B1

Question 1

(……) are prokaryotes
(……) are eukaryotes
Viruses and prions are (…..)

Answer 1

(Bacteria and Archaea) are prokaryotes
( Fungi , algae , slime moles & Protozoa) are eukaryotes
Viruses and prions are ( neither )

** Virus are not living cells

Question 2

Viruses consists of either (….) or (……) surrounded by (…….)

Viroids consist only ( ……) and is (……)

Answer 2

Viruses consists of either ( DNA )or ( RNA) surrounded by ( protein coat capsid )

Viroids consist only ( RNA ) and is ( not surrounded by protein coat )

Question 3

Describe the structure and parts of flagella of a bacterium

Answer 3

• organ of locomotion —> moves bacteria towards nutrients & other attracts ( chemotaxis )
• E for movement provided by ATP
• 3 parts :
  I) filament
• longest portion of the flagellum, extends from cell surface to the tip
• hollow , rigid cylinder made up of a single protein — flagellin

II) Hook
- Short , curved flexible segment that links the filament to the basal body

III) basal body
- portion of the flagellum embedded in the cell

Question 4

State the function of flagella

Answer 4

1) Organ of locomotion for motile bacteria
- Ex : E.coli proteus species , helps propel the bacteria up the urethra into the bladder

2) Flagellar proteins can be used for identification of the bacteria via use of specific antibodies
- ex : Salmonella species

Question 5

State the types of arrangement & structure of flagella

Answer 5

1) No flagellum - Atrichous
2) Single flagellum - Monotrichous
3) Single flagellum at each poles - amphitrichous
4) Tuft of flagella at one pole - Lophotrichous
5) Flagella all over the cell surface - Peritrichous

Question 6

Describe the structure & function of pili ( fimbriae ) of a bacterium

Answer 6

• fine hair like structure
• shorter & straighter than flagella & composed of subunits of pilin

Functions :
I) helps the bacteria adhere to surface ( organ of adhesion) —> enhances virulence of a bacteria
II) a specialised pious — sex pilus forms attachments b/w male & female bacteria during conjugation ( gene transfer )

Question 7

Describe the structure (contents ) & function of bacteria spores

Answer 7

• forms inside the cell

- contains 
I) bacterial DNA 
II) Small amount of cytoplasm 
III) Cell membrane 
IV) Peptidoglycan 
V) small amount of water 

• functions : to ensure survival of the bacterium during extreme conditions ( no nutrients )
• remains dormant until conditions improve —> regenerate into bacterium

Question 8

Bacterial spores are resistant to antibiotics because ( ……..)

Answer 8

Bacterial spores are resistant to antibiotics because ( antibiotics target metabolic pathways within the bacterium , but the metabolic pathways are halted in bacterial spore )

Question 9

Spores are highly resistant to heating and can only be killed at temperature of above ( ……)

Answer 9

Spores are highly resistant to heating and can only be killed at temperature of above ( 121 degree Celsius )

Question 10

Bacteria spores are highly resistant to many chemicals due to its ( ……… )

Answer 10

Bacteria spores are highly resistant to many chemicals due to its ( thick keratin like coat )

** hence only chemicals designated as sporicidals can kill bacterial spores

Question 11

Describe the slime layer / capsule of a bacterium & its function

Answer 11

• glycocalyx is an amorphous , viscid gelatinous materials ( polysaccharide) coating that is secreted by many bacteria
• slime layer & capsule are the same but capsule —> more organised , not easily washed off.
• function : mediates adherence of bacteria to surfaces

Question 12

Which bacterium possesses both slime layer & capsule

Answer 12

Streptococcus salivarius

Question 13

State the function of capsule / slime layer of a bacterium

Answer 13

1) Contribute to bacterial virulence
- protect bacterium from phagocytosis
- helps adhere the bacteria to human tissue
- prevents the cells from drying out ( dessication )
- protect the bacterium from the action of lysozymes & bacteriophages
- prevents complement-mediated bacterial,cell lysis

2) Biofilm formation
- contains millions of adherent bacterial cells within the slime layer which are pathogenic
- can adhere to damaged tissue & plastic surface —> disease

3) Source of nutrient and energy
- due to high content of sugar
- ex : Streptococcus mutans ferments sugar in the capsule & form acid byproducts which contribute to caries

