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Microbiology Lab pra
| Question | Answer |
|---|---|
| OF Medium | Semisolid Agar deep with high carbs and low peptones. Peptones support growth of bacteria that don't use carbs. |
| Description of OF Medium | 2 tubes used: 1 open to the air and 1 sealed to keep air out. Contains bromthymol blue, & it turns yellow in presence of Acids, indicating catabolism of the carb. Alkaline due to use of peptone not the carb turn dark blue due to ammonia production. |
| What has occurred if the carb is metabolized in both tubes of a OF Medium? | Fermenation |
| If an organism uses carbs in an open tube only, what will they produce in an OF Medium? | Acid, acids are produced as intermediates in respiration, and the indicator will turn yellow in the top of the open tube. Organism is called oxidative. |
| OF Test Results and Interpretations | |
| What would be found in the clear area that would not be found in the blue area of a starch agar plate after the addition of iodine? | A-amylase and glucose |
| How can you tell if an organism uses glucose aerobically? Ferments glucose? Doesn't use glucose? | Tube will be yellow throughout & leave the sealed medium green & blue. Yellow throughout or at the top of tube. Green or blue throughout |
| Aerobic organisms degrade glucose, producing carbon dioxide and water. What acid turns the indicator yellow? | Pyruvate acid |
| How can organims that don't use starch grow on a starch plate? | Low levels of peptones are in the media that supports the growth of the non-starch bacteria. |
| What is an fermentation tube? | it's used to detect acid and gas production form carbohydrates |
| What does the fermentation medium contain? | Peptone, and acid-base indicator (phenol red), and inverted tube to trap gas (Durham tube), and .5-1.0% of the desired carb. |
| What color is the tube before inoculation and after acid production? | red (neutral); acid production will turn the indicator yellow (pH of 6.8 or below). |
| Do all bacteria ferment lactose? | No |
| Why are fermentation tubes evaluated at 24 and 48 hours? | they will begin to grow oxidatively (passed 24hrs) on peptone exhausting the carbs and turn the medium red. Masking any evidence of fermentation. |
| If the medium is red for the fermentation tubes what does that indicate? | It has used up all the carbs and is growing oxidatively on peptone and it turns red because of the ammonia products produced. |
| If organism metabolized glucose aerobically, what results will occur in the fermentatin tubes? | increase acid production, turning it yellow & producing gas in the tubes. |
| If bacterium cannot ferment glucose, why not test its ability to ferment other carbohydrates? | b/c its the simplest sugar and other sugars are more complex. |
| If bacterium cannot use glucose, what result will occur in a fermentation tube? | tube will stay the same color but gas may occur. |
| What is the MRVP test? | it's used to distinguish organisms that produce large amounts of acid from glucose and organisms that produce the neutral product acetoin. |
| A positive MR test | only if an organism produces a large amount of organic acid from glucose, medium will remain red when methyl red is added, below pH 4.4 |
| Negative MR Test | methyl red will turn yellow in presence of pH above 6.0 |
| Positive VP Test | upper part of medium turns red in the presence of acetoin with the addition of potassion hydroxide and a-naphthol. |
| Negative VP Test | A negative will turn the upper part of medium brown due to the reaction of KOH and a-naphthol. |
| What is citrate agar used for? | Useful in identifying bacteria that can ferment citrate. |
| What does a bacteria need in order to grow on a citrate medium? | Bacteria with the enzyme citrate lyase can break down citrate to form pyruvate, which can be reduced in fermentation. |
| Positive Citrate test | bacteria use citrate and ammonium, the medium is alkalized because of ammonia produced from NH4. The indicator bromthymol blue changes to blue when medium is alkalized. |
| Negative Citrate Test | |
| What are proteins | large organic molecules that include cellular enyzmes and many structures |
| Amino Acids | Subunits that make up proteins |
| Amino acids consist of | carbon,hydrogen, oxygen, nitrogen, and sometimes sulfur. |
| Peptide bonds | bonding of amino acids forming a peptide or a larger molecule polypeptide. |
| What can bacteria do to peptides or polypeptides | bacteria can hydrolyze to release amino acids and use the amino acids as carbon and energy sources when carbs aren't available |
| Nutrient Gelatin | dissolves in warm water (50 C), solidifies (gels) when cooled below (25 C) and liquefies (sols) when heated to about 25 C. |
| What happens to the gelatin when an organism produces an exoenzyme hydrolyzes the gelatin? | It liquefies it and the gelatin doesn't solidify even when cooled below 20 C. |
| Urea is | a waste product of protein digestion in most vertebrates and is excreted in the urine. |
| Urea Agar | ids bacteria that possess urease, which liberates ammonia from the urea, which raises the pH of the medium turning the indicator fuchsia (hot pink) at pH 8.4 |
| Do all bacteria produce urease? Gelatinase? | No and No bacteria would need either a particular exoenzyme (gelatinase & urease) to overcome these buffers. |
| Name the 5 types of bacteria growth | Obligate Aerobes, Facultative anaerobes, Obligate anaerobes, Aerotolerant anaerobes, and Microaerophiles |
| Obligate aerobes | Oxygen required, presence of enzymes catalase and superoxide dismutase (SOD) allows toxic forms of O2 neutralized, |
