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5. Fungi and Viruses
Fungi belong to kingdom Fungi.
Fungus is a member of a large group of eukaryotic
organisms that includes microorganisms such as yeasts
and molds, as well as the more familiar mushrooms.
More evolutionarily advanced forms of microorganisms,
as compared to the prokaryotes (prions, viruses,
bacteria). They are classified as eukaryotes.
Fungi have a diploid number of chromosomes and a
nuclear membrane.
Have sterols in their plasma membrane.
Eukaryotic multicellular organisms. Most multicellular
fungal bodies, are commonly called molds.
Composed of filaments called hyphae; their cells are long
and thread-like and connected end-to-end. Hyphae that
have walls between the cells are called septate hyphae;
hyphae that lack walls and cell membranes between the
cells are called nonseptate or coencocytic hyphae).
The body of the organism is given the special name
mycelium (tangled network), a term that is applied to
the whole body of any fungus.
When reproductive hyphae are produced, they form
a large organized structure called a sporocarp, or
mushroom. This is produced solely for the release of
spores, and is not the living, growing portion of the
fungus.
Fungal cells often have multiple nuclei. In the chytrids
and zygomycetes, the cells are coenocytic, with no
distinction between individual cells.
Another feature of fungi is the presence of chitin in their
cell walls. This is a long carbohydrate polymer that also
occurs in the exoskeletons of insects, spiders, and other
arthropods.
Yeasts are unicellular fungi.
The budding yeasts reproduce asexually by budding of a
smaller daughter cell; the resulting cells may sometimes
stick together as a short-chain or pseudohypha.
Candida albicans is a common yeast that forms
pseudohyphae; it is associated with various infections in
humans, including vaginal yeast infections, oral thrush,
and candidiasis of the skin. Some fungi are dimorphic,
having more than one appearance during their life
cycle.
Fungi are not able to ingest their food like animals do,
nor can they manufacture their food the way plants do.
Instead, fungi feed by absorption of nutrients from the
environment around them.
Most fungi are saprophytes, feeding on dead or decaying
material. This helps to remove leaf litter and other debris
that would otherwise accumulate on the ground.
All fungi are free-living.
They are not obligate intracellular parasites.
They do not contain chlorophyll and cannot synthesize
macromolecules from carbon dioxide and energy derived
from light rays.
Therefore, all fungi are heterotrophs, living on preformed
organic matter.
Examples of fungi are:
z
Molds
z
Penicillin
z
Yeast
z
Truffles
z
Mushrooms.
Morphology of Fungi
a. General: Fungi vary widely in size and shape, from
unicellular, microscopic organisms to multicellular
forms easily seen with the naked eye. Individual cells
range from 1 to 30 µ. Microscopic fungi exist as either
molds yeasts or both. Internally, fungal cells are fairly
typical eukaryotic cells.
b. Molds: The molds form large multicellular aggregates
of long branching filaments, called hyphae. There are
vegetative hyphae and reproductive hyphae. Spores
are borne on the reproductive hyphae. Fungal spores
should not be confused with bacterial spores that are
resistant bodies formed for bacterial survival rather
than reproductive purposes. Spore size, shape and
structure are used in the classification and identification
of fungi. The tube-like hyphae are responsible for the
fluffy appearance of the macroscopic mold colony.
The hyphae and other structures combine to form an
elaborate network called mycelium.
c. Yeasts: These are large (5–8 µ), single-celled organisms
that rarely form filaments. Most yeasts reproduce by the
asexual process of budding. Yeast colonies are usually
characterized by a smooth surface similar to that of
many bacteria.
Saccharomyces cerevisiae has traditionally been the main
yeast, responsible for most fermentation processes. In
addition to their importance in the food industry, species
of Penicillium and Aspergillus serve in the production of
many biotechnologically produced enzymes and other
Section 5 Microbiology
479478
Classification of Fungi
Class
of fungi
Hypha Type of
reproduction
Phycomycetes Aseptate Asexually
Sexually
Ascomycetes
Septate Asexually
Sexually
Basidiomycetes Septate Sexually
Deutero-
Septate Asexually Thallospore
mycetes
(fungi
imperfecti)
Characteristic
spore
Sporangio-
spore
zygospore
or oospore
Blastospore
Conidium
Ascospore
Basidio-
spore
Conidium
Origin of
spore
Sporangiophore
Fusion of
nuclei
Examples of
fungi
Nuisance fungi
Including
general
Absidia,
Mucor, and
Rhizopus
Budding
Conidiophore
Ascus
Allescheria,
Aspergillus
Neurospora,
Piedraia,
Saccharomyces
Basidium Mushrooms,
smuts and
rusts
Thallus (hypha)
Conidiophore
(Imperfect
mold and
yeast)
Pathogenicity
Very rare
mucormycosis
Rare
maduromycosis
Aspergillosis
Black Piedra
Rare
mushroom
poisoning
Most mycoses
encountered
in medical
mycology
macromolecules, such as gluconic, citric, and tartaric acids,
as well as several pectinases, lipase, amylases, cellulases,
and proteases.