4) Vaccine manufacture
- capsular vaccines available for bacteria such as pneumococcus , meningococcus , & Haemophilus influenza serotypes-B

Question 14

The cell envelope of bacterium is composed of :

Answer 14

In gram + bacteria :
I) cell membrane - phospholipid bilayer
II) Cell wall - containing thick peptidoglycan layer & teichoic acid
III) Glycocalyx layer - slime layer / capsule

In gram negative bacteria :
I) cell membrane - phospholipid bilayer
II) Periplasmic space - containing enzymes ( B-lactamases ) which degrades penicillin and other B- lactam drugs
III) Cell wall - containing thin peptidoglycan layer & lipoprotein & outer membrane containing lipopolysaccharides ( endotoxin) & pore protein ( porin )
IV) Glycocalyx layer

Question 15

The endotoxin / lipopolysaccharide of the outer membrane of Gram negative bacteria is responsible for many of the features of disease such as ( ……..)

Answer 15

The endotoxin / lipopolysaccharide of the outer membrane of Gram negative bacteria is responsible for many of the features of disease such as ( fever & septic shock , diarrhea )

Question 16

The slime layer / capsule consists of polysaccharide , except in the ( …….. ) which is contains polypeptides

Answer 16

The slime layer / capsule consists of polysaccharide , except in the ( bacillus anthracis ) which is contains polypeptides

Question 17

State some general features of fungi

Answer 17

1) Eukaryotic organisms
2) Avascular
3) Reproduces via spores ( asexual or sexual ) which are usually wind disseminated
4) Typically not motile although a few ( eg Chytrids ) have a mobile phase
5) Have an alternation of generation like plants ( has n & 2n at diff life stages )
6) If unicellular —> yeasts if multicellular —> molds
7) Cell wall like chitin instead of cellulose ( like in plants )
8) Heterotrophic
9) Digest then ingest w/ help of exozyme

10] Food storage is in the form of glycogen

Question 18

Classify the fungi based on morphology with examples

Answer 18

1) Yeast ( unicellular)
- grows as round to oval cells that reproduce asexually by budding in which cells form protuberance which enlarge & eventually separate
- ex : Crytococcus neoformans

2) Yeast like fungi
- in some yeast , the bud remains attached to the mother cell , elongates and undergoes repeated budding to form chains of elongated cells known as pseudohyphae
- differentiate from true hyphae as they have constriction at the septa
- ex : Candida albicans

3) Mold
- grow as long branching filament known as hyphae —> can grow to form a branching tangled mass of growth called mycelium
- ex : Trichophyton rubrum —> cause athlete foot ( Penicillum spp )

4) Dimorphic fungi
- can exists as either mold ( 25 C ) or yeast in human tissue at body temperature ( 37 C ) in different life stages
- ex : Talaromyces marneffei—> cause of opportunistic infection in HIV / AIDS related immunodeficiency, Blastomyces dermatitis

Question 19

In dimorphic fungi , the fungi turn into yeast form at (…….) and are (……)
At (……) the fungi turns into mycelium (mass of mold / hyphae) and are (……)

Answer 19

In dimorphic fungi , the fungi turn into yeast form at ( 37 C ) and are ( parasitic / pathogenic )
At ( 25 C ) the fungi turns into mycelium (mass of mold / hyphae) and are ( saphrophytic)

Question 20

Fungi are heterotrophic and can either be (…..)

Answer 20

Fungi are heterotrophic and can either be ( saprophytics , parasitic or mutualists ( symbionts) )

Question 21

List the reagents used in Gram Staining & Their functions

Answer 21

1) Crystal violet - primary stain : stains cell purple or blue
2) Lugol’s iodine - mordant makes dye less soluble so it adheres to cell walls
3) Alcohol : decolorizer washes away the stain from the Gram negative cell walls : Gram negative will become colourless
4) Safranin : counterstain allows dye adherence to gram negative cells : Gram negative cells appear pink or red

Question 22

State the definition of mycosis

Answer 22

Disease cause by fungal infection

Question 23

Classify the different types of mycoses & give examples

Answer 23

1) Superficial / cutaneous mycosis
- present in skin , hair , nails & tissue
- rarely invade deeper tissues
- example : dermatophytes cause jock itch , athletes foot , ringworm ; Malassezia furfur causes dandruff

