Microbiology Quiz 3 PDF

MPharm Programme Introduction to Microbiology Dr Callum Cooper [email protected] Microbiology textbooks • Willey J.M. et al. Prescott’s Microbiology (8th ed.) Publisher: McGraw- Hill Higher Education. • Madigan M.T. et al. Brock Biology of Microorganisms (14th ed.) Publisher: Pearson...

MPharm Programme Introduction to Microbiology Dr Callum Cooper [email protected] Microbiology textbooks • Willey J.M. et al. Prescott’s Microbiology (8th ed.) Publisher: McGraw- Hill Higher Education. • Madigan M.T. et al. Brock Biology of Microorganisms (14th ed.) Publisher: Pearson. • Denyer S.P et al. Hugo & Russell’s Pharmaceutical Microbiology (8th ed.) Publisher: Blackwell publishing • Russell, Hugo & Ayliffe's: Principles and Practice of Disinfection, Preservation and Sterilization, (5th ed.) Publisher Wiley-Blackwell EVERYTHING CAN BE USED FOR EXAM QUESTIONS! Learning Objectives • Gain awareness of basic microbiology principles • • • • What is microbiology What are microorganisms How do we study microbes Describe and provide examples of relevant areas in which microbiology plays an important role • • Human health and wellbeing Pharmaceuticals and biotechnology What is microbiology? • Microbiology is the generic term for the study of microorganisms (microbes) • Includes but is not limited to bacteria, viruses, fungi, archea, parasites and protozoa • Studies individual microbes and also communities of microbes • Microbiology has a huge impact in a variety of fields… • • • • • Fermented foods, baking, brewing, wine making Water and sewage treatment Agriculture and spoilage Study of pathogens and infectious disease Pharmaceuticals and biotechnology What are microbes? • Microorganisms (microbes) are microscopic (<1mm) and often unicellular • Viruses are acellular • Fungi can form multicellular structures Viruses Bacteria RBC (~100nm) (1-2µm) (~8µm) • In this module we will generally be talking about bacteria 1nm Chicken Egg (40-50mm) 10nm 100nm 1µm 10µm 100µm 1mm 10mm 100mm • Among the first organisms to evolve on Earth • Can adapt rapidly to changing conditions • Greatest genetic diversity of all groups of living organisms The Tree of Life Letunic and Bork (2016) Nucleic Acids Res doi: 10.1093/nar/gkw290 http://itol.embl.de What are microbes? • They are present in nearly every environment How is this relevant to me? • Total number of human cells: 1012 or 10 000 000 000 000 • Total microbes in healthy human gut: 1013 or 100 000 000 000 000 Are they all “friendly” and harmless? • Simple answer: NO Ref: By NASA/Crew of STS-132 - http://spaceflight.nasa.gov/gallery/images/shuttle/sts-132/hires/s132e012208.jpg(http://spaceflight.nasa.gov/gallery/images/shuttle/sts-132/html/s132e012208.html), Public Domain, https://commons.wikimedia.org/w/index.php?curid=10561008 Top causes of death in the UK by age and sex, 1915 to 2015 https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/deaths/articles/causesofdeatho ver100years/2017-09-18 Microbes can directly affect our health • Not all microbes are “friendly” (pathogenic) • Major causes of mortality • Introduction of Penicillin G (1st antibiotic) in the late 1940s revolutionised modern medicine • Made many fatal infections treatable • Microbes increasingly shown to have roles in non-infectious diseases; • Stomach ulcers • Obesity Microbes can directly affect our health Ref: Häggström, Mikael (2014). "Medical gallery of Mikael Häggström 2014". WikiJournal of Medicine 1 (2) Microbes can directly affect our health “Friendly” bacteria Commensals E. coli Nissle 1917 “Unfriendly” bacteria Pathogens E. coli O157:H7 Normal (Commensal) Flora • Normal flora are those organisms living in benign symbiosis with host: • e.g. E. coli (non toxigenic), lactic acid bacteria, Staphylococcus aureus, Candida yeast & many more • Some may be pathogenic but unable to enter disease process (lack attachment to suitable surface) But if conditions change: • Microbes may grow more extensively & cause infections, possibly fatal – e.g. MRSA • Changed conditions include hormonal changes, climatic, environmental, stress Medical microbiology, public health and epidemiology • Microbiology plays an important role in public health • Identification of diseases • Tracking and control of disease outbreaks • Tracking of antimicrobial resistance • Identifying appropriate treatments • Vaccination • Allows for the mathematical modelling