Bacterial Structure and Morphology PDF

Module 2 Introduction to General Microbiology: Bacterial Structure & Morphology KHRISTINE KAITH S. LLOREN, DVM, MSC COLLEGE OF VETERINARY MEDICINE AND AGRICULTURAL SCIENCES DE LA SALLE ARANETA UNIVERSITY Learning Outcomes By the end of this lecture, the student must be able to: 1. differentiate...

Module 2 Introduction to General Microbiology: Bacterial Structure & Morphology KHRISTINE KAITH S. LLOREN, DVM, MSC COLLEGE OF VETERINARY MEDICINE AND AGRICULTURAL SCIENCES DE LA SALLE ARANETA UNIVERSITY Learning Outcomes By the end of this lecture, the student must be able to: 1. differentiate the structures of prokaryotic cells (bacteria) and eukaryotic cells 2. describe the external and internal structures of bacteria and their functions 3. differentiate flagella, axial filaments, fimbriae and pili 4. compare the cell walls of gram-positive and gram-negative bacteria 5. describe the function of endospores and explain the sporulation process 6. characterize a bacteria based on its shape Previously … Organisms Prokaryotes Eukaryotes unicellular multicellular monera w/ cell wall w/o cell wall Bacteria protista plantae fungi animalia Size of Bacteria - The length of bacteria varies from 2 um to 8 um and diameter ranges from 0.2 to 2.0 um Source: https://microbiologyinfo.com/different-size-shape-and-arrangement-of-bacterial-cells/  1 2 Structure of a 3 Bacterial Cell 4 5 Cell Wall 6 Plasma Membrane 7 Cytoplasm Pili Plasmid Ribosomes Nucleoid Capsule 8 Flagella 9 Source: https://www.ck12.org/biology/bacteria-characteristics/lesson/Bacteria-Characteristics-MS-LS/ Glycocalyx General term used for substances that surround the cells A coating that covers the outside of prokaryotic cells that provides a protective coat Bacterial glycocalyx is viscous (sticky), gelatinous polymer external to the cell wall, composed of polysaccharide , polypeptide or both Slime Layer – if the Capsule – if the substance substance is unorganized and is organized and firmly only loosely attached to the attached to the cell wall cell wall, the glycocalyx Capsule ▪ Capsules are important in contributing to bacterial virulence. ▪ often protect pathogenic bacteria from phagocytosis by the cells of the host E.g. Bacillus anthracis - capsule of D-glutamic acid Streptococcus pneumoniae Klebsiella Source: Source: https://currentprotocols.onlinel https://www.studyblue.com/notes/note/n/sp ibrary.wiley.com/doi/epdf/10.1 ecial-stain/deck/13600489 002/9780471729259.mca03is1 Glycocalyx ▪ Important component of Biofilms ▪Extracellular polymeric substance (EPS) ◦ a glycocalyx that helps cells in a biofilm attach to their target environment and to each other ◦ Protects cells within it and facilitates communication ◦ Enables the cell to survive by attaching to various surfaces in natural environment Cell Wall ▪ Prevent the bacterial cells from rupturing ▪ Helps maintain the shape of the cell ▪ Point of anchorage for flagella ▪ Contributes to the ability of some species to cause disease ▪ Site of action of some antibiotics (e.g. penicillin) ▪ Chemical composition is used to differentiate major types of bacteria ▪Composed of peptidoglycan (murein) Source: http://myplace.frontier.com/~dffix/medmicro/genmicr.htm Plasma Membrane ▪ Thin structure lying inside the cell wall and enclosing the Source: cytoplasm of cell https://www.researchgate.net/publication/322250138_Pyrazole_pyrazolone_and_enaminonitrile_p yrazole_derivatives_Synthesis_characterization_and_potential_in_corrosion_inhibition_and_antimic robial_applications/figures?lo=1&utm_source=google&utm_medium=organic ▪ Consists primary of *Functions: phospholipids Serve as a selective barrier through which materials enter and exit the cell ▪ Look like two-layered (selective permeability) Breakdown of nutrients and the structures (lipid bilayer) production of energy Flagella ▪ long filamentous appendages that propel bacteria ▪Some bacteria have the capability to move in various patterns ▪ Atrichous – bacteria that lack flagella Arrangements of Bacterial flagella Flagella ▪H antigen – flagellar protein; useful for distinguishing among serovars or variations Example: there are at least 50 different ◦H antigens for E. coli. Those serovars identified as E. coli O157:H7 are associated with foodborne epidemics Axial Filaments Spirochetes – group of bacteria that have unique structure and motility (spiral motion) ◦They move by means of axial filaments or endoflagella ◦E.g. Treponema pallidum – causative agent of syphilis Borrelia burgdorferi – causative agent of Lyme disease  Fimbriae & Pili ▪ Hair-like appendages that are shorter, straighter, and thinner than flagella ▪ Fimbriae - the bacterial cell or can be evenly distributed over the entire surface of the cell ▪ Pili - usually longer than fimbriae and number only one or two per cell ◦involved in motility and DNA transfer Pili Some are used to bring bacteria together, allowing the transfer of DNA from one cell to another (conjugation) Cytoplasm ▪Refers to the substance of the cell inside the plasma membrane ▪Major structures in cytoplasm: ◦Nucleoid (containing DNA) ◦Ribosomes ◦inclusions  Bacteria often contain small Several usually circularkinds of reserve , double Nucleoid deposits stranded in the cytoplasm DNA molecules called plasmids. These are ▪Contains the bacterial extrachromosomal genetic chromosome elements (not connected to ▪ This is the cell’s genetic ▪ Where proteinchromosome) main bacterial synthesis information takes Replicate placeindependently ▪ Bacterial chromosomes ▪ Prokaryotic ribosomes are are not surrounded by a called 70S ribosomes nuclear envelope and no ▪ Contains: 30S subunit and histones 50S subunit ▪ S = Svedberg unit = unit of size Endospores ▪ Specialized “resting” cells formed by some gram-positive bacteria (genera Clostridium and Bacillus) when essential nutrients are depleted ▪ Highly durable dehydrated cells with thick walls and additional layers ▪ can survive extreme heat, lack of water, and exposure to many toxic chemicals and radiation Source: https://paramedicsworld.com/microbiology- practicals/endospore-staining-principle-procedure- interpretation/medical-paramedical-studynotes Endospores ▪ Dipicolinic acid – a large amount of an organic acid contained in endospore; protects the endospore DNA against damage ▪ Can remain dormant for thousand of years ▪ Germination – process in which an endospore returns to its vegetative state ▪ Not a means of reproduction (one vegetative cell forms a single endospore) Endospores ▪ Importance in food industry because of resistance to processes that normally kill vegetative cells ▪ Most vegetative cells can be killed with temp above 70 C ▪ Endospores can survive in boiling water for several hours or more (thermophilic/heat-loving) Shapes of Bacteria A. Cocci or spherical bacteria 1.Diplococci – round bacteria in pairs; remain in pairs after dividing 2.Streptococci – cocci in chains 3.Staphylococci – cocci in cluster resembling bunch of grapes 4.Sarcinae - in groups of 8 in cubical pockets (octads) 5.Tetrads- divide in 2 planes and remain in groups of 4 Shapes of Bacteria B. Bacilli or rod-shape bacteria; may be cigar-like or straw-like 1. Diplobacilli – in paired bacilli 2. Streptobacilli – rods in chain 3. Coccobacilli – short rods 4. Bacilli with rounded ends – e.g Salmonella typhosa 5. Bacilli with square ends – e.g Bacillus anthracis 6. Filamentous bacilli – usually do not separate and tend to form “long threads” 7. Club-shape bacilli – e.g. C. diphtheria  Shapes of Bacteria C. Helical/Spiral (one or more twist) 1. Vibroid/comma-shape – (less than one complete twist); curved rods ex. Vibrio cholera 2. Spirilla – loosely curved cells; have helical shape like a cork-screw and fairly rigid bodies with flagella 3. Spirochetes – tightly coiled form; flexible with axial filaments Other shapes of Bacteria ▪Genus Stella – star-shaped ▪Halophilic Archaea – flat rectangular shape ▪Some are Triangular shapes Shapes of Bacteria ▪Monomorphic – organisms that maintain a single shape ▪Pleomorphic – have many shapes e.g. Rhizobium, Corynebacterium ▪Environmental conditions could alter shape Reference Tortora, G. J., Funke, B. R., Case, C. L., & Johnson, T. R. (2004). Microbiology: an introduction (Chapter 4). San Francisco, CA: Benjamin Cummings.