Bacterial Structure

Microbiology

Microbiology Is a science that deals with study of organisms which unable to be seen by naked eye such as bacteria , viruses etc. Medical microbiology Is a branch of microbiology deals with micro-organism that causes the diseases for human & other organisms and its divided several branch e.g. :- 1 – bacteriology .2 – virology .3 – parasitology .4 – mycology .5 – immunology .

Microorganisms belong to the Protista biologic kingdom include some eukaryotes and prokaryotes, viruses, viroids, and prions , these are classified according to their structure, chemical composition, biosynthetic and genetic organization.

Prokaryotic cells have no organelles, no membrane-enclosed nucleus, and no histones; in rare cases, they contain complex phospholipids, sphingolipids, and sterols. have 70S ribosomes. have a cell wall composed from peptidoglycan-containing muramic acid. are haploid with a single chromosome. have short-lived, unprocessed mRNA. have coupled transcription and translation.

Eukaryotic cells contain organelles and a nucleus bounded by a nuclear membrane these contain complex phospholipids, sphingolipids, histones, and sterols , the lack a cell wall (plant cells and fungi have a cell wall) & have multiple diploid chromosomes and nucleosomes. have relatively long-lived mRNA formed from the processing of precursor mRNA, which contains exons and introns. have 80S ribosomes and uncoupled transcription and translation.

BacteriaTypical bacteriaMycoplasmasRickettsia organismsChlamydiae

Koch's postulates (modified) 1. The organism must always be found in humans with the infectious disease but not found in healthy ones. 2. The organism must be isolated from humans with the infectious disease and grown in pure culture. 3. The organism isolated in pure culture must initiate disease when re-inoculated into susceptible animals. 4. The organism should be re-isolated from the experimentally infected animals.

Structure of Bacteria

Size of Bacteria
Average bacteria 0.5 - 2.0 um in diameter. They havent organelles , no nuclear envelope , have a single chromosome and distinct cell wall .


Shapes of Bacteria
Coccus Chain = Streptococcus Cluster = Staphylococcus Bacillus Single = enteric bacteria Chain = Lactobacillus Cocco-bacillus = enteric bacteria Vibrio = curved Spirillum =Spirochete

Bacterial Structures

Flagella Pili Capsule Plasma Membrane Cytoplasm Cell Wall Lipopolysaccharides Teichoic Acids Inclusions Spores

Flagella

Motility - movement Swarming occurs with some bacteria spread to entire petridish like : Proteus spp. Arrangement basis for classification Monotrichous; 1 flagella Lophotrichous; tuft at one end Amphitrichous; both ends Peritrichous; all around bacteria

Pili

Short protein appendages smaller than flagella Adhere bacteria to surfaces . Antibodies will block adhesion . F-pilus; used in conjugation to Exchange of genetic information

Capsule or Slime Layer

Glycocalyx - Polysaccharide on external surfaceAdhere bacteria to surface . Prevents Phagocytosis . Complement can’t penetrate sugars

Cytoplasm

80% Water {20% Salts-Proteins) Osmotic Shock important DNA is circular, Haploid Plasmids; extra circular DNA may associated with Antibiotic Resistance No organelles (Mitochondria, Golgi, etc.)



Bacterial genome is not surrounded by a nuclear membrane, nor does it contain a mitotic apparatus. is generally called a nucleoid or nuclear body. consists of polyamine and magnesium ions bound to negatively charged, circular, supercoiled, double-stranded DNA; small amounts of RNA; RNA polymerase; and other proteins.


Bacterial ribosomes have a sedimentation coefficient of 70S and are composed of 30S and 50S subunits containing 5S, 16S, and 23S rRNA, respectively. ribosomes are the sites of action of many antibiotics that inhibit protein biosynthesis.

Cell Membrane

Bilayer Phospholipid Water can penetrate Flexible Not strong, ruptures easily Osmotic Pressure created by cytoplasm

Cell Wall

Peptido-glycan Polymer (amino acids + sugars) , Unique to bacteria Sugars : containing N-acetylglucosamine N-acetymuramic acid D form of Amino acids used not L form Hard to break down D form

Cell Wall

Determine shape of bacteria Strength prevents osmotic rupture 20-40% of bacteria Unique to bacteria Some antibiotics effect directly Penicillin

Teichoic Acids

Gram + only Glycerol, Phosphates, & Ribitol Attachment for Phages

LPS

Functions Toxic; kills mice, pigs, humans G- septicemia; death due to LPS Pyrogen; causes fever DPT vaccination always causes fevers Adjuvant; stimulates immunity Heat Resistant; hard to remove

Endospores

Resistant to heat, radiation, cold , Boiling >1 hr still viable .Location important in classification , Central, Sub terminal, TerminalBacillus stearothermophilus –spores Used for quality control of heat sterilization equipment ( autoclaving )

Prokaryotes vs. Eukaryotes

Cell Wall Teichoic Acids LPS Endospores Circular DNA Plasmids