of disease progression and spread • Alemi, A.A., et al. 2015. You can run, you can hide: The epidemiology and statistical mechanics of zombies. Physical Review E, 92(5), p.052801; http://mattbierbaum.github.io/zombies-usa/ Challenges in medical microbiology: Antibiotic resistance • Misuse has accelerated the development of resistance… • Use as a growth promoter in livestock • Non-prescription use • If resistance not tackled estimated 10 million deaths/year due to AMR infections by 2050 • More than cancer and diabetes combined • Economic loss of $60-100 Trillion USD Microbiology in Biotechnology and Industry • Biotechnology is the broad area of biology which uses living systems/organisms to produce products • Molecular biology developments have greatly increased scope of biotechnology Ref: Ingrid Moen, Charlotte Jevne, Jian Wang, Karl-Henning Kalland, Martha Chekenya, Lars A Akslen, Linda Sleire, Per Ø Enger, Rolf K Reed, Anne M Øyan and Linda EB Stuhr: Gene expression in tumor cells and stroma in dsRed 4T1 tumors in eGFP-expressing mice with and without enhanced oxygenation. In: BMC Cancer. 2012, 12:21. doi:10.1186/1471-2407-12-21 What is Biotechnology? • Different types of Biotechnology are colour coded Colour Green White Yellow Blue Red Dark Application Agriculture Industrial Food technology Aquatic Medical and Pharmaceutical Bioterrorism • Industrial use of microbes often termed biotechnology Microorganism Saccharomyces cerevisiae Lactobacillus spp. Aspergillus niger Bacillus licheniformis Penicillium chrysogenum Streptomyces griseus Escherichia coli (GMO) Product(s) Bread, beer, wine Yoghurt, bread Citric acid Alkaline proteases Penicillin Streptomycin Insulin (Human identical) Biotechnology: Industrial chemicals Citric acid • Aspergillus niger (fungus) • Uses raw materials such as brewery waste, coconut oil, rapeseed oils • Part of its normal metabolism • >1,000,000 tonnes/year produced • Uses as an acidity regulator or flavouring Proteases • Bacillus licheniformis (bacterium) • Produces alkaline protease in response to nutrient limitation • Enzymes used in laundry detergent • Alkaline proteases digest protein-based stains • > 1,000 tonnes/year produced Biotechnology: natural medicinal products Natural products of microbial origin include: • Antimicrobials • Penicillins, streptomycin (Fungi) • Endolysins (Viral) • Cholesterol lowering-agents • Lovastatin (Fungi) • Neurotoxins • Botulinum toxin (Bacteria) Biotechnology: recombinant medicinal products • Bacteria can be genetically modified to produce therapeutic proteins; • e.g Insulin (humulin) • First produced in 1978 by Genetech then licenced to Eli Lilly • In use > 25 years • Recombinant Vaccines e.g. Gardasil • Targets Human papilloma virus (HPV) • Contains recombinant viral protein produced in a bacterium Microbial Spoilage • Microbes can utilize almost anything to gain nutrients… • Including NUCLEAR WASTE • Microbial spoilage can be defined as the deterioration of a product by a contaminating microbe • Pharmaceutical products can also be spoiled by microbes • Can target raw materials or finished products • Causes economic loss • Increases risks to patients by affecting safety and quality Practical microbiology: Growing microbes • In general, microbes can be grown in the laboratory using solid or liquid media; • Nutrient rich • Non-selective • Specialist media exists… • Identify unknown microbes • Selectively culture specific microbes Practical microbiology: Looking at microbes Viruses Bacteria RBC (~100nm) (1-2µm) (~8µm) 1nm 10nm 100nm 1µm 10µm 100µm Chicken Egg (40-50mm) 1mm 10mm Naked eye Light microscope Electron microscope 100mm Practical microbiology: Molecular microbiology • Extract genetic components • DNA • Targeted regions e.g PCR • Whole genome sequencing • RNA • Gene expression • Extract cell components • Protein • Immunological Profiling • Structural studies • Sequencing Summary • What is microbiology and what are microbes ? • Areas in which microbiology is important and relevant to pharmacy; • Health and disease • Biotechnology and industry • How microbes are studied in the laboratory Extra reading • Chapter 1: Hugo and Russell’s Pharmaceutical Microbiology • Brock Microbiology Part I section 1 • Prescott's Microbiology Part IX MPharm Programme Microbial Classification Dr Callum Cooper [email protected] Learning Outcomes • Describe the differences between cellular and