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1. Classification Of Bacteria And
Viruses
By Zahid Ali Roll No 03
Section A Group B

2. Classification Of Bacteria:
The first classification scheme was
published in 1773.
Major classification of bacteria is given below:
• Morphological
• Anatomical
• Staining
• Pathogenicity
• Nutrition
• Environmental Factors

3. A. Cocci:
Spherical or Oval Cells.
Types:
Mono-cocci: (Single Cell) e.g. Monococcus spp.
Diplo-cocci: (Paired Cells)e.g. Streptococcus pneumonae
Staphylo-cocci: (Irregular Arrangement) e.g. Staphylococcus
aureus
Strepto-coccus: (Cells in Chains) e.g. Streptococcus pyogenes
Tetrad: (group of four cells) e.g. Micrococcus spp.
Sarcina: (group of 8 cells)
1 Morphological:

4. Rod Shaped bacteria.
Types:
Diplobacilli
Streptobacilli
Palisades
Chinese-letter form
Coccobacilli
Coma shaped
B. Bacilli:

5. Longer, Cylindrical and
non-branched
They have several
coils.
4. Spirilla:
Rigid and helical
bacteria, curved with a
twist.
Vibrio: Incomplete
twist
Helical: One or more
complete twist
3. Spirochetes:

6. Capsule:
Capsulate e.g.
Streptococcus pneumonae
Non-Capsulate e.g.
Viridans streptococci
Flagella:
Aflagellate e.g. Shigella
spp.
Flagellate
Monotrichous
Lophotrichous
Amphitrichous
Peritrichous
2. Anatomical:

7. Spore forming
e.g. Bacillus spp.
Non-Spore
e.g. Escherichia coli
3. Gram
Staning:
Gram Positive: Give
violet color after
staining e.g.
Styphlococcus aureus.
Gram Negative:
appear pink or red
e.g. Neisseria
gonorroheoae
Spore:

8. Pathogens: e.g.
Streptococcus pneumonae
Non-pathogens: e.g.
lactobacilli
Commensals: e.g. E.coli
5. Nutrition:
Autotrophs: e.g. Blue green
algae
Heterotrophs: e.g. Vibrio
cholerae
4. Pathogenicity:

9. Temperature:
Psychrophiles (15-20C) e.g. pseudosomonas
flouresence
Mesophiles (20-40C) e.g. Staphylococcus
aureus
Thermophiles (50-60) e.g. Bacillus
stearothermophillus
Extremely Thermophiles (as 250) e.g.
Sulfolobus
Oxygen Dependence:
Aerobes (grows where oxygen dependence is
21%) e.g. Nocardia sp.
Obligate Aerobes Strictly require oxygen for
growth e.g. Pseudomonas aurigenosa
Microaerophillic Can grow in 5-10% oxygen
dependence e.g. Halycobactor pylori.
6. Based On Environmental Factors:

10. Acidophiles (Lactobacillus acidophilus)
Alkaliphiles (Vibrio)
Neutrophiles (Staphlococci)
7. Other Ways Of Classification:
Mycoplasmas:
~These bacteria lack in rigid cell wall and highly
pleomorphic and indefinite in shape.
~They occur in round or oval bodies and in
interlacing filaments e.g. Micoplasma
pneumonae
Rickettsiae And Chylamidiae:
These are very small, obligate parasite and at
one time were considered closely to
viruses.Now these as regarded as bacteria e.g.
Rickettsia typhi
pH:

11. Classification Of Viruses

12. Classification Parameters
• Several Parameters Are Used for Classification
– Viral classification study is referred to as
Taxonomy
– 73 families exist so far!!
– Type of genomic nucleic acid
– Size of virion and genome
– Capsid structure
– Host
– Replication mechanism

14. Size of Viruses
• Ranges of sizes
– 20 nm to 500 nm (spherical)
– 12 nm to 300-2000 nm (rod like)
– Easily observed with electron microscope
– Ex.1 Mimi virus is 500 nm
• Infects algae
– Ex.2 Parvovirus is 20 nm in diameter
• Infects algae
– Viral genomes range in size 2,000 bp to
1,200,000 bp

15. Comparison Between Cellular
Genome and Viral Genome
• Viral genome
– 2-1,200 Kb
– Encoded proteins: 2-1,200
– Compact and economical
• Cellular genome
– 3x109 bp
– 30,000 proteins
– Massive and with 90% non-coding
DNA

16. ssDNA Viruses
• ssDNA Viruses have the following
characteristics
– Small genome, 2-7 KKB
• Possibly due to unstable nature of
ssDNA compared to dsDNA
– Circular genomes with the exception of
Parvorder (hairpin)
– No envelope
– Predominantly icosahedral capsids

17. dsDNA Viruses
• Examples of dsDNA viruses that infect
humans
– HSV, HPV and adenoviruses
• Among the largest known viruses
• Genome size varies from 5 to 1180 Kb
• Unfragmented genomes
• Both linear and circular
• Large genome size attributed to stability of
dsDNA
• Low error rate during replication
• No dsDNA virus is known to infect plants
• Phages are dsDNA viruses (95%)

18. dsRNA Viruses
• They utilize RNA dependent polymerase
• Icosahedral capsids
• Capsids stays intact inside cell.
Why?Genome protection.
• Transcription occurs via viral RNA
polymerases
• Reoviruses (dsRNA) are capable of
infecting multiple species (plants,
vertebrates, fungi). Not a common
phenomenon.
• Rhabhoviridae infect multiple species as
well
• The fact that they carry their own RNA

19. Viruses With + strand
RNA Genomes
• Very common of plant viruses to be +
ssRNA
• Only one phage family is + ssRNA
• RNA viruses have linear genomes
• Similar to ssDNA viruses they are
susceptible to nucleases and divalant cation
degradation
• Coronavirus has the largest genome of +
ssRNA virus (16-30 Kb)

20. - ssRNA Viruses
• This group includes some of the
deadliest viruses
– Ebola, rabies, influenza, measles
• Only helical nucleocapsids
• Nucleocapsid seems to provide
stability for RNA dependent RNA
polymerase to generate + ssRNA
• + ssRNA=mRNA

21. Viruses With Reverse
Transcription
• 3 families belong to this group
– Retroviridae, Ex. HIV
– Hepadnaviridae, Ex. Hep B
– Caulimoviridae, Ex. Cauliflower Mosaic
Virus
• These families utilize enzyme that uses an
RNA template to make DNA template
• Reverse transcriptase is packaged in capsid
– Similar to + ssRNA and – ssRNA that
package the RNA dependent polymerase
• Retroviruses package 2 copies of their RNA
genome in the capsid

22. Satellite Viruses/Nucleic
Acids
• These viruses require a helper virus
• Their genomes encode for capsid
proteins
• Nucleic acid satellites are either non-
coding or encode for non-capsid
proteins
• Mostly a plant phenomenon
• In humans the Hep  virus resembles
characteristics of satellite virus/viroid

23. Viroids
• These are plant pathogens
• They replicate in the absence of helper
virus
• Genome is circular and single stranded
• 250-400 nt
• Cellular DNA dependent RNA
polymerases are used for replication
• High degree of internal base pairing
• RNA behaves as enzyme
– i.e cut/ligate themselves
– Ribozymes

24. Thank You