This document is a submission by Shan Ali for their M.Sc Botany class at GC University Lahore. It provides definitions and information about viruses, including their discovery in the late 19th century, sizes and shapes, classification systems, life cycles involving adsorption, entry, replication, assembly and release, and examples of viral diseases. It also discusses various methods for controlling microbial growth such as heat, filtration, desiccation, radiation, and chemical disinfectants including phenols, alcohols, heavy metals, and antibiotics.

1. SUBMITTED TO:
Dr. Muhammad Hanif
SUBMITTED BY:
Shan Ali
CLASS:
M.Sc Botany
SEMESTER:
4th
SESSION:
2018-2020
GC UNIVERSITYLAHORE

2. VIRUSES

3. Definition
•A virus is a
non-cellular
particle
made up of
genetic
material and
protein that
can invade
living cells.

4. Discovery of viruses
1892 – Dimitrii Ivanovsky observed
that agent of tobacco mosaic disease
passes through porcelain filters that
retain bacteria.
1898 – Martinus Beijerinck makes
the same observation; concludes
that the pathogen must be a
distinctive agent.
Dimitrii Ivanovsky
Martinus Beijerinck

5. Size
• Most viruses range in size from 5 to
300 nanometres
• Viruses vary in diameter from 20 nm
to 250–400 nm
• The largest, however, measure about 500 nm
in diameter
• About 700–1,000 nm in length.

6. Shapes
•Viruses come in a variety of shapes
•Some may be helical shape e.g.
Ebola virus
•Some may be polyhedral shapes
e.g. influenza virus
•Others have more complex shapes
e.g. bacteriophages

8. POLYHEDRAL VIRUSES
Influenza Virus

10. Baltimore classification
Viruses were divided into six groups based on the
their
nucleic acid and m-RNA production.
i. ds-DNA viruses.
ii. ss-DNA viruses.
iii. ds- RNA viruses.
iv. ss-RNA viruses with positive strands( positive
polarity).
v. ss-RNA viruses with negative strands(negative
polarity).
vi. ss-RNA viruses associated with the enzyme
reverse transcriptase.

11. Modes of viral multiplication
Viral multiplication proceeds as following
manner.
• Adsorption,
• Entry,
• Uncoating,
• Transcription/mRNA production
• Synthesis of virus conmponents
• Virion assembly
• Release

12. Adsorption
• Virus encounters susceptible host cells
• Adsorbs specifically to receptor sites on
the cell membrane
• Because of the exact fit required, viruses
have a limited host range

13. Entry/Penetration
• Flexible cell membrane of the host
is penetrated by the whole virus or
Its nucleic acid
• Endocytosis: entire virus engulfed
by the cell and enclosed in a vacuole
or vesicle
• The viral envelope can also directly
fuse with the host cell membrane

14. Uncoating
• Enzymes in the vacuole dissolve the
envelope and capsid
• The virus is now uncoated

16. Transcription/mRNA production
• Free viral nucleic acid exerts control over the host’s
synthetic and metabolic machinery
• DNA viruses- enter host cell’s nucleus where they are
replicated and assembled
• DNA enters the nucleus and is transcribed into RNA
(mRNA)
• The RNA becomes a message for synthesizing viral
proteins (translation)
• New DNA is synthesized using host nucleotides
• RNA viruses- replicated and assembled in the cytoplasm

17. Synthesis of virus components
• Viral proteins (Structural and non-structural)
and viral nucleic acid are manufactured
by the virus through the host's existing
organelles.

18. Virion assembly
• A virion is simply an active or intact
virus particle.
• In this stage, newly synthesized genome
(nucleic acid), and proteins are assembled
to form new virus particles.

19. Release
• The viruses, now being mature
are released
• Either by sudden rupture of
the cell, or gradual extrusion
(budding) of enveloped viruses
through the cell membrane.