acellular microorganisms • Describe the main taxonomic groups of microorganisms and their features • Describe how microbes can be classified and provide examples Biological systematics • Studies how life changes through time and how living things relate to one another • Taxonomy: define systems by shared characteristics • Classification: arrange organisms into groups • Nomenclature: assign names Classification of Biological entities Biological Entities Cellular Eukarya Acellular Bacteria Archaea The Tree of Life Tree of Life website: tolweb.org/tree/ Development of classification systems: cellular entities Linnaeus Haeckel Chatton Whittaker Woese 1735 1866 1925 1969 1977 2 Kingdoms 3 Kingdoms 2 Empires 5 Kingdoms 3 Kingdoms Not described Protista Prokaryota Monera Bacteria Archaea Protista Vegetablia Plantae Animalia Animalia Eukaryota Plantae Fungi Animalia Eucarya Classification of Biological entities Biological Entities Cellular Eukarya Acellular Bacteria Archaea Viruses Viroids Virusoids Prions Classification systems: Acellular entities • Viruses and prions are anomalous entities • Non-living • Viruses are parasitic (require hosts and resources to reproduce) • Viral classification is an ongoing source of debate • 2 competing systems; • Baltimore system • International committee for taxonomy of viruses (ICTV) system • Classically based on phenotype and nucleic acid type • Prions (PrP) do not reproduce • Misfolded proteins • Can exist as multiple isoforms By Emw - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8821061 Taxonomic ranks Domain Eukaryota Bacteria Phylum Chordata Proteobacteria - Class Mammalia γ-proteobacteria - Order Primates Enterobacteriales Caudovirales Family Hominidae Enterobacteriaceae Subfamily Genus - - Homo Escherichia Species H. sapiens E. coli N.B. Genus and species are normally written in italics Podoviridae Autographivirinae Phikmvvirus Pseudomonas virus phiKMV Taxonomic ranks: Species • What is a species? • A group of living organisms capable of interbreeding, even if geographically isolated; Tigon Liger Panthera tigris Panthera leo WHAT ABOUT ORGANISMS THAT DO NOT REPRODUCE SEXUALLY? (e.g. bacteria) Taxonomic ranks: Species in microbiology • Species: collection of strains that share stable properties but differ significantly from other groups of strains Staphylococcus aureus Staphylococcus epidermidis • Strain: is a genetic variant or subtype of a bacterial species that varies slightly from other members of the same species Staphylococcus aureus E. coli Nissle 1917 Methicillin resistant Staphylococcus aureus E. coli O157:H7 Taxonomic ranks: Species/Strains in microbiology • These organisms are assigned on the basis of phenotype, serotype or genotype; • Phenotype: an organism's observable characteristics or traits (e.g morphology, development, biochemical or physiological properties) • Serotype: distinct variations in cell surface antigens within a species • Genotype: is the part of the genetic makeup of a cell, which determines one of its characteristics Phenotype classification in microbiology • Morphology • Cell shape (bacilli or cocci) • Cell structure (gram staining) • Biochemistry • Enzyme production • Transport proteins activity • Life cycle • Vegetative or spore forming Phenotype classification in microbiology • Ecological niche • Temperature • Thermophile • Psychrophile • Interactions with other organisms • Susceptibility to bacteriophages • Pathogenicity (ability to cause disease) Provides the least detailed information Serotype classification in microbiology • Serotype: distinct variations in cell surface antigens within a species A B • Salmonella genus has over 2600 different serotypes • Kauffman-White classification • O antigen: oligosaccharides on the cell surface • H antigen: flagellar proteins • Vibrio cholerae (cholera causing bacterium) has over 200 serotypes • Only 2 cause cholera: O1 and O139 Requires specific antibodies and pure cultures Genotype classification • Genotype: part of the genetic makeup of a cell which determines one of its characteristics (phenotype) • Genomics • PCR • Amplification of selected region of interest • Base composition (%G/C) • Nucleic acid sequencing • 16S rRNA • Used in phylogenetics due to slow rate of evolution • Can also be used in diagnosis • Whole genome sequencing • • Bacterial species definition: genomes sequences are at least 95% identical Taxonomy based