Microbiology and Health-Related Science: Pathogens and Infection Control
The players
Distinguish prokaryotes (bacteria, no membrane-bound nucleus) from eukaryotes (fungi, protozoa) and from viruses, which are obligate intracellular parasites with a nucleic acid core and a protein coat. Bacteria come in three basic shapes - cocci (spheres), bacilli (rods), and spirilla (spirals). The Gram stain separates bacteria into Gram-positive (purple, thick peptidoglycan) and Gram-negative (pink, thin peptidoglycan plus an outer membrane).
Growth and control
Bacterial growth curves pass through lag, log (exponential), stationary, and death phases. Sterilization destroys all microorganisms including spores; disinfection reduces pathogens on surfaces but does not necessarily kill spores. Antibiotics target bacterial structures such as cell walls or ribosomes and do not work against viruses; antivirals are a separate class. Resistance emerges when antibiotics are overused or courses are stopped early.
Immunity and epidemiology
Innate immunity is fast and nonspecific (skin, mucous membranes, inflammation, phagocytes). Adaptive immunity is slower, specific, and creates memory through B cells (antibodies) and T cells. Incidence counts new cases in a period; prevalence counts all existing cases at a point in time. The chain of infection runs: pathogen → reservoir → portal of exit → transmission → portal of entry → susceptible host.
Traps
Viruses are not killed by antibiotics. Gram-negative organisms stain pink, not purple. Prevalence and incidence are routinely swapped. Disinfection is not sterilization.
Worked example
A town of 10,000 reports 50 new flu cases in March and has 200 people currently ill. Incidence for March is 50 ÷ 10,000 = 0.5%; prevalence is 200 ÷ 10,000 = 2%. Rule of thumb: hand hygiene remains the single most effective general infection-control measure.