PHMP LEC UNIT 2-3.pdf

Unit 2 MICROORGANISMS microscopic organisms  microbes  living organisms that are generally too small to be seen without a microscope Microorganisms are found in each of the three domains of life:  Bacteria, Archaea, and Eukaryota. Check characteristics of bacteria and...

Unit 2 MICROORGANISMS microscopic organisms  microbes  living organisms that are generally too small to be seen without a microscope Microorganisms are found in each of the three domains of life:  Bacteria, Archaea, and Eukaryota. Check characteristics of bacteria and archaea from L1 Eukaryota  Plants  Protozoa  Fungi  Helminths  Eukaryota, whose members are known as eukaryotes, is a Physical Requirements Chemical Requirements diverse domain of organisms whose cells have a Temperature Water NUCLEUS pH Sources of Carbon and Osmotic Pressure Nitrogen Bacteria Minerals Oxygen Carbon Dioxide Organic Growth Factors Nutrition Macronutrients  Acquired in the form of CO2, organic compounds, nitrates, ammonia, sulfates and phosphates Micronutrients  Required as trace elements and are components of enzymes and cofactors. Media  Enriched media (Blood Agar)  Selective media (MacConkey, Sabouraud, Lowenstein- Bacterial physiology Jensen) GROWTH  Differential media (MacConkey Agar) Energy Production  Generation Time o time for the bacteria  Fermentation to double in size and  Respiration split into two  Photosynthesis  Bacterial Replication o Binary Fission Metabolism  Based on oxygen consumption  Based on carbon and energy source   Streptococcus  Enterococcus 1. Clostridium  Rod-shaped, obligate anaerobic cells that contain endospore that usually distend the cell 2. Bacillus  Rod-shaped, endospore-forming cells – Obligate aerobic soil bacteria  Some species produce antibiotics, and some are used as insecticides Bacterial classification  The taxonomy of the bacteria is essentially based on their 3. Lactobacillus morphology. Development on phylogenetics allows for  Rod-shaped more accurate classification of bacteria according to DNA  Some are normal flora of the human body or lineage.  Also used commercially in the production of fermented Major Classification foods like sauerkraut, pickles, buttermilk, and yogurt  Gram Positive Bacteria  Gram Negative Bacteria 4. Listeria L. monocytogenes  Can contaminate foods, especially dairy products – Can survive within phagocytic cells  Capable of growth at refrigeration temperature  Poses the threat of stillbirth or serious damage to the fetus if it infects pregnant women 5. Staphylococcus  Occurs in grape-like clusters  Facultative anaerobes  Can survive at high osmotic pressure and low moisture (nostrils and on skin) 6. Streptococcus GRAM POSITIVE BACTERIA  Typically appear in chains or in pair  Gram-positive bacteria are traditionally classified based  Responsible for more illnesses and on the staining technique developed by Hans Christian causing a greater variety of diseases Gram. than any other group of bacteria  This classification still proves useful in the classification according to genetics. Gram-Positive  True Gram-positive (Firmicutes)  Wall-less (Tenericutes)  Fungi-like (Actinobacteria) FIRMICUTES  Low G+C (referring to nucleoside) gram-positive bacteria are assigned to the phylum Firmicutes.  This group includes common soil bacteria, the lactic acid bacteria, and several human pathogens. o Gram-positive bacilli 7. Enterococcus  Clostridium  Found in large numbers in human stool  Bacillus  Relatively hardy microorganisms adapted to areas of the  Lactobacillus body that are rich in nutrients but low in oxygen  Listeria  Highly resistant to most antibiotics o Gram-positive cocci  Staphylococcus TENERICUTES  Low G+C gram-positive bacteria  Cell wall structure resembles mycobacteria (acid-fast)  From the Latin word for “soft skin”, referring to their LACK OF CELL WALL True Gram Positive (Firmicutes)  Includes wall-less bacteria called Mycoplasma  Rod-shaped (Bacillus, Clostridium, Lactobacillus, Listeria) o Highly pleomorphic  Sphere-shaped (Streptococcus, Staphylococcus, o Produce filaments that resembles fungi Enterococcus) o Have a characteristic “fried egg” appearance Wall-less Gram Positive (Tenericutes) under magnification  Mycoplasma Fungi-like Gram Positive (Actinobacteria) ACTINOBACTERIA  Mycobacterium, Corynebacterium, Cutibacterium  High G+C gram-positive bacteria Streptomyces, Actinomyces, Gardnerella Nocardia  Highly pleomorphic  Some grows filaments, which resembles filamentous GRAM NEGATIVE BACTERIA fungi (mold-like)  Bacteria that do not retain the primary stain in Gram staining are traditionally classified as Gram-negative. 