Micro unit 6

Define culture media. What is its purpose? Why is it important for culture media to be sterile?

Nutrient material prepared for microbial growth in the labatory. Use to differentiate /identify microorganisms. Avoid the contaminationof other microorganism, thuspreventing from miss identification

Oxygen is so pervasive in the environment that it would be very difficult for a microbe to always avoid physical contact with it. What, therefore, is the most obvious way for a microbe to avoid damage?

Produce enzymes to neutralize them against toxicity

Bacteria require nitrogen for the synthesis of

Protein

An organism that you are studying grows at 4°C and at 25°C. However, it grows best at 20°C. This organism would be classified as a _

Psychrotroph

Clostridium can be cultured in an anaerobic incubator or in the presence of atmospheric oxygen if thioglycolate is added to the nutrient broth. The addition of thioglycolate makes the medium

Reduced

Which of the following statements about culture media are true

Reducing media are complex media containing chemicals, such as thioglycolate, that combine with oxygen, creating an anaerobic environment. Complex media are formulated from nutrient-rich whole food sources whose exact ingredients may not be known. A chemically defined medium is specifically formulated, and each ingredient is known.

All of the following can be used to preserve bacterial cultures.

Refrigiration, lyophilisation ( freezing-dry), freezing auickly and storing at -70C

A medium containing chemicals to inhibit the growth of gram-positive bacteria would be called

Selective

A medium containing lauryl sulfate inhibits growth of gram-positive bacteria. This medium is __

Selective

Compare the oxygen requirements of 1.obligate aerobes, 2.facultative anaerobes, 3.obligate anaerobes, and 4.microaerophiles. 5. Aerotolerants anareobes

1. Need O2 to grow. 2. Can grow with or without O2 3. Stop growing in prsence of O2, 4. Grow where there is less O2 present thus need small amount of O2 to grow. 5. O2 does not affect there growth.

An organism that has peroxidase and superoxide dismutase but lacks catalase is most likely an a.aerobe. b.aerotolerant anaerobe. c.obligate anaerobe.

B aerotolerant anareobe

Which of the following types of media would not be used to culture aerobes? a.selective media b.reducing media c.enrichment media d.differential media e.complex media

B reducing media

Why is it critical to prevent biofilm infections in the hospital?

Because they are related to 70% of all nosocomianl infection in the hospital.

Why is the prevention of biofilms important in a health care environment?

Biofilm is responsable of 70% of nosocomial infection in hospital. Cystic fibrosis, native valve endocarditis, otitis media, periodontitis, and chronic prostatitis all appear to be caused by biofilm-associated microorganisms

Describe the formation of biofilms and their potential for causing infection

Biofilms are a natural structure formed by microbes in the environment. They stick to healthy surfaces and will prevent nutrients to go through to keep it healthy. It will block any immune response and antibiotics because of the slime wall. causing problems with dental plaque, catheters, and other indwelling devices. Pseudomonas spp. is an example that forms biofilms.

Martin Lewis agar is an enriched media (containing heated blood) designed for the growth of Neisseria gonorrhea. Antibiotics are added to suppress the growth of normal microbiota that may be found in patient specimens, yet permit the growth of Neisseria gonorrhea. This medium would best be described as

Selective media

Clostridium and Streptococcus are both catalase-negative. Streptococcus grows by fermentation. Why is Clostridium killed by oxygen, whereas Streptococcus is not?

Clostridium lacks cytochromes, enzymes, catalase, and peroxidase. It's a strict/obligate anaerobe. It dies from oxygen, uses fermentation, turns lactic acid into energy. Streptococcus is aerobic, also lacks catalase, has peroxidase which neutralizes superoxide and hydrogen peroxide and allows them to survive in oxygen environments.

