Why is molten agar kept in a 50°C water bath until it is ready to be used?

to prevent it from solidifying while staying cool enough to safely add heat-sensitive ingredients or microbes.

When performing the streak-plate technique, why is it necessary to run the inoculating loop over the first quadrant before streaking the second quadrant?

To gradually dilute the bacteria and help isolate individual colonies

State one possible disadvantage of using the pour plate technique to isolate bacteria?

Some of the bacteria might kill resulting to a decrease of the number of viable colonies

Do you think there are pathogenic microorganisms that have yet to be identified? Explain your answer

Yes, there are likely pathogenic microorganisms yet to be identified, as new diseases emerge and some microbes are hard to detect or grow in labs.

Is it possible to study microbes without them being pure cultures? If so, give an example of how this could be done

Yes, a microbe can be sturdy without pure culture that'll depend on the environment and the microbes

Explain the difference between a direct and an indirect microbial count.

• direct: Placing a known sample on a calibrated called hemocytometers and view under the microscope
• indirect: by using a spectrophotometer to determine the turbidity and absence of light.

Why is it necessary to prepare dilutions when determining the number of bacterial cells in a sample?

For accurate count of bacteria or because it is help reduce the concentration to a countable range

With increasing dilutions, what happens to the number of microbial cells?

the microbial cell decrease because dilutions reduce the concentration of cell in a sample

Explain how to prepare a 10-1 dilution of E. coli Include the amount (in ml) of water and E. coli you would add

To prepare a 10^-1 dilution of E. coli, you would mix 1 ml of E. coli culture with 9 ml of sterile water. This results in a 1:10 dilution, where the original concentration is reduced by a factor of 10.

If 0.1 ml of a 10-2 dilution was added to 9.9 ml of water, what dilution would result?

10 ^ -3 dilution 10 mL

If 250 colonies are seen on a plate labeled 10-5, how many colonies would you expect to see on a plate labeled 10-6?

25 colonies of a 10 ^ -6

Is a viable plate count a direct or indirect method of measuring the number of cells in a bacterial sample? Explain your answer.

It's a direct method because it only count the living cells that are able to grow into visible colonies

Name the instrument you used to determine turbidity and explain how it measures the amount of growth in a bacterial sample.

Spectrophotometer by detecting how much light passes through a bacteria sample. Less light indicate more growth

Which viable plate count procedure, pour plate or spread plate, resulted in a lower number of CFU/ml? Explain why.

Pour plate method always result in lower CFU/ml because some of the bacteria may be trapped or killed by the hot molten agar

If 75 colonies were found on a 10-5 plate, how many CFU/ml were in the original culture?

75 multiply 10^-5 = 7.5 multiply by 10^-6 = 7.5 million CFU/ml

You are given an unknown organism that might be infectious or lethal. Describe the technique you would use to determine this microbe's growth rate. Provide an explanation for why you chose this technique.

turbidity with a spectrophotometer because it is quicker easy and non-destructive

The process by which bacterial cells divide is known as binary fission. Eukaryotic cells divide by mitosis. Explain the differences between binary fission and mitosis, including the cells produced as a result of these processes.

Binary fission is a simple cell divisions in bacteria that makes two identical cell while mitosis is a more complex process in eukaryotic cells that also produce two identical cells

Name a bacterium associated with contaminating ground beef.

Escherichia coli O175:H7

Name a bacterium associated with contaminating chicken

Salmonella and Campylobacter

Name two methods commonly used to decrease the number of bacteria associated with food samples.

heat treatment and refrigeration

Prior to entering a processing plant, beef can be contaminated. What is the source of this contamination?

Animal feces, dirty hides, contaminated water, unsanitary handling drink slaughter and transport.

Name two other food samples that could be tested for their microbial content.

Milk and lettuce

Name one way fresh vegetables can become contaminated with bacteria capable of causing food poisoning prior to entering markets.

through contact with contamination with water or reducing infection

Why are hands washed periodically during food preparation?

to prevent the transfer of harmful bacteria, virus

Name one source of food contamination during its preparation besides human contact.

contamination utensils or equipment

Some historians have theorized that part of the British Empire's success in the nineteenth century and early twentieth century was due to the fact that British colonists drank tea and scotch, and they seldom became ill. Based on this statement, why do you think they didn't become ill when they were serving in the overseas countries?

stronge immune system

Many types of food poisoning, such as staphylococcal food poisoning, are not usually treated with antibiotics. Why do you think this is so?

Because some of them are antibiotic resistance which make it harder to treat

In 2006, there were two major food poisoning incidents in the United States. More than 500 Americans became ill and at least 10 died as the result of eating spinach. What was the pathogen causing this food poisoning and how did the spinach become
contaminated? What are some ways to prevent this type of food poisoning outbreak in the future?

• E. coli O157: H7
• animal feces
• contaminate water
• improve hand hygiene
• monitoring and testing etc

Explain the difference between an antiseptic and a disinfectant?

antiseptic chemical substance used on living things, while disinfectant a chemical substance use on non living things.

Name 2 examples of antiseptics.

• hydrogen peroxide
• alcohol
• iodine
• betadine

Explain the difference between a microcidal and a microstatic agent?

The difference is microcidal is used to kill microbe while microstatic used to stop microbes growth.

What is a zone of inhibition?

