ID: Semester 1

Exam Style Questions for first Semester of Infectious Disease module

Which structure is primarily responsible for maintaining bacterial cell shape?

Cell wall

What is the main function of bacterial ribosomes?

Protein Synthesis

Gram-positive bacteria are characterised by what?

Thick peptidoglycan layer

Which structure is involved in bacterial attachment to surfaces?

Pili

In bacterial taxonomy, the most specific level of classification is what?

Species

Describe the basic structure of a bacterial cell

• Prokaryotic - no nucleus

• Cell wall

• Plasma Membrane

• Cytoplasm + Ribosomes

• Nucleoid DNA

Differentiate between Gram-positive and Gram-negative bacteria

Stain with Crystal violet + Iodine, Counterstain with Safranin.

Gram-positive bacteria: thick peptidoglycan cell wall and no outer membrane, retain crystal violet stain, appear purple.

Gram-negative bacteria: thin peptidoglycan layer and an outer membrane containing lipopolysaccharide, stain pink after counterstaining.

Define bacterial taxonomy

Bacterial taxonomy is the classification, identification, and naming of bacteria based on shared characteristics such as morphology, genetics, and biochemical properties.

What is an Acid – Fast Bacteria?

Appear Gram-Positive Bacteria but their cell wall consists of mycolic acid (+ lipids)

Describe the structure of a bacterial cell and explain the function of each component.

Bacteria are prokaryotic cells lacking membrane-bound organelles. The cell wall, composed of peptidoglycan, provides structural support and protection against osmotic pressure. The plasma membrane acts as a selective barrier and is involved in energy generation.

The cytoplasm contains enzymes, metabolites, and ribosomes, which are responsible for protein synthesis. The nucleoid region contains the bacterial chromosome, which is circular and not enclosed within a nucleus.

Some bacteria possess additional structures such as capsules, which enhance virulence and protect against environmental stress; flagella, which enable motility; and pili, which assist in attachment and genetic exchange.

Together, these structures allow bacteria to survive, reproduce, and adapt to diverse environments.

Discuss the importance of bacterial taxonomy and how it is applied in microbiology

Bacterial taxonomy is essential for organising and identifying bacterial species, enabling scientists to understand relationships between organisms. Classification systems group bacteria based on shared characteristics, including morphology, metabolic traits, and genetic similarities.

Modern taxonomy relies heavily on molecular techniques such as DNA sequencing, particularly 16S rRNA analysis, which provides accurate identification and evolutionary relationships.

Taxonomy is applied in clinical microbiology to identify pathogens and guide treatment decisions, in veterinary practice to diagnose infections, and in research to study microbial diversity. It also aids in communication among scientists by providing a universal naming system.

Overall, taxonomy underpins many areas of microbiology by allowing accurate identification, comparison, and study of bacteria.

How does a bacteria being Gram-negative impact the treatment options available for a patient?

Gram-negative bacteria possess an outer membrane that acts as a barrier to certain antibiotics, making them more resistant. The presence of lipopolysaccharide can also contribute to pathogenicity. As a result, specific antibiotics that can penetrate the outer membrane or target internal processes are required.

Explain the difference between Genotyping and Phenotyping. What are some examples?

Phenotyping: observable characteristics, such as morphology, staining, and biochemical activity.

Examples include:

•Colony Morphology (shape, size)

•Gram Staining

•Biochemical tests (Catalase, Oxidase)

•Growth Tests (Oxygen, Temperature)

•Antibiotic Suscepibility

Genotyping: genetic material (DNA).

Examples include:

•PCR

•Gene Sequencing (Whole and sections like GC)

Genotyping typically more accurate and reliable identification - not affected by environmental factors.

Describe binary fission

Binary fission is the process by which bacteria reproduce. The circular DNA is first replicated, and the cell elongates. The two DNA molecules move to opposite poles, and a septum forms in the middle of the cell. The cell then divides into two genetically identical daughter cells.

Define Aseptic and Disinfectant

Aseptic technique: prevent microbial contamination of

cultures (lab) or wounds (hospitals).

Sepsis: microbial contamination.

Asepsis: absence of significant contamination.

Antimicrobial chemicals, expected to destroy pathogens but not to achieve sterilization

Disinfectant: used on inanimate objects (typically more toxic than antiseptics)

Antiseptic: used on living tissue

Define Biosecurity

Biosecurity:

- On farm= keeping infectious diseases out!

- For laboratories= keeping infectious diseases in!

• Disinfection: Destruction of microorganisms by direct exposure

to chemical or physical agents. Think wellies in footbath.

Generally less extreme physical/chemical methods.

• Sterilisation: Destroy all microbial life on lab and surgical

procedures. Extreme physical/chemical.

• Antisepsis: Chemicals applied to body surfaces to

destroy/inhibit pathogens

• Bacteriostatic: Inhibits bacterial reproduction

• Bactericidal: Kills bacteria

• Fungicide, sporicide, germicide, biocide

Define Acidic-Anionic detergents

Anion reacts with plasma membrane. Nontoxic, non-corrosive, and fast acting. Laundry soap, dairy industry.

Define Cationic detergents

Quaternary ammonium compounds (Quats). Strongly bactericidal against wide range, but esp. Gram+ bacteria

What are Surface Acting ingredients/surfactants?

Soaps and Detergents. Major purpose of soap: Mechanical

removal and use as wetting agent

What are Phenols and Phenolics used for?

Phenol (carbolic acid)

• Rarely used today=skin irritant & strong odour.

• Acts as local anaesthetic.

Phenolics (chemical derivatives of phenol)

• Biphenols (pHisoHex): Effective against gram -positive

staphylococci and streptococci.

• Destroy plasma membranes and denature proteins.

How are Halogens effective disinfectants?

Chlorine

• Oxidizing agent - Broad spectrum, use in pools & drinking water, fair sporicidal activity

Iodine

• More reactive, more germicidal. Alters protein synthesis and

membranes. Tincture of iodine (solution with alcohol)=wound antiseptic. Occasional skin sensitivity. Poor sporicidal activity

How are Alcohols effective Disinfectants?

Kill bacteria, fungi, but not endospores or naked

viruses.

• Denature proteins & disrupting cell membranes.

• Evaporate= no residue.

• Used mechanically wipe microbes off skin before

injections or blood drawing.

• Not good for open wounds, as coagulate proteins.

• Ethanol: Drinking alcohol. Optimum = 70% (v/v).

• Isopropanol: Rubbing alcohol. Better disinfectant than

ethanol = cheaper and less volatile.

How are heavy metals used as a disinfectant?

Include copper, selenium, mercury, silver & zinc.

• Oligo-dynamic action: toxic as metal ions combine

with sulfhydryl (—SH) groups = proteins denatured.

• Silver: 1% silver nitrate used to protect infants against

eye infections.

• Mercury: Compounds e.g. mercurochrome disinfect

skin wounds.

• Copper: Copper sulphate is used to kill algae in pools

and fish tanks. Use in dairy cow footbaths.