Microbiology and Biotechnology: Sterility, Antimicrobials and Recombinant Products
What the domain tests
This domain checks control of microbial contamination and the biotechnological production of modern medicines. Expect sterilisation parameters, sterility testing methods, antimicrobial mechanisms and resistance, vaccines, and recombinant or monoclonal antibody products.
Core rules to hold
- Sterility testing: membrane filtration (0.45 µm for general filtration, 0.22 µm for sterilisation) suits solutions containing preservatives and antibiotics; direct inoculation suits ointments and viscous preparations.
- Validation parameters: the D-value is the time to reduce bioburden by one log cycle; the z-value is the temperature change giving a tenfold change in D-value; SAL is 10⁻⁶.
- Microbial limit tests quantify total aerobic count and screen for specified organisms such as Escherichia coli and Salmonella; preservative efficacy tests confirm self-preservation.
- Antibiotic mechanisms: beta-lactams and vancomycin inhibit cell wall synthesis; aminoglycosides bind the 30S subunit; macrolides and chloramphenicol the 50S; fluoroquinolones inhibit DNA gyrase; sulphonamides block folate synthesis; polymyxin disrupts membranes.
- Resistance: beta-lactamase production, efflux pumps, porin loss, target modification.
- Biotechnology: recombinant DNA steps (isolation, insertion, transformation, selection, expression); PCR amplification; monoclonal antibodies named -mab; biosimilars are not generic equivalents.
Worked example
A preparation carries an initial bioburden of 10⁶ organisms and must achieve SAL 10⁻⁶, a 12-log reduction. With a D-value of 1.5 minutes at the chosen temperature, the minimum holding time is 12 × 1.5 = 18 minutes, before adding any safety margin.
Traps that cost marks
Confusing D-value with z-value; using 0.45 µm filters for sterilisation; calling a biosimilar a generic; assuming Gram-negative resistance arises only from enzymatic degradation.