on genetics can be confused by horizontal gene transfer Vertical & Horizontal Gene Transfer Time • Vertical transmission: passage of genetic information from parent to offspring • Horizontal transmission: the acquisition of genetic information by transfer from an organism that is not its parent Whole genome sequencing • Whole genome sequencing: determines the complete DNA sequence of an organism at a single time How can we characterise with this information? • Presence/absence of genes • mecA gene in Staphylococcus aureus • Gene mutations • Point mutations (SNPs) • Can change protein encoding Normal SNP DNA TTC TCC RNA AAG AGG Protein Lysine • Gene insertions/deletions • Acquired genes from horizontal transfer • Phylogenetics Arginine Visualising Genotypes: Phylogenetics • • Phylogenetics: the study of evolutionary relationships among biological entities (within species) Produces clusters (clades) of similar organisms based on DNA or protein sequences • • For 2 or more sequences, multiple sequence alignments (MSA can be produced) More closely related = more similar the genetic sequences Close Relatives Bacterial Strain 1 2 3 4 5 Sequence ACCTGCAGTA ACGGGTAGTA AACTTGAGCA ACCTGCACTA GCGCGTAAAA Distant Relatives Visualising Genotypes: Phylogenetics • MSA converted into genetic distance (% similarity) • Summarises % similarity between each pair of sequences Bacterial Strain 1 2 3 4 5 Sequence ACCTGCAGTA ACGGGTAGTA AACTTGAGCA ACCTGCACTA GCGCGTAAAA 1 100 2 70 100 3 60 40 100 4 90 40 60 50 100 40 40 100 1 2 20 3 4 5 5 Visualising Genotypes: Phylogenetic Trees Tree of Life website: tolweb.org/tree/ Visualising Genotypes: Phylogenetic Trees • Phylogenetic trees visualise evolutionary relationships between organisms • Rooted: each node is based upon inferred most recent ancestor • Unrooted: only how each leaf relates to others (no inference on ancestry) Where does classification have a practical application? OR How to work with dangerous bugs and not catch something How to work with dangerous bugs and not catch something • Microorganisms are categorised by the Advisory committee on Dangerous Pathogens (ACDP) • 4 classification levels • Pathogens classified on severity of disease and availability of treatment • List available online: http://www.hse.gov.uk/biosafety/information.htm • Impacts upon laboratory facilities required • Facilities categorised on Biosafety level (BSL) • General rule of thumb: BSL ≥ ACDP level • Some exceptions and dispensations Biosafety • ACDP Category 1 organisms • Pose minimal levels of hazard to personnel or the environment • Generally non-pathogenic • e.g. B. subtilis, E. coli, Saccharomyces cerevisiae • BSL-1 facilities • General protective equipment only • Wash hands on entry and exit • Sterilise all potentially infectious material Biosafety • ACDP Category 2 organisms • Can cause human disease and may be hazardous to the environment • Unlikely to spread through the local population • Effective prophylaxis, treatment or vaccination available • e.g Staphylococcus aureus, Pseudomonas aeruginosa, E.coli • BSL-2 facilities • All conditions for BSL-1 with the following; • Highly regulated design and procedures • Specific training • Restricted access to laboratory • Work can be performed in Biosafety (BSL) cabinets Biosafety • ACDP Category 3 organisms • Can cause severe human disease and may be severely hazardous to the environment • Potential to spread through the local population • Effective prophylaxis, treatment or vaccination available • e.g B. anthracis, Mycobacterium tuberculosis, Rabies virus • Some pathogens require additional approvals • BSL-3 facilities • All conditions for BSL-1 and BSL-2 with the following; • Highly regulated design and procedures • All procedures done within BSL • Laboratory specific PPE (or disposable) • Under negative air pressure • All personnel offered available vaccinations Biosafety • ACDP Category 4 organisms • Causes severe human disease (usually death) and may be severely hazardous to the environment • High risk of spread through the local population • No effective prophylaxis, treatment or vaccination available • e.g Ebola virus, Variola virus • BSL-4 facilities • All conditions for BSL-1 and BSL-2 with the following; • Personnel wear pressurised suits with separate air supply • Highly trained personnel only • Highly regulated lab design and procedures • Organisms handled in class 3 cabinet