Gram Positive Bacteria And Gram Negative Bacteria

The Gram stain was used to determine if the bacteria was gram positive or negative. A negative test shows a pink color and a positive test is a purple color. When a bacterium is negative it is because it has an outer membrane and a thin layer of peptidoglycan that is much harder to stain. A positive bacterium has a thick layer of peptidoglycan and no outer membrane that can be penetrated by crystal violet.

Escherichia coli cells would be pink following a gram stain. E. coli is a gram negative cell due to its thin peptidoglycan layer and its outer membrane structure. In the gram staining process, the outer membrane does not play a role in staining but the peptidoglycan

This experiment was given to us to utilized previous knowledge learned throughout the semester to identify a gram negative unknown bacterium. We had to first learn the difference between a gram negative and a gram positive organism. We started off with doing gram stains to determine whether it was positive or negative. Based on the gram stains, a gram positive stains purple and a gram negative stains pink. A gram positive stains purple because the cell walls is made of a thick peptidoglycan layer and doesn’t

8. Discuss a possible mechanism of Gram Staining in terms of differences in structure and chemistry between the walls of gram-positive and gram-negative

Gram staining is a technique used to determine if the bacteria is Gram positive or Gram- negative. Gram staining procedure uses crystal violet stain, iodine moderator, alcohol decolorizer and safarin counter stain. In Gram- negative bacteria the primary stain will be washed out with the decolorizer and it will be stained with the counterstain. Whereas in Gram-positive bacteria the primary stain will not leave the cell wall. This difference comes from difference in the structure of the cell wall that retains the stain.

A four-quadrant method, also known as a streaking technique, was performed to isolate colonies of the two bacteria. Using an aseptic procedure for organism removal, a heated and sterilized loop was used to inoculate bacteria from the unknown test tube and then used to streak two solid nutrient agar plates, one plate was placed in a 37 degree Celsius incubator and the other plate was placed in the laboratory lockers at room temperature. After a 48-hour incubation period, both nutrient agar plates were observed; the plate incubated at 37 degrees Celsius had the more distinguished bacterial colonies of the two nutrient agar plates. The two colonies that were qualitatively identified were a yellow colony and a clear colony. Both colonies were smeared on separate slants and incubated and a Gram stain was performed to observe morphology. Gram staining is an experimental technique that allows an observer to distinguish between colonies of bacteria based on the composition of a bacteria’s cell wall. The information obtained in a Gram stain indicates whether the bacteria is Gram-positive or Gram-negative based on the ability of its cell wall to retain stain. A gram staining technique includes bathing a smear of bacteria in crystal violet to stain the bacteria purple, following a treatment with iodine and decolorizer, and a counterstaining with safranin. Gram-negative

From last week’s test, we achieved pure cultural characteristics from the two slants we made. The growth we saw on the agar slant that contained the yellow specimen was a soft, smooth, yellow growth. The growth we saw on the beige specimen was a thin, even, beige growth. Both cultural characteristics were achieved in the appropriate categories. The categories we were looking for contained abundance of growth, pigmentation, optical characteristics, and consistency. Today we will be preparing two bacterial smears from each specimen and Gram staining them. The reason we are conducting this test is to differentiate between two principle groups, gram positive and gram negative and to further know if a pure culture from both organisms was achieved. This is important for classification and differentiation of microorganisms. The Gram stain reaction will help us tell the difference of the chemical composition of bacterial cell walls. The Gram stain procedure uses four different reagents such as crystal violet, gram’s iodine, ethyl alcohol, and safranin. Before the Gram stain is performed we must make two bacterial smears of the two specimens. We placed one loop of distilled water on a clean slide aseptically. He transferred the specimen from the agar slant that contained the yellow growth and placed it on the slide with the water and gently mixed it together in a circular motion approximately the size of a nickel. He let the smear air dry for one minute and gently heat

The second bacterium was gram positive. There are three tests that are used to identify gram positive bacteria. The three tests are hemolyses on blood agar, Mannitol fermentation on mannitol salt agar, and the coagulase test using plasma-containing serum in coagulase tubes.