Virus
The branch of science related to the study of viruses is
known as virology and scientist who studies virology is
known as virologist. The viruses are very small in size,
able to pass by filters that are used to retain back bacteria
in contaminated fluids. They are like other microorganisms
(e.g. bacteria, fungi, and parasites) that are associated with
disease in humans.
Characteristic Features
An individual virus is called a virion.
They have the characters of both living and non-living
cells.
They do not reproduce by themselves but in a living host
they reproduce at a very fast rate.
They do not have cytoplasm or other cell organelles.
They are incapable of growth and division but in the
host cell they are able to synthesize and assemble new
viral components.
They possess either DNA or RNA as their nuclear
material in their head or capsid region.
Components of the capsid are proteins and glycoproteins.
Components of virus: A fully assembled infectious virus
is called a virion. The simplest virions consist of two basic
Section 5 Microbiology
components: Nucleic acid (single- or double-stranded RNA
or DNA) and a protein coat, the capsid.
1. Nucleoid: It represents the viral chromosome. Nucleoid
or viral chromosome is made of a single molecule of
nucleic acid. It may be linear or circular with various
degrees of coiling. Nucleoid is the infective part of a
virus. The nucleic acid is either DNA or RNA but never
both.
2. Capsid: Capsid of a virus is an example of the coat.
Various protein molecules that join to each other and
make a capsomere structure. These capsomeres join
together and make capsid or coat or shell of virus. Genetic
material of a virus is always enclosed within a capsid,
composed of multiple copies of one protein or a few
different proteins, each of which is encoded by a single
viral gene.
3. Envelope: This structure is found in some animal viruses,
very rarely in plant and bacterial viruses. The virus
which does not have an envelope is called the naked
virus. Envelope composed of proteins (from virus),
lipids and carbohydrates (from host cells). Subunits of
envelope are known as peplomers. Either envelope has
smooth or outgrowths called spike projections. These
spike projections are made-up of glycoproteins and help
virus to move towards the target.
On the basis of capsid structure, the viruses can be
classified into different morphological types as follows:
Helical viruses
Polyhedral viruses
Enveloped viruses
Complex viruses.
Viral symmetry
Three types of symmetry are observed depending on the
arrangement of the capsid around the nucleic acid core
(genome). These are:
Icosahedral (cubical)
Helical
Complex symmetry.
DNAviruses: These belong to the following families:
Adenoviridae: The members of the family Adenoviridae
are medium-sized viruses measuring 20–90 nm in size.
These viruses are non-enveloped, icosahedral viruses with
252 capsomeres.
Poxviridae: These are large-sized, brick-shaped viruses.
They have a complex structure with a core containing a
single linear molecule of double-stranded DNA genome.
Herpesviridae: These are medium-sized icosahedral
nucleocapsid viruses (100 nm) containing 162 capsomeres.
They are enveloped viruses containing linear, doublestranded DNA.
Papovaviridae: These are small (40–55 nm) viruses
containing double-stranded DNA with 72 capsomeres.
They are non-enveloped viruses.
Hepadnaviridae: Hepadnaviridae (hepa: liver; DNA: DNA
core) are so named because they cause hepatitis and contain
DNA as a genome. These viruses differ from other DNA
viruses by synthesizing their DNA by copying RNA using
reverse transcriptase.
RNAviruses: These belong to the following families:
Togaviridae: These viruses include arboviruses and
alphaviruses. Most of these viruses multiply in arthropods
as well as in vertebrates.
Rhabdoviridae: Rhabdoviruses are bullet-shaped viruses.
The lytic cycle of a virulent bacteriophage shows the
stages of:
a. Adsorption: Phase particle attaches to the cell surface of
bacteria involving specific interactions between a phage
protein at the end of the tail and a bacterial receptor.
b. Penetration: Adsorption is followed by penetration of
phage genome into host bacterial cell without exposure
to the surrounding environment. Penetration of bacterial
cell wall occurs by the tail tube tip and insertion of the
genetic material of phage occurs through the tail tube.
c. Synthesis of the phage components: Phage genome
forces bacterial machinery to make phage-specific
replicase that initiates replication of the phage genome.
Then follows a transcription of the late genes that code
for the structural proteins of the head and tail. The new
phage particles are assembled and released from the
host bacterial cell.
d. Release of progeny phases: Steps usually follows the
lysis of the host cell with the help of murein hydrolase
coded by a phage gene that destroys the cell wall.