2) Subcutenous mycosis
- confined to subcutaneous tissue
- rarely spreads systematically
- fungi are found in soils & introduced to the body via trauma ( cuts , puncture wounds )
- ex : mucormycosis , mycetoma

3) Systemic mycoses
- involve skin & deep viscera
- may become widely disseminated
- has predilection for specific organs
- infection occurs via inhalation of spores
- fungi causing systemic are mostly dimorphism - ex : histoplasmosis cause by histoplasma spp ; blastomycosis , talaromycosis

4) Opportunistic mycoses - caused by fungi of low virulence in immunocompromised people
- ex : Candidiasis

Question 24

Which part of the lipopolysaccharide / endotoxin in the outer membrane of a Gram negative bacteria is responsible for toxicity

Answer 24

Lipid A

Question 25

Classify bacteria based on morphology ( shape & arrangement ) & give example

Answer 25

1) Cocci (spherical ) - ex : staphylococci spp, Streptococci spp. , Neiserria spp 2) Bacili ( rod shaped ) Ex : Bacillus spp , Escherichia spp , Salmonella spp , Clostridium spp 3) Spirochaetes ( hellical ) Ex : Campylobacter spp , Helicobactee spp , Leptospira spp , Treponema pallidum

Question 26

Classify bacteria based on their temperature requirement

Answer 26

1) Psychrophiles - Bacteria that can grow at 0C or below - Optimum temperature between -5 ->15C found in Arctic & Antarctic regions - Ex : Arthrobacter spp. 2) Psychrotrops - Bacteria that can grow at 0C but optimum temperature is 20-30 C - Ex : Pseudomonas spp , Staphylococcus spp , Bacillus spp , Clostridium spp 3) Mesophiles - Bacteria that can grow between 25- 40 C but optimum is 37C - Most pathogenic bacteria are mesophiles - exam Escherichia coli , Salmonella spp 4) Thermophiles - Bacteria that best growth above 45C - Ex : Thermus aquaticus , Geobacilus stearothermiphilus 5) Hyperthermophiles - Bacteria that have optimum growth temperature above 80C - ex: Pyrococcus furiosus

Question 27

Classify medically - important bacteria based on O2 requirement with examples

Answer 27

1) Obligate aerobes - require O2 to grow - Ex: Pseudomonas , common nosocomial pathogens , Mycobacterium tuberculosis , Bacillus , Brucella 2) Facultative bacteria - can use O2 but can grow in its absence - ex: E.coli , Staphylococcus , Streptococcus mutans 3) Obligate anaerobes - Cannot use O2 & are harmed by the presence of toxic forms of O2 - ex: Clostridium tetani 4) Aerotolerant - cannot use O2 but can tolerate its presence as it can break down toxic forms of O2 - ex : Lactobacillus 5) Microaerophillic - Requires O2 but at low concentration - Sensitive to toxic forms of O2 - Ex: Campylobacter

Question 28

Describe the phase of the bacterial growth curve

Answer 28

1) Lag phase - rate of growth is zero - last a few minutes to few hours as bacteria are not dividing immediately but undergo a period of adaptation with various metabolic activity - enzymes & intermediate are being formed 2) Log phase - rapid cell division & mass increase in an exponential manner - ideal stage for Gram staining 3) Stationary phase - Rate of growth is zero due to depletion of nutrients & toxic byproduct accumulation causes rate of new cell formation to be equal to rate of cell death - culture now at maximal cell density or yield 4) Death phase - marked by a decline on the number of live bacteria

Question 29

Describe the structure of virion

Answer 29

1) Central genome : consists of either DNA / RNA which can be ss or ds , circular or linear , segmented or singular 2) Capsid : a protective protein shell surrounding the nuclei acid genome , made up of capsomers . It protects the genome and helps in attachment with host cell 3) Matrix protein : protein in between the envelope and capsid , it mediates the interaction b/w capsid & envelope and helps in lab diagnosis 4) Envelope : Made of lipoprotein outside the capsid l It mediates attachment with host cell & contains antigenic proteins

Question 30

Naked virus are ( …………….. ) They are (…………… ) to heat , drying , acids , proteases and detergents Enveloped viruses are (…………………. ) . They are ( ………… ) to heat , drying , detergent and lipid solvent like alcohol , ether

