Chapter 13 Micro Practice

Sterilization

The process by which all living cells, spores, & viruses on an object are destroyed

Disinfection

The killing/removal of disease-producing organisms from inanimate surfaces

Pathogens are killed, but other microbes may survive

Antisepsis

aka degermation

the killing/removal of disease-producing organisms from living tissues

Pathogens are killed, but other microbes may survive

Sanitization

Reduces the microbial population to safe levels & usually involves cleaning an object as well as disinfection.

Bactericidal

Having the ability to kill bacterial cells

Bacteriostatic

Having the ability to inhibit the growth of bacterial cells

Germ

A microorganism that causes disease

Germicide

A chemical that kills germs

Able to kill cells but not spores

Decimal Reduction Time

The length of time it takes for a treatment to kill 90% of a microbial population, & hence a measure of the efficacy of the treatment

___ is the process by which a chemical kills disease-producing microbes on inanimate surfaces.

Disinfection

The effectiveness of a chemical agent is determined by the ___.

Decimal reduction time

Agent A acting on Staphylococcus aureus has a D-value of 5 minutes. If the population of microbes starts at a cell density of 5 × 10⁸ CFUs/ml, how many viable cells will remain after 15 minutes?

5 × 10^5 CFUs/ml

Pasteurization

The heating of food at a temperature & time combination that will kill pathogens such as Mycobacterium tuberculosis.

Lyophilization

Aka freeze-drying

The removal of water from food, by freezing under vacuum to limit microbial growth

Laminar Flow Biological Safety Cabinet

An air filtration appliance that removes pathogenic microbes from within the cabinet

Which of the following processes ensures that all living cells, spores, & viruses on an object are completely destroyed?

Sterilzation

A chemical agent that inhibits the growth of bacteria without necessarily killing them is classified as ___.

Germicidal

What does the decimal reduction time (D-value) represent in microbial control?

The time required to kill 90% of the population

Standard autoclave conditions for sterilizing most materials are:

121C at 15 psi for 20 minutes

Why is the 12D treatment crucial in the commercial canning industry?

To reduce the population of Clostridium botulinum spores by 12 logs

The primary goal of pasteurization is to:

Kill Coxiella burnetii & other pathogens without affecting food quality

Which physical control method involves freezing a culture at low temperatures and then using a vacuum to remove water via sublimation?

Lyophilization

To remove viruses from a liquid solution, a micropore filter would typically require a pore size of:

0.02 μm

Laminar flow biological safety cabinets use HEPA filters to protect lab workers. These filters remove particles as small as:

0.3 μm

Which of the following is a major limitation of using ultraviolet (UV) light for sterilization?

It has very poor penetrating power

Microbial sensitivity to irradiation is largely dependent on which factor?

The amount of DNA in the genome

The presence of 'organic load' (e.g., blood, feces) affects disinfection by:

Binding to the disinfectant and reducing its efficacy

Which test is currently used to evaluate the effectiveness of a disinfectant by drying organisms onto a surface and exposing them to different dilutions?

Use-dilution test

Why is 70% ethanol generally more effective than 100% ethanol at killing microbes?

Water is required to help the ethanol penetrate the cell and denature proteins

A hospital needs to sterilize heat-sensitive plastic syringes and Petri dishes. Which method is most appropriate?

Ethylene oxide gas sterilization

The concept of 'selective toxicity' in antibiotic therapy refers to:

The ability of a drug to inhibit a pathogen without harming the host's cells

Metronidazole is a prodrug that is specifically effective against:

Anaerobic bacteria and certain protozoa

How do quinolone antibiotics, such as ciprofloxacin, kill bacteria?

By inactivating DNA gyrase and stopping replication

Aminoglycosides like gentamicin target the bacterial ribosome to cause:

Misreading of the mRNA

Tetracyclines inhibit protein synthesis by which specific mechanism?

Preventing aminoacyl-tRNA from entering the A site of the ribosome

Macrolides like erythromycin are effective because they bind to the ___.

