Chapter 6 - Microbial Growth Flashcards by Maeryn O

Physical Requirements for Growth

-temperature
-pH
-osmotic pressure

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Chemical Requirements for Growth

-sources of carbon, nitrogen, sulfur, phosphorus, oxygen
-trace elements
-organic growth factors

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True Psychrophiles

-cold-loving microbes
-can grow at 0℃
-optimum: 15℃
-cannot grow in reasonably warm room (20-25℃)
-non-pathogenic (don’t cause diseases)
-ie. bacteria in antarctica or ocean depth

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Psychrotrophs (Psychrophile group)

-aka facultative/flexible
-more common than psychrophile
-can grow at 0℃
-optimum: 20-30℃
-cannot grow: 30℃+
-pathogenic: food spoilage (usually in the fridge)
-ie. mold, odour, slime layer

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Mesophiles

-moderate-temp-loving microbes
-grow at a large range: 35-40℃
-optimum: 37℃ (human body temp)
-cannot grow: 50℃+
-all pathogenic: common spoilage and disease organisms

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Thermophiles

-heat-loving microbes
-cannot grow below 45℃
-optimum: 50-60℃ (hot water)
-max: 70-80℃

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Hyperthermophiles (Thermophile group)

-max temp: 110℃ (boiling water)
-optimum temp: 80℃+
-deep sea thermal vents or volcanoes

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Minimum Growth Temperature

-lowest temp at which the species will grow

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Optimum Growth Temperature

-temp at which the species grows best

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Maximum Growth Temperature

-highest temp at which growth is possible

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-most bacteria grow best between 6.5 and 7.5
-few grow below 4 (acidic)

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Acidophiles

-tolerant of acidity

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Osmotic Pressure

-microbes require water for growth

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Hypertonic

-concentration of solutes is higher outside the cell (environment is hypertonic to the cell)
-cellular water passes into high solute concentration
-cells cytoplasm shrinks (plasmolysis)

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Extreme Halophiles

-adapted to high salt concentrations so they require them for growth

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Facultative Halophiles

-do not require high salt concentration but can tolerate up to 2%

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Isotonic

-same concentration of salt and water

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Hypotonic

-osmotic pressure is unusually low
-water will enter cell

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Carbon

-one of the most important requirements for microbial growth

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Oxygen

-not essential for bacterial life
-divides bacteria into 5 groups

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Obligate Aerobes

-need O₂ to complete ETC and survive
-love oxygen
-extract more energy (ATP)
-most bacteria belong to this group
-grow well
-produce SOD and catalase

Facultative Anaerobes

-flexible
-use O₂ for growth and metabolism when available
-when O₂ not available: goes into anaerobic cell resp or fermentation and growth is slowed
-create a variable # of ATP
-produce SOD and catalase
-ie. Escherichia Coli

Obligate Anaerobes

-unable to use O₂
-harmed by O₂
-undergo glycolysis but not krebs cycle or ETC
-ie. Clostridium
-NO SOD OR CATALASE

Aerotolerant Anaerobes

-tolerate O₂
-fermentative and can’t use O₂ for growth/metabolism
-ie. Lactobacilli
-can tolerate O₂ because they have SOD and catalase

Microaerophiles

-aerobic (require O₂) -grow only in O₂ concentrations lower than the air -ie. Helicobacter pylori, Campylobacter jejuni

Helicobacter pylori

-causes stomach ulcers

Campylobacter jejuni

-GI issues -diarrhea and cramping

Toxic Oxygen

-O₂ starts to generate toxic forms during metabolism

Singlet Oxygen

-normal O₂ that has been boosted to a high energy state ¹O₂⁻ -extremely reactive

Superoxide Radicals

-O₂⁻ is formed in small amounts during normal aerobic respiration -steal electrons from other molecules

Superoxide Dismutase (SOD)

-an enzyme formed by some organisms attempting to grow in atmospheric O₂ -neutralizes toxic O₂⁻ by converting it into O₂ and hydrogen peroxide (H₂O₂)

Peroxide Anion

-O₂²⁻ -produced from the hydrogen peroxide produced in the SOD reaction -is toxic because it steals from other dangerous molecules

Catalase

-enzyme used to neutralize the peroxide anion -converts it to water and oxygen

Perioxidase

-another enzyme that breaks down hydrogen peroxide -reaction doesn't produce oxygen

Hydroxyl Radical

-OH﹒ -most reactive intermediate form of oxygen -no enzyme that can neutralize -irreversible

Biofilms

-communities of bacteria -thin slimy layer encasing bacteria that adheres to a surface -biological systems -how infection can spread

Quorum Sensing

-cell-to-cell communication -coordinate activities

Culture Medium

-nutrients prepared for microbial growth

Inoculum

-introduction of microbes to a medium

Culture

microbes growing in (nutrient broth) or on (agar plate) a medium

Sterile

-medium must be sterile and contain no other microorganisms

Agar

-complex polysaccharide -remains solid and sterile -not metabolized by many microorganisms -liquifies at 100℃ -cool down to 45℃ -incubate at 37℃

Pure Culture

-contains only one species or strain -streak plate method used to isolate cultures

Colony

-population of cells arising from a single cell or spore

Streak Method

-divide petri dish into thirds -move clockwise and dip some in each section

Selective Media

-used to suppress unwanted microbes and encourage desired microbes -Bismuth sulfite agar -ie. growing Salmonella typhus (causes typhoid fever and GI tract hemorrhaging disease)

Differential Media

-make it easy to distinguish colonies if different microbes -uses blood agar -a clear ring/empty region will appear around the colonies where hemolysis of the RBCs has occured -ie. to grow Steptococcus pyogenes (causes strep throat)

Selective and Differential Media

-suppress unwanted organisms -make it easy to distinguish colonies -mannitol salt agar -yellow halo that degraded the mannitol occurs -ie. Staphylococcus aureus (skin infections, TSS, food poisioning)

Binary Fission

-increase in numbers, not size -cells divide and grow exponentially

Bacterial Growth Curve

1. LAG PHASE: intense activity preparing for growth but no increase in population 2. LOG PHASE: exponential population increase, best time to give antibiotics/use radiation 3. STATIONARY PHASE: plateau, equilibrium, deaths balance new growth 4. DEATH PHASE: population decreases at a logarithmic rate

Generation Time

-time required for a cell to divide (population to double) -time (in minutes)/number of generations