Serratia Marcescens are rod-shaped bacteria in the family Enterobacteriaceae. They are a group of Gram negative bacterium that are opportunistic human pathogens humans(Petersen and Tisa 2013). The genus Serratia has 14 recognized species with 2 subspecies(Mahlen 2011). S. marcescens cause in hospital-acquired infections (HAIs) (Sydnor and Perl 2011) and diarrhea associated with HIV/AIDS. Serratia can survive in different environments like water, soil, and the digestive tracts of various animals Petersen and Tisa 2013). In the gastrointestinal tract, it can destroy microvilli and vacuolization. It can also cause nosocomial infections like catheter-associated bacteremia, urinary tract infections respiratory tract infection, meningitis, bacteremia

Escherichia coli is a gram negative bacteria which is the main aerobic commensal bacteria found in the intestines of animals; it can also become pathogenic if it gets into the urinary tract ot the blood (Erb et. al., 2007). Staphylococcus aureus is a gram positive bacteria. It is the leading cause of bacterial infections in humans involving the skin, blood, and lower respiratory tract in America (De Leo et. al., 2009); Natural selection of antibiotic resistance in S. aureus has led to the emergence of increased resistance to penicillin, methicillin, and vancomycin within the human population (De Leo et. al., 2009). One important difference between gram-positive and gram-negative bacteria is the structure of their cell walls. The cell walls

Serratia Marcescens is a rod (bacillus) shaped bacteria known best for its red coloration. It has a single arrangement and is Gram negative. It grows at room temperature and can be found in soil, water, animals and on plants, but it is especially common in damp areas such as bathrooms or kitchens. Like all bacteria, it reproduces by binary fission. Serratia Marcescens mainly causes urinary and respiratory tract infections but can also cause pneumonia, bloodstream infections, wound infections, and meningitis along with a variety of other infections. It can be difficult to treat S. Marcescens as it is resistant to various antibiotics. In this experiment we tested the effects of antiseptics on the zone of inhibition on serratia marcescens.

After viewing the end result of the Gram Stain, I saw that the Gram positive bacterial cells were stained violet, while the Gram negative cells were stained red. In the mixed culture under the microscopes, I was able to notice that the Gram positive cells, Enterococcus durans, were in clusters of short chains. The Gram negative, Proteus mirabilis, were in rod-shaped forms that were spread across the slide. These cells did not seem to cluster.

The most difficult part of the experiment was separating the Gram positive from the Gram negative. I knew my Gram negative was rod-shaped and my Gram positive was coccus-shaped. I had to spend 2 days streaking many plates trying to isolate my two bacteria. The morphology of both were very similar and it was difficult to tell the difference until I was able dilute the colonies by streaking TSA plates multiple times.

4.2 The gram stain is an important tool used to identify the structure and also what group a certain bacteria would belong too. It is essential in identifying the group of bacteria, based on the characteristics of staining it gives the bacteria a way to be properly examined by using a microscope. The gram stain consists of showing if the color of the bacteria undergoes any changes and also judges what is different between both of the physical and chemical properties of the cell wall. (“Importance of a Gram Stain”, 2011, para.

It is found everywhere in the environment but it flourishes in damp conditions like bathrooms, where it is commonly found growing on tile grout, shower corners, toilet water line, and basin, where it manifests as a pink discoloration and slimy film feeding off phosphorus-containing materials or fatty substances such as soap and shampoo residue (Serratia marcescens. (n.d.). The topmost risk factor for Serratia marcescen infection is long drawn out hospitalization. Those who have a weak immune system are more prone to the development of these nosocomial infections. Important triggering factors include: intra peritoneal, intra venous or urinary catheters, instrumentation of the respiratory tract, such as bronchoscopy and ventilators, intra articular injections, trauma to the skull, neuro-surgery, epidural injection, or a lumbar puncture. (Serratiamarcescens.net: What Is Serratia Marcescens? (2016)). Most Serratia marcescen strains are resistant to several antibiotics because of the presence of R-factors, which are a type of plasmid that carry one or more genes that encode