Chapters 6 and 7: Microbial Growth and Control - Vocabulary Flashcards
Chapter 6: Microbial Growth
Key terms
Bacteriostatic: curbs the replication rate of bacteria without killing them. Example: refrigeration slows enzyme activity needed for replication; bacteria remain viable but replicate slowly.
Bactericidal: kills bacteria. Example: boiling water to make it safe to drink.
Physical requirements for growth
Temperature
Temperature optimizes enzyme activity; different bacteria have preferred ranges.
Classifications among Eubacteria and Archaea:
Psychrophiles: cold-loving
Mesophiles: moderate temperatures (overlap with psychrophiles to some extent)
Thermophiles: heat-loving (including moderate and extreme thermophiles in the Eubacteria)
Beyond the extreme thermophiles, Archaea are extremophiles
pH
Most bacteria prefer near-neutral pH: roughly 6.5 \leq pH \leq 7.5
Acidophiles: acidic environments
Neutrophiles: near-neutral environments (most bacteria fall here)
Alkalophiles: basic environments
Examples of ranges:
Escherichia coli (E. coli): optimum around pH = 6-7 (neutrophile); tolerates pH = 4.4\text{ to } 9.0
Staphylococcus aureus: optimum pH \approx 7-7.5; tolerates pH = 4.2\text{ to } 9.3
The ranges illustrate the wide tolerance of some bacteria to pH conditions
Osmotic pressure (water activity, tonicity)
Isotonic environments preferred for most bacteria
Halophiles require salt:
Mild halophiles: 16\%\,salt\ (w/v)
Moderate halophiles: 6-15\%\,salt
Extreme halophiles (often Archaea): 15-30\%\,salt
Note: some bacteria require salt for growth; most eubacteria fall between mild and moderate halophiles
Chemical requirements for growth
Carbon and nutritional types (energy source vs carbon source)
Phototrophs: energy from light; carbon source not specified here
Photoautotrophs: energy from light; carbon source is CO₂
Photoheterotrophs: energy from light; carbon source is organic compounds
Chemoautotrophs: energy from inorganic compounds; carbon from CO₂
Chemoheterotrophs: energy from organic compounds; carbon from organic compounds
Concept: break down names to identify energy source (first part) and carbon source (second part):
Photo-: energy source is light
Auto-: carbon source is CO₂
Hetero-: carbon source is organic compounds
Essential elements and trace elements
Primary elements: nitrogen, sulfur, phosphorus
Nitrogen: incorporated into amino acids, nucleotides, coenzymes, etc.
Sulfur, phosphorus: various cellular roles (not enumerated in detail here)
Trace elements: iron, chlorine, and others; present in small amounts; commonly serve as enzyme cofactors
Oxygen requirements and terminology
Aerobic vs anaerobic growth
Facultative: can grow with or without oxygen
Obligate: requires a specific condition (either aerobic or anaerobic depending on organism)
Aero-tolerant anaerobes: fermentatively produce ATP regardless of oxygen presence; always rely on fermentation; least efficient mode of ATP production
Culture media for growing bacteria
Generalized media
Example: Nutrient Agar
Purpose: support growth of a wide variety of bacteria when the species is unknown (e.g., swabbing a tabletop)
Specialized media
Selective: favors growth of a particular group and inhibits others (e.g., salt concentrations favor Gram-positive bacteria)
Differential: allows differentiation between colonies (often by color changes)
Some media are both selective and differential
Example: Eosin Methylene Blue (EMB) agar
Contains dyes that indicate lactose fermentation by Gram-negative bacteria
Greater lactose fermentation yields darker dye coloration; darker color => higher fermentation activity
Enrichment cultures
Liquid media designed to promote growth of a particular organism from a mixed culture, often by providing a specific composition
Purpose: allow low-abundance organisms to outgrow others (e.g., enrich for E. coli from soil)
Viruses and culture media
Viruses cannot be grown on standard culture media; require living cells for propagation
Discussion on viral culture is reserved for Chapter 13
Preservation of bacterial samples
Lyophilization (freeze-drying)
Bacteria are frozen, then dried under heat and vacuum to remove water from cytoplasm
Used for long-term storage; cultures become dormant but viable
Revival: add nutrient source to resume metabolism and replication
Cryopreservation
Bacteria frozen in liquid nitrogen (~-196°C)
Long-term storage; kept until thawed for revival
Bacterial growth dynamics
Reproduction: asexual binary fission
Generation time (doubling time): time required for population to double
If needed: N(t) = N0 \cdot 2^{\frac{t}{td}} where t_d is the doubling time
Growth curve phases (in a closed system)
Lag phase: cells adjust to new environment; little to no observable growth
Log (exponential) phase: rapid cell division; growth rate exceeds death rate (some cell death occurs)
Stationary phase: growth rate equals death rate; nutrients depleted and waste products accumulate, often causing pH to drop
Death (death) phase: death rate exceeds growth rate; nutrients exhausted and pH becomes highly acidic
Closed system: no addition of nutrients and no removal of waste
Measuring bacterial growth
Direct counts: membrane filtration (colony counting)
Process: filter sample through a membrane; place membrane on nutrient agar; incubate and count colonies
Statistical significance: select plates with 30–300 colonies for reliable counting
From colony counts, calculate the original cell concentration and plot growth curves
Indirect counts: spectrophotometry
Principle: measure light transmission through a sample; more cells absorb more light, so less light passes through
Result: a range (e.g., 100–300 cells) rather than an exact count
Pros: rapid, provides immediate results
Cons: cannot distinguish viable from nonviable cells; organic debris can affect readings
Viability testing recommended: plate a sample after spectrophotometry and compare; growth after incubation confirms viability
Chapter 7: The control of microbial growth (condensed overview)
Why control microbial growth?
