Microbiology - Exam 3

Fomites

non-living objects which can harbor microbes and serve in disease transmission

Sterilization

removal or destruction of all living microbes, including endospores

Commercial sterilization

heats foods in sealed containers just long enough to kill all pathogenic microbes, including Clostridium botulinum endospores

Disinfection

• meant to reduce infection and illness by killing pathogens

• used on non-living surfaces

Antisepsis

• meant to reduce infection and illness by killing pathogens

• used on living tissues

Degerming

physical removal of microbes from a limited area, often using an antiseptic

Sanitization

processes meant to lower microbial counts to levels that prevent disease transmission

Define the meaning “cidal”

Treatments that cause actual death of microbes

• ex. bactericidal

Define the meaning “static”

Treatments that stop or slow microbial growth end

• ex. bacteriostatic

Describe various physical methods of microbial control and know their relative effectiveness (labeled in order of effectiveness)

1. Heat: kills microbes by denaturing proteins

• Pasteurization: mild heating to kill pathogens and spoilage organisms in liquids like milk.

1. Radiation: damages DNA

2. Filtration: removes microbes physically

3. Low temperatures: inhibits growth

Describe the process of pasteurization

1. Heating

• the food or liquid is heated to a high temperature for a short period of time

2. Holding

• the product is kept at that temperature long enough to destroy most harmful microbes and enzymes that could cause food spoilage 

3. Rapid cooling

• the product is quickly cooled to prevent the growth of any remaining microbes

4. Sealing & Storage

• the pasteurized product is placed in clean, sealed containers to keep it safe from recontamination

Explain why pasteurization is used in the food industry.

Pasteurization is used in the food industry because it:

• kills pathogens to reduce illness

• reduces the number of spoilage microbes to extend shelf life

• preserves nutritional content and taste 

Discuss two reasons why it is important to read the label when using a disinfectant.

It is important to read the label because:

• No single disinfectant works in all cases

• It must be effective against desired microbes you are trying to kill

• It must be at the proper concentration to be effective - (instructions for proper use)

Understand how the following factor might influence the effectiveness of a control measure:

• Degree of contamination 

more microbes = longer time or stronger treatment needed

Understand how the following factor might influence the effectiveness of a control measure:

• Temperature 

higher temp = faster/more effective killing of microbes 

low temp = slows or inhibits the killing of microbes

Understand how the following factor might influence the effectiveness of a control measure:

• Interfering substances

organic matter blocks and/or inactivates the disinfectant

Understand how the following factor might influence the effectiveness of a control measure:

• Microbial characteristics 

Some microbes are more resistant than others

Microbes that are hard to kill includen (top = hardest)

1. Prion

2. Endospores 

3. Mycobacterium

Explain the role of soaps and detergents in the process of disinfection and antisepsis.

Soaps and detergents are often added to antiseptics/disinfectants to:

• Aid in the physical removal of microbes through scrubbing - breaks up oil and dirt

• Act as surfactants - aid in the emulsification of skin oils, dead skin, and microbes into droplets that can be easily washed away 

Define “antibiotic”

compounds that kill or inhibit the growth of microbes

know this: the term “antibiotic” usually refers to a drug that is antibacterial

Define “selective toxicity”

the ability of a drug to kill or inhibit microbes without causing harm to the host’s cells

List some common side effects of antibiotic use.

• GI distress (damage to the microbiome)

• Damage to the kidneys, liver, and/or nervous system

• Allergic reactions

Define “spectrum activity”

range of microbes against which an antibiotic is effective 

Explain broad spectrum antibiotics

Effective against a broad range of microbes, including both Gram + and Gram - bacteria

Explain the appropriate uses for broad spectrum antibiotics.

• To begin treatment while waiting for lab ID tests

• When infection is polymicrobial (a mixed infection with multiple species)\

• As preventative measure during surgery

• When a narrow spectrum drug fails

Explain narrow spectrum antibiotics

Effective against a limited group of microbes, only gram + bacteria 

Explain the appropriate uses for narrow spectrum antibiotics. 

when the specific bacterium causing an infection is identified 

What factors need to be considered when determining antibiotic dosage?

• Age/size of patient

• Liver/kidney function

• Half-life of drug

• Effective concentration 

What factors need to be considered when determining route of administration?

• Location of infection

• GI absorption 

• Condition of patient 

• Need for monitoring 

Explain the term “synergism”

two or more drugs are more effective when administered together 

Explain the term “antagonism”

two or more drugs have reduced effectiveness when administered together

Describe the 5 major modes of action of antibacterial drugs

1. Cell wall:

• prevents synthesis of peptidoglycan

• creates a weak cell wall that can result in osmotic lysis = bactericidal

2. Ribosomes:

• interferes with normal protein synthesis

3. Metabolic pathways

• inhibits bacterial folic acid synthesis

4. DNA synthesis 

• can’t make copies of their chromosomes = no binary fission

5. RNA synthesis

• stops transcription = stops protein production 

Describe the four common mechanisms of resistance in bacteria? 

1. Drug Inactivation by Bacterial Enzymes 

• changes the structure of the drug so it no longer binds to its bacterial cell target 

2. Target Modification

• bacteria changes the drug target so it no longer binds

3. Block Penetration

• blocks entry of drug so it cannot reach its target

4. Efflux Pumps

• transport proteins in outer membrane/plasma membrane transport the drug back out of the cell

Describe how antimicrobial resistance evolves

Antimicrobial resistance evolves through:

1. Genetic changes (mutation or gene transfer) that provide survival advantages.

2. Selective pressure from antibiotic use, which favors resistant bacteria.

3. Spread of resistant organisms or resistance genes in communities and healthcare settings.

Explain an action that can be taken to fight antimicrobial resistance and explain why that action is effective.