A prokaryotic cell hitched a ride to Earth on a space shuttle from some unknown planet. The organism is a psychrophile, an obligate halophile, and an obligate aerobe. Based on the characteristics of the microbe, describe the planet

Cold, salty, aerobic

A culture medium consisting of agar, peptone, and beef heart extract is a/an

Complex medium

If bacterial cells were given a sulfur source containing radioactive sulfur (35S) in their culture media, in what molecules would the 35S be found in the cells?

Cysteine residues have sulfhydryl groups and proteins synthesized with cysteine residues are likely to contain 35S provided the bacteria can use the Sulfur to make cysteine.

What is a selective medium? Give an example.

Selective media generally selects for the growth of a desired organism, stopping the growth of or altogether killing non-desired

Bacteria that spoil food in the refrigerator are most likely

psychrotrophs

Martian soil is inoculated into a glucose-containing medium. The radioactive form of carbon, 14C, is used in the glucose. After incubation for five days, which of the following would provide evidence suggesting that there is life on Mars?

radioactive carbon dioxide

Blood agar used to observe hemolysis or clearing around Streptococcus pyogenes colonies is an example of a/an

Differential media

Members of the genus Clostridium display the following properties: Gram-positive bacilli. Endospore formation. Anaerobic growth. Which of the following would be appropriate for the culture of members of this genus?

both a blood agar plate in an anaerobe jar and sodium thioglycolate broth

Which of the following is a step in binary fission

cross-wall formation, invagination of the plasma membrane, cell elongation, replication of chromosomal DNA

They match

extreme halophiles; 30% salt, acidophiles; low pH, psychrophiles; 0°C, extreme thermophiles; 100°C

What is a reducing media?

...

If a single bacterium replicated every 30 minutes, how many bacteria would be present in 2 hours?

16

If 52 bacterial colonies grow on a nutrient agar plate inoculated with 1 ml of a 1:1000 dilution of hamburger, how many bacteria are in the original hamburger sample?

52,000 bacteria per g

Assume that you inoculated potato salad with 10 bacterial cells and stored it at room temperature. After 3 hours, there are 640 cells. How many generations did the cells go through?

6 generations

Differentiate complex and chemically defined media.

A chemically defined medium is one in which the exact chemical composition is known. A complex medium is one in which the exact chemical composition is not known.

Define colony

A group of descendant of an original cell

What is optimum growth temperature?

temperature at which a specific organism exhibits maximum growth and reproduction. Bacteria from the human gut grow well at body temperature (37 C) but bacteria from plants may be killed at that temperature.

What is quorum sensing?

the ability of bacteria in a biofilm to communicate with each other and coordinate their activities

What is the purpose of performing serial dilutions before plating to determine growth?

A serial dilution is a series of sequential dilutions used to reduce a dense culture of cells to a more usable concentration. Each dilution will reduce the concentration of bacteria by a specific amount. So, by calculating the total dilution over the entire series, it is possible to know how many bacteria you started with. The best way to fully grasp serial dilutions is to try out the procedure yourself.

What is an acidophile? What pH range supports the growth of most microorganisms?

Acidophilic organisms are those that thrive under highly acidic conditions ( pH 0.1-pH5.4)

The term trace elements refers to a.the elements CHONPS. b.vitamins. c.nitrogen, phosphorus, and sulfur. d.small mineral requirements. e.toxic substances.

D small mineral requirements

The following steps occur during binary fission. Which step occurs before the others?

DNA replication

What is a reducing media?

Is purpuse is to grow obligated anareobes

What is the unit of measurement of bacterial population growth?

Plate count

Distinguish chemically defined and complex media.

A complex medium is one in which the exact chemical composition varies slightly from batch to batch. Extracts - beef or yeast. Provides vitamins and minerals. Large proteins are not used directly by most bacteria; peptones are partially digested proteins (acid or enzymatically digested) Supplies energy, C, N, and S. May be used as nutrient broth or nutrient agar. A Chemically defined medium is one in which the exact chemical composition is known.

How is agar used?

