Bacterial Structure

WELL COME Dr. Mejbah Uddin Ahmed

Introduction Microbiology: Microbiology is the study of microorganisms. In short; microbiology refers to the study of life and organisms that are too small to be seen with the naked eye. Microbiology includes bacteriology, virology, mycology, parasitology, and other branches.

Introduction There are 5 group of infectious agents for human: Bacteria Virus Fungi Protozoa Helminths * Bacteria are prokaryotes * Viruses are acellular

Important Properties of prokaryotes: ◘ Prokaryote – means Primitive nucleus ◘ Cell wall contain peptidoglycan ◘ No membrane bound organelles ◘ Contains loosely organized DNA ◘ No nuclear membrane ◘ 70s ribosome ◘ No mitotic cell division

capsul e Cell wall Plasma membrane Cytoplas m Ribosom mesosome e Plasmid Pili

Bacterial structure

Bacterial Flagellum Nucleoid Bacterial DNA

Bacterial structure

Bacterial structure Shape and Size: Cocci: Rounded Bacilli: Rod shaped Spirochetes: Spiral Pleomorphic: Many shape. Size may be ranged from 0.2 to 5 µ m

Bacterial structure Bacteria may be arranged: Pair (diplococci) Chain Cluster This arrangements are due to orientation and degree of attachment during cell division.

Cell Groupings Binary division can lead to diplococci , chains (Streptoc occus), packets or clusters (Staphylo coccus)

Bacterial structure Essential 1.cell

structures are

wall 2.Cytoplasmic membrane 3.Nucleoid 4.Mesosome 5.Ribosome 6.Periplasmic space in GNB

Bacterial structure Accessory structures are 1.Flagella 2.Pilus

or Fimbria 3.capsule, slime layer 4.Spore 5.Granules 6.Plasmid 7.Transposon

Bacterial structure Cytoplasm: Amorphous matrix, contains: ribosome, nutrient granules, metabolites, plasmids and nucleoid.

Cytoplasmic membrane: Inside the cell wall, composed of phospholipid bilayer. # Active transport of molecules # Energy generation # Cell wall precursor synthesis # Secretion enzymes and toxins

Bacterial structure Ribosome: Site of protein synthesis, 70S variety of two subunits:50S and 30S. (S stands for Svedburg units, a sedimentation value.) ## Our interest? Antibiotic activity.

Nucleoid: Contains DNA (single, circular molecule), no nucleolus, no mitotic spindle.

Bacterial structure Cell wall: Outer most multilayered structure. Peptidoglycan makes it rigid and determines shape 2 major subunits: NAG and NAM Tetrapeptide chain attached to NAM:L-alanine, Dglutamic acid,diaminopimelic acid/L-lysine, Dalanine. Interpeptide bridge in gram positive cell wall

Gram Positive Bacteria  Thick

layer of peptidoglycan  Negatively charged teichoic acid on surface

Gram Negative Bacteria Cell wall much more complex Thin peptidoglycan layer Surrounded with Periplasm Unique outer membrane Phospholipid (Lipid A): Toxic effect. Core polysaccharide Outer polysaccharide: Somatic or O antigen

Fig 3.34

Bacterial structure Capsule: Gelatinous, Composed of polysaccharide (exceptAnthrax D-glutamic acid) * Anti phagocytic * Helps in diagnosis * Vaccine * Adherence Glycocalyx:  External surface layer composed of polysaccharides  Gel like  Functions in protection and/or attachment

Bacterial structure Flagellum: Whip like, long. Monotrichous-Vivrio, LophotrichousPseudomonous, Peritrichous - E. coli and Amphitrichous - Helicobacter. *Account for most bacterial motility • Diagnosis Pilus: Short, Hair like. Attachment conjugation

Bacterial structure Plasmid: Extrachromosal, circular, double stranded DNA. Capable of independent replication May transmissible or Non transmissible Responsible for: antibiotic resistance, resistance to heavy metals, UV lights, Exotoxin production and carry genes for Pili. Transposon: Pieces of DNA, readily moves, “Jumping genes”. Responsible for drug resistance, toxin, mutation.

Bacterial structure Spore: Highly resistance structure, formed during adverse condition: sources of carbon and nitrogen are depleted. Keratinlike coat. Resistance is mediated by dipicolinic acid Metabolically inert Sensitive to 121°c for 15 minutes.

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