Rushed Exam 2 Lec Micro

What is microbial growth?

An increase in the number of microbial cells, usually through cell division.

What are the four major physical requirements for microbial growth?

Temperature, pH, osmotic pressure, and oxygen.

What are psychrophiles?

Microbes that grow best at cold temperatures.

What are mesophiles?

Microbes that grow best at moderate temperatures.

Why are most human pathogens mesophilic?

Their optimum growth temperature is close to the temperature of the human host.

What are thermophiles?

Microbes that grow best at high temperatures.

Why does temperature affect microbial growth?

It affects enzyme activity, protein structure, and membrane function.

What is an acidophile?

A microbe that grows best in acidic conditions.

What is an alkaliphile?

A microbe that grows best in alkaline conditions.

What is osmotic pressure?

The effect of water movement across a membrane due to differences in solute concentration.

How can high salt or sugar inhibit microbial growth?

It draws water out of cells, causing dehydration and inhibiting growth.

What is an obligate aerobe?

A microbe that requires oxygen to grow.

What is an obligate anaerobe?

A microbe that cannot grow in oxygen because oxygen may be toxic to it.

What is a facultative anaerobe?

A microbe that grows with or without oxygen but generally grows better with oxygen.

What is an aerotolerant anaerobe?

A microbe that does not use oxygen but tolerates its presence.

What is a microaerophile?

A microbe that requires oxygen at concentrations lower than atmospheric levels.

What are four toxic oxygen products?

Singlet oxygen, superoxide ions, hydrogen peroxide, and hydroxyl radicals.

What does superoxide dismutase do?

It converts superoxide into oxygen and hydrogen peroxide.

What does catalase do?

It breaks hydrogen peroxide into water and oxygen.

Why do some microbes live in oxygen-free environments?

They lack sufficient enzymes to neutralize toxic oxygen products.

What are anaerobic culture methods used for?

Growing microbes that cannot tolerate oxygen or grow best without it.

What is selective medium?

Medium that inhibits certain microbes while allowing desired microbes to grow.

What is differential medium?

Medium that distinguishes microbes through visible biochemical or growth differences.

Can a medium be both selective and differential?

Yes. MacConkey agar selects for many Gram-negative bacteria and differentiates lactose fermenters from nonfermenters.

What is enrichment medium?

A medium or culture condition designed to favor a particular microbe in a mixed sample.

What is a pure culture?

A culture containing only one microbial species or strain.

What is batch culture?

A closed culture system with a fixed supply of nutrients and no continuous addition of fresh medium.

What are the four phases of the bacterial growth curve?

Lag, log (exponential), stationary, and death (decline).

What happens during the lag phase?

Cells adapt to their environment and prepare to divide; cell numbers increase little.

What happens during the log phase?

Cells divide rapidly at an approximately constant exponential rate.

What happens during the stationary phase?

Cell division approximately equals cell death, so the population remains relatively stable.

What happens during the death phase?

Viable cell numbers decline.

What is a direct plate count?

A method that counts viable colony-forming units growing on agar.

What is membrane filtration used for in microbial counting?

A sample passes through a filter that traps microbes; the filter is then placed on medium for colonies to grow.

What is the most probable number (MPN) method?

A statistical estimate of viable microbial numbers based on patterns of growth in dilution tubes.

What is a direct microscopic count?

Counting cells under a microscope; living and dead cells may both be counted.

What is turbidity?

Cloudiness caused by suspended cells that indirectly estimates microbial growth.

What are three indirect measurements of microbial growth?

Turbidity, metabolic activity, and dry weight.

What is the difference between direct and indirect growth measurement?

Direct methods count cells or viable colonies; indirect methods estimate growth using related measurements.

LECTURE 8 — CONTROL OF MICROBIAL GROWTH

What is sterilization?

Destruction or removal of all microbial life, including bacterial endospores.

What is disinfection?

Destruction of many or most pathogens on inanimate objects; it does not necessarily destroy endospores.

What is antisepsis?

Using antimicrobial chemicals on living tissue to reduce or inhibit microbes.

What is pasteurization?

Controlled heating of heat-sensitive materials, such as milk, to reduce pathogens and spoilage microbes.

Does pasteurization reliably sterilize milk?

No. It reduces microbial numbers but does not reliably destroy bacterial endospores.

What is an autoclave?

A device that uses pressurized steam to sterilize materials.

What are standard introductory microbiology autoclave conditions?

Approximately 121°C and 15 psi above atmospheric pressure for a sufficient exposure time.

Why is pressurized steam effective in an autoclave?

Steam transfers heat efficiently and denatures microbial proteins; pressure allows temperatures above 100°C.

What is a bactericidal agent?