1. Mycobacterium  Gram-negative bacteria are classified under the major  Aerobic, non-endospore-forming rods phylum, Proteobacteria.  Have distinctive cell wall, structurally similar to Gram- negative bacteria ALPHAPROTEOBACTERIA o The outermost layer is composed of mycolic acid  Obligate intracellular parasites (waxy, resistant layer)  Gram-negative rod-shaped bacteria, or coccobacilli o Related to their pathogenicity, acid-fast staining,  Includes the following medically important genus: and drug resistance, slow growth o Rickettsia – transmitted to humans via insect or tick bites; causes typhus and RMSF 2. Corynebacterium o Ehrlichia  “Coryne” means club-shaped o Bartonella – cat scratch disease  Pleomorphic (depending on the age of the cells) o Brucella – causes diseases to mammals that may be transmitted to humans (zoonotic disease) 3. Cutibacterium; formerly Propionibacterium  Can form propionic acid BETAPROTEOBACTERIA  Found in human skin and the primary bacterial cause of  Bordetella pertussis acne (C. acnes) o Nonmotile, aerobic, gram-negative rod o Cause of pertussis, or whooping cough 4. Streptomyces  Neisseria  One of the bacteria most isolated from soil o N. gonorrheae (also known as gonococcus)  Produce reproductive asexual spores, formed at the ends o Aerobic, gram-negative cocci that inhabit the of aerial filaments mucous membranes of mammals  Strict aerobes o N. meningitidis (also known as meningococcus)  Produce most of our antibiotics GAMMAPROTEOBACTERIA 5. Actinomyces  Several medically, ecologically, and scientifically  Facultative anaerobes that are found in the mouth important groups of bacteria belong to this class  and throat of humans and animals including  Occasionally form filaments called hyphae o Pseudomonas Actinomyces israelii o Legionella  Causes actinomycosis, a tissue- destroying disease usually o Vibrio affecting the head, neck, or lungs o Enterobacter o Pasteurella 6. Gardnerella  Highly pleomorphic morphology Pseudomonas aeruginosa  Gram-variable  Problem of immunocompromised patients  Cause one of the most common forms of vaginitis (G.  Usually infects the urinary tract, burns, wounds and vaginalis) causes blood infections  Can grow in unexpected places e.g., medical equipment, 7. Nocardia catheters, pharmaceuticals, diesel, etc.  Aerobic  Virulence factors  Morphologically resembles Actinomyces o Alginate capsule, pilin, hemolysin, proteases, exotoxin A, exoenzyme S, antibiotic resistance  Shigella Bacillary Inhabitants of Legionella pneumophila dystenteriae dystentery or intestine of  A thin, aerobic, pleomorphic, flagellated, non-spore- shigellosis human only forming, Gram-negative bacterium Klebsiella Pneumonia Capable of  Causative agent of legionellosis or Legionnaires’ disease pneumoniae nitrogen fixation and Pontiac fever Serratia UTI RTI Produce red  Virulence factors marcescens pigments Can be o Outer membrane proteins, peptide toxin, found in catalase, and can invade, survive and replicate catheters inside macrophages Proteus mirabilis UTI and wound Swarming motility Vibrio cholerae Yersinia pestis Plague or Black Can be  Gram-negative, highly motile curved rods with a single Death transmitted by polar flagellum. fleas from urban  Oxidase positive; can tolerate alkaline media but are rats, ground sensitive to acid squirrels  Virulence factors Enterobacter UTI Nosocomial Distributed in o Adherence, cholera toxin cloacae E. infections humans, animals, aerogenes water, sewage, and soil Cronobacter Meningitis and Widespread in sakazakii necrotizing environment enterocolitis in Most notable in infants from contaminated infant formulas Franciscella tularensis  Causative agent of tularemia or rabbit fever, a zoonotic disease obtained from rabbits Moraxella lacunata  Strictly aerobic coccobacilli and implicated in eye ORDER ENTEROBACTERIALES (ENTERICS) infections  Facultative anaerobic, gram-negative rods Some are Coxiella burnetti motile (peritrichously flagellated)  Causes Q fever  Inhabits the intestinal tracts of humans and other  A spore-like body is present that requires a mammalian animals host cell to reproduce  Can ferment glucose and other carbohydrates  Have fimbriae, sex pili, and can produce bacteriocins DELTAPROTEOBACTERIA No common human pathogens. Most