Summary • Describe the main taxonomic groups of microorganisms and their features • How microbes can be classified • Phenotype • Serotype • Genotype • Practical application of classification • Biosafety level Extra reading Prescott's Microbiology: Part V Sections 17,21,22 MPharm Programme Microbial Structure Dr Callum Cooper [email protected] Learning Objectives • Describe general details of bacterial morphology and provide specific examples • Describe general details of bacterial cell structures • Internal subcellular structures • External structures • Describe general details of viral morphology and structures Bacterial cell structure: What do we need to know? • Morphology (structure) • Colonies • Individual cell • Internal components • External components • How these can relate to physiology and pathogenicity Bacterial cell structure: Morphology • On a large scale bacteria form colonies • Aggregates of individual bacteria • Can take on different shapes, colours, sizes • Depends on species • Can be used as a very inaccurate form of classification Bacterial cell structure: Morphology • Huge variety of different bacterial cell shapes; • Size ranges from 1 to 10µm • Have to be observed under a microscope • Cocci (spheres) • Bacilli (Rodshaped) • Spiral bacteria Bacterial cell structure: Cocci • Monococcus- single cells • e.g. Micrococcus flavus • Diplococcus- paired cells • e.g. Nisseria gonorrhoeae • Staphylococci: grouped cells • e.g Staphylococcus aureus Bacterial cell structure: Cocci • Streptococci: chained cells • e.g. Streptococcus pyogenes • Tetrads: groups of 4 cocci in the same plane • e.g. Micrococcus luteus • Sarcina : cuboidal arrangements of 8 cocci Bacterial cell structure: Cocci Diplococcus Tetracoccus Monococcus Bacterial cell structure: Bacilli • Bacillus: Single rod • e.g Bacillus cereus • Diplobacilli: Two Bacilli side by side • e.g Coxiella burnetii • Streptobacilli: Chains of Bacilli • e.g. Streptobacillus moniliformis (Rat Bite Fever) Bacterial cell structure: Spiral bacteria • Spirellum: A rigid spiral Gramnegative bacterium • e.g. Campylobacter jejuni or Helicobacter pylori • Spirochete: thin, long more flexible • e.g Treponema pallidium Bacterial cell components: Overview • Prokaryotic cells are simpler in structure than eukaryotic cells • Share some features but vary in others • WILL ONLY FOCUS ON THE DIFFERENCES • Bacterial cells can adapt more readily to environmental changes than eukaryotic cells • Ability to metabolise wider range of substrates Bacterial cell components: General • Bacterial cell components can be broken into the following general categories; • Structural • • • Genetic material • • • Ribosomes Motility • • • Nucleoid Plasmid Protein production • • Cell wall Plasma membrane Flagella Pilli Specialist structures • • Endopores Capsules and Slime Bacterial external cell components: Cell wall • Nearly all bacteria have a cell wall (peptidoglycan) • • • Provides shape Protects against osmotic lysis Bacteria can be divided into two major groups depending on structure; • • Gram positive cells have a single plasma membrane Gram negative have two plasma membranes Cell surface OM PG PPS IM Gram Positive Gram Negative Cytoplasm Bacterial external cell components: Peptidoglycan • Peptidoglycan is a polymer of sugar and amino acids • Alternating residues of β-(1,4) linked Nacetylglucosamine (NAG) and Nacetylmuramic acid (NAM). • Attached to NAM is a chain of 3 to 5 amino acids. • Peptidoglycan layer lets particles ≤~2nm through in both Gram Positive and Gram negative • Layer varies in thickness between Gram Positive and Gram Negative • 90% of cell weight in Gram Positive • 10% of cell weight in Gram Negative Gram Negative Gram Positive PG Bacterial external cell components: Plasma membrane • Comprises of; • • • Lipid bilayer Proteins Lipopolysaccharide (Gram Neg) • Retains cytoplasm and segregates internal environment • • Provides support for proteins Selectively permeable Plasma membrane: Lipid Bilayer • Comprises of Amphipathic phospholipids • • • Hydrophilic “head points towards external environment Hydrophobic fatty acid “tail” towards bilayer centre NO sterols (e.g. cholesterol) • Pentacyclic hopanoids Plasma membrane: Membrane proteins • Two main types of proteins; • • • Integral proteins • • • • Integral proteins Peripheral proteins ~75% of membrane proteins Tightly attached or stretched across lipid bilayer