Agar media are usually contained in test tubes or Petri dishes. The test tubes: slants when their contents are allowed to solidify with the tube held at an angle so that a large surface area for growth is available. When the agar solidifies in a vertical tube: deep. Petri dishes, named for their inventor, are shallow dishes with a lid that nests over the bottom to prevent contamination; when filled, they are called Petri (or culture) plates.

Outline the structure of a biofilm. What is the advantage of forming a biofilm?

Biofilms reside in a matrix made up primarily of polysaccharides, but also containing DNA and proteins, called slime. is a complex polymer containing many times its dry weight in water Within a biofilm community, the bacteria are able to share nutrients and are sheltered from harmful factors in the environment, such as desiccation, antibiotics, and the body's immune system. The close proximity of microorganisms within a biofilm might also have the advantage of facilitating the transfer of genetic information by, for example, conjugation.

A bacterial medium contains chemicals that inhibit gram-positive bacteria and indicators so that bacteria that ferment lactose produce red colonies, and bacteria that do not ferment lactose produce colorless colonies. Such a medium is called

Both selective and differencial

Which of the following is not a characteristic of biofilms? a.antibiotic resistance b.hydrogel c.iron deficiency d.quorum sensing

C. Iron deficiency

Assume you inoculated 100 facultatively anaerobic cells onto nutrient agar and incubated the plate aerobically. You then inoculated 100 cells of the same species onto nutrient agar and incubated the second plate anaerobically. After incubation for 24 hours, you should have a.more colonies on the aerobic plate. b.more colonies on the anaerobic plate. c.the same number of colonies on both plates.

C.the same number f cooonues on both plates

List the chemical requirements for the growth of microorganisms.

Carbon, Nitrogn, Sulfur, Phosphorus, other elements (K, Mg, Ca), O2, trace elements (iron, copper, zinc molybdenum )

During the lag phase

Cell are engaged in intense enzymatic activity

During log phase, bacteria are

Dividing at the fastest possible rate

Which one of the following temperatures would most likely kill a mesophile? a.−50°C b.0°C c.9°C d.37°C e.60°C

E. 60°C

An organism that grows both in the presence and the absence of oxygen and uses oxygen when it is available is called a/an

Facultative anareobe

You are testing the number of coliforms in a drinking water source. Which of the following test methods would be best to use?

Filtration

Which of the following situations will lead to food being in the "danger zone," with the potential for food poisoning?

Five pounds of homemade potato salad, refrigerated overnight in one huge bowl, and served without any cooling on a warm summer day.

...

Generation times is the time required for a cell to divide andnits population to double. It is calculated during the exponential phase of growth. Time measurements are in hours for bacteria with short generation times.

What is the effect of osmotic pressure on growth?

High osmotic pressures have the effect of removing necessary water from a cell. The growth of the cell is inhibited as the plasma membrane pulls away from the cell wall. Can be used to preserve foods.

Describe the candle jar method used to grow some microorganisms.

In a candle jar, the top is covered and a candle is lit to to consume the oxygen. When the candle stops burning, it means the level of oxygen has lowered and there is a higher concentration of CO2, which microbes grow better in. (This environment resembles the intestinal tract and respiratory tract, where pathogens grow)

What are the four phases of bacterial growth? What is happening in each phase?

Lag phase: individual organism grow in size, minimal or no cell division, period of ajustment to new condition. Log phase: most rapid growth, # cell produce greater then # cell dying, cell more susceptible to adverse environmental factors ( antbx, radiation). Stationary phase: cell produce = cell dying, pop begin to stabilize. Death phase: pop begin to decrease at log rate, cell lose abioity to divide, only a few remain alive

What phase of the cell cycle would be extended in an industrial application designed to maximize yield?

