Clinical microbiology structure of bacteria.pptx

Clinical microbiology introduction to bacteriology cell structure

1. Structure Of Bacterial Cells

2. The outermost component of bacterial cell that provides structural support &maintains its characteristic shape. Multilayered structure. The inner layer is peptidoglycan and there is an outer membrane. In the Gram+ve bacteria peptidoglycan layer is thicker with fibers of teichoic acid penetrating it. Gm- ve have a complex outer layer consisting of ( lipopolysacchride ,lipoprotein & phospholipid ) a periplasmic space and porine proteins. Mycobacteria have high concentration of lipids ( mycolic acid)result in inaility to be Gram stained. The Cell Wall

3. Peptidoglycan : A complex interwoven network , surrounding the cell ,compose of peptides and suger ( glycan ). The carbohydrate backbone is alternating NAG &NAM molecules connected with tetrapeptide bond. Present only in bacterial cell but not human cell (good target for antibiotics). Lysozyme enzyme in human tears , mucus &saliva can cleave it (natural protection).

4. Lipopolysacchride (LPS): Part of the outer membrane of Gm- ve bacteria. It is an endotoxin responsible for fever , hypotension &shock . It comopose of a phospholipid (lipid A) responcible for the toxic effect and polysacchride units used for identification. Teichoic acid: Fiibers of glycerol & ribitol phosphate in the outer layer of Gm+ve bacteria only. It can induce septic shock by the same mechechanism of Gm- ve bacteria .

5. A phospholipid bilayer similer to that of eukaryotic cell but did not contain sterols Function: a)active transport of molecules inside the cell. b)Energy generation. c)synthesis of precursor of cell wall. d)secretion of enzymes and toxins. Mesosome : Invagination in the cytoplasm important during cell division. Cytoplasmic Membrane

6. The cytoplasm has two distinct areas: a)an amorphus matrix contains ribosomes , nutrient granules, metabolites &plasmids. b)an inner, nucleoid reigon contains the DNA. Cytoplasm

7. The site of protein synthesis, it differs from eukaryotes in size&chemical composition They are 70S in size with 50S&30S subunits, while in human ribosomes are 80Sin size with 60S & 40S subunits. This differerences is the base of selective action of some antibiotics. Ribosomes

8. Different types of granules , some for storage , some have certain staining characteristics others are high energy stores . Granules

9. The area where DNA is located Prokaryotic DNA is single , circular contain about 2000 genes. Tnucleiod contain no nuclear membrane , no nucleolus , no mitotic spindles and no histones . Bacterial DNA has no intrones where eukaryotic DNA does. Nucleoid

10. Extachromosomal double-stranded , circular DNA molecules. Capable of replicating independently. Found in both Gm+ve &Gm- ve bacteria. Types: a)Transmissible can transfer from cell to cell by conjugation. b)Non transmissible, small present in many copies per cell. Plasmids carry genes for: Resistance to Antibiotic, heavy metals , UV light. Genes for production of pili and exotoxins , bacteriocins e.g colicns of E.coli & pyocin of Pseudomonas sp . Also nitrogen fixation enzyme , antibiotic production e.g Streptomyces . Plasmids

11. Transposons Pieces of DNA that moves readily between DNS s of bacteria , plasmids and bacteriophages . (jumping genes) Types: a) replicative transposons . b)direct transposons . Functions: can code for drug resistant enzymes and toxins. They are not capable for self-replication.

12. Specialized Structure Outside The Cell Wall

13. A gelatinous layer covering the entire bacterium. It compose of polysacchride , variation in suger type from one species to other. Importance:a ) virulance factor ( antiphagocytic ) b)identification c)vaccination e)adherence a) Capsule

14. Long whip-like appendages move bacteria toward nutrients. It compose of a protien ( flagellin ),the energy provided from ATP. Flagellated bacteria have different no. and locations Medical importance: a)flagella play role in pathogenesis b) used in identification. b) Flagella

15. Hair like filaments , shorter & straighter than flagella , compose of subunits of pilin . Found mainly in Gm- ve bacteria. Importance: a)attachment to specific recepters b)sex pili for conjogation c)Pilli

16. Slime layer of polysacchride coat secreated by many bacteria. Allow firm adherance of bacteria to various structures Glycocalyx producing bacteria are more virulant . d) Glycocalyx

17. Highly resistant structures ,formed in adverse conditions by two genera of medically imp. Gm+ve bacteria ,the genus Bacillus and the genus Clostrridium . The spores formed inside the cell, contain DNA, small amount of cytoplasm , cell membrane,peptidoglycan & v.little water surrounded by a thick keratinized coat. It resistant to heat, dehydration, radiation and chemicals. It had no metabolic activity ,can remain dormant for years. Sterlization can not be achieved by heat. Autoclaving (steam heating under pressure at 121c for 30 minutes)is required. Spores

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