2. Lysogenic cycle: It is also known as temperate cycle. In
this cycle, phage genetic material is integrated with the
bacterial genetic material and replicates with the bacteria
synchronously without causing lysis of the host cell.
Infection of phage to bacteria does not result always in lysis
of the bacterial cell. In some cases, the genetic material of
phase inserted into bacterial genome without a breakdown
of the bacterial cell. Phage genome retains into an infected
bacterial cell. The integrated form of the phage DNA (called
the prophage) is silent, and a host bacterial cell carrying
a phage genome that is generally indistinguishable from
an uninfected bacterial cell. The prophage is eventually
released from the host genome and the phage come
again into the lytic mode and break the next host bacterial
cell.
Reoviridae: They are icosahedral, non-enveloped viruses-
measuring 60–80 nm in size.
Bacteriophages: They are basically viruses that infect
bacteria known as bacteriophage. They are obligate cell
parasites that can replicate inside bacteria by using some or
all of the host biosynthesis machinery. They have a genetic
material enclosed by a protective coat that is formed from
protein. A bacteriophage is bound on specific receptors
present on the surface of host bacteria and insert its genetic
material through the cell wall of bacteria. This forces the
host cells to synthesize more bacteriophages. Either they
have DNA or RNA as their genetic material. They do not
have any enzymatic systems for energy production so they
are incapable to produce proteins on their own. Phages
exhibit two different types of life cycles:
1. Lytic cycle: It is also known as the virulent cycle
of bacteriophage. In this cycle, after completing
multiplication phages break-down host cell and finally
progeny virions are released in surroundings.
Uses
Suitable model for understanding of virus–host
interaction.
They can be used efficiently in modern biotechnology,
as well as alternatives to antibiotics for many antibiotic
resistant bacterial strains.
They play an important role in the transmission of
genetic information by the process of transduction.
Used to control and eliminate bacterial contaminants
from food surfaces, food-borne spoilage bacteria and
bacteria causing gastrointestinal diseases.
Used as cloning vectors for genetic recombination and
manipulations.
Used for phage typing.
Bacteriophages are also potentially useful as surface and
environmental decontaminants.
Phages can be used as vehicles for vaccines both DNA and
protein, for the detection of pathogenic bacterial strain, as
biocontrol agents in the agriculture and the food industry.
Section 5 Microbiology
481480
HIV: Belongs to the family Retrovirideae. They belong
to class retrovirus because of the presence of a special
unique enzyme called reverse transcriptase that instructs
the synthesis of DNA from the viral RNA when it infects
the host cell. These viruses have envelope, spherical
RNA as their genetic material. They show a characteristic
morphology and unusual mode of replication.
Morphological Characters
They are heat sensitive; killed if heat at 56°C for 30 minutes.
They can also inactivate by treating them with mild acids,
ether, and formalin.
Envelope: Viruses are spherical in shape and 80–110 nm
in size, having an envelope; composed of lipid in which
the following two proteins are embedded: 1. Glycoprotein
120 and 2. Glycoprotein 41.
Nucleocapsid: Viruses symmetry is icosahedral compost
of core protein. HIV have 3 structural genes named as gag,
pol, and env and accessory genes (e.g. tat, rev, nef, vif, vpu).
Structural genes encode:
gag gene: Specific antigens, capsid proteins.
pol gene: Enzymes polymerase, protease, and integrase.
env gene: Enveloped glycoproteins.
Antigenic properties: Retroviruses have specific
nucleoprotein antigen found on their virion core and
specific glycoprotein antigen found on their envelope.
Replication: Infection is transmitted when the virus enters
the bloodstream or tissues of a person and comes into
contact with a suitable host cell, principally the CD4 T
lymphocytes.
Binding and fusion: HIV begins its life cycle when binds
to a receptor found on CD4 cells. After fusion, HIV virus
penetrates the host cell, after penetration it releases its
genetic material, into host cell.
Reverse transcription: reverse transcriptase coverts HIV
RNA (single-stranded) into HIV DNA (double-stranded).
Integration: The HIV dsDNA enters into the host cell
nucleus. An enzyme named integrase hides viral DNA
into host nucleus. The integrated virus is called provirus.
Provirus may remain inactive for several years and
producing few or no new copies of HIV.
Transcription: From HIV genome host cell receives an
instruction to become active. The provirus utilizes an
enzyme of host cell called RNA polymerase to form
number of copies of the HIV genomic material as in
the form of messenger RNA. These mRNA is used as a
blueprint to make long chains of HIV proteins.
Assembly: In transcription, long chains of HIV proteins
are produced, which cuts into smaller individual proteins
by proteases (HIV enzyme). The smaller HIV proteins
come with each other along with copies of HIV’s RNA
genetic material. Then a new virus particle is assembled.
Budding: The newly assembled virus buds from the host
cell. Ready to infect other cells.
