Bacterial Classification and Nomenclature Dr. Rashad Shawgi Babiker M.Sc. (Microbiology) (UMST) M.Sc. Stud. (Immunology ) Institute of Tropical Medicine.(SAS)

Review Cell Membrane – regulates what comes in and out of the cell Cell Wall – maintains shape and form Capsule – found in virulent bacteria, helps evade immune system What are the two blank areas?

Bacterial structure a. The cell wall may also be surrounded by an organized capsule called a glycocalyx and/or by a loose jelly-like sheath called a slime layer.  b. In parasitic forms, these outer coverings protect the cell from host defenses. 1. Cell wall – keeps cell from bursting or collapsing due to osmotic changes (changes in water)

Bacterial structure 2. Flagella is used for movement 3.  Pilli (Fimbrae) help bacteria cling to surfaces 4. Prokaryotes do not have organelles or a membrane bound  nucleus! 5.  Nucleoid region contains a circular loop of DNA 6.  Plasmids are rings of DNA, used in reproduction 7.  Ribosomes in cytoplasm synthesize proteins

Outlines Ways for classifying the bacteria (taxonomy & classification) Phenotyping, serotyping and genotyping Bacterial nomenclature Medically important classes

Definitions Classification can be defined as the arrangement of organisms into taxonomic groups (taxa) on the basis of similarities or relationships Nomenclature is naming an organism by international rules according to its characteristics Identification refers to the practical use of a classification scheme

strain or variety – a culture derived from a single parent that differs in structure or metabolism from other cultures of that species (biovars, morphovars) type – a subspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type) and in pathogenicity (pathotype)

Naming and Classifying Microorganisms Linnaeus established the system of scientific nomenclature. Each organism has two names: the genus and specific epithet.

Scientific Names Are italicized or underlined. The genus is capitalized and the specific epithet is lower case. Are “Latinized” and used worldwide. May be descriptive or honor a scientist.

Scientific Names Staphylococcus aureus Describes the clustered arrangement of the cells (staphylo-) and the golden color of the colonies (aur-).

Scientific Names Escherichia coli Honors the discoverer, Theodor Escherich, and describes the bacterium’s habitat–the large intestine or colon.

Scientific Names After the first use, scientific names may be abbreviated with the first letter of the genus and the specific epithet: Staphylococcus aureus and Escherichia coli are found in the human body. S. aureus is on skin and E. coli in the large intestine.

Classification of Bacteria Light microscope was the original tool. Initial classification was based on of the shape of the bacterial cells.

4 Main Shapes of Bacteria Cocci Bacilli Spirilla Spirochetes

Four Groups Based on Cell Wall Composition Gram-positive cells Gram-negative cells Bacteria with chemically unique cell walls Bacteria without cell walls

Peptidoglycan N-acetylmuramic acid (NAM) Provides strong, flexible support to keep bacteria from collapsing because of changes in osmotic pressure N-acetylglucosamine (NAG)

Gram Positive Cell Wall Consists of A thick, homogenous sheath of peptidoglycan 20 - 80 nm thick Tightly bound acidic polysaccharides, including teichoic acid and lipoteichoic acid

Gram Negative Cell Wall Consists of An outer membrane containing lipopolysaccharide (LPS) Thin shell of peptidoglycan between inner and outer membranes Periplasm

Gram Negative

Gram Positive

Bacteria with Chemically Unique Cell Walls Acid-Fast Cells Mycobacterium species

Rickettsia – Chemically Unique Cell Wall

Chlamydia – Chemically Unique Cell Wall

Bacteria without Cell Walls - Mycoplasma Lack a rigid cell wall during their entire life cycle Smallest known organisms – smallest genomes (other than viruses) Diameter ranges from 0.15 m to 0.30 m Do not stain with the Gram stain

True bacteria and disease Modes of access of disease bacteria a) Access from the air ("strep throat", chlamydias) b) Access through contamination of food and drink c) Access through direct contact - Syphilis and Gonorrhea, Anthrax, Brucellosis d) Access through wounds - Tetanus, Gas gangrene e) Access through bites of insects and other organisms i) Bubonic plague (the "Black Death") v) Lyme disease