Chpt 2 Microbial Cultivation

Question 1

Question 1: Microorganisms are generally found everywhere what term describes this characteristic? a. ubiquitousb. axenicc. mixedd. pure

Answer 1

Question 1: a. ubiquitous • Explanation: Ubiquitous refers to the presence of something everywhere. Microorganisms are found in various environments from the soil to the air making them ubiquitous.

Question 2

Question 2: A culture containing only one type of microorganism is referred to as what?a. mixed cultureb. pure culturec. axenic cultured. sterile culture

Answer 2

Question 2: b. pure culture Explanation: A pure culture contains only one type of microorganism. This is achieved through isolation and cultivation techniques to ensure that only a single species is present.

Question 3

Question 3: What is the primary purpose of sterilizing materials and instruments in a microbiology lab?a. To kill all microorganisms b. To prevent contamination of culturesc. To enhance microbial growthd. To preserve microorganisms

Answer 3

Question 3: b. To prevent contamination of cultures • Explanation: Sterilization is crucial for maintaining the purity of cultures. By eliminating microorganisms and contaminants it prevents unwanted organisms from interfering with the desired culture.

Question 4

Question 4: What is the process of eliminating all microorganisms and contaminants from a culture to achieve purity called?a. Confluent growthb. Sterilizationc. Isolationd. Incubation

Answer 4

Question 4: b. Sterilization• Explanation: Sterilization is a process that eliminates all microorganisms and exogenous contaminants from a culture. This is essential for achieving purity and ensuring the reliability of experimental results.

Question 5

Question 5: What is the most common method of sterilization for heat-stable materials like wire loops and inoculation needles? a. Moist heatb. Dry heatc. Filtrationd. Radiation

Answer 5

Question 5: b. Dry heat • Explanation: Dry heat is a common method for sterilizing heat-stable materials. It involves using a Bunsen burner flame to directly heat the material killing any microorganisms present.

Question 6

Question 6: Describe the two basic steps involved in obtaining a pure culture.

Answer 6

Question 6: • Explanation: The two main steps involved in obtaining a pure culture are: * Sterilization: Eliminating all microorganisms and contaminants from materials and equipment. * Isolation and cultivation: Separating and growing a single microbe to generate a clone of progeny. This involves techniques such as streak plating and agar dilution to isolate individual colonies for further study.

Question 7

Question 1: Which sterilization method involves using a pressurized chamber to achieve high temperatures and pressure?a. Dry heatb. Moist heatc. Filtrationd. Radiation

Answer 7

Question 1: b. Moist heat • Explanation: Moist heat sterilization like autoclaving uses high temperatures and pressure in a closed chamber to kill microorganisms. This method is effective for sterilizing various materials and is often used for media preparation.

Question 8

Question 2: What sterilization method is suitable for sterilizing heat-sensitive materials such as liquid media?a. Dry heatb. Moist heatc. Filtrationd. Radiation

Answer 8

Question 2: c. Filtration • Explanation: Filtration is an effective sterilization method for heat-sensitive materials such as liquid media. It involves passing the liquid through a membrane filter with pore sizes small enough to trap microorganisms

Question 9

Question 3: What is the main difference between dry heat and moist heat sterilization?a. The temperature usedb. The time requiredc. The materials that can be sterilizedd. The mechanism of killing microorganisms

Answer 9

Question 3: d. The mechanism of killing microorganisms • Explanation: Dry heat sterilization works by oxidizing cellular components and denaturing proteins. Moist heat sterilization however primarily relies on denaturation of proteins and disruption of cell membranes.

Question 10

Question 4: What type of sterilization involves exposing materials to direct sunlight or ultraviolet rays for a prolonged time?a. Dry heatb. Moist heatc. Filtrationd. Radiation

Answer 10

Question 4: d. Radiation• Explanation: Radiation sterilization utilizes ultraviolet rays or gamma rays to kill microorganisms by damaging their DNA. This method is effective for killing spores and other resistant organisms but may not be suitable for all materials.

