NAJRAN UNIVERSITY College of Applied Medical Sciences

1. NAJRAN UNIVERSITY College of Applied Medical Sciences General Microbiology Course Lecture No. 4 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

2. Structure of bacteria • Bacteria are unicellular organisms. Bacterial cell is composed of 4 essential components: • Cell wall • Cell membrane (cytoplasmic membrane) • Cytoplasm • The nuclear body • Some bacteria contain: • Capsule • Flagella • Fimbriae • Spores

3. Cytoplasm Intracytoplasmic structures 1- Ribosomes 2- Plasmids 3- Transposones (Jumping genes) 4- Nuclear body

4. Capsule • It is the outermost layer in capsulated bacteria (outside cell wall) • Chemical nature is either: • Polysaccharide • Polypeptide • Hyaluronic acid • It is formed in vivo. • Not stained with Gram and so they appear as unstained halos around the organism. • Stained only by special capsule stain. • Protect the bacteria against phagocytosis by host phagocytic cells. • The capsular polysaccharides are used as antigens in certain vaccines as pneumococcal and meningococcal vaccines.

5. Flagella • Outside cell wall • Flagella are long appendages which rotate by means of a basal body "motor" located just under the cytoplasmic membrane. • Made of chains of flagellin. • They are the organ of motility. • Move toward or away from stimuli (taxis) • Flagella proteins are H antigens • Stained only with special stain.

6. Distribution of flagellae: Monotrichate: With one polar flagellum Amphitrichate: With 2 flagellae. One at each pole Lophotrichate: A group of flagellae at one or both poles Peritrichate: With flagellae all around the cell

7. Fimbriae (pili) • These are hollow, hair like structures made of protein (pilin). • Ordinary pili allow bacteria to attach to other cells. • Antigenic (carry fimbrialantigens = F antigens) • Functionally fimbriae are of 2 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.

8. Endospores • Sporulation:Endospore formation • They are formed on exposure to unfavorable conditions such as depletion of nutrients. • They do not develop in animal tissues where nutrients are adequate. So, they develop only in vitro. • Spore formation occurs by: • development of an ingrowth of the cytoplasmic membrane cutting off a portion of the cytoplasm including the nuclear material, ribosomes, glycolytic enzymes and little water (spore core). • Then a thick cortex of peptidoglycan and a tough keratin- like spore coat are formed around. The latter is responsible for the marked resistance of the spore.

9. This resistance is also mediated by calcium dipicolinate which is found only in the spores. • Spores have low content of free water, extremely low metabolic and enzymatic activity. • They are resistant to drought, high temperature and other environmental hazards. • They are destroyed only by autoclaving at 121 C for 20-30 min. • Once the hazard is removed, the spore germinates to create a new population (Germination). • Spores are stained by special stains.

10. Bacterial reproduction • Bacteria replicate 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 membrane between the sites of attachment of the two daughter chromosomes. This transverse membrane grows inward. • Anew 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.