Section 5 Microbiology
Tumour virus: Members of six distinct families of animal
viruses, called tumour viruses, are capable of directly
causing cancer in either experimental animals or humans
can be classified into two main groups:
1. RNA tumour virus: Also known as tumour retrovirus.
Human T cell lymphotropic virus-1 (HTLV-1): Human
T-cell lymphotropic virus type I (HTLV-I) infection is
associated with a variety of human diseases. In particular,
there are two major diseases caused by HTLV-I infection.
One is an aggressive neoplastic disease called adult T-cell
leukaemia (ATL), and another is a chronic progressive
inflammatory neurological disease called HTLV-Iassociated myelopathy/tropical spastic paraparesis
(HAM/TSP).
Hepatitis virus C: It is a viral infection that causes liver
inflammation, sometimes causes critical liver damage. The
modes of transmission is through contaminated blood.
The hepatitis C virus is a blood-borne virus. Infection
may happen through injection drug use, unsafe injection
practices, transfusion of unscreened blood and blood
products, and sexual practices that lead to exposure to
blood. Cirrhosis makes liver cancer more likely.
2. DNA tumour virus
Papillomaviruses: Human papillomavirus (HPV) is the
most common sexually transmitted virus in the world.
Transmission modes are person-to-person through skin-toskin contact. HPV is the most common sexually transmitted
infection (STI). Most HPV infections do not lead to cancer.
But some types of genital HPV can cause cancer of the
lower part of the uterus that connects to the vagina (cervix).
Polyomaviruses: It is small, non-enveloped DNA virus,
which are widespread in nature. After primary infection
it remains in the latent phase. It served as the best model
for the study of molecular oncology.
Adenoviruses: They cause acute respiratory disease
(most frequent), pneumonia (sometimes), acute follicular
conjunctivitis, cystitis, and gastroenteritis (occasionally).
In infants, pharyngitis and pharyngeal-conjunctival fever
are common. Mode of transmission through droplets
when an infected person coughs or sneezes. Other causes
of infection are faecal material, contaminated water and
poor handwashing, etc.
Herpesviruses: They have a special structure made-up
of four-layers: A core having the large, DNA genome is
enclosed by an icosapentahedral protein coat or capsid,
which is composed of capsomers. The capsid is enclosed
by an amorphous protein coat known as tegument. It is
encased in a glycoprotein-bearing lipid bilayer envelope.
Herpes simplex virus 1 transmission is primarily oral, and
herpes simplex virus 2 is primarily genital.
Human hepatitis virus: Hepatitis B virus (HBV) is
an enveloped DNA hepadnavirus that can cause
hepatocellular carcinoma (HCC). HBV can integrate itself
into the human genome and replicate within liver cells,
directly increasing carcinogenic activity through several
signalling pathways in the liver.
MULTIPLE CHOICE QUESTIONS
1. Fungi are ______________.
A. Prokaryotic
B. Eukaryotic
C. Prokaryotic and lack chlorophyll
D. Eukaryotic and lack chlorophyll
2. The edible fungi are:
A. Rusts B. Moulds
C. Mildews D. Mushrooms
3. Hyphalwallconsistsofmicrobrilscomposedof
___________________.
A. Hemicellulose or chitin
B. Cellulose
C. Lipids
D. Proteins
4. For uncoating viruses use:
A. Specific receptors
B. Lysozyme
C. The mechanism called viropexia
D. The synthetic machinery of host cell
5. Mycorrhiza exhibits the phenomenon of:
A. Parasitism B. Symbiosis
C. Antagonism D. Endemism
6. During stationary phase:
A. Microorganisms phase increase in the size of a
cell and metabolic rate
B. The cells start dividing and their number
increase by geometric progression
C. The rate of multiplication and death becomes
almost equal
D. The population of the cells decreases
7. Sabouraudmedia forthegrowth offungi is
composed of ____________________.
A. Glucose and ammonia
B. Maltose and peptone
C. Sucrose and peptone
D. Peptone
8. In thefungal classicationsystem Ascomycetes
come under the division of ________________.
A. Amastigomycota B. Zymnomycota
C. Mastigomycota D. Gymnomycota
9. Whenmoist bread iskept exposedto air, it
becomes mouldy and black because:
A. Spores are present in the water
B. Spores are present in the bread
C. Spores are present in the air
D. The bread decomposes
10. For penetration viruses use:
A. Specific receptors
B. Lysozyme
C. The mechanism called viropexia
D. The synthetic machinery of host cell
11. Which of thefollowing isthefirst stepin
replication by bacterial phages?