Question 11

Question 5: Why are chemical sterilization agents generally not used for media sterilization?a. They are expensiveb. They are difficult to usec. They can render the media toxic to microorganismsd. They are not effective against all microorganisms

Answer 11

Question 5: c. They can render the media toxic to microorganisms• Explanation: Chemical sterilizing agents can be toxic to microorganisms and often unsuitable for media preparation as they might inhibit the growth of the desired culture.

Question 12

Question 6: Describe the isolation process and explain the difference between a single cell and a colony.

Answer 12

Question 6: • Explanation: Isolation is a crucial step in obtaining pure cultures. It involves separating a single cell of a microorganism from others and allowing it to grow in a sterilized liquid or gelled medium (agar). This controlled environment encourages the individual cell to multiply and form a visible cluster called a colony. A single cell is a single individual microbe while a colony represents a group of millions of identical microorganisms originating from that initial cell

Question 13

Question 1: What is the primary objective of streak plating?a. To determine the viability of an organismb. To determine if a culture contains only one organism c. To obtain single

Answer 13

discrete isolates for further study d. All of the above

Question 14

Question 2: What is the basic principle of streak plating?a. Separating microbial colonies by dilutionb. Separating microbial colonies by incubationc. Separating microbial colonies by filtrationd. Separating microbial colonies by chemical treatment

Answer 14

Question 2: a. Separating microbial colonies by dilution• Explanation: Streak plating involves repeatedly dragging an inoculum across a solid agar surface which gradually dilutes the microbial concentration leading to the formation of isolated colonies.

Question 15

Question 3: What type of agar medium is typically used for streak plating?a. Liquid agarb. Solid agarc. Semi-solid agard. Both b and c

Answer 15

Question 3: d. Both b and c• Explanation: Streak plating is commonly performed on either solid or semi-solid agar media. Solid agar provides a firm surface for colony isolation while semi-solid agar allows for some degree of mobility for the microorganisms.

Question 16

Question 4: What is the main purpose of flaming the inoculating loop before and after each streak?a. To sterilize the loop and prevent contaminationb. To heat the agar and promote growthc. To spread the inoculum evenlyd. To soften the agar for easier streaking

Answer 16

Question 4: a. To sterilize the loop and prevent contamination• Explanation: Flaming the loop before and after each streak is essential for maintaining sterility and preventing contamination. It kills any microorganisms that may be present on the loop and prevents them from spreading to the agar.

Question 17

Question 5: What is the most important precaution to take when picking up single colonies for streak plating?a. To use sterile instruments b. To flame the loop before and after each streak c. To ensure the culture medium is properly sterilized d. To avoid picking up colonies that are too close together

Answer 17

Question 5: d. To avoid picking up colonies that are too close together• Explanation: Picking up single colonies that are too close together can lead to a mixed culture instead of a pure culture. Care should be taken to ensure that only a single colony is picked up for streaking.

Question 18

Question 6: Describe the step-by-step procedure for streak plating.

Answer 18

Question 6:• Explanation: The streak plating procedure involves the following steps: 1. Prepare materials: Use sterilized petri dishes inoculating loops and the desired agar media. 2. Sterilize the loop: Flame the inoculating loop thoroughly to ensure sterility. 3. Spread the inoculum: Streak the inoculum across the agar surface in four quadrants starting with the first quadrant and ending with the fourth. Each subsequent streak should begin from the end of the previous streak and extend across a new area of the agar. 4. Incubate: Incubate the petri dish at the appropriate temperature for the organism to grow. 5. Observe: Once the colonies have grown observe the resulting isolated colonies for their characteristics including shape size and color

Question 19

Question 1: What is the purpose of streaking an inoculum across a solid agar plate in a zig-zag pattern?a. To evenly distribute the inoculum across the surfaceb. To create a gradient of microbial concentrationc. To facilitate the formation of isolated coloniesd. All of the above

Answer 19

Question 1: d. All of the above• Explanation: The zig-zag streaking pattern serves multiple purposes: it distributes the inoculum evenly creates a gradient of microbial concentration and ultimately facilitates the formation of isolated colonies.

