GPAT Microbiology Syllabus

What is a bacterial endospore and why is it significant?

A dormant, highly resistant survival structure (e.g., in Bacillus, Clostridium) that withstands heat, desiccation, and chemicals — important because it resists ordinary sterilization.

How do archaea differ from bacteria in cell wall composition?

Archaeal cell walls lack peptidoglycan; they may contain pseudopeptidoglycan (pseudomurein), proteins, or polysaccharides instead.

Name the three domains of life and which contains the archaea.

Bacteria, Archaea, and Eukarya; archaea form their own domain, distinct from bacteria despite being prokaryotic.

In what environments are archaea (extremophiles) commonly found?

Extreme habitats — high temperature (thermophiles), high salt (halophiles), acidic/alkaline conditions, and anaerobic methane-producing environments (methanogens).

What are protists?

A diverse group of mostly unicellular eukaryotic microorganisms that are not fungi, plants, or animals — including protozoa (animal-like) and algae (plant-like).

How do protists differ fundamentally from bacteria?

Protists are eukaryotes with a true membrane-bound nucleus and organelles, whereas bacteria are prokaryotes lacking these.

What are the main causes of food/pharmaceutical spoilage?

Microbial growth (bacteria, yeasts, molds), enzymatic and chemical reactions (oxidation, rancidity), and physical factors — favored by moisture, warmth, nutrients, and pH.

Which intrinsic factors of a product most influence microbial spoilage?

Water activity (aw), pH, nutrient content, redox potential, and presence of antimicrobial substances.

How does low water activity (aw) prevent spoilage?

Most spoilage microbes need aw above ~0.85–0.90; reducing available water (by drying, salting, or adding sugar) inhibits microbial growth and enzyme activity.

Name common methods used to prevent microbial spoilage of products.

Refrigeration/freezing, drying/dehydration, heat treatment (pasteurization/canning), salting or sugaring, acidification, modified-atmosphere packaging, and chemical preservatives.

What is pasteurization and what does it achieve?

A mild heat treatment (e.g., 72°C for 15 s, HTST) that kills most pathogens and spoilage organisms to extend shelf life without sterilizing the product.

What is a vaccine?

A biological preparation containing antigens (whole or part of a pathogen) that stimulates active acquired immunity and immunological memory against a specific disease.

Differentiate live attenuated and inactivated (killed) vaccines.

Live attenuated vaccines use weakened but living pathogens (e.g., BCG, MMR) giving strong, lasting immunity; inactivated vaccines use killed pathogens (e.g., injectable polio/Salk) which are safer but often need boosters.

What is a toxoid vaccine? Give an example.

A vaccine made from an inactivated bacterial toxin that retains antigenicity, inducing antitoxin antibodies — e.g., tetanus and diphtheria toxoids.

What are subunit/conjugate vaccines?

Vaccines containing only specific purified antigens (proteins/polysaccharides) of a pathogen; conjugate vaccines link a polysaccharide to a carrier protein to boost the immune response (e.g., Hib, pneumococcal).

What is antiserum (sera) and what type of immunity does it provide?

Serum containing preformed specific antibodies; when injected it gives immediate, short-lived passive immunity (e.g., antitetanus serum, antivenom).

Describe the basic process of producing immune sera (antiserum).

An animal (e.g., horse) is immunized with repeated antigen doses to stimulate antibody production; blood is collected, allowed to clot, the serum is separated, then purified, concentrated, tested, and sterilized.

Distinguish active and passive immunity.

Active immunity is produced by the host's own immune system after infection or vaccination (slow onset, long-lasting); passive immunity is acquired by transfer of preformed antibodies (immediate but temporary).

What are the key characteristics of fungi?

Eukaryotic, heterotrophic (absorptive nutrition), cell walls of chitin, non-photosynthetic; mostly multicellular (hyphae forming mycelium) but some unicellular (yeasts); reproduce by spores.

What is the structural difference between molds and yeasts?

Molds are filamentous, forming branching hyphae that make a mycelium; yeasts are unicellular and typically reproduce by budding.

What is the main component of the fungal cell wall?

Chitin (a polymer of N-acetylglucosamine), along with glucans — unlike plant cellulose walls or bacterial peptidoglycan.

Describe the basic structure of a virus.

A nucleic acid core (DNA or RNA) enclosed in a protein coat (capsid made of capsomeres); some viruses have an outer lipid envelope with glycoprotein spikes.

Why are viruses considered obligate intracellular parasites?

They lack metabolic machinery and ribosomes, so they cannot reproduce on their own and must hijack a living host cell's machinery to replicate.

What is a bacteriophage?

A virus that specifically infects and replicates within bacteria.

What is aseptic technique?

A set of practices that prevent contamination by unwanted microorganisms, maintaining sterility of materials, surfaces, and the working environment.

State the key principles of aseptic technique.

Sterilize all materials and surfaces, work near a flame or in a laminar-flow/biosafety cabinet, minimize air exposure of sterile items, disinfect surfaces and hands, and avoid touching sterile parts.

Define sterilization and how it differs from disinfection.

Sterilization is the complete destruction or removal of all microorganisms including spores; disinfection only reduces/kills most pathogenic vegetative microbes (not necessarily spores) on inanimate surfaces.

What are the main physical methods of sterilization?

Heat (dry heat in hot-air oven; moist heat in autoclave), filtration, and radiation (UV, gamma rays).

What are the standard operating conditions of an autoclave?

Moist heat (saturated steam under pressure) at 121°C and 15 psi for about 15–20 minutes; it kills microbes and spores by protein coagulation.

How is heat-sensitive (thermolabile) liquid sterilized?

By membrane filtration through filters of pore size 0.22 micrometers (or 0.45 µm), which physically remove bacteria without heat.

What is the principle of a microbial assay and when is it used?

It quantifies the potency of a substance (e.g., antibiotic or vitamin) by measuring its inhibitory or growth-promoting effect on a test microorganism, compared against a standard — used when chemical assays are not feasible.