BIO 171 Module 4 Exam Questions With Complete Answers!!

Growth media - nutrient-rich environment for isolating and culturing microorganisms, includes sugars, amino acids, and vitamins, also called nutrient broth, grows microbes in a suspension Lysogeny broth - most common nutrient broth, can grow a vast array of microbes, plates are yellow, non-selective and non-differential media, commonly used for growing e coli (easily produces recombinant proteins) Selective media - suppress growth of unwanted bacteria and encourage growth of desired microbes, uses limited amounts of nutrients, varying degrees of pH, or various chemical additives like antibiotics that limit microbial growth, often used to grow Neisseria meningitides (fungi and mold outgrow this slow growing bacteria) Differiential media - distinguishes between 2 unrelated microbes, e.g. E coli and salmonella are both gram negative but can be distinguished by the presence of lactose fermentation- e coli ferments lactose and turns the culture red, salmonella doesn't and culture remains white/tan enriched media - contains complex organic substances such as blood, serum, hemoglobin, or special growth factors required by fastidious microbes, used to grow fastidious 2 forms of growth media - liquid and solid solid growth media - housed in a sterile petri dish, liquid growth media with hardening agent added Agar - a gel-like polysaccharide compound used for culturing microbes; extracted from certain red algae, creates a solid smooth surface Colonies - microbial growth in a media, appears as individual isolated dots- isolates merge into one anotherLawn - microbial growth of the entire petri dish Agar characteristics - : Outside of the lab you've probably come across the 'cousin' of agar, gelatin. Gelatin is an animal-derived product that gives Jello its classic texture and form. Agar is simply the plantbased form and acts in a very similar way. In both cases, as you increase the amount of agar/gelatin the firmer the composition becomes. The dehydrated agar (and other necessary components) is mixed with water and heated to a high temperature to dissolve the agar into solution. The high temperature also ensures sterility as it will kill most, if not all, foreign microbes. Once poured into a sterile petri dish and cooled, the agar plate is a sterile environment on which microbes can grow. Agar plates are made by - agar melted, sterilized, and poured into a sterile petri dish, solidifies at room temperature Trypticase Soy Agar - grows a wide variety of microorganisms, non-selective and non-differential, yellow in color, serves as a base when formulating specialized enriched medias Blood Agar - BAP, derivative of TSA, blood usually from a sheep added to plate compensation as a concentration range of 5-10%, red in color, enriched non-selective but differential media BAP promotes the growth of - fastidious microorganisms- strains of Streptococcus BAP detects - hemolytic activity Hemolysis classification - alpha, beta, gamma Alpha hemolysis - incomplete lysis of red blood cells producing a greenish -brown halo around colonies because hemoglobin is oxidized to methemoglobin beta hemolysis - complete lysis of red blood cells around a colony (results in a clear zone surrounding colonies)gamma hemolysis - No hemolysis, and no change in the blood agar around the colony, white/tan in color Columbia CNA agar - selective and differential media, enriched and red in color from blood enrichment (allows for differential based on hemolytic patterns) , has antimicrobial agents colistin and Nalidixic acid, suppresses growth of Gram-negative bacteria, used for isolation of Gram-positive microbes Chocolate agar CHOC or CBA - enriched non-selective non-differential media derived of blood agar plates, contains RBC lysed by heat- gives appearance of dark brown, lysed RBC release various growth factors required for cultivation of fastidious pathogenic bacteria, e.g. haemophilus influenza, Neisseria meningitidis MacConkey Agar - selective-differential, selects for gram negative enteric organisms, isolate intestinal pathogenic microbes belonging to the Enterobacteriaceae family such as Salmonella and Shigella species. 2 factors are present in MacConkey Agar - crystal violet and bile salts, restricts the growth of Gram + bacteria 2 factors in MacConkey Agar to differentiate Gram - bacteria - lactose and the pH indicator neutral red—it is only red when under acidic conditions—are added to differentiate between lactose fermenters (lac+; red colonies) and non-fermenters (lac-; white/tan colonies) T/F: The base color of the agar plate also often changes color as the microbes consume the nutrients within the MacConkey Agar plate - True Color of MacConkey Agar pH >8.0 - agar can turn yellow (pH > 8.0) within the surrounding area of a growing non-fermenting microbe. Color of MacConkey Agar pH<6.8 - agar may turn pink or even a darker red within the region surrounding a lac+ microbe given its level of acid production during fermentation, e.g. Gramnegative/lac+ bacteria Escherichia coli- vibrant pink (pH < 6.8)Sorbitol MacConkey Agar (SMAC) - variant of MacConkey agar specifically formulated to detect the presence of the pathogenic strain of Escherichia coli O157:H7 (unable to ferment sorbitol), under enteric conditions E coli is able to ferment lactose and sorbitol