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Microbiology Lab
Exam 2
| Question | Answer |
|---|---|
| were any plates completely lacking in colonies | Variable answers |
| why do you suppose this habitat contains such a high microbial count? | possible answers include, temperature, moisture, amount of human traffic. |
| Types of organisms we find on skin? | (gram+ cocci, gram- cocci), soil (gram+ bacilli endosporeformers, gram+ filamentous, molds), in water (gram- bacilli), in dust (gram+ cocci, gram+ bacilli endosporeformers, mold spores, variable) |
| do you think that habitat sampled was really sterile? | no/yes |
| if you answer to be is no, then how can you count for the lack of growth on the plate? | Organisms sampled were not able to grow on the kind of nutrient agar used, or organisms sampled require longer time to grow. |
| if your answer to b is yes defend it? | Students may feel an area sampled is sterile because it was recently cleaned. |
| in what ways do the macroscopic features of bacterial colonies differ from those molds? | Bacterial colonies are generally smooth and small as compared to fungal colonies, which are large and “fuzzy.” |
| why is the level of contamination measured as number of colonies rather than size of colonies? | Since each colony is produced from a single cell, the number of colonies indicates the number of cells originally present or level of contamination. Colony size reflects growth rate. See Ex 38 |
| should one be concerned to find bacteria on the skin? how about molds? | Bacteria, such as the staphylococci and the diphtheroids, are part of the normal skin flora. Molds, however, are likely transient contaminants picked up from the environment. |
| how can microbial levels be controlled on the skin? on surfaces in the environment? in the air? | Microbial levels on skin are best controlled by hand washing, on surfaces in the environment with use of disinfectants like bleach, and in the air by HEPA filtration systems. |
| compare the following features of bacteria to those eukaryotic microorganisms? size | Bacteria are smaller, about 0.510 µm in diameter. |
| compare the following features of bacteria to those eukaryotic microorganisms? organization of genetic material? | Bacterial DNA is not enclosed in a nucleus but rather is organized in the cytoplasm. |
| compare the following features of bacteria to those eukaryotic microorganisms? ribosomes? | Bacteria have 70S ribosomes. |
| compare the following features of bacteria to those eukaryotic microorganisms? cell wall? | Bacteria have a cell wall composed of peptidoglycan. |
| compare the following features of bacteria to those eukaryotic microorganisms? respiration and photosynthesis? | Bacteria lack mitochondria and chloroplasts but can carry out respiration and photosynthesis. |
| compare the following features of bacteria to those eukaryotic microorganisms? motility? | Bacteria may have flagella that are simpler in structure but may be more numerous. |
| WHAT KIND OF CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING BROTH CULTURES? | Nature of growth on the surface (ring, pellicle, flocculent, membranous), subsurface (turbid, granular, flocculent, flaky), and bottom of tube (sediment). Also, amount of growth. |
| WHAT KIND OF CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING SLANT CULTURES? WHY ARE THESE CHARACTERISTICS DIFFERENT THAN BROTH CULTURES? part 1 | Amount of growth, color (pigment), opacity (opaque, transparent, translucent), form or shape (filiform, echinulate, beaded, effuse, arborescent, rhizoid). |
| WHAT KIND OF CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING SLANT CULTURES? WHY ARE THESE CHARACTERISTICS DIFFERENT THAN BROTH CULTURES? part 2 | Bacteria growing on a solid surface takes characteristic shapes that are unique to their species that cannot be observed in broth cultures. |
| WHAT CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING ISOLATED COLONIES ON AGAR PLATES? WHAT KIND OF CULTURES ARE BEST TO OBSERVE AND WHY? 1 | We can determine size, color, opacity, form (shapes and configurations include round – scalloped/raised/radiating margin, wrinkled, concentric, irregular and spreading, filamentous, L-form, filiform, rhizoid, complex), |
| WHAT CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING ISOLATED COLONIES ON AGAR PLATES? WHAT KIND OF CULTURES ARE BEST TO OBSERVE AND WHY? 2 | elevation (flat, raised, convex, drop-like, umbonate, hilly, ingrowing, craterform), and margin (smooth or entire, wavy or undulated, lobate, irregular, ciliate, branching, wooly, thread-like, hair-like). |
| WHAT CHARACTERISTICS CAN WE DETERMINE ABOUT BACTERIA FROM OBSERVING ISOLATED COLONIES ON AGAR PLATES? WHAT KIND OF CULTURES ARE BEST TO OBSERVE AND WHY? 3 | Pure cultures with isolated colonies are best to observe, because if more than one species of bacteria contribute to a colony, it will have a mixture of growth characteristics, and therefore cannot be used to help identify an unknown. |
| which bacterial species exhibited true motility on the slides? | Proteus is motile. |
| Did the semisolid medium inoculations concur with the slides results? | Variable; however, the semisolid medium inoculations should concur with slide results. Pink spreading due to TTC oxidation in motile organism (Proteus). |