20. Viral Diseases
Viruses cause many diseases, some are as follows ;
• Anaplasmosis
• Botulism
• Chancroid
• COVID-19 (Coronavirus Disease 2019)
• Dengue, 1,2,3,4 (Dengue Fever)
• Enterovirus infection
• Giardiasis (Giardia)
• Human immunodeficiency virus/AIDS (HIV/AIDS)
• Influenza (Flu)
• Leprosy (Hansens Disease)
• Malaria
• Norovirus

21. Viral diseases
• Pneumococcal Disease (Pneumonia)
• Poliomyelitis (Polio)
• Q-Fever
• Rabies
• Smallpox
• Tetanus Infection, tetani (Lock Jaw)
• Tuberculosis (TB)
• Typhoid Fever, Group D
• Vibriosis (Vibrio)
•West Nile Virus
• Yellow Fever
• Zika Virus Infection (Zika)

22. CONTROL OF MICROBIAL GROWTH

24. HEAT
Kills microbes by denaturing enzymes.
Heat resistance varies among different
microbes.
• Boiling - Kills many
Vegetative Cells.
• Inactivates Viruses Within 10
Minutes
• No effect on spores.

25. AUTOCLAVING

26. PASTEURIZATION
Process used in preserving heat sensitive
foods.
• Milk, beer, and other
beverages.
• 63 °C for 30 Minutes.
• Wine - Pasteur
• Milk - VH & F soxhlet .
• Reduction of microorganism in milk.
• Pasteurization is not a method of sterilization.

27. Low Temperatures
• Decreasing temperature decreases
chemical activity.
• Low Temperature are Not Bactericidal.
• Restrict enzyme activity.
• Ordinary Refrigerator Temperature 0° – 7°C
• Do not Reproduce.
• Survive, Restrict rate of growth.
• Use – Food Preservation, Drug, Culture
Preservation.

28. DRY HEAT STERILIZATION
Direct Flaming – Burning contaminants
Incineration - Burns and Physically Destroys
Organisms
Used for
a. Needles
b. Inoculating Wires
c. Glassware
d. Body Parts
Hot Air Sterilization – Oxidation
160° C for 2 Hours or 170° C for 1 hour
Used for
a. Objects That Won’t Melt
b. Glassware
c. Metal

29. FILTRATION
• The passage of a liquid or gas through a
filter with pores small enough to retain
microbes.
• Separate bacteria from suspending
liquid.
• Filter – Nitrocellulose, acetate.
• Bacteria, virus large protein.
• High efficiency particulate air
filters.
• Filterable viruses.

30. DESICCATION
• Removing water from microbes.
• Viruses & Endospores can resist.
• Disruption of metabolism.
• Use – Food Preservation.
• Stops Growth / Microbes are still viable.
• Freeze-drying ( Lyophilization) – remove water
from
specimen.
• Gonorrhea bacterium – with stand for only 1 hour.
• Tuberculosis bacterium – viable for months
( Mycolic acid).
• Powdered milk – 85% water is removed.

31. OSMOTIC PRESSURE
• Plasmolysis
• High zone of salt & sugar.
• Salt – Preservation of fish, meat, food.
• High osmotic pressure.
• Low availability of sugar solution to
prevent
microbial growth.
• Honey, high sugar content preserved.
• Loss of H2O.

32. RADIATION
 Its Efficiency is Dependent on the Wavelength,
 Intensity, and Duration.
Two types :-
Ionizing
 Destruction of DNA by gamma rays & high energy
electron
beams.
 Use –
Sterilizing pharmaceuticals medical & dental supplies.
Food preservation and other industrial processes.
 More penetrating.
Food is exposed to high levels of radiation to kill insects,
bacteria and mold.

33. Non – Ionizing
Damage to DNA by UV light.
Effective germicide wave length 260nm.
Poor penetration
UV radiation is only useful for disinfecting
outer surfaces.

34. Chemical Methods
• Phenols and Phenolics
• Halogens
• Alcohols
• Heavy Metals and Their Compounds
• Surfactants
• Quaternary Ammonium Compounds
• Chemical Food Preservatives
• Aldehydes
• Antibiotics

35. Phenols and Phenolics
Another Name for Carbolic Acid / Lysol / Pine-Sol
- Joseph Lister
- Exert Influence By
1. Injuring Plasma membranes
2. Inactivating Enzymes
3. Denaturing Proteins
Use – Skin surface, Environmental surface,
Instruments, Mucous
membranes.
Common – Cresols, Hexachlorophene.
Phenolics are Long Lasting.
No Effect on Spores.
Effective antibacterial agents, fungi and many
viruses.

36. CHLORHEXIDINE
• Damages plasma membranes.
• Use – Skin degerming, Surgical scrubs.
• Only Operates in Narrow pH Range (5-7).