deltaproteobacteria Bacteria diseases notes prey on other bacteria. Escherichia coli UTI Very common Traveler’s Presence in water EPSILONPROTEOBACTERIA diarrhea (certain or food indicates  Curve to spirilloid-shaped strains) fecal  Inhabits the digestive tract of animals as pathogens contamination  Include Campylobacter and Helicobacter Salmonella Typhoid fever Serovars – enterica serologic NONPROTEOBACTERIA serovars Typhi varieties; Planctomycetes, Chlamydiae, Spirochetes, Bacteroidetes, and serotypes; Fusobacteria are phyla of gram-negative, chemoheterotrophic difference in bacteria. antigen Other Salmonella Salmonellosis K, O, H Chlamydia enterica serovars Inhabitants of  Do not contain peptidoglycan in their cell wall intestine of  Gram-negative, coccoid or ovoid bacterium humans and  Have a unique developmental cycle animals o Elementary bodies ⇄ Reticulate bodies  Obligatory intracellular bacteria  Some cause chlamydia, trachoma, and pneumonia darkfield microscopy Treponema Gram-negative- Motile like Do not grow in spirochete; very culture thin; T. pallidum better viewed by (subspecies T. darkfield pallidum microscopy pallidum) Bacteroides  Obligate anaerobic rod-shaped bacteria Abundant in the human gastrointestinal tract  Usually mutualistic, although some species are opportunistic pathogens EUKARYOTA Fusobacterium  Anaerobic rod-shaped bacteria with pointed ends Fungi  Form biofilms; some species cause disease in humans  Eukaryotic microorganisms that occur ubiquitously in (periodontitis, ulcers) nature in the domain Eukarya. The kingdom fungi (Mycota) has over 50,000 different species but only 200 SPIROCHETES have been identified as human pathogens.  Have a coiled spring morphology  Includes yeasts, molds, and fleshy fungi (mushrooms)  Have axial filaments or endoflagella—By rotating its axial filaments, the cells rotates in opposite direction mycology efficiently in liquid  It is the branch of biology that deals with the study of  Include Treponema, Borrelia, and Leptospira fungi, including their genetic and biochemical properties, their taxonomy as well as pathogenesis and toxicity  Fungi are EUKARYOTES  They are mostly multicellular, EXCEPT yeasts  Unique from other kingdoms by: o Nutrition Example genus Microscopic Unique o Structural Organization Morphology Characteristics o Growth Leptospira Spiral-shaped Aerobic, o Reproduction bacterium abundant in (spirochetes); shallow water Fungal nutrition gram negative- reservoirs; infect Absorptive nutrition enables fungi to live as decomposers and like (better rodents and symbionts viewed by domestic  Heterotrophic darkfield animals; can be  Saprophytic microscopy); very transmitted to thin humans by All fungi are carbon heterotrophs: infected animals’  Dependent on exogenous nutrient substrates as sources urine; may cause of organic carbon, and with a few exceptions, fungi are severe disease obligate aerobes. Borrelia Gram-negative- B. burgdorferi  None are obligate anaerobes like spirochete; causes Lyme Known Metabolic Types: very thin; better disease and B.  Thermophilic viewed by recurrens causes  Psychrophilic relapsing fever  Acidophilic  Substrate mycelia (specialized for nutrition) penetrate  Halophilic into the nutrient substrate  Aerial mycelia (for asexual propagation) develop above Fungal growth the nutrient medium Fungi can grow in acidic, low-moisture, aerobic environments. They are unable to metabolize complex carbohydrates. Fungal structure Fungal thallus:  This is the entirety of the mycelia and is also called the fungal body or colony Fungal cell wall:  Chitin o a polysaccharide composed of long chains of N- acetylglucosmine and plenty of polysaccharides such as β- glucan  β- glucan o a long polymer of D- glucose o Site of action of Echinocandin Fungal cell membrane:  Ergosterol (the alternative of human cholesterol) o Site of action of Amphotericin B and Azoles Hypha  this is the basic element of filamentous fungi with a branched, tubular structure, 2–10 μm in width. Mycelium  this is the web or mat-like structure of hyphae. yeasts  Yeasts the basic element of the unicellular fungi.  It is round to oval and 3–10 μm in diameter.  