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Microbiology Lab
Exam 2 Part 2
| Question | Answer |
|---|---|
| which chemical was the most effective for inhibiting the growth of s. aureus? of p. aeruginosa? | Variable – consult your results chart for the largest zones of inhibition. Are they the same for gram+ and gram- species? |
| which chemical was the least effective for inhibiting the growth of s. aureus of p. aeruginosa? | Variable– consult your results chart for the smallest zones of inhibition. Are they the same for gram+ and gram- species? |
| what do your results indicate about the relative chemical resistances of these two species? | Which species, overall, was more resistant to chemicals? Less resistant? |
| differentiate between antiseptic and disinfectant. Include examples of each in answer and indicate whether any chemical can be used as both. | Antiseptics, such as alcohol or iodine, are used on living tissues (e.g., skin). Disinfectants, such as bleach, are used on inert surfaces (e.g., tabletops). |
| differentiate between antiseptic and disinfectant. Include examples of each in answer and indicate whether any chemical can be used as both. | Most antiseptics (e.g., alcohol, iodine, peroxide) can be used as disinfectants, but most disinfectants are not recommended for use on skin (e.g., bleach, Lysol, ammonia). |
| what factors influence the size of the zone of inhibition produced by a chemical? | The size of the zone of inhibition is influenced by the molecular weight of the agent and its rate of diffusion in the agar. |
| what factors influence the size of the zone of inhibition produced by a chemical? | The disinfectant’s ability to then attack the bacterial structure that it is most effective against will vary, since each type of disinfectant is targets one or more cell structures. |
| how might the physical difference between gram positive and gram negative bacteria contribute to differences in chemical resistance? | Gram-negative bacteria have outer membranes that may limit penetration of chemicals that harm cytoplasmic targets. |
| what is the role of oxygen in aerobic respiration? | Oxygen acts as a terminal electron acceptor during respiration. |
| what types of metabolism can occur in the absence of oxygen? | In the absence of oxygen, anaerobic respiration or fermentation occurs. |
| name two enzymes that are present in obligate aerobes but lacking in obligate anaerobes. What function of each enzyme | Obligate anaerobes lack superoxide dismutase, which converts toxic superoxide to a harmless compound, and catalase, which converts toxic peroxide to oxygen. |
| differentiate between a microaerophile and aerotolerant organism | Microaerophiles require low amounts of oxygen for metabolism, although higher concentrations are lethal. Aerotolerant organisms can grow in oxygen but do not use it for metabolism and are thus indifferent to its presence. |
| why is resazurin a useful media additive for the study of anaerobes. | Resazurin is an indicator for the presence of oxygen. |
| why is gaspak anaerobic jar necessary for the culture of anaerobes on brewers anaerobic agar plates but not in tubes of fluid thioglycollate medium | Change the question to regular TSA instead of Brewer’s Agar: The GasPak anaerobic jar is necessary to remove the oxygen for anaerobic growth. |
| why is gaspak anaerobic jar necessary for the culture of anaerobes on brewers anaerobic agar plates but not in tubes of fluid thioglycollate medium | Anaerobes grow in fluid thioglycollate medium because in the depths of the tube, the conditions are anaerobic; therefore the GasPak is unnecessary. |
| where in the human body would you expect to find an obligate aerobe? where would you expect to find an obligate anaerobe? | Aerobes can be found on the human skin, e.g. Staphylococcus. Anaerobes can be found in hair follicles, e.g., Propionibacterium acnes and in the intestinal tract, e.g., Bacteroides fragilis. (knowing names of these species is not important) |
| hyperthermophile | deep sea vents heated by volcanic activity |
| thermophile | compost piles |
| mesophiles | most environments, e.g., human body, soil water systems |
| psychrophile | super cooled waters of the Arctic and Antarctic |
| differentiate between psychrophile and psychrotroph | Psychrophiles grow best at low temperatures whereas psychrotrophs are mesophiles that are capable of growth at lower (e.g., refrigerator) temperatures. |
| why are psychrotrophic bacteria of concern to those in the food service industry | Refrigeration is used to control spoilage microbes in food but psychrotrophs, such as Pseudomonas, are still capable of growth at these temperatures. |