Log phase

All of the following are true of the plate count method

Measures numbers of viable cells, dependable, most commonly use for assay of bacterial cell number, involves cell plating and growth

Two culture media were inoculated with four different bacteria. After incubation, the following results were obtained: Organism medium 1 medium 2 Escherichia coli red colonies No growth Staphylococcus aureus no growth Growth Staphylococcus epidermidis no growth Growth Salmonella enterica colorless colonis no growth

Medium 1 is: both selective and differential media Medium 2 is: selective

Most laboratory media contain a fermentable carbohydrate and peptone because the majority of bacteria require carbon, nitrogen, and energy sources in these forms. How are these three needs met by glucose-minimal salts medium?

Minimal Media contains the essentials for bacterial species to grow. The media is often used to define if a particular microbial species is a heterotroph, namely an organism that does not have any nutritional requirements beyond core sources of carbon (sugars) and nitrogen (to synthesize amino acids and nucleic acid bases).

Which bacterium would theoretically be more likely to grow at refrigerator temperatures: a human intestinal pathogen or a soilborne plant pathogen?

Mold mycelium, A bacterium that is used to live inside the human gut, will have an optimum temperature of 37 degrees Celcius (about 100 degrees F). It will probably not grow at 4 degrees C, the temperature inside a fridge. A soil bacterium however, is more adapted to grow at much lower temperatures. It will probably survive much better inside a fridge.

Describe the special culture technique used to grow Mycobacterium leprae

Mycobacterium leprae is grown in armadillos because of their low temperature.

Could Louis Pasteur, in the 1800s, have grown rabies viruses in cell culture instead of in living animals

No he would have had to produce a whole new technology on his own, one that took 50 or 60 years (at least) of experimenting to perfec

Niacin, when added to a medium, would be considered a/a

Organic growth factor

List the three physical requirements for the growth of microorganisms

Osmostic pressure, Temperature, pH

Nitrogen and phosphorus added to beaches following an oil spill encourage the growth of natural oil-degrading bacteria. Explain why the bacteria do not grow if nitrogen and phosphorus are not added.

Petroleum can meet the carbon and energy requirements for an oil-degrading bacterium; however, nitrogen and phosphate are usually not available in large quantities. Nitrogen and phosphate are essential for making proteins, phospholipids, nucleic acids, and ATP

Given a shallow pan and a deep pot with the same volume, which would cool faster? Why?

Shallow pan because there is less surface to cool down.

List four oxygen intermediates that can be toxic for some microorganisms, and describe their mode of action.

Singlet oxygen: extremely reactive, present in phagocytotic cell. superoxude free radicalSOD: extremely toxic and reactive, all aerobic microbes need to produce some to get rid of them hydrogen peroxide: peroxide ion is toxic and is the active ingreadiant of several antimicrobial

Before bacteria can be identified, mixed cultures must be separated. What technique is used to separate bacteria and get individual colonies?

Streak plate

To look for bacteria that degrade petroleum, a culture medium containing crude oil, sodium nitrate, phosphate buffer, and magnesium sulfate is inoculated with soil. This medium is

Sélective

Why are carbon, nitrogen, sulphur, and phosphorus important for growth?

They are important forbynthesis of cell material. Nitrogen is essentiel for the synthesis f protein; DNA and RNA. Sulfur is important for the synthesis of amino acid like cysteine, thiamine vitamine; biotin vitamin; methionine. Phosphorus is important component of nucleic acid and phospholipids

An unknown culture is assayed via the plate count method. After dilution of cells and incubation, no colonies are observed. Which of the following is not a possible explanation?

The bacteria were streaked for isolation

How are anaerobic bacteria cultured?

The keys to effective anaerobic bacteria cultures include collecting a contamination-free specimen and protecting it from oxygen exposure.Cultures should be placed in an environment that is free of oxygen, at 95°F (35°C) for at least 48 hours before the plates are examined for growth.

Which of the following statements regarding biofilms is true?

The microbes in biofilms can work cooperatively to carry out complex tasks

Whyis agar used to grow bacteria

The reason agar is used to grow bacteria is because of its gel-like properties. It allows nutrients to be evenly suspended within it while being non-toxic to literally every organism cultured to date. The little buggers could eat as much as they want and it wouldn't harm them because it is neutrally charged and, for all intents and purposes, just plain nonreactive with biological molecules. Even your blood cells can be plated on agar, which creates plates known as blood-agar plates which microbiologists use for culturing some hemolytic bacteria. Another reason is that it is cheap, and easy to get a hold of.