Question 20

Question 2: What is the significance of the lines of streaks on the agar plate?a. They represent the path of the inoculating loopb. They indicate the areas where microbial growth has occurredc. They demonstrate the dilution of the inoculumd. All of the above

Answer 20

Question 2: d. All of the above• Explanation: The lines of streaks on the agar plate represent the path of the inoculating loop indicate the areas where microbial growth has occurred and visually demonstrate the dilution of the inoculum.

Question 21

Question 3: Why are the microorganisms growing in discrete colonies rather than forming a continuous lawn on the agar plate?a. The agar inhibits their growthb. The bacteria are clumped togetherc. The streaking technique dilutes the inoculumd. The microorganisms are naturally dispersed

Answer 21

Question 3: c. The streaking technique dilutes the inoculumExplanation: As the inoculum is streaked across the agar surface it is diluted with each subsequent pass. This results in fewer microorganisms being deposited in each successive quadrant leading to the formation of isolated colonies.

Question 22

Question 4: What would you expect to observe in the first quadrant of the streak plate where the initial inoculum was introduced?a. A dense continuous lawn of bacterial growthb. A few isolated coloniesc. No visible growthd. A gradient of microbial concentration

Answer 22

Question 4: a. A densecontinuous lawn of bacterial growth• Explanation: The initial quadrant where the concentrated inoculum was first applied would show the highest density of microbial growth forming a continuous lawn.

Question 23

Question 5: Which quadrant on the streak plate would you expect to show the highest density of microbial growtha. Quadrant 1b. Quadrant 2 c. Quadrant 3 d. Quadrant 4

Answer 23

Question 5: a. Quadrant 1• Explanation: Quadrant 1 where the initial inoculum was applied would have the highest density of microbial growth as the inoculum is concentrated in this area.

Question 24

Question 6: What is the relationship between the streaking technique and the dilution of the inoculum? How does this affect the pattern of microbial growth

Answer 24

Question 6: • Explanation: The streaking technique is directly related to the dilution of the inoculum. As the inoculating loop is dragged across the agar a portion of the microorganisms is transferred to the next area while the rest remain on the previous streak. This repeated dilution leads to a decrease in the number of microorganisms present in each subsequent streak. The result is a pattern of microbial growth where the first streak has the highest density of organisms and the density progressively decreases in subsequent streaks eventually leading to isolated colonies in the final quadrant.

Question 25

Question 1: What is the primary purpose of dilution plating?a. To kill microorganismsb. To concentrate a microbial suspensionc. To obtain a suspension with a specific number of cells per unit volumed. To create a pure culture

Answer 25

Question 1: c. To obtain a suspension with a specific number of cells per unit volume• Explanation: Dilution plating is a technique used to obtain a microbial suspension with a specific number of cells per unit volume making it easier to count colonies and estimate the original concentration of microorganisms.

Question 26

Question 2: What is the primary difference between the pour plate and the spread plate method?a. The method of inoculating the agarb. The type of agar usedc. The number of dilutions performedd. The type of microorganisms being cultured

Answer 26

Question 2: a. The method of inoculating the agar• Explanation: The pour plate method involves mixing the diluted sample with molten agar before pouring it into a petri dish. The spread plate method on the other hand involves spreading a diluted sample directly onto the surface of solidified agar.

Question 27

Question 3: In a ten-fold serial dilution how much of the previous dilution is transferred to the next tube?a. 1 mlb. 10 mlc. 0.1 mld. 0.01 ml

Answer 27

Question 3: c. 0.1 ml• Explanation: In a ten-fold serial dilution 0.1 ml of the previous dilution is transferred to the next tube creating a ten-fold dilution in each subsequent tube.

Question 28

Question 4: What is the dilution factor for the third tube in a ten-fold serial dilution series?a. 10^-1b. 10^-2c. 10^-3d. 10^-4

Answer 28

Question 4: c. 10^-3• Explanation: The dilution factor represents the reciprocal of the dilution. In the third tube the dilution factor is 10^-3 meaning the original concentration is diluted 1000 times.

