,
  surgical equipment, cardiac/urinary catheters
• SEMI-CRITICAL
• comes in contact with skin, e.g.respiratory
  therapy, anesthetic machines
• NON-CRITICAL
• nil significant risk, e.g.furniture, bedpan, ECG
  leads

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STERILISATION VS DISINFECTION

• Sterilisation
• total elimination of microorganisms

• Disinfection
• reduction in the number of pathogenic organism

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PRINCIPLES OF STERILISATION

• Principle of Death Rates
• Principle of Numbers of Organisms
• Principle of Varying Susceptibility

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Methods of Sterilisation

• HEAT - cheap, efficient, easy to control
• RADIATION - heat-sensitive
• GAS
• CHEMICALS
• FILTRATION

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H E A T

• MOIST HEAT
• disrupts H-bonds of proteins and NA, melt lipids,
  sporicidal
• excellent penetration
• requires proper technique and index organism
• autoclave (pressure cooker)

• DRY HEAT
• chars organic compounds, oxidising
• slow penetration
• sterilises metal objects, glassware, oils
• hot-air oven, open flame (incineration)

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R A D I A T I O N

• Ionising radiations - gamma and x-rays
• dislodge electrons from atoms creating ions that
  damages DNA and produces peroxides that oxidises
  cells
• plastic materials, medical equipment,
  pharmaceuticals, food
• use of index organism

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GAS STERILISATION

• Ethylene and propylene oxide
• disrupts protein and NA, effective sporicides
• for plastic materials, rubber goods, tubings, IV
  lines, even mattresses
• require proper techniques owing to properties of
  gas

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CHEMICAL STERILISATION

• glutaraldehyde
• disrupt bacterial proteins, broad-spectrum,
  non-corrosive, for heat-sensitive materials
  (lap instruments), but unstable, toxic and
  allergenic
• low temperature hydrogen peroxide
• peracetic acid

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FILTRATION

• passing material through filter (natural or
  synthetic) to remove microorganisms
• membrane filters with less than 0.025 um remove
  all bacteria, viruses and mycoplasmas selective
  removal
• practical limitation - liquid viscosity, clogging
• for heat sensitive materials

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DISINFECTION METHODS

• HEAT
• RADIATION
• FILTRATION
• CHEMICALS

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Methods of Disinfection

• Heat - boiling, pasteurisation, UHT
• Radiation - UV, break DNA, thymine dimers
• Filtration - HEPA filter

• Chemicals -
• Potency dependent on-
• effect of time
• temperature
• pH
• concentration
• presence of organic matter
• IDEAL DISINFECTANT

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Chemical Disinfectants

• Mechanism of Action
• denature proteins
• alter cell membrane proteins
• dissolve lipids
• distort nucleic acids
• distort NA and proteins of viruses

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Antiseptics vs Disinfectants

• Chemicals applied to skin, mucous membranes and
  exposed tissues

• Chemicals applied to inanimate objects

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Classes of chemical disinfectants

• Soaps / detergents - QUATS
• Organic acids - benzoic acid
• Heavy metals - Ag, Hg
• Halogens - iodine, chlorine
• Alcohols - ethyl and isopropyl alcohol
• Phenols - chlorhexidine
• Oxidising agents - benzyl peroxide, KMnO4
• Aldehydes - formaldehyde
• Dyes
• Essential oils

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ANTIBACTERIAL DRUGS

• Antimicrobial - kill/inhibit growth of
  microorganisms
• Antibiotic - chemical produced by organism that
  kill/inhibit micoorganisms
• Broad-spectrum - active against different types,
  narrow-spectrum - limited activity
• Bacteriocidal vs bacteriostatic

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An ideal antimicrobial .

• Soluble, selective, toxicity not easily altered,
  nonallergenic, stable, resistance not easily
  acquired, long shelf life, cheap
• Selective Toxicity - kill/inhibit the pathogen
  without damaging the host cells

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C L A S S I F I C A T I O N - modes of action

• inhibition of cell wall synthesis, e.g.
  penicillin, cephalosporins
• disruption of cell membrane function, e.g.
  polymyxins
• inhibition of protein synthesis, e.g.
  tetracyclines, aminoglycoside, macrolides
• inhibition of nucleic acid synthesis, e.g.
  sulphonamides, rifampicin, quinolones
• action as an antimetabolite

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SIDE EFFECTS

• TOXICITY
• ototoxicity, nephrotoxicity, bone marrow
  suppression
• ALLERGY
• hypersensitivity
• DISRUPTION OF NORMAL FLORA
• EMERGENCE OF RESISTANT STRAINS

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ANTIBACTERIAL DRUGS

• Penicillin - G, G- , b-lactamase resistant
• Cephalosporins - widely used
• Vancomycin - MRSA infections
• Aminoglycosides - used for synergistic effect,
  ototoxic
• Tetracyclines - malaria, acne, yellow teeth etc
• Macolides - erythromycin for pen substitute
• Sulphonamides - UTI and Salmonella
• Quinolones - G- and UTI

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Misuse of Antibacterial Drugs

• Relationship between antibiotic use and emergence
  of drug resistant microbes
• selection pressure
• broad-spectrum
• superinfection
• delay emergence of resistance

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ANTIBIOTIC SELECTION

• Identify infecting organism
• Determine susceptibility / sensitivity to
  antimicrobial agent
• Consider host factors - age, renal/liver
  impairment, site, how acquired

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ANTIBIOTIC THERAPY

• Advantages/disadvantages of combined therapy -
  synergism antagonism
• Mechanisms of microbial drug resistance
• Importance of completing the full course of
  prescribed drug
• Excessive or unnecessary use of antibiotics
• Hospital strains compared with community strains

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Antimicrobial Prophylaxis

• As a rule, antimicrobial agents should not be
  used to prevent spread of bacterial infection
  among contacts of an active case. Prophylaxis
  includes
• with STDs, contacts, new born
• close contact with pts with meningitis
• travelling to places with endemic disease
• high-risk individuals - elderly, occupations
• recurrent UTIs and neutropenia
• surgical patients - non-sterile areas
• orthopaedic procedures, heart valves/prosthetic
  joints, dental work for those with prosthetic
  heart valves

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LIMITATIONS OF ANTIMICROBIAL THERAPY

• Elimination of normal flora
• Adverse side effects
• Emergence of resistant bacteria

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Clinical Practice

• SPECIMEN COLLECTION
• prior to antimicrobial therapy
• information
• DRUG ADMINISTRATION
• doses, routes, timing, effect of food, check
  recommendations orders