A. Adsorption
B. Penetration
C. Transcription
D. Assembly and release
12. During log phase:
A. Microorganisms phase increase in size of cell
and metabolic rate
B. The cells start dividing and their number
increase by geometric progression
C. Rate of multiplication and death becomes
almost equal
D. Population of the cells decreases
13. Amanita,apoisonousfungusisa:
A. Mushroom B. Bracket fungus
C. Toadstool D. Puffball
14. Coenocytic hyphae have ________________.
A. Septate with uninucleate cells
B. Septate with multinucleate cells
C. No septate
D. No septate with uninucleate cells
15. The feeding structure of the fungus is the:
A. Mycelium B. Rhizomorph
C. Sclerotium D. Penicillus
16. Whichofthefollowingistrueaboutfungi:
A. Eukaryotes
B. Prokaryotes
C. Obligately parasitic
D. Cannot be grown on cell-free media
17. Pathogenic fungi have a temperature optimum at
__________.
A. 30–37° C
B. 22–30° C
C. 37–42° C
D. 42–50° C
18. Viruses largely lack metabolic machinery of their
owntogenerateenergyortosynthesize:
A. Protein B. Carbohydrate
C. Alcohol D. All of these
19. Whichofthefollowingcoliphageshasatadpole
shape?
A. T1 B. T4
C. T5 D. T7
20. Whichdivisionoffungilacksagella?
A. Mastigomycota B. Amastigomycota
C. Gymnomycota D. Basidiomycetes
21. Dark-ground microscopy is used for the detection of:
A. Spirochetes B. Chlamidia
C. Fungi D. Virus
Section 5 Microbiology
483482
22. Asexual fruiting bodies have name such as
________________.
A. Perithecium B. Pycnidium
C. Antheridium D. Apothecium
23. Whichofthefollowingaretheoxygenrequirements
of molds?
A. Strictly aerobic
B. Facultatively aerobic
C. Anaerobic
D. Microaerophilic
24. Whatarethedimensionsofthelamentsthatthe
thallus of a fungus consists of?
A. 1 micrometre B. 5–10 micrometres
C. 1 metre D. 1 centimetre
25. Organisms that are the indicator of SO
pollution
2
of are:
A. Mosses B. Lichens
C. Mushrooms D. Puffballs
26. Whichofthe following virusespossess an
envelope?
A. Herpesvirus
B. Reovirus
C. Tobacco mosaic virus
D. Papillomavirus
27. Nakedvirusesare:
A. Enveloped
B. Viruses are genetically deficient and so
incapable of producing infectious daughter
virion
C. Infective agents with protein free, with low
molecular weight RNA
D. Non-enveloped
28. Capsid in nature is a:
A. Protein B. Lipid
C. Polysaccharide D. Lipoprotein
29. Thecrosswallsconstrictatwhichofthefollowing
partsandthengrowinwardstoformseptum?
A. Hyphae B. Lumen
C. Protoplasm D. Plasmalemma
30. For adsorption viruses use:
A. Specific receptors
B. Lysozyme
C. The mechanism called viropexia
D. The synthetic machinery of host cell
31. Plasmalemmasurroundswhichofthefollowing?
A. Lumen B. Wall
C. Protoplasm D. Hyphae
32. Forbiosynthesis,virusesuse:
A. Specific receptors
Section 5 Microbiology
B. Lysozyme
C. The mechanism called viropexia
D. The synthetic machinery of host cell
33. Therstphaseofviralmultiplicationcyclesis:
A. Penetration
B. Biosynthesis
C. Uncoating
D. Adsorption or attachment
34. Forth phase of the viral multiplication cycles is:
A. Penetration
B. Biosynthesis
C. Uncoating
D. Adsorption or attachment
35. Which ofthefollowing isa familyof lambda-
phage viruses?
A. Pedoviridae B. Microviridae
C. Styloviridae D. Corticoviridae
36. Whichamongthefollowingareasexualspores?
A. Blastospores B. Ascospores
C. Basidiospores D. Zygospores
37. Fungi aresensitive towhich of thefollowing
antibiotics?
A. Penicillins B. Tetracyclins
C. Chloramphenicol D. Griseofulvin
38. Which incubation temperature is required for the
adsorptionofphageT4andDNAinjectioninto
E. coli?
A. 50°C B. 15°C
C. 37°C D. 80°C
39. Whichofthefollowingistruthaboutanenvelope?
A. Derived from host cell membrane
B. Lipoprotein in nature
C. Has projecting spikes on the surface
D. All of the above
40. Prions are:
A. Viruses that are genetically deficient and so
incapable of producing infectious daughter
virion
B. Protein free infective agents with low molecular
weight RNA
C. Infectious protein particles, lack detectable
nucleic acid
D. Extrachromosomal genetic elements
41. Spores formed by sexual reproduction on a clubshaped structure are _______________.
A. Basidiospores B. Ascospores
C. Zygospores D. Oospores
42. Theblackrustofwheatisafungaldiseasecaused
by:
A. Albugo candida
B. Puccinia graminis tritici
C. Melampsora lini
D. Claviceps purpurea
43. Thethread-likelamentsthatformtheplantbody
of fungi are:
A. Rhizoids B. Paraphyses
C. Hyphae D. Haptera
44. Reverse transcriptase is a useful enzyme to have
when:
A. An RNA virus converts its RNA to DNA
B. There are no host cells present
C. Nutrients are scarce
D. Spikes are forming in the new virus
45. The delayedearlygenes codefor whichofthe
followingenzymes?
