Test: History, Taxonomy, Morphology and Physiology of Bacteria- 2 - NEET PG MCQ

The correct sequence for the Gram staining process is crucial for identifying bacterial types. Here is the simplified order:

• Methyl violet - This is the primary stain that colours all bacteria.
• Iodine - This acts as a mordant, helping the dye to adhere to the cell walls.
• Acetone - This is used for decolourisation. It differentiates between gram-positive and gram-negative bacteria.
• Carbol fuchsin - This is used as a counterstain to highlight the gram-negative bacteria.

Following these steps accurately is essential for effective Gram staining, leading to reliable identification of bacteria.

A Gram stain consists of four stages. Methylene blue serves as a counterstain for the acid-fast stain.

India ink stain is employed to illustrate the capsule. Among the cocci, Pneumococcus and Meningococcus possess a capsule.

In a Gram stain procedure:

• During decolorisation: All cells will appear gram-positive (violet).
• With excessive decolorisation: All cells will seem gram-negative (pink).

Intermittent heating is applied in acid-fast staining (but not in Gram staining).

During the lag phase of the growth curve, the following events occur:

• The bacterial cell size increases as the cells prepare for division.
• Cells are metabolically active, synthesising proteins and other essential molecules.
• There is no significant increase in the number of cells at this stage.

This phase allows bacteria to adapt to their environment before entering the next growth phase.

Microaerophilic organisms need a minimal level of oxygen (around 5%). Examples include:

• Campylobacter
• Helicobacter
• Mycobacterium bovis

The term viable but not cultivable refers to organisms that can survive and reproduce but cannot be grown in standard laboratory conditions. This means that while these organisms are alive and functional, they do not multiply in artificial environments, making them difficult to study.

• M. leprae: This bacterium causes leprosy and is known to be non-cultivable in the lab.
• M. tuberculosis: The bacterium responsible for tuberculosis can be cultivated under specific conditions.
• Treponema pallidum: This bacterium, which causes syphilis, is also considered viable but not cultivable in artificial media.
• Salmonella: This bacterium can be easily cultivated in laboratory settings.
• Staphylococcus: This group of bacteria can also be cultivated in the lab.

In summary, the term viable but not cultivable primarily applies to certain pathogens like M. leprae and Treponema pallidum, highlighting the challenges in studying them due to their inability to grow in typical lab conditions.

The bacterial growth curve consists of several distinct phases that describe how bacteria multiply over time. The correct order of these phases is:

• Lag Phase: This initial phase is where bacteria adapt to their environment. They are not yet dividing, but they are getting ready to grow.
• Log Phase: Also known as the exponential phase, this is when bacteria start dividing rapidly. The population increases exponentially.
• Stationary Phase: Here, the growth rate slows down as resources become limited. The number of new cells created equals the number of cells dying.
• Decline Phase: In this final phase, the number of living bacteria decreases due to depletion of nutrients and accumulation of waste products.

Understanding this sequence is important for studying bacterial behaviour and growth dynamics.

The time it takes for the population of E. coli to double, or its generation time, is 20 minutes. In contrast, M. tuberculosis has a doubling time of 20 hours, while M. leprae takes 20 days.

Phototropism is the process by which plants grow towards sunlight. This happens because plants need light to make their food through a process called photosynthesis. When light shines on a plant, certain hormones called auxins are produced. These hormones help the plant cells on the side that is away from the light to grow faster. As a result, the plant bends towards the light source.

• This growth towards the light helps the plant to receive more sunlight.
• More sunlight means more energy for the plant to produce food.
• Phototropism is essential for the overall health and growth of the plant.

The organism that thrives in alkaline pH is Vibrio. This bacterium is well-suited to environments with higher pH levels, which can be found in various aquatic habitats.

• Klebsiella typically prefers neutral pH.
• Pseudomonas can survive in a range of pH levels but does not specifically prefer alkaline conditions.
• E. coli generally thrives in neutral pH environments.

In summary, Vibrio is the best choice for growth in alkaline conditions.

An obligate intracellular organism is one that can only survive and reproduce inside the cells of a host. These organisms depend entirely on their host for nutrients and replication. Here are some key points about such organisms:

• They cannot grow or multiply outside of a living host cell.
• They often cause diseases in the host.
• Examples include certain bacteria, like Chlamydia, which are known to infect human cells.

Understanding these organisms is crucial for studying infectious diseases and developing treatments.

Exotoxins are specific types of toxins produced by bacteria that are secreted into their environment. Here are some key points about them:

• Not LPS: Unlike lipopolysaccharides (LPS), which are found in the outer membrane of Gram-negative bacteria, exotoxins are proteins.
• Heat Stability: Many exotoxins are heat-labile, meaning they can be inactivated at high temperatures, although some may retain activity under certain conditions.
• Antigenic: Exotoxins are generally antigenic, which means they can provoke an immune response in the body.
• Toxoid Preparation: Toxoids can be prepared from exotoxins. A toxoid is a modified toxin that has lost its harmful properties but can still stimulate an immune response.

Exotoxins are toxic substances produced by certain bacteria. Here are some key characteristics:

• Highly antigenic: Exotoxins can stimulate a strong immune response, meaning the body can produce antibodies against them.
• Heat stable: This statement is incorrect. Exotoxins are generally heat labile, meaning they can be inactivated by heat.
• Neutralized by antibody: Antibodies can effectively neutralise the effects of exotoxins, providing immunity.
• Active in very minute doses: Exotoxins can cause significant effects even in tiny amounts.

Endotoxins are components of the outer membrane of certain bacteria. Here are some key points about them:

• Heat stable: Endotoxins can withstand high temperatures, making them resistant to heat.
• Poorly antigenic: They do not provoke a strong immune response, hence they are considered poorly antigenic.
• Somatic antigen: Endotoxins are associated with the bacterial structure, specifically the cell wall.
• However, endotoxins are not neutralised by specific antibodies, unlike some other toxins.