Microbial Physiology

• Metabolism impacts


  • Disease
  • Food spoilage
• Microbial metabolism processes


  • Nitrogen cycle
  • Beverages and food
  • Sewage treatment
  • Drugs
• Important metabolic processes


  • Carbohydrate catabolism
  • Respiration
  • Fermentation
  • Lipid catabolism
  • Protein catabolism
• Carbohydrate catabolism


  Glycolysis followed by Krebs cycle and electron transport chain which generates the most ATP
• Respiration


  38 ATPs can be generated from 1 glucose molecule
• Fermentation


  • Does not require Krebs cycle or ETC, and produces end products such as lactic acid or ethanol
  • 2 ATPs are produced from 1 glucose molecule
• Lipid catabolism


  • Lipids are first broken down into component fatty acids and glycerols by lipases
  • Each component can then enter the Krebs cycle
• Protein catabolism


  • Proteases and peptidases break down proteins into component amino acids
  • AAs must undergo enzymatic conversion into substances that can enter the Krebs cycle
• Metabolic diversity


  • Phototrophs
  • Chemotrophs
  • Autotrophs
  • Heterotrophs
• Most medically important organisms are chemoheterotrophic, because typically, infectious organisms catabolize substances obtained from the host
• Physical requirements for microbial growth

  • Temperature (psychrophiles, mesophiles, thermophiles)
  • pH
  • Osmotic pressure

  
• Temperature requirements


  • Most bacteria grow within a limited range of temperatures
  • Min and max growth temps are only 30°C apart
  • Optimum temperature - temperature at which the species can best grow

  
• pH


  • Most bacteria grow best between pH 6.5-7.5
  • Few bacteria grow below pH 4
• • When bacteria are cultured in the lab, they often produce acids which interfere with their growth
  • Chemical buffers such as phosphate salts and peptones are included
• Osmotic pressure


  • Microbes obtain nutrients in solution from water
• Adaptations to high salt environments

  • Extreme halophiles
  • Obligate halophiles
  • Facultative halophiles - do not require high salt concentrations but can grow at concentrations up to 2%
• Chemical requirements for microbial growth

  • Carbon
  • Nitrogen
  • Sulfur
  • Phosphorus
  • Trace elements
  • Organic growth factors
• Carbon


  Structural backbone of living matter; needed for all organic compounds that make up a living cell
• Nitrogen


  For forming the amino group of amino acids
• Sulfur


  For synthesis of sulfur-containing amino acids and vitamins such as thiamine and biotin
• Phosphorus


  For the synthesis of nucleic acids and phospholipids of the cell membrane; also in ATP
• Trace elements


  • Essential for some enzymes, sometimes as cofactors
  • Includes iron, copper, molybdenum, and zinc
• Organic growth factors


  • Essential compounds not synthesized which are obtained from the environment
  • Include enzymes for vitamin synthesis, amino acids, purines, pyrimidines
• Oxygen requirements


  • Obligate aerobes
  • Facultative anaerobes
  • Obligate anaerobes
  • Aerotolerant anaerobes
  • Microaerophiles
• Culture media


  Nutrient material prepared for the growth of microorganisms
• Inoculum


  Microbes that are introduced into a culture medium to initiate growth
• Culture


  Microbes that grow and multiply in a culture medium
• Culture media must be initially sterile
• Agar


  • A solidifying agent
  • Few microbes can degrade it
  • Liquefies at 100°C
  • Remains liquid until temperature drops to 40°C
  • NOT a nutrient
• Forms of culture media

  • Broth (liquid)
  • Slants
  • Stab tubes / deeps
  • Plates
• Broth


  • Pellicle: A mass of organisms is floating on top of the broth
  • Turbidity: The organisms appear as a general cloudiness throughout the broth
  • Sediment: A mass of organisms appears as a deposit at the bottom of the tube
• The most commonly used method for obtaining pure cultures is the streak plate method
• Preservation methods


  • Refrigeration for short-term storage
  • Deep-freezing
  • Lyophilization (freeze-drying)
• Five "I"s of culturing microbes

  • Inoculation: Producing a pure culture
  • Isolation: Colony on media, one kind of microbe, pure culture
  • Incubation: growing microbes under proper conditions
  • Inspection: Observation of characteristics (data)
  • Identification: use of data, correlation, to ID organism to exact species
• Microbial growth


  • Produces more cells thus increases microbial count and consequently microbial growth
  • Binary fission is the most common mode of reproduction
  • Budding is another mode of reproduction
• Sterilization, disinfection, and sanitization


  • Sterilization - the removal or destruction of all living microorganisms
  • Disinfection - control of harmful organisms
  • Antisepsis (antiseptic) if directed at living tissue
  • Sanitization - lower microbial counts to safe public health levels and minimize the chances of disease transmission
• Aseptic technique


  • To protect yourself from contact with bio hazards
  • To protect your sample from contamination
  • To protect others in the lab
  • Preventing contamination of a culture with environmental microbes
  • Preventing contamination of yourself or the environment with the organism in the culture
  • Remember everything is contaminated with a variety of environmental microbes
• Sterilization and antimicrobial methods

  • Moist heat
  • Pasteurization
  • Dry heat
  • Filtration
  • Refrigeration
  • Deep-freezing and freeze-drying
  • High pressure
  • Desiccation
  • Osmotic pressure
  • Radiation
• Moist heat


  • Best for dishes, various equipment; autoclave for media and other items that can withstand pressure
  • Kills vegetative bacterial and fungal pathogens and almost all viruses within 10 min; less effective on endospores
  • Autoclaving - at about 15 psi of pressure (121°C), all vegetative cells and their endospores are killed in about 15 min
• Pasteurization


  • Heat treatment that kills all pathogens and most nonpathogens
  • Best for food