To reproduce, fission yeast divide symmetrically, whereas budding yeast divide asymmetrically. Hypha: o Buds that do not  Hyphae of septate fungi are divided into cells by cross- separate from the walls/transverse walls called septa mother cell form the  Hyphae of aseptate fungi (coenocytic) lack cross walls pseudohyphae  Parasitic fungi have modified hyphae called haustoria, which penetrate the host tissue but remain outside cell membrane Dimorphic fungi Mycelium:  Some fungal species can develop either the yeast or the o Sporangiospores: formed within a sac mycelium form depending on the environmental (sporangium) on a stalk by molds such as  conditions, a property called dimorphism. Rhizopus and Mucor.  Pathogenic dimorphic fungi take the form of yeast cells in the parasitic stage and appear as mycelia in the saprophytic stage.  They are yeast-like at 37°C and mold-like at 25°C. Fungal reproduction  Fungi can reproduce asexually by budding and by asexual spore production. o The hyphae and asexual spores are haploid (1N) like the gametes of higher organisms (eggs and sperm).  Under certain conditions a fruiting body is formed. o It is the product of two opposite mating “types” combining to form a diploid (2N) cell. Comparison of fungi and bacteria feature Fungi Bacteria Diameter Approx. 4 Approx.. 1 micrometers micrometer (candida) (staphylococcus) Nucleus Eukaryotic Prokaryotic Cytoplasm Mitochondria and Mitochondria and ER present ER absent Cell membrane Sterols present Sterols absent Sexual reproduction: (except  They reproduce sexually by mycoplasma) mating and forming sexual spores Cell wall content Chitin Peptidoglycan  Zygospores: Single large spore Spores Sexual and Endospores for with thick walls asexual spores for survival (not  Ascospores: Formed in a sac reproduction reproduction) called ascus Thermal Yes (some) No  Basidiospores: Formed externally dimorphism on the tip of the pedestal called metabolism Require organic Many do not basidium carbon: no require organic obligate carbon: many Asexual reproduction: anaerobes obligate  Formation of conidia (asexual anaerobes spores) from the sides or the ends of specialized structures Fungal classification o Arthrospore: arises by fragmentation of the The taxonomy of the fungi is essentially based on their ends of the hyphae morphology. (mode of transmission of Coccidiodes immitis)  Dermatophytes – causes infection of the keratinized o Chlamydospore: rounded, thick-walled and quite tissues resistant.  Yeasts – single cells o Blastospores: formed by budding process of  Molds – grow in filamentous structures yeast. Some yeast, such as Candida albicans, can  Dimorphic fungi – They exist as molds in the environment form multiple buds that do not detach, thus at ambient temperature and as yeasts (or other producing sausage-like chains (pseudohyphae). structures) in human tissues at body temperature Summary 1. Bacteria 1. The nucleus undergoes multiple divisions before the cell Characteristics divides Archaea 2. A small portion of cytoplasm concentrates around each Gram Positive Bacteria nucleus Gram Negative Bacteria 3. The single cell separates into daughter cells 2. Fungi Characteristics Fungal Growth and Nutrition Fungal Structure Fungal Reproduction Unit 3 EUKARYOTA PROTISTS  Any unicellular eukaryotic organism that is not an animal, plant, or fungus  Do not form a natural phylogenetic group  May be closely related to animals, plants or fungi than to other protists Slime molds Protozoa Algae Absorptive Ingestive animal- Photosynthetic fungus-like like protists plant-like protists  Sexual reproduction is by conjugation. protists  During ciliate conjugation, two haploid nuclei fuse to produce a zygote.  Some protozoa can produce a cyst for protection during adverse environmental conditions. A cyst also enables a parasitic species to survive outside a host.  The cyst formed by members of the phylum Apicomplexa is called an oocyst Study of protists – Protistology Study of protozoa – Protozoology Protozoal nutrition Study of algae – Phycology / Algology  Most protozoa are heterotrophs and the feeding and growing stage, or trophozoite, feeds upon bacteria and Protozoa small particulate nutrients.  Are unicellular eukaryotes in the Kingdom Protista.  Protozoa are mostly aerobic heterotrophs, although  Protozoa are found in soil and water and as normal many intestinal protozoa are capable of anaerobic microbiota in animals. growth.  Chlorophyll-containing protozoa, dinoflagellates and Protozoa life cycle euglenoids, are photoautotrophs. Asexual reproduction is by fission, budding, or schizogony. Schizogony is multiple fission: cycle  All protozoa live in areas with a large supply of water. Some protozoa transport food across the plasma membrane.  