An agent that kills bacteria.

What is a bacteriostatic agent?

An agent that inhibits bacterial growth.

What is selective toxicity?

A drug harms a microbe more than its host by targeting differences between microbial and host cells.

What are the five major antimicrobial drug targets?

Cell wall synthesis, cell membrane structure or function, DNA and RNA functions, protein synthesis, and key metabolic pathways.

How do beta-lactam antibiotics work?

They inhibit enzymes involved in peptidoglycan cross-linking, weakening the bacterial cell wall.

Why are beta-lactams often effective against actively growing bacteria?

Growing bacteria actively synthesize and remodel their cell walls.

How do aminoglycosides work?

They bind the 30S ribosomal subunit and cause mRNA misreading, producing incorrect proteins.

How do tetracyclines work?

They bind the 30S ribosomal subunit and block tRNA attachment at the A site.

Why can some antibiotics harm host cells despite targeting bacterial ribosomes?

Eukaryotic mitochondria have ribosomes with similarities to bacterial ribosomes.

How do drugs that inhibit nucleic acid synthesis work?

They interfere with DNA replication or RNA transcription.

How do drugs that disrupt the cell membrane work?

They damage membrane integrity or function and disrupt essential cellular processes.

How do antimetabolites work?

They block essential metabolic pathways by interfering with enzymes or molecules needed for metabolism.

What is an antibiotic?

Traditionally, a substance produced by microbes that inhibits or kills other microbes; the term is also used more broadly.

What is an antimicrobial?

An agent that acts against microorganisms.

Why must the correct antimicrobial drug be selected?

Different drugs target different microbes and cellular processes; an ineffective drug may contribute to resistance.

What is the difference between pasteurization and autoclaving?

Pasteurization reduces microbial numbers but does not reliably destroy endospores; autoclaving can sterilize materials, including destroying endospores when performed correctly.

What is the difference between disinfection and antisepsis?

Disinfection is used on inanimate objects; antisepsis is used on living tissue.

LECTURE 9 — MICROBIAL GENETICS

What is a gene?

A DNA sequence that encodes a functional product, such as a protein or functional RNA.

What is a bacterial chromosome?

The main DNA molecule containing much of the bacterium's essential genetic information.

What is a plasmid?

A usually small, independently replicating DNA molecule separate from the chromosome that may carry genes such as antibiotic-resistance genes.

What is DNA replication?

The process of copying DNA before cell division.

What does semiconservative replication mean?

Each new DNA molecule contains one original strand and one newly synthesized strand.

What is transcription?

Making RNA from a DNA template.

What is translation?

Using mRNA information to build a protein at a ribosome.

What is the usual flow of genetic information?

DNA to RNA to protein.

What is mRNA?

Messenger RNA that carries coding information used to make a protein.

What is tRNA?

Transfer RNA that brings amino acids to the ribosome and matches its anticodon to an mRNA codon.

What is rRNA?

Ribosomal RNA, a structural and functional component of ribosomes.

What is a codon?

A sequence of three nucleotides in mRNA that specifies an amino acid or stop signal.

What is an operon?

A group of bacterial genes regulated together and transcribed from a shared promoter.

What is the lac operon?

An inducible operon that regulates genes involved in lactose use; lactose availability and glucose levels influence its expression.

What is the arg operon?

A typically repressible operon regulating genes involved in arginine biosynthesis.

What is an inducible operon?

An operon typically switched on in response to an inducer.

What is a repressible operon?

An operon typically switched off when its end product is abundant.

What is DNA supercoiling?

The coiling of DNA upon itself to compact and organize it.

What does DNA gyrase do?

It changes DNA supercoiling and helps manage twisting during DNA replication and other DNA processes.

What is genetic recombination?

The acquisition or rearrangement of genetic material that produces new genetic combinations.

What is conjugation?

DNA transfer between bacterial cells in direct contact, often involving a pilus and a conjugative plasmid.

What is transformation?

Uptake of free DNA from the environment by a competent recipient cell.

What is transduction?

Transfer of bacterial DNA from one bacterium to another by a bacteriophage.

Which recombination mechanism requires direct donor-recipient contact?

Conjugation.

Which recombination mechanism involves free DNA?

Transformation.

Which recombination mechanism uses a bacteriophage?

Transduction.

What is Griffith's experiment associated with?

The discovery of bacterial transformation, in which material from heat-killed virulent bacteria transformed live nonvirulent bacteria.

What is the difference between conjugation and transformation?

Conjugation involves direct contact between cells; transformation involves uptake of free environmental DNA.

What is the difference between transformation and transduction?

Transformation involves free DNA; transduction uses a bacteriophage to transfer DNA.