D.r Ohanu Anaerobe and Viruses.pptxppppyyyyyy

D.r Ohanu Anaerobe and Viruses.pptx

1. BY DR. OHANU M. Anaerobe

2. Bacteriodaecea 99% of flora of intestine is made up of gram-negative rods. Bacteriodes fragilis involved in Injuries involving the intestine Abscesses – Abdominal, obstetric and Gynaecologic infections Bacteriodes melaninogenicus fund in mouth, vagina and intestine, involved in anaerobic pneumonias eg in aspiration of sputum of alcoholic Fusobacterium – involved in Periodental disease Abdominal, pelvic abscesses and otitis media. Anaerobic Gram-positive cocci Peptostreptococcus – Gram positive anaerobes found in mouth, vagina and intestine (normal flora) involved in abscesses and aspiration pneumonias.

3. Clostridia - Anaerobic spore formers Diseases caused by the Cl include – botulism, tetanus, gas gangrene and pseudomembranous colitis. Clostridium botulinum (botulism classified as foodborne botulism , infant botulism, wound botulism, iatrogenic botulism, botulism of undetermined etiology, or inhalational botulism. ) potent neurotoxin. There are seven botulinum neurotoxins (types A–G). These are the most potent toxins known (as little as 30  ng is sufficient to cause illness and possibly death ), Rx heptavalent antitoxin. Adult botulism preformed toxin in food Infant botulism – ingest food contaminated with Cl. botulinum spores. Spores germinate and the organisms colonises the infants intestinal tract and release botulism toxin – floppy babies Rx ventilation support.

4. Clostridium t etani Found in soil and animal faeces Spores germinate and toxin tetano spamine released – sustained contraction of skeletal; muscle – called tetany Rx tet . Toxoid . 10yrs – duration of immunization. Neutralise toxin Immunization booster Clean wound-excising any devitalized tissue Antibiotics – penicillin Intenssive support (muscle relaxant) Cl. Perfringens (gas gangrene) Cellulitis -wound infections(spongy crackling consistency Clostridial myonecrosis – pockets of gas within the muscle. Cl. Difficile ( pseudomenbranous Enterocolitis ) Clostridium difficile toxin test (in the stool) condition associated with antibiotic administration. Rx stop the antibiotic, use metronidazole and vancomycin

5. Classification and General Properties of Viruses Characteristics: They are energy-less They are basic life forms composed of a protein coat, called a capsid , that surrounds genetic material. Some have external lipid bilayer membrane that may contain glycoproteins. Some have structural proteins and enzymes inside their capsids. The genetic material is either RNA or DNA. (never both) that contains instructions to make millions of clones of original virus. The virus replicates by taking control of host cell’s synthetic machinery. (they contain all the genetic information, but not the enzymes, needed to build millions of replicas of the original virus).

6. Nucleic Acid RNA Viruses There are 3 types of RNA, positive (+) stranded, negative (-) stranded, or the RNA of the retroviruses. The positive (+) is just a messenger RNA mRNA that can immediately be translated by host ribosomes into proteins. Translate Transcription R.T Transcription Translate The negative (-) Stranded RNA must first be transcribed into a positive (+) strand of RNA and this is done by an enzyme RNA – dependent RNA polymerase carried by the virus. In Retroviruses, the RNA is transcribed in reverse fashion (“Retrograde”) into DNA using an enzyme called reverse transcriptase DNA viruses. For these, it must first be transcribed into mRNA with subsequent translation into structural proteins and enzymes. Every DNA virus has both a negative (-) strand and a positive (+) strand, that is read, the (-) is ignored. RNA DNA mRNA Structural protein/ Enzymes

7. Capsids There are 2 tpyes – Icosahedral and helical Icosahedral symmetry capsids: composed of globular protein subunit called capsomer . These are arranged into triangular forms to form icosehedron . Helical symmetry capsids (only RNA viruses) Here the protein capsomers are bound to RNA. Most assume a spherical shape except for Rhabdo viruses (rabies virus that have a bullet shaped capsid . Envelope : The lipid bilayer membrane that they acquire from host cell nuclear or cytoplasmic membrane. Viruses without membranes are referred to as naked.

8. Classification Viruses are classified according to their Nucleic acid (RNA, DNA, double/single strand (-) (+) Capsid ( Icosehedral , helical) Envelope (naked or enveloped) Size ( dimeter in helical, No. of capsomers in icosehedral ) DNA viruses (most double stranded) HHAPPP Herpes Hepadna Adeno Papova Parvo POX – extremely complex-codes for hundreds of proteins.

