MBIO 1010 - L19

• Filtration

  • avoids the use of heat on sensitive liquids and gases (would denature and become ineffective - so need filtration)
• poors of filter are too small for organisms to pass through

  • allow liquid of gas to pass through
  • ex. HEPA filters, membrane filters
• is picture looks 3d most likely a SEM
• The longer it takes to reach a ten fold reduction the more heat resistant
• Membrane filters filtration can be accomplished by

  • syringe
  • pump
  • vacuum
• consider the size of the pores relative to the size of some of the bacteria

  leptospira interrogans (0.1 x 8 to 20 micrometers) on a 0.2 micrometer filter is most probably okay since they are long and the chances of it fitting exactly in the pore with its long body is small
• HEPA filter - High Efficient Particulate Absorbing filters

  • different layers
  • have different efficiency
  • does not sterilize
• Membrane filters are useful for liquids and its goal is to force liquid through
• we are filtering for the average size
• pore is the defining point
• Antimicrobial agents can be classified as

  • static
  • cidal
  • lytic
• static

  • prevents cell growth as long as the antimicrobial agent is present
  • typically inhibitor - pause cell growth
  • antibiotics
• static

  • prevents cell growth as long as the antimicrobial agent is present
  • typically inhibitor - pause cell growth
  • antibiotics
• cidal

  • kills the cells (does not lyse them)
• lytic

  • kills and lyses
  • not considered a cell anymore
• Y axis is the log of cell number
• x axis is the time
• MIC - Minimum inhibitory concentration

  • the smallest amount of an agent needed to inhibit growth of a microorganism
  • varies with the organism used, inoculum size, temperature, pH
  • increasing concentration of antibiotic from left to right
  • lowest concentration with no growth = MIC
  • may still have living (non-growing) organisms
  • the antibiotic may be bacteriostatic
• MLC - Minimal Lethal Concentration

  • plate aliquots of broth from the MIC and from tubes with high concentration of antibiotic, on appropriate nutrient agar plates, without antibiotic
  • no colonies = MLC
  • MLC usually higher than MIC
  • Killing
• Disc diffusion assay

  • uses solid media
  • antimicrobial agent is added to filter paper
  • the MIC is reached at some distance
  • forms a zone of inhibition
  • area of no growth around disc
• antimicrobial agents can be divided into two categories

  • products used to control microorganisms in commercial and industrial applications
  • chemicals in foods, air conditioning cooling towers, textile and paper products, fuel tanks
  • products designed to prevent growth of human pathogens in inanimate environments and on external body surfaces
• products designed to prevent growth of human pathogens in inanimate environments and on external body surfaces

  • sterilant
  • disinfectant
  • sanitizer
  • antiseptic
• sterilant

  • destroys all microorganisms including endospores
• disinfectant

  • kills microorganisms but not all endospores
  • used on inanimate objects
• sanitizer

  • reduces the numbers of microorganisms on surfaces (hand sanitizer)
• antiseptic

  • kills or inhibits the growth of microorganisms (non-toxic enough to be applied on living tissue (mouth wash)