| what is the optimum growth temperature for most human pathogens | Most human pathogens grow best at 37°C, which is body temperature. |
| name three cellular components involved in metabolism that are influenced by temperature changed and explain the changes that occur to those components | Temperature affects metabolism by influencing enzymes, cell membranes, and ribosomes. Elevated temperatures denature proteins, disrupt membranes, and inhibit ribosome function. |
| which has a greater impact on survival of an organism, temperatures above its max temp or temperature below its mini temperature. explain why and how this related to typical methods used to control microbial growth. | Elevated temperatures have the greatest impact because of destruction of essential molecules and function. Low temperatures are actually used to preserve microbial cultures. Low temperatures slow metabolism and are used to control growth. |
| how does pH negatively affect the metabolism of microorganisms? | Extremes of pH may affect the solubility of molecules and cause proteins to denature and lose enzymatic activity. |
| how would the pH of the culture medium be influenced by sugar fermentation? by urea hydrolysis? | Fermentation produces organic acids that would produce an acid environment. Hydrolysis of urea produces ammonia that would result in an alkaline environment. |
| helocobacter pylori survives in the acidic environment of the human stomach but this organism is actually a neutriphile how is it possible? | The bacterium invades the lining of the stomach to produce a microenvironment. In that microenvironment, the bacterium degrades urea to neutralize the stomach acid and produce conditions more conducive for its growth. |
| why are bacteria generally resistant to hypotonic environment whereas animal cells are not? | Bacteria have cell walls that resist osmotic pressure that causes cells to swell. Animal cells do not have cell walls and will burst under hypotonic conditions. |
| how do hypertonic environments negatively affect most bacterial cells | Hypertonic environments cause water to diffuse out of a cell and cause the cytoplasm to shrink away from the cell wall (plasmolysis) and damage the metabolic machinery of the cells. |
| why are staphylococci well suited for the colonization of skin? | Staphylococci are halotolerant and can exist on the skin, which is hypertonic because of salts contained in perspiration. |
| differentiate between halophiles and osmophiles. which type would more likely cause spoilage of jams and jellies? | Halophiles require high salt concentrations for growth. Osmophiles, in contrast, grow in environments where sugar concentrations are excessive, so they are more likely to cause spoilage of jams and jellies that have high sugar concentrations. |
| 0.5% | isotonic |
| 5% | hypertonic |
| 10% | hypertonic |
| 15% | hypertonic |
| describe the damaging effects of UV radiation on living cells | UV radiation causes the formation of thymine dimers in DNA that result in replication errors during reproduction. These errors cause gene defects, which ultimately lead to cell death. |
| why does exposure to UV radiation cause death in vegetative cells but not endospores | Endospores are non-dividing cells and are not subject to the same effects as reproducing vegetative cells. |
| at which wavelength is UV radiation most germicidal | UV radiation is most germicidal at 260 nm because that is the wavelength at which DNA maximally absorbs UV light. |
| what limited protection do cells have against damaging effects of UV radiation? | Cell protection against UV damage includes the repair mechanisms, such as the SOS system, which enzymatically removes dimers and inserts in their place new pyrimidine molecules. |
| what types of damage to human tissues can result from prolonged exposures to UV radiation? | UV radiation can cause damage to skin cells and can cause skin cancers. It also can cause cataracts and eye injury. In this experiment, goggles are worn to protect the eyes and one should avoid looking directly at the UV light source. |
| what protective measures can be taken to limit these types of damage both during the experiment and in everyday life | In everyday life, wearing long clothing, a hat, and/or sunscreen will protect against the damaging UV rays of the sun. |
| which b. megatherium culture a culture in the exponential growth phase or culture in the stationary phase. would show the best survival following exposure to UV radiation. | A culture in stationary phase will contain more endospores as nutrients become limited, and therefore that culture would demonstrate the best survival following exposure to UV radiation. |
Created by:
zachflemings