Lecture 2 Bacterial growth and disinfection

Bacterial reproduction

Asexual by binary fission, it is a direct division of a single cell, involving the replication of a single circular DNA chromosome and the splitting of the cell into two. 

Cycles of life Pathogen

the time it takes for the population to double through
one round of binary fission

Growth curve pathogen

bacterial growth pattern in a closed culture system plotted as a
function of time

4 phases

Growth curve 4 phases

1.Lag phase

2.Log phase

3.Stationary phase

4.Death or decline phase

1.Lag phase

No increase in number of living bacterial cells

2.Log phase

Exponential increase in number of living bacterial cells

3.Stationary Phase

Plateau in number of living bacterial cells; rate of cell division and death roughly equal

4 Death or decline phase

Exponential decrease in number of living bacterial cells

All microbes find a niche by adapting to specific conditions including:

Temperature, pH, salinity, oxygen levels, nutrient availability

3 principal temperatures specific to each microbe:

Minimum, optimal, maximum

Minimum

Lowest that supports growth

Optimal

Cellular growth at highest

Maximum

Highest that supports growth

Bacterial Classification using pH

1. Every microbe has a minimum, optimum, and maximum range of pH for growth
2. Extreme pH affects the structure of all macromolecules – evolutionary adaptions
3. Optimum growth pH is the most favorable pH for the growth:

Acidophiles

Grow at pH 1-4

Neutrophiles

Grow best in pH range of 5-8, make up majority of microorganisms

Alkaliphiles

Grow in the basic pH range 9-11

Plasmolysis

the process where the protoplast (the cell membrane and its contents) of a plant cell shrinks and pulls away from the cell wall, cytoplasm shrinks

Halophiles

Salt loving and thrive in high salt enironments

Facultative halophiles – Halotolerant

Do not require high concentrations of salt for growth, but can survive and divide in presence

Anaerobic environments

Pathogens thrive in this environment with little to no oxygen

Reactive oxygen species (ROS)

unstable molecules derived from oxygen that have crucial physiological roles as cell signaling molecules and in the immune system's fight against pathogens

Aerobic organisms must

Be able to detoxify by superoxide dismutases (SOD), peroxidases, and catalase

Anaerobes have none of these but aerobes have all 3

Essential nutrients

• Required to replicate, build new cells, and maintain/repair
• Found in the organic and inorganic compounds of a microbe’s environment

Macronutrients and micronutrients

Fastidious

Organisms that need multiple growth factors

Liquid media

broth media; ideal for growing large batches of microbes

Solid media

broth + agar poured into Petri plates, used for
isolating colonies & observing growth characteristics

Semisolid media

Useful for motility testing

Growth (culture) media

mixtures of nutrients that support microbial growth in an artificial setting

Complex media

general all-purpose media that support growth of a
large variety of bacteria

Enriched media

complex media + added growth factors, vitamins, and
other essential nutrients to promote the growth of fastidious organisms

Chemically defined medium

individual chemical components are added in exact amounts, complete chemical composition known

Selective media

Inhibit the growth of unwanted microorganisms and support the growth of the organism of interest by supplying specific nutrients and reducing competition

Differential media

Easy to distinguish between different bacteria by a change in the color of the colonies
or the color of the medium.
• Color changes are the result of end products created by interaction of bacterial
enzymes with differential substrates in the medium 29

Hemolysins

a type of exotoxin that is an extracellular enzyme that lyses red
blood cells (hemolysis)

Hemolysis

can be observed by growing bacteria on complex agar media
containing animal blood (TSA + 5% sheep blood)

Streak plate technique

is used to identify and isolate the potential pathogen it must first be isolated

Major decontamination strategies

to remove /reduce microbes to prevent infection and disease

Clean - disinfection and antiseptic

Sterilization

Suffix -cide (or -cidal)

methods that kill the targeted microorganism

Suffix -stat (or -static)

methods that do not kill organisms but stop growth, making their population static (in check)

Common control methods include the application of:

Temperature, radiation, filtration, desiccation

Temperature control methods

Refrigeration and freezing slow microbial growth

Heat controls microbial control, moist heat (boiling, pasteurization, autoclaves)

Dry heat (incineration)

Germicides

Chemicals that control microbial contamination
• microbiocidal or microbiostatic
• Two key classes:
A. Disinfectants—used to treat inanimate objects
B. Antiseptics—applied to living tissue

Three tiers of germicides:

A. Low-level agents

B. Intermediate level agents

C. High level agents

Low-level agents

destroy / decrease contamination by most bacteria (but not
Mycobacteria), fungi, and some viruses, but not endospores

ex: detergents targets lipid membrane

Intermediate level agents

potential to destroy bacteria & fungi; but not all
viruses and endospores; presence of organics can interfere with effectiveness

ex: alcohols + phenols target protein and lipids membranes

High level agents

destroy all microbes and endospores – sterilizing

ex: Aldehydes, peroxides, halogens, ethylene ide targets proteins and luncliec acids