50S ribosomal subunit to inhibit translocation

Polymyxin B is primarily used topically because ___.

It can damage human cell membranes as well as bacterial ones

Empirical therapy is best defined as ___.

Using a broad-spectrum antibiotic based on clinical symptoms before a pathogen is identified

A bactericidal agent is distinguished from a bacteriostatic agent by its ability to ___.

Directly kill the bacteria

Lyophilization

A method of freeze-drying that permits living cultures to remain viable for years

Gamma irradiation

A process that destroys microorganisms by breaking down their DNA and cellular structure

Results in a longer shelf life

Pasteurization conditions are designed to kill which of the following microbes from milk?

Coxiella burnetii

You are developing a liquid food supplement for populations of developing nations after natural disasters. It must have a long shelf life without refrigeration. Which microbial control technique would best accomplish your goal?

Gamma irradiation

Which process is defined as the destruction of all living cells, spores, and viruses on an object?

Sterilization

What is the primary difference between a disinfectant and an antiseptic?

Disinfectants are used on inanimate surfaces, while antiseptics are used on living tissue.

If an antimicrobial agent merely inhibits the growth of bacteria rather than killing them, it is described as:

Bacteriostatic

Which of the following factors would likely INCREASE the time required to achieve sterilization?

The presence of organic material like blood or feces

The D-value (decimal reduction time) represents the time required to kill what percentage of a microbial population?

90%

What are the standard conditions for a steam autoclave to ensure the destruction of endospores?

121C at 15 psi for 20 minutes

Why is 70% ethanol often more effective than 100% ethanol for disinfection?

Water is needed to help ethanol penetrate the cell and dehydrate proteins.

The 12D treatment used in the canning industry is specifically designed to eliminate the spores of which organism?

Clostridium botulinum

Which pasteurization method involves heating milk to $72^{\circ}C$ for only 15 seconds?

High-temperature short-time (HTST)

Which technique uses a vacuum to cause frozen water to transition directly from a solid to a gas, preserving microbial cultures as a powder?

Lyophilization

Laminar flow biological safety cabinets use HEPA filters to remove what percentage of airborne particles $0.3\ \mu m$ or larger?

More than 99.9%

What is the main limitation of Ultraviolet (UV) light for sterilization?

It does not penetrate solids or liquids well.

Which form of radiation is most effective at killing microbes by breaking the DNA backbone?

Gamma rays and X-rays

According to the text, which of the following is most resistant to approved doses of irradiation for food?

Prions

Which chemical agent is used to decontaminate skin before surgery and is an example of an iodophor?

Betadine

What is the primary mode of action for quaternary ammonium compounds (Quats)?

Disruption of cell membranes

Which gas is used to sterilize disposable plasticware like Petri dishes and syringes that would melt in an autoclave?

Ethylene oxide

Why are metallic copper surfaces being incorporated into hospitals?

Copper ions trigger the lysis of bacterial membranes on contact.

In the context of antibiotic therapy, what does 'selective toxicity' mean?

The drug inhibits the pathogen but has little to no effect on the host.

The lowest concentration of a drug that prevents the growth of an organism is called the:

Minimum inhibitory concentration (MIC)

A drug is considered to have a bactericidal mode of action if its MBC is no more than how many times its MIC?

4

In a Kirby-Bauer disk susceptibility test, what does a larger zone of inhibition indicate?

The bacteria are more sensitive to the antibiotic.

Which of the following antibiotics targets the bacterial cell wall by inhibiting the enzymes that cross-link peptidoglycan chains?

Penicillin

Why is Vancomycin often considered a 'drug of last resort'?

It is effective against penicillin-resistant bacteria like MRSA.

Gram-negative bacteria are generally more resistant to many antibiotics (like Penicillin G) because of which structure?

The outer membrane

Metronidazole is a 'prodrug' that is particularly effective against which type of organisms?

Anaerobic bacteria

Which of the following antibiotics is known to be bactericidal despite being a protein synthesis inhibitor?