A. Phage enzymes
B. RNA polymerase
C. Nucleases
D. Oxidases
46. A structural component that is found in all viruses
is:
A. Envelope B. DNA
C. Capsid D. Tail fibres
47. Whichofthefollowingisfalseaboutthegeneral
characteristics of viruses?
A. Do not possess cellular organization
B. They are lack biosynthetic enzymes
C. They are sensitive to antibiotics
D. They are multiplied by a complex process
48. Whatarethecellwallstructuralcomponentsof
fungi?
A. Peptidoglycan
B. Cellulose
C. Chitin
D. Chitin, cellulose, or hemicellulose
49. Rootrotofsweetpotatoiscausedby
A. Mucor mucedo
B. Rhizopus oryzae
C. Rhizopus stolonifer
D. Penicillium notatum
50. Defective viruses are:
A. Genetically deficient and so incapable of
producing infectious daughter virion.
B. Protein free infective agents with low molecular
weight RNA
C. Infections protein particles, lack detectable
nucleic acid
D. Extrachromosomal genetic elements
51. The mode of nutrition of rhizopus,yeast and
penicillium is:
A. Parasitic B. Saprophytic
C. Symbiotic D. Autotrophic
52. Whichof thefollowing are saidto havebinal
symmetry?
A. M13 B. T4
C. T7 D. MV-L2
53. Viroids are:
A. Genetically deficient and so incapable of
producing infectious daughter virion
B. Protein free infective agents with low molecular
weight RNA.
C. Infectious protein particles, lack detectable
nucleic acid
D. Extrachromosomal genetic elements
54. Inthegrowthcurveofplaque-formingunits,the
timefrominfectionuntillysisisknownas:
A. Latent period B. Eclipse period
C. Rise period D. Burst period
55. Thecellwallofyeastiscomposedof:
A. Cellulose B. Pectose
C. Pectin D. Chitin and mannan
56. Whichdivisionoffungilacksagella?
A. Mastigomycota B. Amastigomycota
C. Gymnomycota D. Basidiomycetes
57. The capsid is composed of:
A. Peplomers B. Nucleic acid
C. Capsomers D. Envelope
58. Whatdoes viral DNA becomeafter being
associatedwiththebacterialchromosome?
A. Gene B. Prophage
C. Plasmid D. Plaque
59. In which ofthe followingprocessesthe male
nucleus migrates through a fertilization tube into
the female gametangium?
A. Gametic copulation
B. Gamete-gametangial copulation
C. Gametangial copulation
D. Somatic copulation
60. Whichofthe following virusespossess an
envelope?
A. Herpesvirus
B. Reovirus
C. Tobacco mosaic virus
D. Papillomavirus
61. During the lag phase:
A. Microorganisms increase in the size of a cell and
metabolic rate
B. The cells start dividing and their number
increase by geometric progression
C. Rate of multiplication and death becomes
almost equal
D. Population of the cells decreases
62. Whichofthefollowingmethodsisusedforthe
productionofvaccinesagainstyellowfever?
A. Tissue-culture method
B. Through susceptible animals
C. Through appropriate media
D. Chick-embryo method
63. Inwhichofthefollowingmethods,theviralparticles
are transmitted through the lysis of the cell?
A. Lytic cycle B. Lysogeny
C. Replication D. Translation
Section 5 Microbiology
485484
64. Whichamongthefollowingaresporesformedby
budding?
A. Arthrospores B. Chlamydospores
C. Blastospores D. None of these
65. Whichofthefollowinggenescodesforanenzyme
whichdirectstheinsertionofthephageDNAinto
the bacterial chromosome?
A. recA gene B. cro gene
C. int gene D. gal gene
66. Fleming discovered penicillin from:
A. Penicillium notatum
B. P. roqueforti
C. P. camemberti
D. P. chrysogenum
67. What is the shape of helical phages?
A. Regular solids B. Polyhedral
C. Rod-shaped D. Icosahedral
68. LSD is derived from:
A. Fungus B. Bacteria
C. Alcohol D. 2, 4-D
69. Aspergillus niger is used in the production of
_______________.
A. Cheese
B. Citric acid
C. Gluconic acid
D. Citric acid and gluconic acid
70. Which of thefollowing phagesdoes notcause
lysogeny?
