Microbial control methods — A/L Biology

What must I remember about Microbial control methods?

• Microbial control aims to prevent infection, food spoilage, and contamination through physical, chemical, and antimicrobial pharmacological interventions.
• Sterilization completely destroys or eliminates all viable forms of microbial life, including bacterial endospores (the most resistant biological structures known), via autoclaving, dry heat ovens, ionizing radiation, or ethylene oxide gas.
• Disinfection reduces pathogenic microorganisms on inanimate objects to safe public health levels (does not guarantee endospore destruction); Antisepsis applies chemical agents (antiseptics: povidone-iodine, 70% ethanol, chlorhexidine) to living tissues to inhibit or kill microbes.
• Physical control methods: Moist heat under pressure in Autoclave (121°C at 15 psi for 15-20 min, coagulates/denatures proteins and destroys endospores), Dry heat (hot air oven at 160-170°C for 2 hours for glassware/metal instruments), Pasteurization (HTST: 72°C for 15 sec, kills heat-sensitive vegetative pathogens in dairy without ruining nutritional quality), Membrane filtration (0.22 μm pores for heat-labile antibiotic/vitamin solutions), and Radiation (UV at 260 nm damages DNA thymine dimers; gamma radiation sterilizes packaged medical equipment).
• Antimicrobial chemotherapy: Antibiotics act selectively against bacterial targets — cell wall synthesis inhibitors (Penicillins, Cephalosporins), protein synthesis inhibitors (Tetracyclines, Aminoglycosides binding 30S/50S ribosomes), nucleic acid inhibitors (Fluoroquinolones), and metabolic pathway antimetabolites (Sulfonamides).

Test yourself (1 minute)

1. Autoclave operating standard

   121°C (250°F) at 15 psi (103 kPa) for 15-20 minutes is the universally validated minimum standard required to denature proteins and incinerate resilient Bacillus stearothermophilus / Clostridium botulinum endospores.

2. 70% Alcohol efficacy paradox

   70% aqueous ethanol/isopropanol penetrates bacterial cell walls more effectively than 100% absolute alcohol, because water is essential to hydrolyze cellular proteins and facilitate intracellular denaturation.

3. Antimicrobial Resistance (AMR) crisis

   Overuse and misuse of antibiotics selects for resistant bacterial mutants harboring beta-lactamases, efflux pumps, or altered target enzymes (e.g., MRSA, multidrug-resistant TB), threatening modern surgical and therapeutic procedures.

Practise Microbial control methods questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 9

What should I study first?

What comes next?

Next in the syllabus

Where does Microbial control methods fit in the syllabus?

Year 2 · Term 3