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Microbiology: Gram-negative and Gram-positive Bacteria

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    Out of 28 Unknown microorganisms, slant 6O was randomly selected, and subjected to testing in order to identify it’s species. Seventeen of the unknown bacteria were classified as Gram-negative bacilli: Corynebacterium pseudodiphtheriticum, Enterobacter aerogenes, Eschirichia coli, Flavobacter capsulatum, Helicobacter pylori, Klebsiella pneumonia, Klebsiella oxytoca, Proteus hauseri, Proteus mirabilis, Proteus vulgaris, Pseudomonas aeroginsoa, Alcaligenes faecalis, Rhizobium radiobacter, Salmonella typi, Serratia marcescnes, Shigella flexneri, or Yersina pseudo tuberculosis.

    Ten of the unknown bacteria were classified as Gram-positive bacilli: Bacillus cereus, Bacillus circulans, Bacillus coagulans, Bacillus megaterium, Bacillus subtilis, Bacillus thuringiensis, Brevibacillus brevis, Geobacillus stereothermophilus, Lysinibacillus sphaericus, Clostridium perfringens.

    Lastly, there were also 11 Gram-positive cocci microbes: Enterococcus faecalis (Streptococcus), Streptococcus lactis (Lactococcus), Streptococcus mutans, Streptococcus pneumoniae, Micrococcus (Kocuria) roseus, Sarcina lutea (Micrococcus luteus), Sporosarcina ureae, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Rhodococcus rhodochorous. Procedure: A gram stain was performed to identify if unknown 6O is a gram positive or gram negative and determine its shape.

    The gram stain was performed as stated in Laboratory Exercises In Microbiology, 8th Ed, pages 45-49 (Harley, 2011). A minor adjustment was made in the process of decolorization with crystal violet, allowing the time to be reduced to 20 seconds to prevent over decolorization. Purpose: In order to determine a unknown microbe, a gram stain is the first procedure used to determine if the bacteria is a gram negative or a gram positive. This process will eliminate a substantial amount of microbes, and will provide the cell shape.

    Gram-positive cells do not decolorize with alcohol, and Gram-negative cells do decolorize. This allows the Gram-positive bacteria to appear purple and Gram-negative bacteria to appear pink after staining. A Gram-positive cell has a thick peptidoglycan cell wall that is able to retain the crystal violet stain during staining, while a Gram-negative cell has only a thin layer of peptidoglycan Data: The gram stain procedure resulted in microbe 6O as having a clear view of long purple rods.

    Analysis: The gram stain determined 6O as a gram-positive bacillus, eliminating thirty microbes: Corynebacterium pseudodiphtheriticum, Enterobacter aerogenes, Eschirichia coli, Flavobacter capsulatum, Helicovacter pylori, Klebsiella pneumoniae, Klebiella oxytoca, Proteus hauseri, Proteus mirabilis, Proteus vulgaris, Pseudomonas aeroginosa, Alcaligenes faecalis, Rhizobium radiobacter, Salmonella typi, Serratia marcescens, Shigella flexneri, Tersina pseudotuberculosis, Erwina persicinus, Serratia liquifacens, Enterococcus faecalis, Streptococcus lactis, Streptococcus mutans, Streptococcus pneumoniae, Micrococcus roseus, Sarcina lutea, Sporosarcina ureae, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Rhodococcus rhodochorous.

    Ten possible microorganisms remained, Gram Positive Bacilli: Bacillus cereus, Bacillus circulans, Bacillus coagulans, Bacillus megaterium, Bacillus subtilis, Bacillus thuringiensis, Brevibacillus brevis, Geobacillus stereothermophilus, Lysinibacillus sphaericus, Clostridium perfringens (Bergey’s, 1984). Error: Many errors can occur when performing a Gram stain. Some Gram-positive bacteria may lose the stain easily and therefore appear as a mixture of Gram-positive and Gram-negative bacteria (Gram-variable). When sterilizing the inoculating loop, If it is not cooled to proper temperature, the microbe can be killed.. Finally, do not blot the slide vigorously with bibulous paper or the Gram-stain can be rubbed off (Harley, 2011).

    Microbiology: Gram-negative and Gram-positive Bacteria. (2016, Dec 20). Retrieved from https://graduateway.com/microbiology-notes/

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