A. T2 B. T1
C. Lambda D. P1
71. Thefringesonanimalviruseslikeinuenzavirus
is made-up of ______________.
A. Lipoproteins
B. Glycoproteins
C. Cellulose
D. Polysaccharides
72. The nucleic acid core of phages is covered by a
proteincoatknownas_______________.
A. Capsomere B. Capsid
C. Outer envelope D. Nuclear membrane
73. In papovaviruses,DNA occurs inwhich ofthe
followingforms?
A. Linear dsDNA
B. Linear ssDNA
C. Supercoiled circular dsDNA
D. Supercoiled circular ssDNA
74. Howmanyascosporesarepresentineachascus?
A. Four B. Six
C. Two D. Eight
75. HowmanydsRNA segments arepresent in the
Section 5 Microbiology
reovirus genome?
A. 1 B. 3
C. 50 D. 10
76. Fruiting bodies of slime moulds are called
______________.
A. Acervulus B. Sori
C. Apothecium D. Perithecium
77. The envelope surrounding the nucleocapsid of
someanimalvirusesismade-upofwhichofthe
followingstructures?
A. Lipoproteins
B. Lipopolysaccharides
C. Peptidoglycan
D. Chitin
78. What type of symmetry has Coxsackaevirus?
A. Icosahedral B. Complex
C. Helical D. All of these
79. Whichofthefollowingvirusesdoesnotbelong
to the genera Enterovirus?
A. ECHO B. Cocsackievirus
C. Poliovirus D. Mumps virus
80. Whichofthefollowingsporesareformedatthe
tips of sterigmata?
A. Zygospores B. Oospores
C. Basidiospores D. Blastospores
81. Which fungicause theblack wart diseaseof
potatoes?
A. Saprolegnia parasitica
B. Synchytrium endobioticum
C. Rhizopus stolonifer
D. Saccharomyces cerevisiae
82. What type of symmetry has poliovirus?
A. Icosahedral B. Complex
C. Helical D. All of these
83. Whichofthefollowingisasingle-strandedRNA
virus?
A. ECHO B. Cocsackievirus
C. Poliovirus D. All of these
84. Whichofthefollowingsymmetryisexhibitedby
rod-shaped viruses?
A. Icosahedral B. Helical
C. Complex D. Circular
85. Which of thefollowing sporesare formed by
disjointingofhyphalcells?
A. Conidiospores
B. Chlamydospores
C. Oidia
D. Zoospores
86. The enteroviruses are:
A. Small, naked capsid, double-strand DNA
B. Small, naked capsid, plus-strand RNA
C. Small, naked capsid, double-strand RNA
D. Large, naked capsid, plus-strand RNA
87. Themostcomplextypeofbacterialvirushaswhich
ofthefollowingmorphologicalfeatures?
A. Hexagonal head and tail fibres
B. No contractile sheath
C. Hexagonal head but no tail
D. Hexagonal head, rigid tail with contractile
sheath
88. Theenterovirusesgrowreadilyin:
A. Chick embryo
B. Tissue cultures of primate
C. Rabbits
D. All of the above
89. Cryptococcosis is a disease of ________________.
A. Bacterial infection
B. Parasitic infection
C. Viral infection
D. Mycotic infection
90. Effectivepoliomyelitisvaccinesweredeveloped
by culturing the virus of poliomyelitis on the
kidneycellsofwhichanimal?
A. Cow B. Monkey
C. Giraffe D. Pig
91. Aplanospores are ___________________.
A. Motile sporangiospores
B. Non-motile sporangiospores
C. Oidia chlamydospores
92. Cocsackievirus produced pathological changes
in:
A. Adult mice B. Adult rabbits
C. Suckling mice D. Suckling rabbits
ANSWER KEY
1. D 2. D 3. A 4. B 5. B 6. C 7. B 8. A 9. C 10. C 11. A 12. B 13. C 14. C
15. A 16. A 17. A 18. A 19. D 20. B 21. A 22. B 23. A 24. A 25. B 26. A 27. D 28. A
29. D 30. A 31. C 32. D 33. D 34. B 35. C 36. A 37. D 38. C 39. D 40. C 41. A 42. B
43. C 44. A 45. A 46. C 47. C 48. D 49. C 50. A 51. B 52. B 53. B 54. A 55. D 56. B
57. C 58. B 59. B 60. A 61. A 62. D 63. A 64. C 65. C 66. A 67. C 68. A 69. D 70. A
71. B 72. B 73. C 74. D 75. D 76. B 77. A 78. A 79. D 80. C 81. B 82. A 83. D 84. A
85. C 86. B 87. D 88. B 89. D 90. B 91. B 92. C
6. Aseptic Technique, Sterilization and Disinfection
Disinfectants and antiseptics: There are a number of
chemicals that can act as disinfectants or antiseptics. These
include:
Phenolanditsderivatives,e.g.
z
Dettol (widely used chemical for sterilization of
instruments, thermometers, etc. 5–50% of the solution
is used for drawings and wound irrigation).
z
Carbolic acid (phenol): It is a good disinfectant for
faeces, pus, blood and sputum. It is a skin irritant and
a poison. Dissolves early in hot water. For thermometer
1 : 20 solution for a duration of 10 minutes is used.
z
Lysol: This is a phenol preparation mixed with soap.