Answer 30

Naked virus are ( non enveloped viruses ) They are ( resistant ) to heat , drying , acids , proteases and detergents Enveloped viruses are ( enveloped viruses ) . They are ( sensitive ) to heat , drying , detergent and lipid solvent like alcohol , ether

Question 31

State the different types of viral symmetry with example

Answer 31

1) Icosahedral - viral capsomeres are arranged in 20 triangles to form a sphere-like outline - ex: adenovirus , all positive stranded RNA virus except coronavirus ( retrovirus , Hepevirus , picornavirus ) 2) Helical - viral capsomeres are arranged in a hollow coil that appears rod shaped - ex: influenzavirus , tobacco mosaic virus , coronavirus , all negative strand RNA virus except deltavirus 3) Complex - neither helical nor icosahedral - ex: polyvirus

Question 32

Give an example of a : 1) Gram positive cocci ( ………………) 2) Gram negative cocci ( …………..) 3) Gram positive bacilli ( ……………. ) 4) Gram negative bacilli (……………… )

Answer 32

Give an example of a : 1) Gram positive cocci ( Staphyloccocus aureus , Streptococcus mutans , Streptococcus pneumonia) 2) Gram negative cocci ( Neisseria gonorrhoeas , N. meningitis ) 3) Gram positive bacilli ( Clostridium spp , Bacillus anthracis ) 4) Gram negative bacilli ( E. Coli , Pseudomonas Aeruginosa , Salmonella spp.)

Question 33

Viruses can be classified based on :

