Chapter 6 - Microbial Growth 2023

Psychrotrophs

Grow between 0°C and 20-30°C

Cause food spoilage

mesophiles

moderate temperature loving microbes (20-40C), most microbes grow at these temps

thermophiles

growth at higher temps, 50-60oC, hot springs

hyperthermophiles

Archaea, optimum growth temperature >80*C, volcanic vents, deep ocean vents

acidophiles

grow in acidic environments, 5.5 , pump out excess protons; or lower, most fungi and algae

Alkaliphiles (alkalophiles)

growth optimum between pH 8.5 and pH 11.5, pump in protons

psychrophiles

live at very cold temperatures, freezers, artic

Neutrophiles pH range

pH of 6.5-7.5, most organisms fall into this range

plasmolysis

A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment.

obligate halophiles

salt-loving bacteria; require high osmotic pressure (dead sea)

facultative halophiles (osmotolerant)

tolerate high osmotic pressure

obligate aerobes

require oxygen

facultative anaerobes

can survive with or without oxygen, prefer to use aerobic respiration, however in the absence of oxygen, can use either fermentation or anaerobic respiration

obligate anaerobes

unable to use oxygen, and oxygen is toxic due to lack of enzymes to break down toxic byproducts

aerotolerant aerobes

do not use oxygen but are not killed by it

microaerophiles

require oxygen concentration lower than air concentrations

biofilms in microbial growth

microbial communities; form slime or hydrogels that adhere to surfaces; bacteria communicate cell-to-cell via quorum sensing; share nutrients; shelter bacteria from harmful environmental factors

1000x resistant to microbicides; involved in 70% of infections in hospital (catheters, heart valves, contacts, dental caries)

CFU

population of cells arising from single cell or spore or from group of attached cells; often called colony-forming unit (CFU)

bacterial division

do not go through mitosis; go through binary fission

increase number of cells, not size

budding

Conidiospores (actinomycetes)

Fragmentation of filaments

generation time

time required for cell to divide

20 minutes to 24 hours

binary fission doubles number of cells each generation

total number of cells = 2^number of generations

growth curves are represented logarithmically

lag phase of bacterial growth

The first phase of the bacterial growth curve, in which organisms acclimate to their surrounding; they grow in size but do not increase in number.

Log phase of bacterial growth

The second of the four phases of bacterial growth, in which cells divide at an exponential rate.

stationary phase of bacterial growth

The third of the four phases of the bacterial growth curve, in which new cells are produced at the same rate as the old cells die, leaving the number of live cells constant.

death phase of bacterial growth

as resources become insufficient, bacteria die off

direct measurement of microbial growth

direct measurements-direct count of microbial cells; plate count; filtration; most probable number (MPN) method; direct microscopic count

direct microscopic count

Volume of a bacterial suspension placed on a slide

Average number of bacteria per viewing field is calculated

Uses a special Petroff-Hausser cell counter; live and dead bacteria are included

MPN (most probable number)

a statistical determination of the number of bacter per 100ml , only live bacteria are included

turbidity method

- Indirect method

- Counts both live and dead cells

- uses spectrophotometer

serial dilution

take initial stock sample of bacteria, successive tubes, dilute down to smaller numbers

turbidity

measurement of cloudiness with a spectrophotometer

metabolic activity

amount of metabolic product is proportional to the number of bacteria

dry weight

bacteria are filtered, dried, and weighed; used for filamentous organisms

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