37. HALOGENS
Can be Used Alone or in Solution.
Inactivated by Sunlight
Alter cellular component.
Inactive enzymes.
Chlorine
- Purifies Drinking Water
- 2-4 Drops of Chlorine per Liter / 30 Min
- Forms an Acid - hypochlorous acid –Bactericidal
- Gaseous form or in Solution as Calcium Hypochlorite.
- Good disinfectants on clean surfaces.
- Inexpensive / Chlorox.
- Never Mix with Other Cleaning Agents!
- Kills legionella species ( Legionella Pneumophila
Bacteria ).

38. Iodine
Least toxic of the disinfectants.
Combines with Amino Acids.
a. Inactivates Enzymes
b. Tincture / Alcohol
c. Iodophor
 Betadine
Wound treatment.

39. ALCOHOL
• Denature Proteins and Dissolve Lipids.
• Evaporates
• Fast Acting
• Wet Disinfectants
a. Aqueous Ethanol (60% - 95%)
b. Isopropyl Alcohol
• Not effective against endospore.
• Use – Thermometer, Instruments, before
injection swabbing skin.

40. HEAVY METALS
• Silver, Mercury – germicidal or antiseptic
• Silver nitrate – prevent gonococcal eye infections.
• Copper sulfate – Algicide
• Mercurochrome – Disinfects skin and mucus
membrane.
• Used for Burn Treatment
- Denature Proteins
- Example / Silvadene Ointment / Silver
• Mercuric chloride – Bacteriostatic
• Copper sulphate – destroy green algae in reservoirs.
• Zinc chloride – ingredients in mouth washes.
• Zinc oxide – anti fungal in paints.

41. SURFACTANTS
• Include Soaps and Detergents.
• Soaps – Anionic detergents.
• Skin degerming.
• Triclocarbon – inhibit gram positive bacteria.
• Decrease Molecular Surface Tension
• Limited Germicidal Action.
• Removal of Organisms by Scrubbing.

42. CATIONIC DETERGENTS
• Quaternary Ammonium Compounds (QUATS)
- Cationic Detergents Attached to NH4
+
- Disrupt Plasma Membranes
- Most Effective on Gram-Positive Bacteria
• Enzyme inhibition, protein denaturation.
• Fungicide, Amoebocide.
• Two popular QUATS – Zephiran.
• Cepacol – Anti microbial

43. ORGANIC ACIDS
Chemical Food Preservatives
- Sorbic Acid
- Benzoic Acid Inhibit Fungus
- Propionic Acid
- Nitrate and Nitrite Salts / Meats
• To Prevent Germination of Clostridium
botulinum endospores.
• Calcium Propionate – Bread

44. Aldehydes
• Antimicrobial.
• Inactivate Proteins.
• Covalent crosslink formation.
• Formaldehyde – preserve biological specimens.
• Glutaraldehyde – Sterilize hospital instruments.
• Most Effective of all Chemical Disinfectants.
• Carcinogenic.
• Oxidize Molecules Inside Cells.

45. Antibiotics
 Used to Preserve Cheese.
 Used in Feed Given to Food Animals.

46. Antimicrobial Drugs
Beta Lactam Derivatives
Inhibitors of Cell Wall Synthesis : Penicillins
Penicillins
– Natural penicillins:
G, V
– Semisynthetic
penicillins
• “-cillin “ suffix
• Carbapenems
• Monobactam

47. Beta Lactam Derivatives
Inhibitors of Cell Wall Synthesis :
Cephalosporins
Cephalosporins
– 2nd, 3rd, and 4th
generations more
effective against
gram-negatives

48. Macrolides
 antibacterial action
 binding with 50S ribosomal subunit
 inhibit protein synthesis
e.g. Erythromycin, Clarithromycin
and azithromycin

49. Tetracyclines
 Like the macrolides they are also
bacteriostatic
 But binding to the 30S subunit of the bacterial ribosome
 inhibit protein synthesis
e.g. doxycycline and minocycline

50. Antifungal Drugs
• Inibitors of
Ergosterol Syntehsis
– Miconazole,
– fluconazole
– Triazoles
Nystatin
 was the most common antifungal agent
 used for
–oral candida infections

51. Antibacterial Antibiotics
– Vancomycin
• Glycopeptide
• Important "last line"
against antibiotic resistant
S. aureus (e.g. MRSA)

52. Antibacterial Antibiotics
• Quinolones and fluoroquinolones
– Ciprofloxacin
– Inhibits DNA gyrase so blocks DNA
polymerase
– Urinary tract infections

53. THANK YOU