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NAJRAN UNIVERSITY College of Medicine

Explore the structure and reproduction of bacteria including nuclear body, flagellae, fimbriae, capsule, spores, and bacterial reproduction process. Learn the key features that define bacterial properties and behavior in this lecture.

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NAJRAN UNIVERSITY College of Medicine

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  1. NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 3 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

  2. The Nuclear Body ‑ Bacteria have a primitive nucleus (prokaryotic), which has no nuclear membrane and does not contain nucleoli. ‑ The bacterial chromosome is a single circular double‑stranded DNA molecule, which carries the genetic material (determinants) that control the bacterial properties and behaviour. ‑ The chromosome is duplicated prior to cell division and each daughter cell will contain an identical copy of the chromosome.

  3. Flagellae ‑ These are long relatively thick filamentous appendages extended outside the cell ‑ They are the organs of bacterial cell motility. ‑ Protein in nature (composed of flagellin). ‑ Antigenic (carry flagellar or "H" antigen).

  4. Fimbriae (Pili) • -Filamentous appendages that are shorter, thinner and more numerous than flagellae. • -Protein in nature (composed of pilin). • -Antigenic (carry fimbrial or F antigens). • -Functionally of two types. • Common pili(fimbriae) are organ of attachment or adhesion. • Sex pili(F pili) through which genetic material (e.g. plasmids) are transferred from donor (male or F+) cells to recipient (female or F‑) cells.

  5. Capsule • -Is the outermost layer in capsulated bacteria (outside cell wall). • -A viscous material with well‑defined border • -Antigenic (capsular or K antigen) • -They are important virulence factors that protect bacteria against phagocytosis by the host phagocytic cells.

  6. Spores • -Some bacteria are spore‑forming and can develop spores upon exposure to adverse environmental conditions (e.g. heat, dryness, poor nutrition, etc.) • -Steps: • Spore core: By ingrowth of the cytoplasmic membrane cutting off a portion of the cytoplasm including the nuclear material, ribosomes and little water • Spore cortex:a thick cortex of peptidoglycan • Spore coat: Around the cortex. Responsible for the marked resistance of the spore. This resistance is also mediated by calcium • - Once the hazard is removed, the spore germinates to create a new population (Germination)

  7. Bacterial reproduction • -Being a prokaryote, bacteria multiply by simple binary fission. • -The chromosome duplicates itself and each copy is attached to the cytoplasmic membrane at the mesosome. • -The cytoplasmic membrane forms a new transverse mmembrane between the sites of attachment of the two daughter chromosomes. This transverse membrane grows inward. • -A new transverse cell wall is formed and grows inward. • -A complete transverse septum is formed and two daughter cells are generated which may separate or remain attached resulting in formation of cell groupings (e.g. clusters or chains).

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