Bacterial Growth and Metabolism

• Bacterial growth is the increase of all chemical constituents in the cell, involving replication of cellular structures and components from surrounding nutrients.
• Increase in cell size occurs if nuclear division isn't accompanied by cell division (coenocytic).
• Increase in cell number occurs through budding or binary fission, where a parent cell produces two progeny cells.

Bacterial Growth Stages

• Lag phase involves little multiplication but active enzymes, representing an adjustment phase as bacteria adapt to the new environment.
• Cellular division doesn't occur, but bacterial enzymes are active, initiating biosynthesis and increasing metabolic rate.
• Logarithmic (log) phase is when organisms grow at the maximum exponential rate with a constant rate of cell division.
• Biochemical and antimicrobial testing is conducted during the log phase, as bacteria are most susceptible to antibiotics.
• Stationary phase, or plateau phase, occurs when growth ceases due to nutrient exhaustion or accumulation of toxic metabolic products.
• Cell division equals cell death, with a 1:1 ratio, as cellular death begins, and toxic waste accumulates from dying cells.
• Decline and death involves direct microscopic count remaining, but the viable count slowly decreases as the death rate increases.
• Complete cessation or stoppage of the bacterial infection occurs when the death number of bacterial cells exceeds the living and there are no more nutrients and more waste present.

Generation and Generation Time

• Generation is the doubling of cell number through binary fission.
• Generation or doubling time is the time needed for the bacterial population to double, like E. coli (20 minutes) and M. tuberculosis (15-20 hours).

Bacterial Reproduction

• Transverse binary fission: Asexual reproduction, where a single cell divides into two daughter cells after developing a transverse cell wall.
• Binary fission: Asexual reproduction leads to daughter cells, growing exponentially.

Growth Measurement

• Cell count involves colony counts (urine samples x1000) for diagnosis of DNA and direct microscopic counts using gridlines.
• Cell mass is determined by turbidimetric tests like SIM
• More turbid = More bacterial growth
• Cell Activity

Bacterial Growth Requirements

• Bacteria cultivated in vitro (outside human body).

Atmospheric Requirement

• Adequate oxygen enhances metabolism and growth, acting as a hydrogen acceptor in the final steps of energy production catalyzed by flavoproteins and cytochromes.
• Bacteria needs two enzymes to manage toxic molecules from oxygen use
• Hydrogen peroxide (H2O2) and radical superoxide (O2) induce cellular damage.
• Superoxide dismutase (SOD) catalyses the reaction of O2 in the presence of water or hydrogen converting the O2 into H2O2.
• Catalase conferences H2O2 into water and oxygen
• Catalase-positive bacterium produce effervescence or bubbling.
• Oxygen for aerobic respiration results in ATP.

Atmospheric Requirement: Oxygen

• Aerobes require oxygen for growth.
• Obligate aerobes grow well at room air (21% oxygen, 0.03% CO2), contain SOD and catalase, e.g., P. aeruginosa and M. tuberculosis.
• Anaerobes do not require oxygen.
• Obligate anaerobes cannot survive in oxygen, e.g., Clostridium and Bacteroides.
• Facultative anaerobes are aerobes but can survive and grow best in oxygen, contain SOD and catalase, e.g., Enterobacteriaceae and S. aureus.
• Aerotolerant can grow with or without oxygen, use anaerobic metabolism, contains only SOD, e.g., Lactobacillus and Propionibacterium.
• Microaerophiles require low oxygen tension (5-10% oxygen, 8-10% CO2), e.g., Campylobacter jejuni and Helicobacter pylori.
• Capnophiles require 5-10% CO2, incubated with increased CO2 concentrations, e.g., N. gonorrhoeae and S. pneumoniae.

Temperature Requirement

• Psychodurics: Extreme cold loving, optimum temperature <0°C.
• Psychrophilic/Psychrophiles: Cold loving, grow below 10°C, optimum 4-8°C, e.g., L. monocytogenes.
• Mesophilic/Mesophiles: Body temperature. Most pathogens optimum at 30-37°C, e.g., Enterobacteriaceae.
• Thermophilic/Thermophiles: Heat loving, optimum temperatures at 60°C, e.g., B. stearothermophilus & T. aquaticus.
• Thermodurics: Extreme heat loving.
• Extremophiles: B. infernus (volcano plumes)
• L. monocytogenes is associated with food poisoning of frozen goods.
• Y. enterocolitica is associated with blood bags stored at ref temperature.
• 35-37°C is incubation temperature for most bacteria and viruses.

pH Requirement

• Acidophiles: pH 0 to 5.5, e.g., Lactobacillus acidophilus in the female vagina.
• Neutrophiles: pH 5.5 to 8.9, optimum pH 6.5 to 7.5, culture media pH should be 7.02-7.5.
• Alkalophiles: pH 8.5 to 11.5, e.g., Vibrio.

Salt Concentration

• Halophiles survive in salt, e.g., Enterococci (6.5% NaCl) and S. aureus (7.5% NaCl).
• Facultative halophiles may survive at 2% salt.
• Non-halophiles grow in salt conc

Nutritional Requirement

• Energy source: phototrophic (light) and chemotrophic (chemical compound).
• Carbon source: autotrophic (inorganic) and heterotrophic (organic).
• Photoautotrophs: Does not require organic matter, use light to convert CO2 to organic compounds, e.g., Cyanobacteria.
• Photoheterotrophs: Require organic matter, use photosynthetic energy utilize carbon from other microorganisms
  • Green sulfur and purple sulfur bacteria.
• Chemoautotrophs: Need to use inorganic substrates, e.g., Archaea and some bacterial genera.
• Chemoheterotrophs/Heterotrophs: Need Glucose

Other Requirements

• Moisture water for a bacterium to survive.
• Pressure
• Growth Factors Fastidious Bacteria
• Nitrogen

Explore bacterial growth phases, enzyme functions, and environmental factors. Identify the roles of lag, log, stationary, and decline phases. Understand bacterial metabolism, enzyme functions, and the role of oxygen.