Test: History, Taxonomy, Morphology and Physiology of Bacteria- 1 - NEET PG MCQ

Treponema pallidum, the causative agent of syphilis, was identified in 1905 by Schaudinn and Hoffmann.

The administration of a broad-spectrum antimicrobial agent reliably eliminates the organisms and treats the diseases.

Corynebacterium diphtheriae is commonly referred to as the Klebs-Loeffler bacillus.

Antony van Leeuwenhoek, a Dutch scientist, was the initial individual to accurately observe and describe microorganisms through the use of lenses. He is regarded as the pioneer of the simple microscope (1694).

• Zacharias Jansen and his father were responsible for the creation of the first compound microscope.
• Ernst Ruska invented the electron microscope in 1931.

Concept of disease causation: The spontaneous generation of life suggests that life can emerge from chemical reactions. This notion was debunked by Louis Pasteur.

• The germ theory of life, also known as the single cause theory (by Louis Pasteur), proposes a direct relationship between a causative agent and a disease, represented as [Agent → Man → Disease].
• However, this theory faced criticism because not everyone who is exposed to an agent develops the corresponding disease.

Multifactorial causation was introduced by Pettenkofer and the Munich group. The theory of the web of causation, proposed by MacMahon, Pugh, and Ipsen in their 1960 publication, Epidemiologic Principles and Methods, posits that disease results from a complex interplay of various predisposing factors, each with different levels of relative risk.

The vaccination against smallpox using cowpox was suggested by Edward Jenner. Louis Pasteur developed vaccines for:

• Anthrax
• Rabies
• Cholera

A low-level disinfectant like Isopropyl alcohol is sufficient since a stethoscope is considered a non-critical item based on Spaulding’s classification.

Parasites and fungi are classified as eukaryotes (for instance, Entamoeba is a type of parasite), while bacteria and blue-green algae fall under the category of prokaryotes.

Shigella and Klebsiella are non-motile members of the Gram-negative Enterobacteriaceae family.

Swarming behaviour is displayed by:

• Cl. tetani
• Proteus
• Vibrio parahemolyticus
• Vibrio alginolyticus

Prokaryotes encompass bacteria and blue-green algae. Eukaryotes comprise:

• fungi
• algae (excluding blue-green)
• protozoa
• helminths
• slime moulds

The primary function of the bacterial capsule is to evade phagocytosis. Additionally, the capsule assists in the formation of biofilms and promotes adhesion.

• Capsulated bacteria are a type of microbe characterised by a protective outer layer known as a capsule.
• This capsule serves various functions, including shielding the bacteria from the host's immune response.
• Additionally, it aids in adherence to surfaces and enhances the bacteria's ability to cause disease.
• Examples of capsulated bacteria include:
• Streptococcus pneumoniae - associated with pneumonia and meningitis.
• Neisseria meningitidis - known for causing meningococcal disease.
• Haemophilus influenzae - implicated in respiratory infections.
• Escherichia coli - certain strains are known to be pathogenic.

In Gram-negative bacteria, certain structures are present, while others are not. Here’s a breakdown of the components:

• Peptidoglycan: This is a key component of bacterial cell walls and is typically found in Gram-negative bacteria, although in smaller amounts compared to Gram-positive bacteria.
• Teichoic acid: This substance is primarily found in Gram-positive bacteria and is not present in Gram-negative bacteria.
• LPS (Lipopolysaccharide): This is a major component of the outer membrane of Gram-negative bacteria and plays a crucial role in their structure and function.
• Porin channels: These are proteins located in the outer membrane of Gram-negative bacteria, allowing the passage of small molecules.

In summary, the key component that is not found in Gram-negative bacteria is teichoic acid.

The Craigie’s tube method is primarily used to differentiate between various types of bacteria based on specific characteristics. Here’s a simplified breakdown:

• Motile and nonmotile strains: This method helps identify if bacteria can move on their own.
• Virulent and avirulent strains: It distinguishes between harmful and non-harmful bacteria.
• Capsulated and noncapsulated strains: This indicates whether bacteria have a protective capsule or not.
• Rough and smooth strains: This refers to the texture of the bacterial surface.

Each of these categories is important in microbiology for understanding bacterial behaviour and characteristics.

To be suitable for visualization by electron microscopy (EM), the specimen must be exceptionally thin, with a thickness ranging from 20 to 100 nm.

The resolving power of a microscope is influenced by both the wavelength and the numerical aperture. The latter, in turn, is affected by the refractive index and the angular aperture.

Gram-negative bacteria are readily decolourised due to several factors:

• A thin peptidoglycan layer with minimal cross-linking.
• The presence of a lipid-rich lipopolysaccharide layer that is easily disrupted by the decolouriser.

• ZN stain consists of three parts:
• Primary stain: Basic fuchsin + Phenol.
• Decoloriser: Sulfuric acid or acid-alcohol.
• Counter stain: Methylene blue or Malachite Green.

Acid fast bacilli can be effectively identified through a specific staining technique. The most commonly used method for this purpose is the Ziehl–Neelsen stain, which is designed to highlight these bacteria.

• This technique uses a special dye that binds to the cell wall of acid-fast organisms.
• It is crucial for diagnosing infections caused by bacteria such as Mycobacterium tuberculosis.
• Other staining methods, like Albert, Neisser, and Ponder, are not typically used for this purpose.

In summary, the Ziehl–Neelsen stain is the key method for identifying acid fast bacilli.