[01.17] General Concepts in Microbiology 2

By increase in population, not cell size.

How is microbial growth primarily measured?

Binary fission.

What is the most common form of bacterial reproduction?

Doubling time.

What is another term for generation time?

20 minutes.

What is the approximate generation time for Escherichia coli under ideal conditions?

Lag, Exponential, Stationary, Death.

Name the four distinct phases of a standard bacterial growth curve.

Logarithmic/Exponential Growth Phase.

In which bacterial growth phase is an organism most sensitive to drugs and radiation?

Number of new cells equals the number of dead cells.

What characterizes the stationary phase of bacterial growth?

Enzyme inactivation.

What causes bacterial death above their maximum growth temperature?

Mesophiles.

What classification of microorganisms grows best between 20°C and 40°C?

15°C.

What is the optimal growth temperature for psychrophiles?

Between pH 6.5 and 7.5.

What is the typical pH range for the growth of most bacteria?

Extreme or obligate halophiles.

What term describes microorganisms that require high osmotic pressure for growth?

Plasmolysis (shrink and die).

What happens to a microorganism placed in a hypertonic solution?

50%.

What percentage of a bacterium’s dry weight is composed of carbon?

Amino acids and proteins.

Name two essential components for which nitrogen is required in bacteria.

Obligate aerobes.

What classification of prokaryotes absolutely requires oxygen for growth?

Facultative anaerobes.

What type of bacteria can grow with or without oxygen?

Die.

What happens to obligate anaerobes in the presence of oxygen?

Enzyme cofactors.

What is the primary role of trace elements like iron and zinc for bacteria?

To produce a dormant, highly resistant cell to preserve genetic material during stress.

What is the purpose of endospore formation?

Bacillus and Clostridiums.

Name two gram-positive bacterial genera known to form endospores.

Food used to grow and control microbes.

What is culture media?

Defined media has known quantities of all ingredients; undefined media has complex ingredients in unknown proportions.

What is the key difference between defined and undefined media?

To suppress unwanted microbes and encourage desired microbes.

What is the primary function of selective media?

Indicator media.

What is another name for differential media?

Biochemical characteristics of a microorganism.

How do differential media distinguish between microorganisms?

Properly collected specimen.

What is considered the single most important step in diagnosing an infection?

Gram Stain and Acid-fast Stain.

Name two common staining techniques for microscopic identification of microorganisms.

Gram-positive and gram-negative bacteria.

What does the Gram stain differentiate?

Mycobacterium species.

Which specific genus is identified using the Acid-fast Stain?

Mordant to seal the dye inside gram-positive bacteria.

What is the role of Gram's iodine in Gram staining?

Red.

What color do gram-negative bacteria stain with Safranin in the Gram staining process?

Hemolytic properties.

What characteristic does Blood agar help to indicate in certain organisms?

Lowenstein-Jensen.

Which culture medium is specifically used to isolate Mycobacterium tuberculosis?

MacConkey or EMB.

Which differential media distinguish lactose fermenters from non-lactose fermenters?

Chocolate agar.

Which culture media is used to identify Neisseria and Haemophilus species?

Enzyme immunoassays (EIA).

What type of immunoassay detects the presence of an antigen/ligand, such as for Legionella pneumophila urinary antigen?

Agglutination tests.

What type of test detects substances through cell-clumping in the presence of antibodies?

Polymerase chain reaction (PCR).

Which molecular diagnostic technique amplifies small amounts of DNA?

Using labeled probes specific for bacterial 16S RNA.

How is bacterial 16S RNA utilized for identification in molecular diagnostics?

Identify which antibiotics organisms are susceptible or resistant to.

What is the primary purpose of the Disk Diffusion Susceptibility Test?

A more potent antimicrobial.

In a Disk Diffusion Susceptibility Test, what does a wider diameter of the inhibition zone signify?

Minimum Inhibitory Concentration.

What does MIC stand for in antimicrobial susceptibility?

The lowest concentration of a drug which prevents visible growth of bacteria.

Define Minimum Inhibitory Concentration (MIC).

Susceptible/sensitive, intermediate, or resistant.

How are MIC results typically graded?

Cell membrane and cell wall enlargement, and increased cell volume.

What are the initial requirements for a bacterial cell during its elongation phase in binary fission?

Septum.

What protein-dependent structure forms a ring in the middle of an elongated bacterial cell during division?

Ammonium salts or nitrates.

What are common inorganic nitrogen sources in defined media?

Yeast Extract.

Name a common complex ingredient found in undefined media.

~40°C.

At what approximate temperature does agar solidify when used in culture media?