Microbiology and Immunology: Pathogens, Host Defense, and Control
Core concepts
Separate the microbial groups by structure. Bacteria are prokaryotes with peptidoglycan cell walls (Gram-positive thick, Gram-negative thin plus outer membrane with LPS), 70S ribosomes, and no membrane-bound nucleus. Archaea lack peptidoglycan. Fungi are eukaryotic with ergosterol membranes and chitin walls. Viruses are obligate intracellular parasites with capsids and either DNA or RNA genomes; they need host machinery. Know growth phases (lag, log, stationary, death), and the effect of temperature, pH, and oxygen class. Sterilization kills all microbes; disinfection reduces pathogens on surfaces; antibiotics target cell wall, ribosome, or folate synthesis, and resistance arises via mutation, plasmids, and efflux pumps. Immunology: innate immunity (barriers, complement, phagocytes, inflammation) versus adaptive immunity (B cells and antibodies, T cells and cytokines). Know antibody classes and their roles, MHC I presenting to CD8 T cells and MHC II to CD4 T cells, and the primary versus secondary response. Vaccines exploit immunologic memory.
Traps
Antibiotics do not treat viruses; Gram staining does not classify archaea. Do not confuse sterilization with sanitization. In immunology, the trap is MHC restriction: MHC I to CD8, MHC II to CD4. Autoclaving relies on pressurized steam, not dry heat. Also remember that the secondary response is faster and higher-titer, not merely equal.
Worked example
A culture grows from 10³ to 10⁶ cells in 3 hours, a 1000-fold increase (about 10 doublings). Generation time = 180 min / 10 ≈ 18 min. Use log-phase data only; stationary-phase counts underestimate growth rate.