It is less poisonous than carbolic acid but has a greater
bactericidal action. 2% of solution for 6–8 hours is used
for disinfecting viruses.
Halogens,e.g.chlorine,tinctureiodine.
z
Tincture of iodine: 1-2% iodine is used for cleaning
the skin and treating injuries to the skin.
z
Chlorideoflime(bleachingpowder): This is used for
disinfection of drinking water, stools, urine, sputum.
As it decomposes quickly when exposed to air, solution
must be prepared fresh for each use.
Alcohols, e.g. ethyl alcohol (70% is effective for skin
disinfection. Certain gases like formaldehyde and
glutaraldehyde are used in disinfection of rooms).
Aldehydes, e.g. glutaraldehyde (Cidex), formalin.
Quaternary ammonium compounds (cationic detergents)
Savlon: 1 : 30 solution is used to destroy or kill vegetative
bacteria.
Formalin: A 40% solution is used to disinfect faeces,
urine and sputum. It is not used for the skin and tissue,
as it is an irritant.
Hydrogen peroxide: 1–5% of the solution is used in
cleaning wounds and removing pus from infected ears.
Hydrogen peroxide is also used to clean the mouth. It is
an oxidizing agent.
Potassium permanganate: It is an oxidizing agent used
for cleaning the mouth with 1:1000 strength. It is also
used for the irrigation of wounds.
Sterilization describes a process that destroys or eliminates
all forms of microbial life and is carried out in health care
facilities by physical or chemical methods. Steam under
pressure, dry heat, EtO gas, hydrogen peroxide gas,
plasma, and liquid chemicals are the principal sterilising
agents.
Dry heat is sufficient for glassware, instruments and
articles not affected by very high temperature. Water,
impermeable oils and waxes can be sterilized by dry
heat.
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487486
Moist heat is effective at low temperature and is suitable
for culture media, laboratory discards and porous packed
materials.
Gaseous chemical sterilization may be used for heat
sensitive articles. Filter sterilization is the only means of
sterilizing heat labile fluids.
Radiation is used in the manufacture of sterile packaged
products such as disposable plastic syringes and materials
being used in clinical microbiology laboratories.
Disinfection: Describes a process that eliminates many or
all pathogenic microorganisms, except bacterial spores, on
inanimate objects.
Cleaning: Cleaning is the removal of visible soil (e.g.
organic and inorganic material) from objects and surfaces.
It is normally accomplished manually or mechanically
using water with detergents or enzymatic products.
Decontamination: Decontamination removes pathogenic
microorganisms from objects so they are safe to handle,
use, or discard.
Antisepsis is the use of chemicals (antiseptics) to
make skin or mucus membranes devoid of pathogenic
microorganisms.
Bacteriostasis is a condition where the multiplication of the
bacteria is inhibited without killing them. Bactericidal is a
chemical that can kill or inactivate bacteria. Such chemicals
may be called variously depending on the spectrum
of activity, such as bactericidal, virucidal, fungicidal,
microbicidal, sporicidal, tuberculocidal or germicidal.
Antibiotics are substances produced by one microbe that
inhibits or kills another microbe. Often the term is used
more generally to include synthetic and semisynthetic
antimicrobial agents.
MECHANICAL METHOD
Scrubbing: Handwashing is one of the important
procedures of a nurse in order to control and prevent selfinfection as well as cross-infection.
Filtration: Filtration is the passage of a liquid fluid or gases
through a filter with pores small enough to retain microbes:
vaccine, toxins, enzymes, e.g. HEPA filter, membrane filters
(nitrocellulose).
Sedimentation: It is used in the purification of water, by
this method the suspending material together with bacteria
settles down at the bottom of a liquid.
PHYSICAL METHODS
Name of Method Principle Application Advantage Disadvantage
Red heat Holding objects in
Bunsen ame till they
become red hot
Flaming Passing the object
through the ame
of Bunsen burner
Section 5 Microbiology
without heating to
redness
Bacteriological loops,
tips of forceps
Glass slides, mouth of
culture tubes
This is a simple
method for effective
sterilization of articles
Cost effective This method too
Limited to those
articles that can be
heated to redness in
ame
is limited to those
articles that can be
exposed to ame
Cracking of the
glassware may occur
Contd...