Answer 33

``` A) Genome : I) DNA or RNA II) Single stranded or Double stranded III) Circular or linear IV) Segmented or singular V) Positive or negative ``` B) Symmetry I) Icosahedral II) Helical III) Complex C) Presence of envelope I) Naked virus II) Enveloped virus

Question 34

Most RNA viruses are single stranded except ( ………………….)

Answer 34

Most RNA viruses are single stranded except ( reoviruses )

Question 35

Describe the stages of viral replication

Answer 35

1) Adsorption / attachment : Involves receptor interaction - viruses have attachment sites on their envelope / capsid protein that bind complementarily to receptor sites present on the host membrane - Ex: HIV surface glycoprotein gp120 binds to a CD4 molecule on the host cell 2) Penetration - viruses penetrate the host cell by membrane fusion or injection of nucleic acid I) Membrane fusion - membrane fusion occurs in enveloped viruses - the envelope merges with the cell membrane of the host cell , resulting in the entry in the nucleocapsid into the cytoplasm - envelope remains attached to cell membrane II) Injection of nucleic acid - occurs in bacteriophages - Nucleic acid is injected while capsid remain attached to cell wall 3) Uncoating - process by which capsid is removed ( hence absent for bacteriophages ) - occurs via viral enzymes or host cell enzyme or by simple disassociation - viral nucleic acid become free to act as a template for viral mRNA synthesis 4) Biosynthesis - viral components are synthesised ( nucleocapsid , enzymes of viral replication , regulatory proteins to shut down host cell metabolism ) 5) Assembly - viral nucleic acid & capsid proteins are packaged to form progeny viruses - assembly can either be in nucleus ( DNA virus ) or cytoplasm ( RNA virus ) - maturation of the progeny take place either in nucleus , cytoplasm or membrane ( Golgi , ER or cell membrane ) 6) Release - either by lysis of host cell or budding off I) lysis - as shown by non- enveloped viruses and bacteriophages - released when cell dies & ruptured II) Budding - as shown by enveloped viruses - via exocytosis - Nucleocapsid binds to cell membrane which pinches off & sheds the virus gradually - part of the cell membrane become the virus’s envelope - host cell is not immediately destroyed

Question 36

State the cytopathogenic effects of viral infection

Answer 36

1) Cell lysis ( in non enveloped virus & bacteriophages ) 2) Cell rounding ( in enveloped virus) 3) Cell syncytium 4) Inclusion bodies - ex : Owl’s eyes inclusion in CMV virus , Negri bodies in Rabies virus

Question 37

Compare prokaryotic & eukaryotic chromosome

Question 38

State the types of plasmids

Answer 38

R -factors : 2 components ( RTF & r-determinant ) - RTF responsible for conjungation transfer ; r-determinant responsible for antibiotic resistance - R factors are known to have resistance to up to 8 or more drugs - commonly occurs among Gram -negative bacteria F- factor - contains genetic info for formation of sex pilus & self transfer - does not carry drug resistance markers - when integrated with host cell chromosome —> episome

Question 39

Describe transposons ( jumping gene)

Answer 39

- sequences of DNA that can move / transpose themselves from one position to another within the genome of a single cell ( eg : from plasmid DNA -> chromosome DNA) - occurs via cut and paste method or copy and paste method - may contain a number of genes coding for antibiotics resistance or other traits -> contribute to transmission of antibiotics resistance among a population of bacteria

Question 40

State a mechanism of bacterial gene transfer

Answer 40

1) Vertical gene transfer I) mutations ( inversion , deletion , translocation etc ) 2) Horizontal gene transfer I) transformation II) transduction III) conjugation

Question 41

Describe the transformation in bacterial gene transfer

Answer 41

- the bacteria acquired new DNA fragments from the environment - DNA fragments may be obtained from naturally dying / lysine bacterium in the environment - DNA fragment as naked DNA or plasmid ) gets incorporate into chromosomal DNA of the live bacterium

Question 42

Describe transduction in bacterial gene transfer

Answer 42

- Bacteriophages carry DNA from a donor bacteria to a recipient bacteria - Bacteriophage injects viral nucleic acid into bacteria which get incorporated into bacterial chromosomal DNA - viral genome + bacterial chromosomal DNA is known as prophase which can be replicated & get passed on to daughter cell via cell division - prophase gives special traits / characteristics to the bacterium ( eg toxin production in Corynebacterium diphtheriae ) - when the prophase is induced ( eg by UV lights ) —> parts of bacterial DNA & viral DNA may be improperly excised - new virion assembly occurs , incorporating both bacterial & viral DNA - cell lysis occurs —> virion containing bacterial + viral DNA released —> infects other cell &can confer special traits to infected bacterial cells

Question 43

Describe conjugation in bacterial gene transfer

Answer 43

- involves F + ( donor ) and F- bacteria ( recipient ) - F+ bacteria contains F factor plasmid which contains genes coding for formation of the sex pilus - The plasmid DNA replicated & a copy of it is passed onto the F- bacteria ( recipient ) - F- bacteria becomes F + and gains the ability to form a sex pilus - Multi drug resistance can also be transferred via R factor plasmid

Question 44

