Environmental Effects

Microbiology Lab 7 Quiz

Psycrophiles Optimal Growth

Psycrophiles Optimal Growth

-5 to 20 degrees

Mesophiles Optimal Growth

20 to 50 degrees

Thermophiles Optimal Growth

60 to 80 degrees

Hyperthermophiles Optimal Growth

Above 80 degrees

Psychrotrophs

Bacteria classified to grow at higher temperatures but capable of growing at low temperatures

Prodigiosin

A red pigment and antibiotic

Oxygen

Makes up 21% of Earth’s atmosphere

Strict (Obligate) Aerobes

Bacteria that must grow in oxygen

Why Aerobes Must Grow in Oxygen

Their metabolism requires oxygen and they carry out respiration in which oxygen is used as the terminal electron acceptor in the electron transport chain

Microaerophiles

Aerobic bacteria that prefer 2-10% oxygen

Why Microaerophiles Prefer Less Oxygen

The lower oxygen concentration is necessary for their respiratory metabolism

Facultative Anaerobes

Bacteria that grows well in aerobic conditions but can also grow anaerobically when oxygen is not available

Why Can Facultative Anaerobes Grow in Both Conditions

Their flexible metabolism allows them to produce energy by carrying out respiration in aerobic conditions or fermentation in anaerobic conditions

Aerotolerant Anaerobes

Anaerobes that can tolerate oxygen and grow in its presence, but do not require it for energy production

Why Aerotolerant Anaerobes Do Not Need Oxygen

They only use fermentation to produce energy

Strict (Obligate) Anaerobes

Bacteria that are harmed or killed by oxygen and produce energy through fermentation

Why Strict Anaerobes Need Aerobic Conditions

They lack the systems that can convert toxic forms of oxygen to less harmful compounds that will not damage the cell

Fermentation

Inorganic compounds (such as nitrates and sulfates) take the place of oxygen in the electron transport chain as the terminal electron acceptor

Toxic Forms of Oxygen

Hydrogen peroxide and superoxide

H2O2 and Superoxide

Can damage biological molecules (such as nucleic acids, proteins, and coenzymes)

Catalase

Degrades hydrogen peroxide to oxygen and water

Peroxidase

Degrades hydrogen peroxide

Superoxide Dismutase

Convert superoxides to oxygen and hydrogen peroxide

FTM

Fluid Thioglycollate Medium

Fluid Thioglycollate Medium

A rich medium that supports the growth of both aerobic and anaerobic bacteria

FTM Composed of

Glucose, cystine, and sodium thioglycollate (to reduce its oxidation/reduction potential)

FTM Contains

Resazurin

Resazurin

A dye that turns pink in the presence of oxygen (and an oxygen indicator)

Brewer’s Anaerobic Agar

A solid medium for cultivating anaerobic bacteria

Brewer’s Anaerobic Agar Contains

Thioglycollate and Resazurin

Thioglycollate

A reducing agent

Antiseptics and Disinfectants

Chemical agents that are used to control microorganisms

Antiseptics

Substance that inhibit microbial growth or kill microorganism but are gentle enough to be applied to living tissue; do not destroy endospores

Disinfectants

Chemical agents that are applied to inanimate objects to kill microorganisms (too harsh for living tissue)

Disinfectants Classified as Sterilants or Sporocides

Destroy all microbial life, including endospores

Sanitizers

Agents that reduce microbial numbers to a safe level but do not completely eliminate all microbes

Bacteriostatic

An agent that inhibits the growth of bacterial cells but does not kill them (when removed, the growth resumes)

Bactericidal

Agents that kill bacterial cells

Psycrophiles Location

Icy waters of the Arctic and Antarctic

Mesophiles Extra

Most bacteria; Most pathogens grow between 35 and 40 degrees

Thermophiles Location

In soils where midday temps can reach greater than 50 degrees or in compost piles where temps exceed 60 to 65 degrees

Hyperthermophiles Location

Isolated from thermal vents in the ocean floor or volcanic heated hot springs

Examples of Pychrotrophs

Proteus, Pseudomonas, and Leuconostoc (mesophiles in fridges→food spoilage) & Listeria monocytogenes and Campylobacter (foodborne pathogens)

Enzymes Above Maximal Temperatures

Denature and lose activity

Enzymes Below Minimal Temperatures

Chemical activity slows down

As Temperature Drops

Transport of nutrients into the cell decreases and membrane fluidity changes

As Temperatures Rise

Membrane lipids can be destroyed resulting in serious damage to the membrane and death of the organism

Ribosomes

The energy centers of cells

Ribosomes in High Temps

Cease to function adequately

S. marcescens

Produces prodigiosin in a certain temperature range

Examples of Strict Aerobes

Pseudomonas, Micrococcus, and Bacillus

Helicobacter pylori and Campylobacter

Pathogens found in the human gastrointestinal tract (microaerophiles)

Examples of Facultative Anaerobes

E. coli and Salmonella

Examples of Aerotolerant Anaerobes

Streptococci (produces cheese, yogurt, and sour cream) and Streptococcus pyogenes (causes strep throat)

Examples of Strict Anaerobes

Clostridium

Strict Anaerobes Location

Soil, rumen of cattle, and septic systems

Pink of the FTM

Top of the medium

Colorless of the FTM

Middle and bottom of the medium

FTM Agar

A small amount is added to the medium to localize the organisms and favors anaerobic conditions in the bottom of the tube

GasPal

Capable of producing hydrogen, placed in an anaerobic jar to form water from the present oxygen

Anaerobic Indicator Strip

Used to make certain the anaerobic jar is an oxygen-free environment which is checked by being colorless in anaerobic conditions and blue in the presence of oxygen

Two Common Antibiotics

Penicillin and streptomycin

MRSA

Methicillin-resistant S. aureus

HAI

Health-care acquired infections

Antimicrobial Agents

Can vary their effectiveness against various pathogenic bacteria

Narrow Spectrum Antimicrobial Agents

More effective against gram positive bacteria OR gram negative bacteria

Broad-Spectrum Antimicrobials

More effective against both kinds of organisms

Broad vs Narrow Spectrum

Depends on mode of action, ability to be transported into the cell, and permeability

Antimicrobials Can Target

-Cell wall synthesis

-DNA and RNA synthesis

-Protein synthesis

-Vitamin Synthesis

Gram Negative Bacteria

The outer membrane acts as a permeability barrier and can restrict antimicrobial access

Zone of Inhibition

The zone around the disk where no growth occurs due to the agent inhibiting or killing the organism

Zone Can Vary With

-Diffusibility of the agent

-Size of the inoculum

-Type of medium

-Etc.

Inoculation in the Kirby-Bauer Method

Made with a cotton swab from broth culture

Kirby-Bauer Method

A way to determine the sensitivity or resistance of a bacterium to an antimicrobial that is standard, reliable, simple, and fast

Kirby-Bauer Method Procedure

Performed by uniformly streaking a standardized inoculum of the test organism on Mueller-HInton medium, and then paper disks containing specific concentrations of an antimicrobial or antibiotic are deposited on the agar serface

Antimicrobial in the Kirby-Bauer Method

Diffuses out and forms a concentration gradient