However, some have a protective covering, or pellicle, and thus require specialized structures to take in food.  CILIATES take in food by waving their cilia toward a mouthlike opening called a cytostome.  AMOEBAE engulf food by surrounding it with pseudopods and phagocytizing it.  In all protozoa, digestion takes place in membrane- enclosed vacuoles, and waste may be eliminated through the plasma membrane or through a specialized anal pore. EUGLENOZOA  Trypanosoma Medically important phyla of protozoa  Hemoflagellates (blood parasites)  Excavata (Flagellates)  T. brucei causes African sleeping sickness which is  Amoeba  transmitted by the tsetse fly  Apicomplexa  T. cruzi, the causative agent of Chagas disease, is  Ciliates transmitted by the “kissing bug,” so named because it bites on the face FLAGELLATES AMOEBA  Also referred to as Excavata  Move by extending blunt, lobe-like projections of the  Single-celled eukaryotes o With feeding grooves in cytoskeleton cytoplasm called pseudopods Entamoeba histolytica o Most are spindle-shaped o possess flagella  The only pathogenic amoeba found in the human intestine (causes amoebic dysentery)  Includes the phyla which includes Giardia, Trichomonas, and the phylum Euglenozoa.  Uses proteins called lectins to attach to the galactose of the plasma membrane and causes cell lysis GIARDIA Acanthamoeba & Balamuthia spp.  Grows in water, including tap water, can infect the cornea  Giardia intestinalis and cause blindness  A.k.a. G. lamblia or G. duodenalis  Reported as the cause of brain abscesses called GAE  Lack mitochondria  Found in small intestine of humans APICOMPLEXA and other mammals  Obligate intracellular parasites Nonmotile in their mature  Excreted in the feces as a cyst and form survives in the environment before  Characterized by the presence of complex of special being ingested by the next host organelles at the apexes (tips) of their cells  The organelles in these apical complexes contain enzymes that penetrates the host’s tissues  Apicomplexans have a complex life cycle that involves transmission between several hosts Plasmodium TRICHOMONAS  The causative agent of malaria Erythrocytic parasite  Trichomonas vaginalis  Plasmodium grows by sexual reproduction in the  Lack mitochondria Anopheles mosquito (definitive host) and asexually in  Has an undulating membrane, which consists of a human (intermediate host). membrane bordered by a flagellum  Lack a cyst stage  Found in the vagina and in the male urinary tract (STI)  BABESIA  Babesia microti  Another erythrocytic parasite  Causes fever and anemia in immunosuppressed individuals.  Transmitted by the tick Ixodes scapularis. TOXOPLASMA  Toxoplasma gondii  Intracellular parasites of humans  Life cycle involves domestic cats Dangerous to pregnant women  Can cause congenital infection in utero CRYPTOSPORIDIUM  Lives inside the cells lining the small intestine  Can be transmitted to humans through the feces of  cows, rodents, dogs, and cats  Inside the host cell, each Cryptosporidium organism forms four oocysts, each containing four sporozoites  Cause diarrhea in immunocompromised px Cilliates  Have cilia that are similar to but shorter than flagella The cilia are arranged in precise rows on the cell  They are moved in unison to propel the cell through its environment and to bring food particles to the mouth. Balantidium coli  Cysts transmitted via feco-oral route  Produce proteases and other substances that destroy host cells (causing rare type of dysentery). The trophozoite feeds on host cells and tissue fragments. Algae  Dinoflagellates o Unicellular algae collectively called plankton or free-floating organisms o Dinoflagellates in the genus Alexandrium produce neurotoxins (called saxitoxins) that causes paralytic shellfish poisoning (PSP)  o Monoecious worms – have both male and female reproductive organs in single individual HELMINTHS o Dioecious worms – have individual worms each  Helminths (parasitic worms) are animals that are often having either male or female reproductive included within the study of microbiology because many organs species of these worms are identified by their microscopic eggs and larvae.  