| Facultative Anaerobes | aerobic and anaerobic growth, greater growth in O2. Catalase and (SOD) enzymes present |
| Obligate Anaerobes | Only anaerobic growth, lacks enzymes to neutralize O2. |
| Aerotolerant Anaerobes | only anaerobic growth but continues in presence of O2, has one enzyme SOD, tolerates it. |
| Microaerophiles | only aerobic growth but in low O2 concentration and high CO2, they produce superoxide radicals and peroxide in lethal concentrations. |
| Majority of Bacteria are | Facultative anaerobes - capable of living with or without O2 |
| 5 bacteria lacking catalase are | Streptococcus, Enterococcus, Leuconostoc, Cactobacillus,(these 4 are aerotolerant anaerobes and Clostridium. |
| Species of Clostridium | are obligate anaerobes |
| Streptococcus, Enterococcus, Leuconostoc, and Cactobacillus are | aerotolerant anaerobes and lack the cytochrome system to produce hydrogen peroxide and therefore do not need catalase. |
| Catalase test | determining the presence or absense of catalase can help ID bacteria. by adding a few drops of 3% hydrogen peroxide to a microbial colony and if catalase is present molecular O2 is released as bubbles. |
| Why does Thioglycolate broth appear red or blue? | Resazurin (dye) is added to the broth which is pink in the presence of excess oxygen an colorless when reduced. Methylene blue is also and indicator. |
| Generation or doubling time | is the time it takes for one cell to divide into 2 cells or the time required for the population of cells to double. |
| Shorter the generation time represents | the faster the growth |
| Minimum growth temperature | is the lowest temperature at which a species will grow. |
| Optimum Growth | species grows the fastest |
| Maximum growth temperature | highest temperature at which a species can grow. |
| At temperatures near the max growth temp | growth ceases, presumbably because of inactivation of enzymes. |
| Lag Phase | Little or no cell division, undergoing a period of intense metabolic activity, involving synthesis of enzymes and various molecules |
| Log Phase | Growing at fastest possible rate |
| Stationary Phase | Period of equilibrium, microbial deaths balanced production of new cells. Due to possible accumulation of waste products, exhaustion of nutrients and harmful changes in pH. |
| Death Phase | Population is decreasing at a logarithmic rate. Death rate exceeds new cells rate. |
| Phases of Growth | Lag phase, Log phase, stationary phase, and Death phase |
| What is the optimum growth temp. for human pathogens | 37 C |
| What are the types of bacteria live in relation to environment | Psychrophilic, Psychrotrophic, Mesophilic, thermophilic, hyperthermophilic |
| Psychorophilic | 0 to 20 degrees C, cold-loving microbes, found in ocean depths or certain polar regions. |
| Psychrotrophic | 20 to 30 degrees C, cold-loving, can't grow above 40 degrees, low temp food spoilage, grow well in refrigerators. |
| Mesophilic | 25 to 40 degrees C, moderate-temp loving microbes, most common, most common spoilage and disease organisms |
| Thermophilic | 45 to 65 degrees C,heat-loving microbes, temp of hot water tap, sunlight soil and hot springs. can't survive in temps below 45C |
| Hyperthermophiles | about 80 or higher degrees, heat-loving, hot springs associated with volcanic activity, sulfur usually metabolic activity |
| Dry Heat | hot-air ovens or incineration denatures enzymes, dehydrates microbes, and kills oxidation effects. |
| Moist Heat | methods include pasteurization, boiling, and autoclaving. It transfers heat energy to the microbial cell more efficiently than dry air, resulting in denaturing of enzymes. |
| Pasteuriztion | the temp is maintained at 63 degrees for 30 min or 72 degrees for 15 sec. to kill designated organisms that are pathogenic or cause spoilage |
| Boiling | 100 degrees C for 10 minutes will kill vegetative bacterial cells; however does not inactivate endospores. |
| Autoclaving | the use of steam under pressure, increase pressure raises the boiling point of water and produces steam with a higher temp. Most effective. Standard conditions are 15 psi, at 121 degrees for 15 minutes. this usually kills endospores. |
| Thermal Death Time | is the length of time required to kill all bacteria in a liquid culture at a given temp. |
| Thermal death point | is the temp required to kill all bacteria in a liquid culture in 10 minutes. |
| Decimal Reduction time | is the time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed. |
| Antimicrobial Agents | are chemicals used to control the growth of microbes. |
| Disinfectants | are chemical agents used on inanimate objects to lower the level of microbes on their surface. |
| Antiseptics | are chemicals used on living tissue to decrease the number of microbes. |
| Bactericidal Agents | result in bacterial death |
| Bacteriostatic Agents | causes temporary inhibition of growth. |
| In evaluating the effectiveness of antimicrobial agents | the concentration, length of contact, and whether it's lethal are the important criteria. |
| The use-dilution test | is limited to bactericidal compounds and cannot be used to evaluate bacteriostatic compounds. |
| Zones of Inhibition | the size of inhibition of bacterial growth around a disk that is impregnated with various antimicrobial agents. |
| Minimum inhibitory Concentration, MIC of an antibiotic | is determined by testing for bacterial growth in dilutions of the antibiotic in nutrient broth. |
| Antimicrobial Drugs | antimicrobial chemicals absorbed or used internally, whether natural (antibiotics) or synthetic. |
Created by:
Twixy565