State an example of a spore forming bacteria

Answer 44

1j Clostridium spp | 2) Bacillus spp"

Question 45

Define sterilization

Answer 45

A process by which all living microorganism including viable spores are either destroyed or removed from an articles surface of medium.

Question 46

Classify the types of sterilization ( physical , chemical )

Question 47

Describe the autoclave ( working principle , holding time & temperature, articles sterilised , controls )

Answer 47

- a type of moist heating - consists of : I) pressure chamber : large cylinder + steam jacket II) Lid III) Electric heater - Holding time & temperature : 121C at 15 mins at 15psi - Uses : I) surgical instrument II) aesthetic equipment III) dental equipment IV) Implanted medical devices V) Surgical drapes & linens Sterilisation controls : spores of Geobacillus stearothermophilus Working principles : high pressure increase boiling point of water - in autoclave there is high pressure -> higher temperature / more heat requires to cause water to boil & make steam - extremely hot steam —> kill off bacteria & bacterial spores by causing protein denaturation & nucleic acid degradation

Question 48

Describe the hot air oven ( working principles , uses , holding time & temperature , sterilisation control )

Answer 48

- used for materials that might be damaged by / impenetrable to moist heat Uses : 1) glasswares ( Petri dishes , flasks , pipettes , test tubes ) 2) Powders ( starch , zinc oxides , sulfadizine ) 3) Petroleum products 4 ) Sharp instruments Holding time & temperature : 160C for 120 min / 2 hours Sterilisation control : spores of Bacillus atrophaeus Working principe - via conduction —> the outer surface is sterilised first , then the heat is conducted to the inner layers of the item , eventually reaching the temp required for sterilization to occur — dry heating causes oxidation of molecules —> destroy cell constituents

Question 49

List the controls of sterilization with examples

Answer 49

1) Physical indicators - digital displays of the sterilizer equipment showing these parameters : temperature , time , pressure 2) Chemical indicators - uses heat / chemical sensitive materials which undergo colour change when sterilization parameter is achieved - eg : autoclave tale , internal pack control indicator 3) Biological indicator - bacterial spores which are thermophilic - eg : Geobacillus stearothermophilus , Bacillus atropheus

Question 50

List the methods of sterilization by filtration & radiation

Answer 50

Filtration I) filtration of air - eg high efficiency particulate air (HEPA ) ) filters , N95 respirator , 3 ply mask II) filtration of liquids - bacteriological examination of water in hospital settings , dialysis water - remove bacteria from heat lability liquids, sera , toxins , sugars , vaccine , antibiotics solutions Radiation m I) Ionizing - eg cobalt 60 gamma rays II) Non-ionizing eg UV , infrared

Question 51

Define the term of disinfectant

Answer 51

A chemical used to destroy / remove most pathogenic organism but may or may not destroy bacterial spores ** normally used on inaminate object , not body surface

Question 52

Classify disinfectant based on their efficacy

Answer 52

High level disinfectant ( HLD ) I) Aldehydes - glutaraldehyde , ortho-phthaladehydes ( OPA ) II) Pericetic acid III) H2O2 ( 4-5% = sporoidal ) Intermediate levels disinfectant( ILD) I) Alcohols ( 60-80%) - ethyl alcohol , isopropyl alcohol II) Phenol ( carbolic acid ) - creosol , Lysol III) Halogens - iodine , chlorine ( free chlorine , sodium hypochlorite IV) UV radiation Low level disinfectant ( LLD ) I) Quadternary ammonium compounds - benzyl ammonium chloride ( QAC) , ceptylpyridium chloride II) Chlorhexidine glauconate ( CHG)

Question 53

Hydrogen peroxide is sporocidal at concentration of (…………… ) - Sodium hypochlorite is sporocidal at only concentration of (………………)

Answer 53

Hydrogen peroxide is sporocidal at concentration of ( 4-5% ) - Sodium hypochlorite is sporocidal at only concentration of ( >0.5% )

Question 54

As a disinfectant , glutaraldehyde has to be activated by ( ……………………. ) before use & remains active only for 14 days once activated . Ortho-phthaladehydes however ( …………….. ) . But , they ( ……………….. )

Answer 54

As a disinfectant , glutaraldehyde has to be activated by ( alkalisation ) before use & remains active only for 14 days once activated . Ortho-phthaladehydes however ( do not require alkalisation ) . But , they ( don’t kill spores & stains the skin gray )

Question 55

( …………………. ) is used as a skin antiseptic

Answer 55

( Spirit (70% alcohol) ) is used as a skin antiseptic

Question 56

Describe the stages of infectious disease

Answer 56

Incubation period - interval between the entrance of pathogen into the body and the appearance of first symptoms Prodromal stage - interval from the onset of nonspecific signs & symptoms - during this time , microorganism grow & multiply & the patients may be more capable of spreading disease to others Illness stage - interval when the patient manifests signs & symptoms specific to the type of infection -ex : common cold is manifest by sore throat , sinus congestion : mumps is manifests by earache , high fever , parotid & salivary gland swellings Convalescence - interval when the acute symptoms of infectious disappear & the body tries to replenish its resources and return to a state of homeostasis - length of recovery dependent on patient general health & severity of the infection

