Pharmaceutical Microbiology- I Dr. Rasheeda Hamid Abdalla Assistant professor of Microbiology E-mail rasheedahamed12@hotmail.com

Bacterial Morphology and Structure

Bacterial cells Morphology Structure of Bacteria OBJECTIVES Bacterial cells Morphology Structure of Bacteria Functions of the bacterial organelles

Bacterial cells Morphology Cocci: sphere, 1μm Bacilli: rods , 0.5-1 μm in width -3 μm in length Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in  width. Unit for measurement Micron or micrometer, μm: 1μm=10-3mm Size: Varies with kinds of bacteria, and also related to their age and external environment

Bacterial Shapes and Arrangements

Structure of Bacteria 1-Essential structure Cell wall Cell membrane Cytoplasm Nuclear material 2-Particular structures Capsule flagella pili Spore

Gram Stain 1884: Christian Gram: First publication for the Gram stain method. Gram staining is a common technique used to differentiate two large groups of bacteria based on their different cell wall constituents. The Gram stain procedure distinguishes between Gram positive and Gram negative groups by coloring these cells red or violet.

Cell Wall of Bacteria

Cell Wall: common peptidoglycan layer A back bone of N-acetyl glucosamine and N-acetyl muramic acid: Both discovered in Gram positive and Gram negative bacteria. A set of identical tetrapeptide side chain attached to N-acetyl-muramic acid: different components and binding modes in Gram positive and Gram negative bacteria. A set of identical peptide cross bridges: only in Gram positive bacteria

Special Components of Gram Positive Cell Wall Teichoicacid

Special Components of Gram Negative Cell Wall lipopolysaccharide

Functions of Cell Wall Maintaining the cell's characteristic shape The rigid wall compensates for the flexibility of the phospholipid membrane keeps the cell from assuming a spherical shape Countering the effects of osmotic pressure Providing attachment sites for bacteriophages Providing a rigid platform for surface appendages- flagella, fimbriae, and pili all emanate from the wall and extend beyond it Play an essential role in cell division Be the sites of major antigenic determinants of the cell surface Resistance of Antibiotics

Wall-less forms of Bacteria  When bacteria are treated with 1) enzymes that are lytic for the cell wall e.g. lysozyme or 2) antibiotics that interfere with biosynthesis of peptidoglycan, wall-lles bacteria are often produced Usually these treatments generate non-viable organisms. L-form bacteria, also known as L-phase bacteria, L-phase variants, and cell wall-deficient (CWD) bacteria, are strains of bacteria that lack cell walls

Cell membrane Site of biosynthesis of DNA, cell wall polymers and membrane lipids. Selective permeability and transport of solutes into cells Electron transport and oxidative phosphorylation Excretion of hydrolytic exoenzymes

Mesosomes Mesosomes are folded invaginations in the plasma membrane of bacteria  that are produced by the chemical fixation techniques used to prepare samples for electron microscopy. Although several functions were proposed for these structures in the 1960s, and are no longer considered to be part of the normal structure of bacterial cells.

Cytoplasm Composed largely of water, together with proteins, nucleic acid, lipids and small amount of sugars and salts   Ribosomes: numerous, 15-20nm in diameter with 70S; Distributed throughout the cytoplasm; sensitive to streptomycin and erythromycin site of protein  synthesis    Plasmids:  Extra-chromosomal genetic elements   Inclusions:  Sources of stored energy, e,g volutin

Ribosomes

Plasmid Plasmids are small，circular/line， Extrachromosomal，double-stranded DNA molecules。 They are capable of self replication and contain genes  that confer some properties，such as:  -antibiotic resistance， -virulence factors。 Plasmids are not essential for cellular survival.   

Cell Inclusions and Storage Granules Bacteria have different methods of nutrient storage that are employed in times of plenty, for use in times of want. Inclusions are aggregates of various compounds that are normally involved  in storing energy reserves or building blocks for the cell Inclusions accumulate when a cell is  grown in the presence excess nutrients  and they are often observed under laboratory conditions.

Nucleus Lacking nuclear membrane absence of nucleoli, hence known as nucleic material  or nucleoid one to several per bacterium.

Capsules and slime layers These are structures surrounding the outside of the  cell envelope. They usually consist of polysaccharide; however, in  certain bacilli they are composed of a polypeptide  (polyglutamic acid).  They are not essential to cell viability and some  strains  within a species will produce  a capsule, while others do not.  Capsules are often lost during in vitro culture.  

Capsules and slime layers Functions: Attachment Protection from phagocytic engulfment. Resistance to drying. Depot for waste products. Reservoir for certain nutrients. Protection A bacterial capsule is similar, but is a well ordered structure that is resistant to washing off

Flagella Some bacterial species are mobile and possess locomotory organelles - flagella.  Flagella consist of a number of proteins including flagellin The diameter of a flagellum is thin, 20 nm, and long with some  having a length 10 times  the diameter of cell. Due to their small diameter, flagella cannot be seen in the light  microscope unless a special stain is applied. Bacteria can have one or more flagella arranged in clumps or spread all over the cell. Functions -Pathogenesis -Motility of bacteria -And also used in Identification of Bacteria

Flagellum Structure

Pili Pili are hair-like projections of the cell They are known to be receptors for certain  bacterial viruses Chemical nature is pilin Classification and Function: a. Common pili or fimbriae: fine , rigid numerous, related to bacterial adhesion  b. Sex pili: longer and coarser, only 1-4, related to bacterial conjugation

Bacterial Pili& Flagella

Endospores(spores) A bacterial spore is a spore or spore- like structure produced by bacteria Spore formation in bacteria is not a method of reproduction but simply a method of surviving in an unfavorable conditions Produced when starved Contain calcium dipicolinate DPA, Dipicolinic acid E.g.Bacillus and Clostridium Dormant cell Resistant to adverse conditions - high temperatures - organic solvents

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