Functions include ion transport Peripheral proteins • • • ~25 % of membrane proteins Aqueous solubility Cholesterol oxidases (depletes eukaryotic cells of cholesterol) Plasma membrane: Lipopolysaccharide • Lipopolysaccharide (LPS) contributes to structural integrity of bacterial cells • • Can stimulate a pro-inflammatory immune response • • • Consists of 3 domains • O antigen • Core antigen • Lipid A Small amounts can cause illness Endotoxemia → septic shock LPS content highly controlled in sterile manufacturing • Limulus amebocyte lysate (LAL) assay By Mike Jones - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10422301; By Asturnut (talk) - I (Asturnut (talk)) created this work entirely by myself., CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=27534108 Bacterial external cell components: Flagella • • Involved in bacterial motility (movement) Positioning and quantity of flagella are dependent on species • Most commonly; • • • • • • • Monotrichous (e.g. V. cholerae) Lophotrichous Amphitrichous Peritrichous (e.g. E. coli) Long compared to bacterial cell (~10µm) Powered by H+ flow (occasionally Na+) Involved in pathogenesis • • Crucial for virulence of V. cholerae Flagella propel H. pylori through mucus lining in stomach Bacterial external cell components: Pilli • • • Can also be known as Fimbriae Found mainly in Gram negative bacteria Two main types; • • Conjugative pili (allows transfer of DNA between 2 bacteria) Type IV pili (can generate twitching motility) Bacterial external cell components: Capsules and Slime layers • Usually comprised of polysaccharides • • • • • • Exact composition varies by species (e.g. D-glutamic acid capsule in B. anthracis) If organised and permanent = Capsule If loosely formed = Slime layer Not required for in vitro growth • Has to be induced Can help in attachment to surfaces Protection from adverse conditions Bacterial internal cell components: Nucleoid • • • Main component of bacterial genetic material Not membrane bound Single chromosome of double stranded DNA • Bacterial genome of approx. 0.6-10Mbp (human genome 3000Mbp) • RNA and protein also present • DNA highly coiled and wrapped around nucleoid proteins • NOT the same as histones Bacterial internal cell components: Plasmids • Extra chromosomal pieces of DNA • • • • • Can replicate autonomously within the host Can vary in size between 1- >200Kbp Can sometimes be present in Eukaryotic cells Can be transferred between cells Often only contain non-essential genes; • • Antibiotic resistance Virulence characteristics (e.g. pXO1 in B. anthracis) Bacterial internal cell components: Ribosomes • • • Ribosomes are sites of protein synthesis Bacterial ribosomes contain 2 subunits • Small 30S • Large 50S Different to Eukaryotic ribosomes (size, sequence and structure) make them a target for antibiotics Bacterial endospores • Ability to form spores exists in some bacterial species • • Sporulation triggered by adverse conditions (e.g lack of nutrients) • • Most notably Bacillus spp. and Clostridial spp. Acts as a survival mechanism increasing resistance to Temperature, pH, chemical biocides etc • Metabolically inert • Important in some human disease • Clostridium difficile associated diarrhoea (CDAD) • Anthrax (caused by B. anthracis) Can be viewed using phase contrast microscopy or stained Bacterial cell structure: Multicellular microorganisms • Chains of cells forming long filaments • Trichomes (e.g. cyanobacteria) • Cells remain attached following cell division • Cells separated by cross-walls (septa) • Hyphae (e.g. Streptomycetes) • Tube-like filaments which may or may not have septa • (crosswalls) - i.e. cytoplasm may be continuous • May form a dense mycelial mat • cf. filamentous fungi • Close spatial and physiological relationships allow specialization Viral Structures • Simpler than bacterial or fungal cell structures; • • • • Genetic material Protein coat Receptors Lipid envelope (optional) • Viruses can also infect prokaryotes • Bacteriophages • Phages are non-pathogenic • Useful model organism • Most bacteriophages (~95%) belong to the Caudovirales • Myoviridae • Siphoviridae • podoviridae Viral Structures Summary • Definition of different bacterial structures • Important components of bacterial cell and their roles • Introduced viral structures Extra reading • • Prescotts Microbiology: Parts I; sections 3 & 5 Brock Microbiology Part I; section 2