Hygiene Atlas

Atlas · Plate VI · Microbiology and Immunology · 01

Microbiology basics

Bacteria are grouped by shape (cocci, rods and spirochetes) and by Gram stain: gram-positive cells have a thick wall and stain purple, while gram-negative cells have a thin wall, an outer membrane carrying endotoxin, and stain pink. Viruses hold DNA or RNA and replicate only inside host cells. Bacterial endospores and prions are the hardest agents to destroy.

High-yield facts · 7

  1. Gram-positive bacteria have a thick peptidoglycan wall and stain purple; gram-negative bacteria have a thin wall plus an outer membrane with endotoxin (LPS) and stain pink.S50
  2. Endotoxin (LPS) from gram-negative bacteria drives much of the inflammation in periodontitis.S38
  3. Bacterial shapes: cocci (spheres), bacilli (rods), spirochetes (spirals).S50
  4. Bacterial endospores (e.g., Bacillus, Clostridium, Geobacillus) are the most resistant life form, so they are used to test sterilizers.S50S9
  5. Viruses carry DNA or RNA but not both, and replicate only inside host cells.S50
  6. Prions are infectious proteins that resist routine sterilization (e.g., Creutzfeldt-Jakob disease).S50
  7. Facultative anaerobes can live with or without oxygen; obligate anaerobes are killed by oxygen and dominate deep pockets.S50

Facts are written in our own words; each tag links to its source. Values marked "sources vary" differ between references, so check the one your program uses.