Action: not taking antibiotics unless necessary

Effective because it:

• stops the bacteria from adapting 

• avoids “superbugs”

• protects helpful bacteria 

Explain an action that can be taken to fight antimicrobial resistance and explain why that action is effective.

Action: taking antibiotics as prescribed

Effective because it:

• kills the strongest bacteria

• prevents infection recurrence 

• maintains the drug effectiveness 

How does a disk diffusion test determine antibiotic susceptibility?

It determines antibiotic susceptibility by measuring how effectively an antibiotic inhibits bacterial growth on an agar plate — the larger the zone of inhibition, the more susceptible the bacteria are to that antibiotic.

How does a broth dilution test determine antibiotic susceptibility?

It determines antibiotic susceptibility by measuring the lowest concentration of an antibiotic that inhibits visible bacterial growth (MIC) in liquid media, providing a precise and reliable guide for antibiotic selection and dosing.

Define MIC and its importance in choosing an antibiotic regimen.

• minimal inhibitory concentration (lowest concentration that stops growth)

• important for selecting the right antibiotic and dosage to effectively treat infections and prevent resistance

Define MBC and its importance in choosing an antibiotic regimen.

• minimal bactericidal concentration (lowest concentration that kills bacteria)

• important for selecting antibiotics and dosages in serious or hard-to-treat infections where complete bacterial killing is essential 

Know ways in which viruses differ from all other cellular life forms.

• No cells; acellular

• Lack a plasma membrane, ribosomes, and most enzymes 

• Unable to carry out essential metabolic pathways such as ATP synthesis

• Chromosomes are often made of RNA instead of DNA

• Not capable of independent reproduction; must infect another living cell in order to replicate 

Define the term “host range”

the spectrum of host cells a particular virus can infect

Describe the structure of a nucleic acid genome in a virus particle.

• made of DNA or RNA

• double or single-stranded

Describe the function of a nucleic acid genome in a virus particle.

• stores genetic information

• directs viral protein production and replication

Describe the structure a capsid in a virus particle.

protein coat made of capsomeres

Describe the function of a capsid in a virus particle.

• protects the viral genome

• helps recognize and attach to host cells

Describe the structure of an envelope in a virus particle.

lipid bilayer from host membrane with embedded proteins

Describe the function of an envelope in a virus particle.

• helps the virus enter host cells

• protects the virus

• assists in evading the immune system

Describe the structure of spikes in a virus particle.

carb-protien projections on the envelope or capsid

Describe the function of spikes in a virus particle.

• bind to host cell receptors

• help the virus enter the cell

• act as key targets for the immune response

Define “bacteriophage”

viruses that infect and destroy bacteria

Describe the lytic cycle of a bacteriophage.

1. Attachment: phage attaches to the surface of the host

2. Penetration: the viral DNA enters the host cell

3. Biosynthesis: phage DNA replicates and phage proteins are made 

4. Maturation: new phage particles are assembled

5. Release: the cell lyses, releasing the newly made phages 

Describe the lysogenic cycle of a bacteriophage. 

1. The page infects a cell

2. The phage DNA becomes incorporated into the host genome

3. The cell divides, and prophage DNA is passes on to daughter cells

4. Under stressful conditions, the prophage DNA is excised from the bacterial chromosome and enters the lytic cycle

5. The phage DNA replicates and phage proteins are made

6. New phage particles are assembled 

7. The cell lyses, releasing the newly made phages

Define “colony”

a visible mass of cells consisting of only the original cell type

Define “colony forming unit” (CFU)

A CFU is a unit used to estimate the number of living microorganisms capable of forming colonies in a sample

State the purpose of streaking for isolation.

to obtain pure cultures from a mixed sample of microorganisms

Discuss the key reasons why agar is an ideal solidifying agent for culturing media.

• Bacteria can’t digest it

• It melts and solidifies at convenient temperatures

• It remains solid at incubation temps

• It is clear and non-toxic

• It has the right texture

Explain selective medium

the composition of the medium selects for the growth of some microbes and prevents the growth of others 

Example: there are selective media that allow gram negative microbes to grow, but not gram positive microbes 

Explain differential medium

the composition of the medium creates a visual difference between various microbes in a mixed sample that can aid in identification

• results in colonies that differ in color or change in the color of the medium

Explain how the composition of mannitol salt agar (MSA) makes it selective. 

Selective: high NaCl concentration

• staphylococcus species will grow because they are salt-tolerent

• all other species will die due to plasmolysis

Explain how the composition of mannitol salt agar (MSA) makes it differential.

Differential: mannitol (sugar) and pH indicator phenol red

• Only staph. aureus can ferment mannitol, produce acid, and turn the media yellow

• All other staph species cannot ferment mannitol, no acid is produced, and the media stays red

Explain how the composition of MacConkey agar (MAC) makes it selective.

Selective: crystal violet and bile salts

- Gram + species cannot undergo cell division, so no growth will be observed

- Gram - species can undergo cell division, so growth will be observed

Explain how the composition of MacConkey agar (MAC) makes it differential.

Differential: lactose and ph indicator (neutral red)

Lactose fermentation + species: can ferment lactose, produce acid, turn the media hot pink

Lactose fermentation - species: cannot ferment lactose, do not produce acid, media stay purple