Aminoglycosides

A chemical agent that can kill mycobacteria and spores but not prions is considered a(n) ___.

High-level disinfectant

Which of the following agents is effective for sterilizing plasticware such as Petri plates?

Ethylene oxide gas

Selective toxicity

The ability of a drug, at a given dose, to harm a pathogen without harming its host.

Spectrum of Activity

The group of pathogens for which an antimicrobial agent is effective.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of a drug that will prevent the growth of an organism.

Minimum Bactericidal Concentration (MBC)

The lowest concentration of an antibiotic that kills the test cells.

Kirby-Bauer Assay

A method for determining antibiotic susceptibility. Antibiotic-impregnated disks are placed on an agar plate whose surface has been confluently inoculated with a test organism. The antibiotic diffuses away from the disk and inhibits growth of susceptible bacteria. The width of the inhibitory zone is proportional to the susceptibility of the organism.

True or False

In reference to the Kirby-Bauer Assay, the width of the inhibitory zone is disproportional to the susceptibility of the organism.

False

Therapeutic Dose

The minimum dose of an antibiotic or antimicrobial per kilogram of body weight that stops the growth of a pathogen in a patient.

Toxic Dose

The maximum dose of an antibiotic or antimicrobial that is tolerated by a patient.

Chemotherapeutic Index

The ratio of the toxic dose to the therapeutic dose

Synergistic

Referring to antibiotics used in combinations whose mechanisms of action complement one another and hence intensify their effectiveness.

Antagonistic

Referring to antibiotics used in combinations whose mechanisms of action interfere with one another and hence diminish their effectiveness.

A series of culture tubes containing dilutions of an antibiotic are inoculated with a bacterial pathogen. Tube 1 has the highest concentration of drug, and tube 6 has the lowest. Growth occurs in tubes 5 and 6; no growth is seen in tubes 1–4. What can we conclude from this serial dilution?

The drug concentration in tube 4 is the MIC.

Which of the following antibiotic classes and host targets are matched correctly?

Aminoglycoside / 30S ribosome

Which of the following antibiotic classes and host targets are matched correctly?

Penicillin / cell wall

Which of the following antibiotic classes and host targets are matched correctly?

Macrolide / 50S ribosome

Which of the following antibiotic classes and host targets are matched correctly?

Tetracycline / 30S ribosome

Which of the following antibiotic classes and host targets are matched correctly?

Quinolone / DNA gyrase & topoisomerase IV

What is the primary reason why there are fewer antiviral drugs compared to antibacterial drugs?

Viruses use host cell machinery, making selective toxicity difficult to achieve.

Which antiviral drug is a neuraminidase inhibitor used to prevent the release of influenza viruses from host cells?

Oseltamivir (Tamiflu)

Which of the following targets cell wall synthesis?

Penicillin, cephalosporin, bacitracin, vancomycin

Which of the following targets cell membrane integrity?

Polymyxin, gramicidin (antibacterial) Amphotericin, imidazoles (antifungal)

Which of the following targets mycolic acid synthesis?

Isoniazid (Mycobacterium tuberculosis)

Which of the following targets DNA replication and integrity?

Quinolones, metronidazole, nitrofurantoin, some antiviral compounds

Which of the following targets transcription?

Rifampin, fidaxomicin (Clostridioides difficile)

Which of the following targets protein synthesis?

Chloramphenicol, tetracycline, aminoglycoside, macrolide, glycosamide

Which of the following targets intermediary metabolism?

Sulfonamides, trimethoprim (inhibits folic acid synthesis)

Bedaquiline (inhibits ATP synthase in M. tuberculosis)

Platensimycin (inhibits bacterial fatty acid synthesis)

Penicillin-Binding Proteins (PBPs)

Any of a group of bacterial proteins involved in cell wall synthesis that are the target of penicillin or other beta-lactam antibiotics.

Cephalosporin

Any of a class of semisynthetic beta-lactam antibiotics that are used to fight penicillin-resistant microbes