| describe the differences between the two stabs in the soft agar plate and based on these results which species appears to be motile | Growth extends farther from the stab location for the motile bacterium. Proteus is motile. |
| describe the structure of flagellum. | A bacterial flagellum is a fibrous appendage composed of protein subunits and anchored in the membrane. |
| how do flagella general cell motility? | Flagella rotate counterclockwise to propel the cell forward and clockwise to tumble and change direction. |
| if you compared tow motile bacterial species and determined one was considerably more motile than the other which arrangement of flagella would you expect to be associated with the highly motile species and how would you confirm this? | Peritrichous flagella, which are numerous arrangements across the entire cell surface, are characteristic of highly motile bacteria, such as Proteus. Confirm the flagellar arrangement with a flagella stain |
| differentiate between the following types of movement observed in a wet mount or hanging drop slide? directional motility | Rapid swimming and directional change indicate true motility. |
| differentiate between the following types of movement observed in a wet mount or hanging drop slide? brownian movement | Jiggling motions without movement in a particular direction indicate Brownian movement. |
| differentiate between the following types of movement observed in a wet mount or hanging drop slide? water current movement | Sweeping motion indicates water currents. |
| between wet mount and hanging drop slides preparations which is more resistant to evaporation? | Hanging drop slides are more resistant to evaporation, |
| between wet mount and hanging drop slides preparations which woks best with phase contrast microscopy? | although wet mount slides work better with phase contrast microscopy. |
| what concentration of agar is used in a semisolid medium for motility determination? how does this compare to a typical solid medium? | Less agar is used to make semisolid media, which when stabbed, allow motile bacteria to swim but hold nonmotile in place. Typical solid medium contains 1.5% agar, which when stabbed, would not allow movement of motile bacteria. |
| why are semisolid media sometimes preferred over slide techniques for evaluation bacterial motility? 1 | Exposure of individuals to pathogens is more likely when making wet slides as opposed to stabbing a semisolid medium where the bacteria are contained. |
| WHAT IS THE FUNCTION OF TTC IN THE MOTILITY MEDIA? | TTC is useful in easily determining motility. |
| why are semisolid media sometimes preferred over slide techniques for evaluation bacterial motility? 2 | There are also fewer false positives when using semisolid media because there is no Brownian movement or water current. |
| complex media | The exact composition of defined media is known whereas it is not known for complex media. Complex media are typically made for rich extracts of meat or plants. |
| defined media | are made by individually measuring out all components. |
| name 6 basic nutritional requirements supplied in all culture media | Basic nutritional requirements in all culture media include a carbon source, an energy source, nitrogen, minerals, vitamins, growth factors, and water. |
| what growth factor is often supplied for cultivation of fastidious bacterial pathogens? | blood |
| autoclaving destroys living cells as well as what other bacterial stage that could cause contamination? | endospours |
| an autoclave is typically used for | sterilization of media? |
| define sterilization | Sterilization is the complete removal or destruction of all microbes including bacterial endospores. |
| under what conditions are media typically sterilized in an autoclave | Media are sterilized at 121ºC with 15 psi of steam for at least 15 minutes. |
| what type of media components cannot be sterilized in an autoclave | Heat-sensitive media additives (e.g., antibiotics or milk or enzymes) cannot be sterilized by autoclaving. |
| what is an alternative to an autoclaving for sterilization heat sensitive materials? | Filter sterilization can be used for liquid components that cannot be autoclaved. |
| what compounds or chemicals might be added to a medium to make it selective | A selective medium allows one type of microbe to grow while another is inhibited. It might contain a high/low pH, or a higher salt concentration, or another growth limiting ingredient. |
| agar is solidifying agent used in | media prepration |
| agar is solidifying agent used in media preparation. agar is solidifying agent used in media preparation. what is it's origin | Agar is a complex polysaccharide isolated from seaweed (red algae). |
| agar is solidifying agent used in media preparation. how and why does the agar concentration in semisolid media differ from conventional solid media? | A semisolid medium has an agar concentration of 0.4%, which is in contrast to conventional solid media that has a concentration of 1.5%. Semisolid media can be used for motility studies because they allow movement. |
| agar is solidifying agent used in media preparation. what makes it ideal for cultivation of microbes? | Agar melts at 100ºC but does not solidify until it reaches 45ºC, which will not kill microbial cells so inoculation of molten media (e.g., pour plates) is possible. Agar is also relatively inert and is not degraded by most microbes. |
Created by:
zachflemings