After incubations if an antiseptic or disinfectant inhibit the microbial growth of a microorganisms an area of no growth will happen around the disk and it's called zone of inhibitions

How is the size of the zone of inhibition related to the effectiveness of an antimicrobial agent?

it all the dependent on the size for example, the larger the size the more effective of a particular agent

You are asked to design an antibacterial agent to clean kitchen countertops. Would you make this agent (a) more effective against Gram-positives, (b) more effective against Gram-negatives, or (c) effective against both Gram-positives and Gram-negatives?
Provide an explanation for the choice (a, b, or c) you selected

both of them

Name 2 structures bacteria may possess that make them more resistant to antiseptics and/or disinfectants

spore, capsule

An operating room physician recommends periodically changing the hand soap used in the operating room. Is this recommendation valid? Explain your answer

yes, because it could prevent bacteria from developing a resistance to the soap

Recently, there have been a number of incidents where travelers have become seriously ill from microbial infections while aboard cruise ships. Suppose you were asked to help resolve such continuing problems. What specific recommendations would you offer the cruise ship company and its employees?

• frequent monitoring and testing food
• regular testing and treatment of water
• strict hygiene practice
• proper cleaning and disinfecting

Hexachlorophene was once an over-the-counter antiseptic. However, now a prescription is required for hexachlorophene solutions with concentrations greater than 3%. Explain
Why do you think this requirement was initiated?

safety to concern because it could lead to neurological damage to infant or the skins

Are there other ways to combat disease besides using antibiotics? Explain your answer.

Vaccination, improve head hygiene, antiseptic

What is a pyrimidine dimer?

Double bonds that form between adjacent pyrimidine in a strand DNA

Besides decrease in the number of cells, what happens to Serratia marcescens when exposed to ultraviolet light?

The pigment may also be affected

Which organism, Bacillus subtilis or Escherichia coli, would be less affected by exposure to ultraviolet light? Explain your answer

Bacillus subtilis will be affected by exposure to ultraviolet than E. coli because it can form endospore

Explain how ultraviolet light inhibits microbial growth.

By causing formations of pyrimidine dimers in DNA

Name one object to which UV light is applied for sterilization?

Laboratory workbench or biosafety cabinet

Ultra-pasteurized milk has been pasteurized as well as treated with ultraviolet light. State a possible benefit for using both pasteurization and UV light.

Is enhance microbial safety

Why is ultraviolet light used on inanimate objects to kill microbes and not on human skin?

Because it can harm human cells, leading to skin burns and eye damage, it increase risk of skin cancer

Provide an explanation as to why ultraviolet light does not kill all bacteria.

Because some might have protective feature like endospore

Describe other methods used in hospitals and the food industry to inhibit microbial growth.

autocleaving, refrigeration and/or freezing, radiation filtration, aseptic technique, etc.

A new method to treat drinking water has recently been developed that involves wells that have ultraviolet lights installed in them. Explain both the advantages and disadvantages of this new technique.

• Advantage helping kill microbes before chemicals
• disadvantage no lasting disinfectant effect

Explain why lysozyme is part of nonspecific resistance

Because it attacks and break down bacteria cell wall in a general way, protecting the body against a wide range of bacteria without targeting specific pathogens

Name one source of lysozyme in the human body.

Tears, saliva, mucus

Explain why lysozyme is more effective against Staphylococcus aureus than Escherichia coli ?

Because it's a gram-positive bacterium with an exposed peptidoglycan layer that lysozyme can easily break down, while E. coli is a gram negative and has an outer membrane that protect its peptidoglycan layer from lysozyme

What is an antibiotic?

Chemical substance by another organism to use against another organism like penicillin

what is broad-spectrum antimicrobial ?

Chemical substances that work to kill multiple different microorganism groups, such as Betadine, alcohol

What is narrow spectrum ?

Chemical substance that only work in specific microorganisms for example penicillin, only work in peptidoglycan-positive bacteria

what is ionizing ?

Wavelength= any type of energy that can knock electrons off atoms or molecules, forming ions.

what is non- ionizing ?

wavelength, causes pyrimidine dimers in DNA by inducing covalent bonding between adjacent thymine . example wavelenght

Which microorganisms are commonly found on the skin?

Normal skin bacteria are Gram-positive bacteria that normally don't cause diseases however, when it getting inside the body, it can cause disease.

why do we use catalase?

The catalase test is used to determine if bacteria produce the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen, causing the formation of bubbles, and helping identify if the bacteria are aerobic or facultative anaerobic.

The bubbles are the key indicator of a positive catalase test

why do we use dnase test?

We use the DNase test to see if bacteria produce the enzyme DNase, which breaks down DNA; after adding hydrochloric acid, a clear zone around growth means the bacteria produced DNase, while a foggy appearance means they didn't.

why do we use blood agar?

Blood agar is enriched and differential; it is enriched with 3% sheep blood. In blood agar we are looking for hemolysis. hemolysis mean breaking down blood .

Why do we use mannitol salt agar?

We use Mannitol Salt Agar (MSA) to test for growth of gram-positive bacteria and mannitol fermentation; it contains the pH indicator phenol red, which is red at pH 7, and turns yellow if fermentation occurs.

Why do we use the coagulation test?

We use the coagulase test to detect the presence of the coagulase enzyme, which causes blood to clot.

Why is HCI used to test for Dnase activity?

HCl is used in the DNase test because it precipitates DNA, making the agar look cloudy;

Explain how DNase-producing bacteria damage host cells.

DNase-producing bacteria damage host cells by breaking down DNA from destroyed cells, which helps the bacteria spread through tissues

Name the medium used to test for coagulase activity

rabbit plasma

Describe the appearance of coagulase positive organisms in this medium

a thick or solid appearance instead of remaining liquid.

Why does hydrogen peroxide bubble when it's added to cut on the skin

Hydrogen peroxide bubbles on a cut because it reacts with an enzyme called catalase, making oxygen gas, which forms the bubbles.

Name the enzyme that break down hydrogen peroxide into non-toxic product

catalase

Can anaerobe produce catalase

Most anaerobes do not make catalase because they don’t live with oxygen