9. Those with envelope – Herpes, Hepadna , PoX , Naked DNA vs – (PAP) papova , adeno , Parvo . RNA viruses (most are single stranded, ½(+), ½(-), enveloped and with helical capsid. Toga, corona, Retro, Picorna , calici , Reo, Orthormyxo , paramyxo , Rhabdo , Bunya, Arena, Filo NB : Reoviridae are double stranded, picorna , Calici and reoviridae are non enveloped. 5 have Icosehedral symmetry Two undergo replication in the nucleus (Retro and orthormyxo ).

10. Viral Replication NB: Adsorption and penetration Uncoating of virus Synthesis and assembly of viral products Release of virions – either by lysis or budding.

11. Host cell outcome Death – cells own function shuts down Transformation (introduce oncogens ) Latent infection (sleeping state – activate) Chronic slow infection (decades of indent infection) Viruses make use of the metabolic machinery of the host cell by blocking the synthesis of any host DNA, RNA, or proteins. This forces the host cell to construct only viral proteins and copies of the viral genetic material.

12. Replication takes place in a systematic manner: thus Attachment of virus to host cell (Adsorption) Penetration Uncoating Transcription of early mRNA Translation of early proteins Replication of viral genome Transcription of late mRNA Translation of late proteins Assembly of virions Release

13. Attachment (Adsorption): A specific process in which structures present on the surface of the virus ( Ligands ) bind to the receptors on the surface of the host cell. Penetration : Mechanisms for the virus to enter the host cell – via – Translocation, (non env virus move through cell membrane. Endocytosis (engulfment of virus by invagination of a section of plasma membrane non env virus). Fusion – endocytosis of env of viruses fuse with the membrane of the endosome ). Direct fusion of the virion env . with surface membrane.. Transcription, translation, replication, RNA Vs undergo the above 3 processes in the cytoplasm. For DNA Vs the 3 processes take place in the nucleus.

14. Cultivation and Assay of Viruses A living cell system is required to cultivate viruses as they are obligate intracellular parasites. Three systems are known Laboratory animals Embryonated eggs Cell lines (Tissue culture) Lab. Animals Suckling mice, Rabbits, Hamsters, Monkeys

15. Disadvantage: expensive, difficult to handle, maintenance problem, Biological diversity, may have latent V infection, campaign by animal friendly groups. Advantages: isolation of vs that can’t grow on cell line or egg, understanding pathogenesis, understanding immune response, to study vaccine and drug efficacy.

16. Embryonated Eggs Simpler to handle, available, inexpensive, and usually do not interfere with growth of viruses. Usually embryo of 8-11 days old. After inoculation incubate for 2-9 days. Sites for innoculation include, chorioallantoic membrane, Haemagglutinating activity in amniotic or allantoic fluids (Amniotic cavity, allantoic cavity, yolksac ) signs of viral activity: killing of chick embryo production of pocks on chorioallantoic membrane.

17. Cell lines (Tissue culture) Type of cell line Primary – African green monkey (only 5 -10 divisions) – Chick embryo fibroblast Diploid cell (undergo around 50 divisions) Human fetal lung (W – 38, MRC -5) Continuous (immortal cell lines – from malignant or by spontaneous transformation) Hela HEP – 2 MDCK RD Vero

18. Uses of cell cultures Isolation of viruses from clinical samples Production of vaccines and antigens Biochemical studies of viral replication

19. Recognition of viral growth in cells Cytopathic effect (CPE) (cell/morphological changes) Haemagglutination and haemadsorption ( rbc ) from diff animals Immunofluorescence (Anti body with a fluorescent dye) Interference (some viruses do not multiply in the presence of another virus.)

20. Assay of Viral Infectivity – Measurement of the infectivity of the virus Electron microscope count (for viral particles) Quantitative assay- In eggs In cell cultures By plague formation Haemagglutination assay

21. Genetics of Vs Varying of viral genomic structure is by Mutations – chances of error as parent genome is copied Recombination and interaction between viral gene products, to give rise to new phenotypes of viruses Recombination – seen whenever a host cell is infected by two varions . This takes place via: Intramolecular recombination: seen in double stranded DNA viruses Reassortment - in vs which have segmental genomes eg influenza virus with 8 segments Reactivation in virions of same strain Marker rescue or cross reactivation takes place when an infectious virion and an inactivated virus infect a host cell simultaneously.

22. Interaction between viral Gene Products of 3 types Complementation ( eg proteins and enzymes) Phenotypic Mixing (two genetically diff vs ) Interference (inhibition of growth of one virus due to simultaneous infection by another virus.) Polyploidy: Except retroviruses that are diploid others are haploid. Sometimes many nucleocapsids in one envelop.