Question 29

Question 5: What is the primary advantage of using the spread plate method over the pour plate method?a. It allows for better isolation of coloniesb. It is easier and faster to performc. It is more effective for diluting dense suspensionsd. It is more suitable for culturing anaerobic organisms

Answer 29

Question 5: a. It allows for better isolation of colonies• Explanation: The spread plate method typically provides better isolation of colonies as the microorganisms are evenly spread on the surface of the agar reducing the chance of overcrowding and overlapping colonies.

Question 30

Question 6: Describe the process of ten-fold serial dilution including the steps involved and the rationale behind it.

Answer 30

Question 6: • Explanation: Ten-fold serial dilution involves transferring a specific volume (usually 1 ml) of the original microbial suspension into a tube containing a known volume of diluent (usually 9 ml). This creates a 1:10 dilution (1/10 of the original concentration). This process is repeated by transferring 1 ml of the diluted suspension from the first tube to a second tube containing 9 ml of diluent creating a 1:100 dilution. This process can be repeated multiple times creating a series of ten-fold dilutions. Each tube in the series has a specific dilution factor (10^-1. 10^-2. 10^-3. etc.) indicating the degree of dilution from the original suspension. The purpose of this serial dilution is to reduce the microbial concentration to a countable level allowing for the estimation of the original microbial concentration in the stock culture

Question 31

Question 1: What is the primary goal of both spread plating and pour plating techniques?a. To sterilize the culture mediab. To obtain a pure culture of a specific microorganismc. To count the number of viable microorganisms in a sampled. To identify the morphology of microorganisms

Answer 31

Question 1: c. To count the number of viable microorganisms in a sample• Explanation: Both spread plating and pour plating techniques are used to obtain countable colonies which allows for an estimation of the original concentration of microorganisms in a sample.

Question 32

Question 2: What is the main difference between the spread plating and the pour plating techniques?a. The method of inoculating the agarb. The type of agar usedc. The incubation temperatured. The type of microorganisms being cultured

Answer 32

Question 2: a. The method of inoculating the agar• Explanation: Spread plating involves spreading the diluted sample directly onto the surface of solidified agar. Pour plating on the other hand mixes the diluted sample with molten agar before pouring the mixture into a petri dish.

Question 33

Question 3: What is the purpose of flaming the glass spreader in the spread plating technique?a. To sterilize the spreader and prevent contaminationb. To heat the agar and promote microbial growthc. To spread the inoculum evenlyd. To soften the agar for easier spreading

Answer 33

Question 3: a. To sterilize the spreader and prevent contamination• Explanation: Flaming the glass spreader sterilizes it killing any microorganisms that might be present on the spreader preventing them from contaminating the agar surface.

Question 34

Question 4: Why is it necessary to dilute the microbial sample before plating?a. To kill any harmful microorganismsb. To prevent the growth of colonies that are too densec. To obtain a countable number of coloniesd. To ensure that the colonies are evenly distributed on the agar

Answer 34

Question 4: c. To obtain a countable number of colonies• Explanation: Diluting the sample reduces the number of microorganisms in a specific volume making it easier to count the resulting colonies. Too many colonies would be difficult to count accurately

Question 35

Question 5: What is the main advantage of using the pour plate method over the spread plate method?a. It allows for better isolation of coloniesb. It is easier and faster to performc. It can be used for more types of microorganismsd. It is more effective for diluting dense microbial suspensions

Answer 35

Question 5: b. It is easier and faster to perform• Explanation: The pour plating technique is generally considered simpler and faster than spread plating because it involves fewer steps. However the spread plate method often provides better isolation of colonies.

Question 36

Question 6: Describe the steps involved in the pour plating technique.

Answer 36

Question 6:• Explanation: The steps involved in the pour plating technique include: 1. Carry out ten-fold serial dilution: Dilute the original microbial suspension sufficiently.2. Mix the diluted sample with molten agar: Transfer a specific volume of the diluted sample into a tube of molten agar. 3. Pour the mixture into Petri dishes: Carefully pour the agar-microbial mixture into sterile Petri dishes and allow the agar to solidify. 4. Incubate: Incubate the Petri dishes at an appropriate temperature for the specific microorganism. 5. Count colonies: After incubation count the colonies that have grown on the surface of the agar.