Molecular Biology and Genomics in Veterinary Microbiology
What you must know
Molecular questions test nucleic acid structure and replication, gene expression (transcription, translation), PCR principles (primers, denaturation, annealing, extension, amplicon detection), sequencing, whole-genome sequencing, and bioinformatics interpretation. Understand DNA vs. RNA viruses, reverse transcription, plasmids and horizontal gene transfer (conjugation, transformation, transduction), and mobile genetic elements in resistance spread. Know molecular diagnostics (conventional PCR, real-time PCR with Ct values, sequencing for typing) and the limitations of each (inhibitors, contamination, colonization vs. infection).
Traps
Questions love Ct value interpretation - lower Ct means more target nucleic acid, not less. Another trap is confusing PCR detection with viability or assuming sequencing always identifies species without reference databases. Watch for questions that conflate horizontal gene transfer mechanisms (conjugation requires contact; transduction uses phage; transformation takes up free DNA). Also beware of amplicon contamination causing false positives.
Rule of thumb
If the stem asks about spread of resistance genes between bacteria, think horizontal gene transfer, most often conjugation via plasmids.
Worked example
A question states that a real-time PCR result has a low Ct value and asks what it means. The answer is a high target load, because fewer amplification cycles were needed to cross the threshold. The discriminator is the inverse relationship between Ct and target quantity.