Question

Which of the given statements are correct? (i) Bacillus subtilis is a Gram (+) bacteria. (ii) Escherichia coli is a Gram (-) bacteria. (iii) Washing of the Gram's stain in Gram (-) bactent! due to high lipid content of the cell wall, which ç dissolved in organic solvents like acetone. (a) (i) and (ii) (b) (ii) and (iii) (c) (i) and (iii) (d) (i), (ii) and (iii)

Short answer

Statements (i), (ii), and (iii) are correct. So, the correct answer is (d) (i), (ii) and (iii).

Step-by-step solution

Verify Statement (i)

Bacillus subtilis is known in microbiology as a Gram-positive bacterium due to its thick peptidoglycan layer in the cell wall which retains the crystal violet dye during the Gram staining process.

Verify Statement (ii)

Escherichia coli (E. coli) is a well-studied Gram-negative bacterium. Its cell wall contains a thin peptidoglycan layer and an outer membrane with lipopolysaccharides, which does not retain the crystal violet dye and hence takes up the counterstain (safranin or fuchsin).

Verify Statement (iii)

Gram-negative bacteria, including E. coli, lose the initial crystal violet stain when washed with a decolorizer such as alcohol or acetone. This happens because the decolorizer dissolves lipids in the outer membrane of the Gram-negative bacteria, making the cell wall more permeable and allowing the dye to escape.

Key concepts

Bacillus subtilis

Understanding the nature of Bacillus subtilis is essential in microbiology. Often used as a model organism, this bacterium is known for its robustness and ability to form endospores, which can survive extreme conditions. It belongs to the Gram-positive category of bacteria due to its particularly thick cell wall consisting mainly of peptidoglycan. This layer traps the crystal violet dye during the Gram staining process, which is why it appears purple under a microscope after staining.

Knowing its Gram-positive characteristics is not only key in identifying Bacillus subtilis in laboratory settings, but also in understanding its responses to antibiotics, as its thick cell wall presents a different set of challenges and targets for treatment compared to Gram-negative bacteria.

Escherichia coli

Another critical organism in the study of microbiology is Escherichia coli, often abbreviated as E. coli. This bacterium is a prime example of Gram-negative bacteria. It is widely researched due to its rapid growth and the simplicity with which it can be manipulated genetically. Unlike Gram-positive bacteria, E. coli has a thin peptidoglycan layer and an additional outer membrane containing lipopolysaccharides.

During Gram staining, the outer membrane of E. coli doesn't retain the crystal violet dye, and after a decolorization step with a solvent such as alcohol or acetone, it takes on a pink or red color from the counterstain, typically safranin. This distinction is pivotal in microbiology for diagnosing infections accurately and prescribing the correct antibiotics, as Gram-negative bacteria are often more resistant to certain types of antibiotics.

Gram-positive bacteria

Gram-positive bacteria are characterized by their thick cell walls predominantly composed of peptidoglycan. A critical aspect of these bacteria is their response to Gram staining; they retain the violet dye, resulting in a purple appearance under a microscope.

Because of their cell wall structure, Gram-positive bacteria are typically more susceptible to antibiotics that target peptidoglycan, such as penicillin. These bacteria are often responsible for causing a variety of infections and diseases, but their Gram-positive status can be used to narrow down the types of antibiotics that might be effective for treatment.

Gram-negative bacteria

In contrast to their Gram-positive counterparts, Gram-negative bacteria have thinner peptidoglycan layers and an additional outer membrane rich in lipopolysaccharides. In a Gram stain, these bacteria do not retain the violet dye after a decolorization step and instead are visualized as pink or red after being counterstained.

This structural difference has significant clinical implications; Gram-negative bacteria are often resistant to antibiotics that are effective against Gram-positive organisms. They have defense mechanisms such as efflux pumps and the ability to modify their porins, making them a challenging opponent in infection control and treatment.

Microbiology

Microbiology is the scientific study of microorganisms, encompassing numerous disciplines including virology, bacteriology, and parasitology, to name a few. Techniques like Gram staining play a crucial role in microbiology by aiding in the identification and classification of bacteria.

Understanding the differences between Gram-positive and Gram-negative bacteria is vital not just for basic science but also for clinical applications, as it guides physicians in choosing the correct therapeutic strategies. The field of microbiology continues to advance with the development of new techniques, enhancing our comprehension of the microbial world and its impact on health, ecology, and beyond.