Multicellular  Have limited organ systems  Have complex reproductive cycles with several different life stages (some in more than one type of host) Types  Roundworms (nematodes)  Flatworms (Platyhelminths) o Flukes (trematodes) Flukes (Trematodes) o Tapeworms (Cestodes)  Non-segmented flatworms that have an oral sucker and attach to the inner walls of intestines, lungs, large blood Nematoda vessels, or the liver  Phylum Nematoda (The  Have complex life cycles, often with multiple hosts Roundworms)  Unsegmented worms that have full digestive system  Eggs (ova) can sometimes be identified in feces or around the anus of infected individuals Examples Ascaris lumbricoides Common roundworm Enterobius vermicularis Pinworm Necator americanus New-World hookworm Ancylostoma duodenale Old-World hookworm Strongyloides stercolaris Threadworm Trichuris trichiura Whipworm Trichinella spiralis Pork worm Dracunculus medinensis Guinea worm Ascaris lumbricoides Examples:  Liver flukes (Clonorchis and Opisthorchis)  Intestinal fluke (Fasciolopsis buski)  Oriental lung fluke (Paragonimus westermani)  Blood flukes (Schistosoma mansoni, S. haematobium, S. japonicum) Fasciola hepatica Tapeworms (cestodes)  Segmented flatworms that may have suckers or hooks at Platyhelminths the scolex  Phylum Platyhelminthes (The Flatworms)  They use these suckers or hooks to attach to the wall of  Includes the flukes, tapeworms, and the turbellarians, the small intestine which include planarians  The flukes and tapeworms are medically important parasites  The body of the worm is made up of segments called proglottids that contain reproductive structures  Proglottids (containing eggs) detach when the gametes are fertilized  Egg – oncosphere (within intermediate host) – cysticerci – Genome adult tapeworms (definitive host)  Molecule of nucleic acid functioning as the genetic Examples: material of the virus. Codes for the synthesis of viral Taenia saginata (beef tapeworm) components and viral enzymes for replication. Taenia solium (pork tapeworm) o Single or segmented Diphylobotrium latum o Circular or linear Echinococcus granulosus (dog tapeworm) o Single-stranded or double-stranded o DNA or RNA (but never both) Capsid  A.k.a. protein coat, core  A protein shell surrounding the genome and is usually  composed of protein subunits called capsomeres.  The capsid serves to protect and introduce the genome into host cells. Taenia solium  Some viruses consist of no more than a genome VIRUSES surrounded by a capsid and are called nucleocapsid or  Viruses contain a single type of nucleic acid (DNA or RNA) naked viruses. and a protein coat, sometimes enclosed by an envelope  Attachment proteins (spikes) project out from the capsid composed of lipids, proteins, and carbohydrates. and bind the virus to susceptible host cells.  an infectious agent with both living and nonliving characteristics envelope  Viruses with an envelope surrounding a polyhedral or Living characteristics Nonliving characteristics helical nucleocapsid are called enveloped viruses.  Reproduce at an  Acellular (no  The envelope is composed of phospholipids and extensive rate (only in cytoplasm, cell glycoprotein and for most viruses, is derived from host living host cells) membrane, nor cell membranes by a process called budding.  Has the ability to organelles) mutate  Cannot metabolize on their own  Possess DNA or RNA but never both  An intact infectious viral particle is called a virion and consists of: 1. Genome 2. Capsid 3. Envelope  The envelope may come from the host cell's nuclear membrane, vacuolar membranes (packaged by the Golgi apparatus), or outer cytoplasmic membrane HOST RANGE A. The shape of their capsid (helical or polyhedral) Refers to the spectrum of host cells in which a virus can B. Whether they are enveloped or naked multiply. C. The type of nucleic acid they have for their genome (DNA Most viruses infect only specific types of cells in one host or RNA) species. Host range is determined by the specific attachment site on Helical viruses resemble long rods, and their capsids the host cell’s surface and the availability of host cellular are hollow cylinders surrounding the nucleic acid. factors. Polyhedral viruses are many sided. Usually, the capsid is an icosahedron. SIZE Enveloped viruses are covered by an envelope and are Viral size is ascertained by electron microscopy. roughly spherical but highly pleomorphic. Viruses range from 20 to 14,000 nm in length. Complex viruses  have complex structures. For example, many bacteriophages have a polyhedral capsid with a helical tail attached.  