Question 57

Describe the significance in antigenic variation with example

Answer 57

- infectious agents are able to express alternate versions of antigens on their cell surface - alters the carbohydrates / proteins on the cell surface -> avoids host immune response -> antigenic escape 2 types : I) antigenic drift - mutations in the genes for the surface proteins Neuraminidase & hemagluttinin result in small antigenic changes or over time II) antigenic shift : Simultineous infections of a cell with 2 different influenza viruses results in mixing of the genes -> resultant virus possesses a mixture of the proteins of the original virus - can cause influenza pandemics

Question 58

Describe the methods of transmission of pathogens

Answer 58

A) Contact : I) Direct contact : with skin , mucosa of an uninfected person via kissing , unclean hands , sexual contact - ex: agents of common cold , skin and eye infections ( Haemophillus - pink eye ) , agnpengs of STi such as HIV , N . Gonorrhea , Chlamydia trachomatis , Treponema pallidum ( syphilis ) II) Indirect contact - through the agents of fomites ( clothes , toys , and towels ) 2) Inhalation - agents causing the respiratory infections are acquired via inhalation route - shed into environment via secretions from nose or throat during sneezing , coughing , speaking 3) Air-borne transmission I) droplets ( dust ) transmission - larger droplets ( >5um size ) travel for a shorter distance - only infect persons who come into close contact with source - ex: respiratory viruses ( influenza , parainfluenza , adenovirus , respiratory syncytial virus ) and Bordetella pertussis -> pertussis ( whooping cough ) II) droplets ( < 5um) can travel a larger distance —> infect people along its way - ex : tuberculosis , chicken pox , measles 4) Ingestion - intestinal infections & parasitic infections are acquired by ingestion of contiminated food or water - ex : cholera , dysentery , food poisoning , poliomyelitis 5) Inoculation- pathogen directly inoculated into the skin or tissue of the host - ex: animal bite -> rabies 6) Blood borne transmission - via contaminated blood transfusion , contaminated needles , cut on skin with infected instruments Ex: hepatitis , HIV 7) Vector borne ( mechanical or biological ) -occurs by arthropod vectors ( mosquitoes , lice , ticks , fleas ,mite , flies - 2 types of vector : mechanical & biological Mechanical vector :carry the microorganism but they do not multiply in the vector & transmit them to eatables Biological factor : pathogen multiplies in the vector ( female Anopheles mosquito in malaria ; Culex mosquito in filariasis , JEV n Aedes aegypti , A. Albopticus in dengue virus 8) Vertical transmission - from mother to fetus - transmission maybe transplancental ( TORCH ) infection or via the birth canal ( Hep B , Hep C, HIV)

Question 59

What is TORCH infection

Answer 59

Infection that can transmit through placental barrier T - Toxoplasma gonodii O- other ( Treponema pallidum ( syphilis ) R - Rubella virus C - cytomegalovirus H - Herpes Simplex Virus

Question 60

Describe the factor upon which bacterial pathogenicity is dependent upon :

Answer 60

1) Route of transmission - different bacteria have different optimal routes of transmission - ex : V. Cholerae are infective orally but cannot cause infection when introduced subcutaneously , Streptococci can initiate infection whatever be the route of entry 2) Adhesion - mediated by special molecules called adhesin which bind to the specific host cell receptors - functions : prevents the bacteria from being washed away , facilitate bacteria invasion into the host cells - ex: pili / fimbriae , non-pilus adhesions ( M protein on S. pyogenes , Lipoteichoic acid ; adhesin P1 on S. mutans ), biofilm formation 3) Pathogenicity islands - large genomic island located in the chromosomal regions of some bacteria containing sets on genes encoding for virulence factors , such as adhesins , secretion systems , toxins , invasions , iron uptake systems etc . - can transfer to other bacteria via horizontal gene transfer - detected in Shigella , Salmonella , V. Chlolerae , S , aureus , Helicobacter 4) Infective dose of the organism - minimum inoculum size that is capable of initiating an infection - pathogens with low inoculum size : Shigella - pathogen with high inoculum size : E.coli 5) Invasion - some microorganism are highly invasive ( produce & spread generalized lesions -> streptococcal infections ) , some are less invasive ( produce localised lesions -> streptococcal abscess ) , some lack of invasiveness but are confined to site of entry & produce potent toxins 6 ) Intracellular survival - pathogens that develop strategies to inhibit phagocytosis 7) Toxins - endotoxins cause fever , hypotension shock — example sepsis by gram negative rods 8) Bacterial secretion system - protein complexes present on the surface of a cell involved in the translocation of effector molecules ( proteins , enzyme , toxins ) across the cell membrane from the cytoplasm to the exterior - 6 specialised systems ( type 1-> 6 )

Question 61

State the name of adhesin protein of Streptococcus mutans

Answer 61

Adhesin P1

Question 62

Explain the role of microbial enzymes in enhancing their pathogenicity with examples

Answer 62

- enzymes help to overcome body defences & establish themselves in the host - ex :hyaluronidase , collaginase , coagulase