Prevent food spoilage and ingestion of contaminated food
Sterilize medical equipment to ensure patient safety
Key control terms
Sterilization: kills all microbes, including vegetative cells and endospores
Vegetative cell: actively replicating form of the cell
Disinfection: kills vegetative cells only (does not kill endospores)
Antisepsis: kills vegetative cells on living tissue (human host)
Sanitation: reduces microbial counts to public health standards (e.g., glasses, utensils) without achieving sterility
Variables affecting microbial death rate
Number of microbes present: more organisms take longer to kill
Presence of endospores: highly resistant to many methods
Presence of organic material: organic debris can shield microbes from treatment (e.g., UV light may be absorbed by debris, protecting organisms underneath)
Methods of control
Physical methods
Temperature: hot and cold can kill microbes; hot denatures proteins; freezing and thawing can cause ice crystal damage
Filtration: physically removes cells
Desiccation: dehydration inhibits microbial metabolism
Ultraviolet (UV) light: damages DNA, creating mutations; severe damage prevents repair and replication
Chemical methods
Alcohols: dissolve lipids (disrupt membranes and proteins)
Soaps: act as surfactants and aid in mechanical removal
Preservatives (nitrates and nitrites): inhibit growth or kill microbes
Exceptions and notable organisms
Pseudomonas species: can survive and grow in disinfectants; a problem in medical facilities due to contamination of cleaning agents and equipment
Endospores: extremely resistant to many physical and chemical control methods; remain a major challenge in sterilization
Summary
Chapter 6: covers microbial growth physics, biochemistry, growth measurement, and preservation techniques
Chapter 7: covers rationale and methods for controlling microbial growth, including definitions of sterilization, disinfection, antisepsis, sanitation, and considerations of when these controls fail due to resistant organisms or protective organic matter
Chapter 6: Microbial Growth
Key terms
Bacteriostatic: curbs the replication rate of bacteria without killing them.
Example: refrigeration slows enzyme activity needed for replication; bacteria remain viable but replicate slowly.
Bactericidal: kills bacteria.
Example: boiling water to make it safe to drink.
Physical requirements for growth
Temperature
Temperature optimizes enzyme activity; different bacteria have preferred ranges.
Classifications among Eubacteria and Archaea:
Psychrophiles: cold-loving
Mesophiles: moderate temperatures (overlap with psychrophiles to some extent)
Thermophiles: heat-loving (including moderate and extreme thermophiles in the Eubacteria)
Beyond the extreme thermophiles, Archaea are extremophiles
pH
Most bacteria prefer near-neutral pH: roughly 6.5 \leq pH \leq 7.5
Acidophiles: acidic environments
Neutrophiles: near-neutral environments (most bacteria fall here)
Alkalophiles: basic environments
Examples of ranges:
Escherichia coli (E. coli): optimum around pH = 6-7 (neutrophile); tolerates pH = 4.4\text{ to } 9.0
Staphylococcus aureus: optimum pH \approx 7-7.5; tolerates pH = 4.2\text{ to } 9.3
The ranges illustrate the wide tolerance of some bacteria to pH conditions
Osmotic pressure (water activity, tonicity)
Isotonic environments preferred for most bacteria
Halophiles require salt:
Mild halophiles: 1-6\%\,salt\ (w/v)
Moderate halophiles: 6-15\%\,salt
Extreme halophiles (often Archaea): 15-30\%\,salt
Note: some bacteria require salt for growth; most eubacteria fall between mild and moderate halophiles
Chemical requirements for growth
Carbon and nutritional types (energy source vs carbon source)
Phototrophs: energy from light; carbon source not specified here
Photoautotrophs: energy from light; carbon source is CO₂
Photoheterotrophs: energy from light; carbon source is organic compounds
Chemoautotrophs: energy from inorganic compounds; carbon from CO₂
Chemoheterotrophs: energy from organic compounds; carbon from organic compounds
Concept: break down names to identify energy source (first part) and carbon source (second part):
Photo-: energy source is light
Auto-: carbon source is CO₂
Hetero-: carbon source is organic compounds
Essential elements and trace elements
Primary elements: nitrogen, sulfur, phosphorus
Nitrogen: incorporated into amino acids, nucleotides, coenzymes, etc.