Assume that after washing your hands, you leave ten bacterial cells on a new bar of soap. You then decide to do a plate count of the soap after it was left in the soap dish for 24 hours. You dilute 1 g of the soap 1:10^6 and plate it on heterotrophic plate count agar. After 24 hours of incubation, there are 168 colonies. How many bacteria were on the soap? How did they get there?

There were 168 x 10^6 bacteria on that 1g of soap. The bacteria could of been on the soap before washing hands because the soap was not sterile but is new. You could of also left bacteria on the soap then it would multiply.

You inoculate two tubes of liquid culture media with 100 bacterial cells and incubate one tube at 37 degrees Celsius and the other at 55 degrees Celsius. After 48 hours, there are 20,000 bacteria per ml in the 37-degree tube and 1,568,000 bacteria per ml in the 55-degree tube. You conclude that this species is a

Thermophile

What is a halophile?

Thrive in high salt concentration, salt loving microorganisms

Why is agar a suitable culture medium

Used to suppress the growth of unwanted microbes and encourage the growth of desired microbes

Could human exist on chemically defined media, at least under laboratory conditions?

Yes if the chemically defined media had the proper nutrients and environment for humans

How would one determine whether a microbe is a strict anaerobe?

You can tell by the way it grows. If its a strict anaerobe then it will only grow at the BOTTOM where there is NO O2

Flask A contains yeast cells in glucose-minimal salts broth incubated at 30°C with aeration. Flask B contains yeast cells in glucose-minimal salts broth incubated at 30°C in an anaerobic jar. The yeasts are facultative anaerobes. a.Which culture produced more ATP? b.Which culture produced more alcohol? c.Which culture had the shorter generation time? d.Which culture had the greater cell mass? e.Which culture had the higher absorbance?

a. Flask A; If the yeast is facultative anaerobic, this means that it prefers aerobic conditions, but can also live anaerobically. Flask A has oxygen (was aerated), so the cells will be able to do aerobic cellular respiration, which produces much more ATP than the fermentation process that is conducted in anaerobic conditions. b. Flask B; alcohol is produced under anaerobic conditions, when the yeast is forced to undergo fermentation. c. Flask A; the yeast prefer to have oxygen, so they will reproduce more quickly in aerobic conditions. d. Flask A; again, the yeast prefer to have oxygen, so they will reproduce faster and have the greatest mass in aerobic conditions. e. Flask A; absorbance means the amount of light absorbed when light is passed through the culture flask; it is directly proportional to the cell mass inside the flask. Since flask A will grow faster, the cell mass will be higher, and the absorbance will also be higher.

Heat lamps are commonly used to maintain foods at 50 oC for up to 12 hours in cafeteria serving lines. The following experiment was conducted to determine whether this practice poses a potential health hazard. Beef cubes were inoculated with 500,000 bacterial cells and incubated at 43-53 oC to establish temperature limits for bacterial growth. The following results were obtained from standard plate counts performed on beef cubes at 6-12 hours after inoculation: (look at powerpoint) What holding temp. would you recommend? Assuming that cooking kills bacteria in foods, how could these bacteria contaminate the cooked foods? What disease does each organism cause? (Ch. 25)

holding temp. at 43 degrees -they could have produced spores that were resistant -S. aureus: staphylococcal food poisoning -S. typhimurium: typhoid fever -C. perfringens: Clostridium perfringens gastroenteritis

Bacteria growing in and on the human body, including normal microbiota as well as pathogens, are classified as

mesophilic and heterotrophic

Campylobacter bacteria are grown with a CampyPak that produces 5% carbon dioxide and 15% oxygen. This bacterium is

microaerophile