Bacte

• Growth is the orderly increase of all chemical constituents of the cell
• Bacterial growth refers to an increase in the number of organisms rather than an increase in their size or mass of an individual bacterium
• Bacteria increase in size before cell division
• Under favorable conditions, almost all bacteria reproduce very rapidly
• Generation Time:

  • Time it takes for a cell to divide by binary fission and its population to double
  • Slow growers have a doubling time of 24 hours (e.g. Mycobacterium tuberculosis)
  • Rapid growers have an average doubling time of 20 minutes (e.g. Escherichia coli)
• Growth Curve:

  • Balanced growth state with enough nutrients and no toxic products present
  • Increase in bacterial numbers is proportional to increase in bacterial properties such as mass, protein content, and nucleic acid content
  • Measurement of these properties are indications of bacterial growth
• Four Phases of Growth Curve:

  • Lag phase: period of adaptation to new environment, little or no multiplication, active synthesis of enzymes and energy generation
  • Logarithmic Phase (Log phase or Exponential phase): maximal rates of cell division, mass increase, constant generation time, susceptibility to antibiotics
  • Stationary phase (Phase of Equilibrium or Plateau Phase): rate of cell reproduction equals rate of cell death, growth ceases due to waste accumulation, nutrient exhaustion, and pH changes
• • Death phase (Phase of Decline): complete cessation of multiplication, death rate exceeds growth rate
• • Organisms based on source of nitrogen: Nitrogen is a major component of proteins and nucleic acids, sources include nitrate ion, nitrite, atmospheric nitrogen, ammonium ion
• Nutritional Requirements:

  • All bacteria have three major nutritional needs for growth: source of carbon, source of nitrogen, source of energy (ATP)
  • Organisms based on source of energy: Phototrophs (use light), Chemotrophs (use chemicals), Chemolithotrophs (oxidize inorganic compounds), Chemoorganotrophs (use organic compounds)
  • Organisms based on source of carbon: Autotrophs (use CO2), Heterotrophs (require organic source like glucose)
• Physical or Environmental Requirements:

  • Three factors influencing bacterial growth rate: temperature, pH, gaseous composition of the atmosphere
  • Temperature classification: Thermophiles (high temp), Mesophiles (moderate temp), Psychrophiles (cold temp), Psychroduric (tolerate cold)
  • pH classification: Acidophiles (below pH 5.5), Neutrophiles (pH 5.0-8.0), Alkalophiles (pH 8.4-9.0)
  • Gaseous composition: obligate aerobes (require oxygen), use oxygen for aerobic respiration
• Obligate aerobes:

  • Require oxygen for growth in concentration found in room air (20-21% O2)
  • Transform energy through the process of aerobic respiration
  • Example: Pseudomonas
• Facultative anaerobes:

  • Grow best in the presence of O2
  • Capable of surviving in either the presence or absence of O2
• Microaerophiles:

  • Require oxygen for multiplication but in concentration lower than that found in room air (5% O2)
  • Example: Campylobacter spp.
  • Air contains approximately 21% O2, this type of atmosphere can only be generated in culture jars or pouches using a commercially available microaerophilic atmosphere-generating system
• Aerotolerant anaerobes or facultative aerobes:

  • Can survive in the presence of O2
  • Use fermentation to produce ATP
  • Example: Streptococcus pyogenes
• Obligate anaerobes:

  • Cannot grow in the presence of O2
  • May transform energy by anaerobic respiration or fermentation
  • Example: Clostridium botulinum
• Oxygen toxicity:

  • Molecular oxygen can form hydrogen peroxide (H2O2), superoxide free radicals (O2-), and hydroxyl radicals (OH-) which are toxic unless broken down
  • Bacteria possess enzymes to breakdown these oxygen products to non-toxic form:
  • Superoxide dismutase breaks down superoxide radicals
  • Catalase breaks down hydrogen peroxide
  • Peroxidase also breaks down hydrogen peroxide
• Carbon Dioxide:

  • Most clinically relevant microorganisms tolerate atmospheric CO2 levels
  • Certain microorganisms grow best when the atmosphere is enriched with CO2 (5% to 10%)
  • Referred to as capnophilic bacteria or capnophiles
  • Examples: Neisseria spp., Brucella spp., Bacteria belonging to the HACEK group
• Bacterial Metabolism:

  • Sum of all chemical reactions in a bacterial cell
  • Energy is generated during catabolism of the substrate
  • Regulation of metabolism is achieved through enzymes
  • Control of enzyme synthesis, degradation, and activity
  • Bacteria vary widely in their ability to use various compounds as substrates and in the end products generated
• Fermentation and Respiration:

  • Bacteria use biochemical pathways to catabolize carbohydrates and produce energy by two mechanisms: fermentation and respiration
  • Respiration is an efficient energy generating process where molecular oxygen is the final electron acceptor
  • Fermentation is less efficient in energy generation than respiration
  • Pathways from Glucose to Pyruvic acid:
  • Embden-Meyerhof-Parnas (EMP) pathway or glycolytic pathway
  • Pentose Phosphate pathway or Warburg-Lipmann-Dickens-Horecker shunt
  • Entner-Doudoroff pathway
• Anaerobic Utilization of Pyruvic Acid (Fermentation):

  • Different pathways yield different end products
  • Examples:
  • Alcoholic fermentation: major end product is ethanol
  • Homolactic fermentation: end product is lactic acid
  • Heterolactic fermentation: end products include carbon dioxide, alcohols, formic acid, and acetic acid
  • Propionic acid fermentation: major end product is propionic acid
  • Mixed Acid fermentation: produces acids like lactic, acetic, succinic, and formic acid
  • Butanediol fermentation: end products are acetoin and 2,3-butanediol
• • Butyric Acid fermentation: produces butyric acid as the primary end product
• Aerobic Utilization of Pyruvic Acid (Oxidation):

  • Krebs Cycle or Tricarboxylic Acid Cycle or Citric Acid Cycle is the most important pathway for the complete oxidation of a substrate under aerobic conditions
  • Pyruvate is oxidized, carbon skeletons for biosynthetic reactions are created, and energy is generated in the form of ATP
• Carbohydrate Utilization and Lactose Fermentation:

  • Ability of microorganisms to use various sugars for growth is important in diagnostic identification schemes
  • Fermentation of sugars is detected by acid production and color change
  • Lactose fermentation involves two steps with enzymes like β-galactoside permease and β-galactosidase
  • All organisms that can ferment lactose can also ferment glucose
• are organisms that are too small to be seen by the unaidedor naked eye and requires a magnification tool called the microscope
• inventor of the first compound microscope

  Zacharias Janssen
• Microorganisms that cause infectious diseases are

  bacteria, fungi, viruses,protozoa, parasitic animals (helminths), and prions
• Main roles of a diagnostics or clinical microbiologists

  Isolate Identify Analyze