Sulfur, phosphorus: various cellular roles (not enumerated in detail here)
Trace elements: iron, chlorine, and others; present in small amounts; commonly serve as enzyme cofactors
Oxygen requirements and terminology
Aerobic vs anaerobic growth
Facultative: can grow with or without oxygen
Obligate: requires a specific condition (either aerobic or anaerobic depending on organism)
Aero-tolerant anaerobes: fermentatively produce ATP regardless of oxygen presence; always rely on fermentation; least efficient mode of ATP production
Culture media for growing bacteria
Generalized media
Example: Nutrient Agar
Purpose: support growth of a wide variety of bacteria when the species is unknown (e.g., swabbing a tabletop)
Specialized media
Selective: favors growth of a particular group and inhibits others (e.g., salt concentrations favor Gram-positive bacteria)
Differential: allows differentiation between colonies (often by color changes)
Some media are both selective and differential
Example: Eosin Methylene Blue (EMB) agar
Contains dyes that indicate lactose fermentation by Gram-negative bacteria
Greater lactose fermentation yields darker dye coloration; darker color => higher fermentation activity
Enrichment cultures
Liquid media designed to promote growth of a particular organism from a mixed culture, often by providing a specific composition
Purpose: allow low-abundance organisms to outgrow others (e.g., enrich for E. coli from soil)
Viruses and culture media
Viruses cannot be grown on standard culture media; require living cells for propagation
Discussion on viral culture is reserved for Chapter 13
Preservation of bacterial samples
Lyophilization (freeze-drying)
Bacteria are frozen, then dried under heat and vacuum to remove water from cytoplasm
Used for long-term storage; cultures become dormant but viable
Revival: add nutrient source to resume metabolism and replication
Cryopreservation
Bacteria frozen in liquid nitrogen \approx -196\text{°C}
Long-term storage; kept until thawed for revival
Bacterial growth dynamics
Reproduction: asexual binary fission
Generation time (doubling time): time required for population to double
If needed: N(t) = N0 \cdot 2^{\frac{t}{td}} where t_d is the doubling time
Growth curve phases (in a closed system)
Lag phase: cells adjust to new environment; little to no observable growth
Log (exponential) phase: rapid cell division; growth rate exceeds death rate (some cell death occurs)
Stationary phase: growth rate equals death rate; nutrients depleted and waste products accumulate, often causing pH to drop
Death (death) phase: death rate exceeds growth rate; nutrients exhausted and pH becomes highly acidic
Closed system: no addition of nutrients and no removal of waste
Measuring bacterial growth
Direct counts: membrane filtration (colony counting)
Process: filter sample through a membrane; place membrane on nutrient agar; incubate and count colonies
Statistical significance: select plates with 30–300 colonies for reliable counting
From colony counts, calculate the original cell concentration and plot growth curves
Indirect counts: spectrophotometry
Principle: measure light transmission through a sample; more cells absorb more light, so less light passes through
Result: a range (e.g., 100–300 cells) rather than an exact count
Pros: rapid, provides immediate results
Cons: cannot distinguish viable from nonviable cells; organic debris can affect readings
Viability testing recommended: plate a sample after spectrophotometry and compare; growth after incubation confirms viability
Chapter 7: The control of microbial growth (condensed overview)
Why control microbial growth?
Prevent food spoilage and ingestion of contaminated food
Sterilize medical equipment to ensure patient safety
Key control terms
Sterilization: kills all microbes, including vegetative cells and endospores
Vegetative cell: actively replicating form of the cell
Disinfection: kills vegetative cells only (does not kill endospores)
Antisepsis: kills vegetative cells on living tissue (human host)
Sanitation: reduces microbial counts to public health standards (e.g., glasses, utensils) without achieving sterility
Variables affecting microbial death rate
Number of microbes present: more organisms take longer to kill
Presence of endospores: highly resistant to many methods
Presence of organic material: organic debris can shield microbes from treatment (e.g., UV light may be absorbed by debris, protecting organisms underneath)
Methods of control
Physical methods
Temperature: hot and cold can kill microbes; hot denatures proteins; freezing and thawing can cause ice crystal damage
Filtration: physically removes cells
Desiccation: dehydration inhibits microbial metabolism
Ultraviolet (UV) light: damages DNA, creating mutations; severe damage prevents repair and replication
Chemical methods
Alcohols: dissolve lipids (disrupt membranes and proteins)
Soaps: act as surfactants and aid in mechanical removal
Preservatives (nitrates and nitrites): inhibit growth or kill microbes
Exceptions and notable organisms
Pseudomonas species: can survive and grow in disinfectants; a problem in medical facilities due to contamination of cleaning agents and equipment
Endospores: extremely resistant to many physical and chemical control methods; remain a major challenge in sterilization
Summary
Chapter 6: covers microbial growth physics, biochemistry, growth measurement, and preservation techniques
Chapter 7: covers rationale and