Viruses can store their genetic information in six different types of nucleic acid which are named based on how that nucleic acid eventually forms the viral mRNA able to bind to host cell ribosomes and be translated into viral proteins. These types of nucleic acid are: Classification of viruses Viruses are often classified by the following characteristics: 1. (+/-) double-stranded DNA. The (-) DNA strand is directly The first usual step is the replication of the mRNA (except for transcribed into viral mRNA e.g., bacteriophages, (+)RNA viruses). Papovaviruses, Adenoviruses, Herpesviruses. Then the viral mRNA are used to synthesize different proteins 2. (+) DNA or (-) DNA. Once inside the host cell, its needed by the virus. converted into dsDNA and the (-) DNA strand is 5. Assembly transcribed into viral mRNA. Phage M13, Parvoviruses. Step after the synthesis of viral parts. 3. (+/-) double-stranded RNA. The (+) of the (+/-) RNA All the viral parts needed to complete a virion are assembled. functions as viral mRNA. Reoviruses. 6. Release 4. (+) RNA. Functions as mRNA after entry into the cell. Viruses are then released from the cell by lysis of the cell (lytic Picornaviruses, Togaviruses, Coronaviruses. cycle) or if the virus is enveloped, 5. (-) RNA. The (-) RNA is copied into a (+) RNA which by budding. functions as viral mRNA. Orthomyxoviruses, Paramyxoviruses, Rhabdoviruses. 6. (+) RNA in retrovirus. The (+) RNA is reverse transcribed into (-) DNA that makes a complementary copy to become (+/-) DNA. The (-) DNA is transcribed into viral mRNA. Retroviruses. 7. (+/-) dsDNA-RT. Double-stranded DNA with an RNA intermediate in their life cycle.  Some viruses undergo a lysogenic cycle where the viral genome would be integrated in the host cell’s chromosome and becomes a provirus, or a prophage if in bacteria.  When the cell replicates, it replicates along with it, the Stages of viral replication viral genome. Until such time that the genome would 1. Adsorption or attachment synthesize the virus, the cell would now be lysed. The process in which the virus adheres to the host cell surface Isolation, Cultivation, and Identification of Viruses This process is selective, in which the virus will adhere only to Viruses must be grown in living cells. selected host cells it can infect (permissive cells) depending  The easiest viruses to grow are bacteriophages. on the receptors found on the host cell (receptor) and on the viral surface (anti-receptor). GENERAL INFORMATION 2. Penetration Taxonomy of Viruses Also called viral entry  Classification of viruses is based on type of nucleic acid, This process follows attachment and happens almost morphological class, and presence or absence of an instantaneous the moment the virus attaches to the cell. envelope. Three (3) types:  Virus family names end in –viridae; genus end in –virus. Viral translocation across the plasma membrane; endocytosis; membrane fusion  A viral species is a group of viruses sharing the same 3. Uncoating genetic information and ecological niche. Happens after viral entry wherein the capsid protecting the  Nucleic acid of all DNA viruses are double-stranded, viral genome is removed. Most viruses with icosahedral except Parvovirus symmetry are naked, except Toga, Herpes, Retro and Flavi,  While all RNA are single-stranded, except Reovirus Bunya, Hepadna virus.  Most viruses have linear genome, except Papovavirus Smallest: Parvovirus, Picornavirus Largest: Poxvirus which have supercoiled, circular genomes Removed by degradation by enzymes, whether viral or host or  Most viruses with icosahedral symmetry are naked, by simple dissociation. except Toga, Herpes, Retro and Flavi, Bunya, Hepadna This results in the release of the viral nucleic acid. virus. 4. Synthesis  Smallest: Parvovirus, Picornavirus Largest: Poxvirus After the genome is liberated, viral parts are now synthesized from the genome. RNA viruses  Picornaviridae (icosahedral)  Astroviridae (icosahedral)  Calicivirus (icosaheral)  Reoviridae (icosahedral- outer and inner capsid) (dsRNA) Enveloped  Flaviviridae (icosahedral)  Togaviridae (icosahedral)  Coronoviridae (pleomorphic)  Retroviridae (icosahedral)  Bunyaviridae (icosahedral)  Orthomyxoviridae (pleomorphic)  Arenaviridae (pleomorphic)  Filoviridae (helical, rod-shaped)  Rhabdoviridae (helical, rod-shaped)  Paramyxoviridae (helical, pleomorphic) DNA viruses  Adenoviridae (icosahedral)  Papovaviridae (circular DNA)  Parvoviridae (icosahedral, ssDNA) Enveloped  Hepadnaviridae (icosahedral)  Herpesviridae (icosahedral)  Poxviridae (oval, large) (complex structure)